My 147 has been suffering from an excess of 'free' brake pedal travel. It's not that the brakes need bleeding, they don't. It's to do with the rear brake callipers. There is movement in the caliper, i.e. it's possible to manually move the caliper body in and out by about 0.5mm (or so) on the slider pins, because the piston retracts that far. This means that the piston has to be moved this amount before the pads make proper contact with the rotor, which equates to unwanted pedal motion.
Multiply this by 2, because there are two rear calipers, and the brake pedal travel (before the brakes start to work) is excessive. This may not be a significant issue for many drivers, but it means that the brake pedal moves substantially below the height of the accelerator pedal, which makes 'heel / toe' braking action quite awkward. Add to this the additional pedal motion that is a result of the rubber hoses expanding under heavy use (normal) and it's not a good thing.
This seems largely to do with the handbrake mechanism on the Lucas calipers. To assist heel / toe braking I have already bent the throttle pedal shaft so that the pedal pad is statically closer to the floor, and significantly below the height of the brake pedal pad when the brake is not being used (this is not all that easy to do since the shaft on the throttle pedal is unnecessarily thick and rigid). But, it's still not enough, the throttle pedal pad is still too high when the brake is being used, and there is still that icky free play.
So, experimentally I adjusted the piston rotation in the rear callipers until it was quite difficult to slide the caliper body over the pads as the body was fitted to the caliper bracket (i.e. with the caliper bracket fitted to the strut with the pads already in position against the rotor surfaces). Only a small rotation of the pistons was needed. This resulted in some significant pad drag as the rotor was turned by hand, but not a great amount.
So, now, the brake pedal motion is a lot less and the brake pedal pad does not move below the static height of the throttle pedal pad. Heel / toe is now much much easier and more consistent (because brake pedal travel is now more consistent as well as less). Additionally, the brakes feel far more responsive and more confidence inspiring, the pedal feels so much firmer than before. I now no longer have to make sure that the edge of my shoe does not catch the edge of the throttle pedal when braking firmly (when not doing heel / toe, note that my pedal pads are closer together than standard, to facilitate heel / toe).
I'm not sure how long this will last. The pads will wear, and the issue will probably reappear in time. However, the improvement is so great that having to adjust the piston rotation every few weeks (or however long) will be worth it. Since the pads are now significantly dragging (but not heavily dragging), the rear pad wear will probably increase to some degree, but again the improvement is so great it will be worth it (unless pad wear rate increases a lot more than I expect it will).
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I wonder if there is a rear caliper that does not suffer from this problem that might be substituted for the Lucas caliper? I know that there is an ATE brand caliper used in earlier model Alfas that uses a different handbrake mechanism (and is a dual piston design as opposed to the single piston in the Lucas caliper). I vaguely recall reading of some owners of earlier model Alfas swapping these for the Lucas caliper because the Lucas caliper handbrake mechanism works much better. I wonder if the swap can be done the other way? I'd be happy to trade a weaker handbrake for a better pedal action...
Regards,
John.
Further thoughts on sliding pin single piston rear calipers;
Looking at a typical sliding pin / single piston front caliper, the pins usually seem to be a close fit with the bushes in which they slide. This means that the caliper body is not fee to move relative to the bracket, other than to slide in and out on the pins.
Looking at a typical rear sliding pin / single piston caliper, the pins seem to be a fairly loose fit in the bushes. This means that the caliper body is free to move in and out, but also has some small degree of freedom to move in other axes. Take the wheel off, grab the innermost part of the caliper body, try and move it longitudinally (toward the front and rear of the car). The caliper body will most probably wiggle to a significant degree. Now try and move it up and down, again it will most probably wiggle significantly. The caliper body will 'wiggle' with vibration and with 'impacts' due to road bumps etc.
With either the longitudinal or vertical caliper body wiggling, the motion will tend to push the piston back into the caliper to some degree. This cannot be a good thing because if the piston is pushed back into the caliper then upon brake application the piston must be pushed back out again, which equates to 'free' motion at the pedal.
What can be done? Can we re-machine the pins and bushes for a much closer fit, as front calipers seem to commonly have? Perhaps, but why are the pins so loose in the first place? Is there some not particularly obvious reason why they are engineered this way, maybe to do with how the handbrake mechanism works?
I don't know, but some years ago I came across loose pins in the rear calipers of my Accord (which had a similar handbrake mechanism to the 147 rear callipers). I assumed the pins / bushes were worn (hadn't played with such calipers before, and unaware that this looseness was common in such rear calipers), and as an experiment I inserted some metal shim (curved into a tube) between the pins and bushes to take up most of the clearance, which substantially reduced the 'wiggling' between the caliper body and the bracket. Pedal motion decreased and became more consistent, and the handbrake still worked fine...
Alternatively, could we fit a residual pressure valve into the brake line leading to the caliper? These valves permit free flow of pressure one way, but limit pressure release back the other way. They are available in different pressure settings, i.e. some may retain 2lbs pressure in the caliper, some 10lbs, and probably other settings. So, if there were say a 2lb valve in the line, the valve would always retain 2lbs of pressure in the caliper, to lightly apply the pads at all times and eliminate (in some degree) pad 'knock off' (i.e. piston 'push back').
This would increase pad wear to some degree, and have at least some affect on fuel economy, but if these effects were not too great then it may well be worth it.
It occurs to me that a somewhat similar effect might be had if light compression springs were fitted over the rubber boots that cover the pins. These springs would exert light pressure between the caliper body and the caliper bracket, helping to limit caliper 'wiggling' and the resultant piston 'push back'...?
Regards,
John.
What do you actually like (as in, have no desire to change) about the 147 as it was made? One gets the impression it isn't much at all. I'm honestly starting to become puzzled by all these changes.
Surely one "cure" for perceived inadequacies, is a change of car, or a hobby vehicle - like a Seven style project - or even a kart?
With the brakes, bypassing the ABS completely (within its housing, so as not to disturb the interface with ECU etc) might help your pedal feel, it would be an interesting project...
Hi John
Not sure if this helps, as I am not qualified to add much light on Brake Design, but from my knowledge the clearance fit of pins and bushes on the brake calipers, is all to do with coefficient of expansion to cater for the variations in temperature under NORMAL braking conditions. The toe and heel method of braking you refer to is more consistent with racing rather than normal city and highway driving.
Regards
bonno
I suspect that for cars I can conceivably afford, none would satisfy me entirely in every respect. I've never owned a car that I didn't feel a need to change / improve something, and usually quite a few things.
I like my 147 very much, it has a lot going for it, but also it has a number of faults and things that might have been done better, like all other cars, none are perfect. I have a kart already, just no time to take it to the track. I've owned a "Seven style" / clubman type road car too, and I made a heap of changes to that, many more than any other car I've owned (that car was a frantic roller skate!).
I really don't think the issue with the 147 brake pedal travel is anything to do with the ABS, so doubt that bypassing it would improve it. I'm 99% sure it's the fundamental design of the rear calipers with a lose fit for the rear pins, a design feature that seems shared with quite a few other cars.
For instance my Accord had close tolerance pins in the front calipers and loose in the rear calipers, my sone's old Prelude ditto, his current Mazda 323 ditto, my mothers' 323 ditto, and other cars I strongly suspect. Now it could possibly be that these cars all just happened to not wear the pins / bushes in their front brakes while significantly wearing the pins bushes only in the rear brakes, but I tend to doubt it. I recall buying new pins for the rear brake in the Accord, and they were the same OD as the old ones I had assumed must be worn.
My wifes' Saab 95 does have tight tolerance pins in all it's calipers, but the handbrakes are 'mini-drums' inside the brake rotors, i.e. seperate mechanisms to the main rear brakes. We used to have a Cressida that was ditto...
Regards,
John.
Quote from: bonno on April 25, 2018, 03:30:47 PM
Hi John
Not sure if this helps, as I am not qualified to add much light on Brake Design, but from my knowledge the clearance fit of pins and bushes on the brake calipers, is all to do with coefficient of expansion to cater for the variations in temperature under NORMAL braking conditions. The toe and heel method of braking you refer to is more consistent with racing rather than normal city and highway driving.
Regards
bonno
Bonno,
I learnt to heel / toe many years ago driving the Nota I used to own (the above mentioned 'Clubman' style car). Once you've mastered the skill it becomes unthinkingly automatic, you will probably tend to use it quite a lot, and miss it if the pedal layout doesn't permit it, or makes it too awkward / impractical to use (as does a brake pedal that moves excessively...).
The expansion with heat of the pins inside the bushes can't account for the significant clearance between them (that exists with it at least seems quite a lot of rear calipers). If it did, then the pins in the front calipers would also need a similar clearance, or greater, considering that the front calipers are likely to get hotter than the rear ones. Front calipers don't seem to have a loose fit between the pins and their bushes, at least I have never seen a front caliper that 'wobbles' in the same way as seems common with rear calipers...
Regards,
John.
Quote from: Citroënbender on April 25, 2018, 02:16:25 PMWith the brakes, bypassing the ABS completely (within its housing, so as not to disturb the interface with ECU etc) might help your pedal feel, it would be an interesting project...
I am curious as to what you are trying to achieve here. The ABS system is nonexistent till it is activated by skidding of one of the wheels, as the brake lines just run straight through the unit and its valves as if it was a solid pipe.
Less chance of there being small amounts of air in the system. I'm never convinced with the monobloc Bosch ABS/ESP type systems that I have got it all out.
Update on this. It's about a week since I manually tightened the clearance between the pads and the pistons in the rear calipers. So far the pedal is still as good as it was the day I did it, with no adverse issues with how well the brakes work. The pedal is till 'high' on application, heel / toe is much easier than previously. The brake pedal in general is much more confidence inspring and pleasant to use. I haven't yet checked for pad wear, but think it should probably be OK.
Regards,
John.
What about the little dogs or pins on the pad back - are they still indexed with the divots in the caliper piston?
CB,
The pistons do each have two "divots" / slots at their periphery (180° apart), but the pads have no corresponding 'dogs', their backs are all quite flat. This is the same as was the case with the old pads that I replaced. Since the pad backs are flat, I assume that the piston slots are intended to fit a piston winding tool (but I find that multigrips work fine).
If the pads were of the type that do have dogs, then fine adjustment of the piston rotation would not be possible, because the piston slots could only fit over the dogs at 180° rotational increments. I found that a quite small piston rotation made a quite significant difference to the clearance between the piston / pads / disc (180° would be a very substantial difference). With the experience I'm having with this now, were I to buy a set of rear pads that did have dogs, I think I'd grind them off (in order to be able to fine tune the piston rotation and associated clearances).
I've also done a similar rear caliper piston rotation adjustment on my sons' Mazda 323, and reduced the pedal travel with some success. This car also had no dogs on the rear pads, and no slots at all in the pistons, and a similar tendency for the rear caliper bodies to wobble on what seem to be slider pins that have an excessive clearance to the pin bushes, causing excessive brake pedal travel.
This morning I took took a rear wheel off the Alfa and checked the caliper for any return of unwanted play / wobble, and, this was much the same as when I first rotated the piston to tighten the piston to pad clearance (i.e. some very slight and much reduced wobble). The only difference is that the disc is now a tad freer to manually rotate, but still a little bit draggy.
Regards,
John.
Quote from: Citroënbender on April 29, 2018, 08:16:25 PM
What about the little dogs or pins on the pad back - are they still indexed with the divots in the caliper piston?
147 doesn't have any locators on the back of the pads? ???
Quote from: bazzbazz on May 01, 2018, 12:34:58 PM
147 doesn't have any locators on the back of the pads? ???
Not on mine.
Regards,
John.
Nor my spare Valeo rear pads. But I'm sure whatever I fitted last time I did the rears on the '01, did have.
I've always seen them as integral to the self-adjusters working properly. Odd they're not present.
Quote from: Citroënbender on May 01, 2018, 01:02:49 PM
Nor my spare Valeo rear pads. But I'm sure whatever I fitted last time I did the rears on the '01, did have.
I've always seen them as integral to the self-adjusters working properly. Odd they're not present.
My handbrake works very well with no dogs on the pad backs. I've never needed to adjust it as the lever action and effectiveness has never noticably changed since I bought the car, and I assume the adjuster is working as it's supposed to.
My car hasn't had 'dogged' pads since before I bought it, obviously the dogs are not essential for the Lucas handbrake adjuster to work. It would be my guess that where pad dogs are used, with a caliper using the same or similar kind of handbrake adjusting mechanism as the 147 Lucas calipers use, that the dogs are probably redundant...
Regards,
John.
I've been trawling the interweb trying to find a specific reason as to why calipers fitted with a handbrake mechanism seem to commonly be designed with a fairly loose fit betwen the pins and the bushes (and wobble quite a bit, causing piston push back), while those without a handbrake mechanism seem to have a much closer fit between the pins and the bushes (and don't significantly wobble). And, I've found nothing to answer this question.
This does at least appear to be a design thing, and not a wear thing.
I have found a significant number of forum posts where people are asking about the loose fit between the pins and bushes, seemingly far more to do with rear calipers than front ones. Most complaints seem to be to do with loose pins causing the rear calipers to rattle, not so much to do with the affect on pedal travel (which is the issue I have with it).
Regards,
John.
I've attached a typical integrated handbrake caliper piston image, mainly to illuminate the ability of the "adjuster" to turn independently of the piston, albeit with appreciable friction.
Getting back to my earlier comment about trapped air, there are 12 electrovalves in the brake bloc that might entrain a bubble or two, and also the pressure pump chambers (I believe it runs two divorced chambers to maintain some failsafe attributes). Pressure bleeding from the reservoir down is the first step in reducing this air, then whatever software is available to cycle the pump and electrovalves. The Pug/Cit software is great, it just locks off the wheels not being bled and uses the pump to push fluid through. I wish they were all so easy.
Aren't there some parts missing in the photo? I'm mainly thinking there should be a rod with a course pitched thread at one end, which is what automatically alters the effective rod length because the rod gradually rotates on this thread in use, which is what keeps the handbrake mechanism in adjustment as the pads wear down (note that my understanding of the mechanism is rudimentery, at best).
It's this effective rod length that I assume I have altered when I rotated the piston, limiting how far the piston can retract into the caliper body, so the piston 'leans' on the rod and cannot retract (or be pushed) enough to create a clearance between thre piston face and the pad to which the piston abuts.
To the possibility of bubbles in the system, there are no symptoms that I would associate with air in the hydraulics. The pedal isn't squishy in that way. I don't think changing the brake fluid would be a problem (which I keep meaning to do...), but I live in fear of ever having to bleed air out of this brake system...
Regards,
John.
The only explanation I have come across (as to why significant pin clearance is necessary) is that it allows the caliper to still apply an even force to the pads, even if (when) the pads develop some tapered wear, by allowing the caliper body to freely 'tilt' in two axes (other than moving in / out). This makes some sense, but doesn't explain why rear calipers often seem to be built with so much more pin clearance than front calipers.
And, fixed calipers seem to work very well without any capacity to 'tilt'. Though having said that, with a fixed caliper tapered pad wear does result in increased pedal travel, because the taper worn pads can be statically close to the disc only at the point of least pad wear, necessitating more piston travel to fully present the pad face to the disc. In this instance a sliding caliper can be superior to a fixed caliper.
I'd still prefer to have fixed calipers (than sliding) because with reasonably 'flat' pads there is still likely to be less piston movement, and the caliper body is more likely to be more rigid, so the pedal will probably feel firmer under heavy braking (due to less caliper flex with higher fluid pressures).
The best brakes with the best pedal travel and feel that I've ever had on a car I've owned were those on my Nota (clubman type sports car), which were Cortina GT front discs with fixed calipers, and Morris rear drums, all unassisted with a balance bar at the pedal. This set up had minimal pedal travel and very strong braking, albeit requiring a strong pedal application (very light car, if it were as heavy as a sedan it would have needed a booster).
Later I fitted rear disc brakes from a Fiat 124 Sports, which used sliding calipers similar to the 147 rear calipers. These Fiat disc brakes were stronger than the much smaller Morris drums (i.e. more effective rear braking for X fluid pressure, necessitating a master cylinder change in the rear brake circuit as the balance bar didn't offer enough adjustment), but had significant pad knock off resulting in more 'free' pedal travel than with the Morris drums (when the drums were properly adjusted). This meant more braking for somewhat less pedal effort, but really it would have been better to have kept the Morris rear drums, and adjust them manually as needed.
I only changed the rear brakes because I had the Fiat brakes already and I was changing from a Morris rear axle (which kept breaking) to an RX2 rear axle (which was bullet proof). The Fiat brake conversion on this axle was fairly easy, so I went down that road rather than use the relatively huge and heavy Mazda rear drums (that came with the RX2 axle). Besides, the disc brakes looked much nicer...
Regards,
John.
I found this product related to caliper pins and bushes, and the clearance between them:
https://www.ecstuning.com/b-ecs-parts/performance-caliper-guide-bushing-set/003326ecs01-02kt/
Should I think greatly reduce the caliper wobbling on the pins, and I expect lessen piston 'push back' caused by it. Of course it's for VWs and Audis, not Alfas, but it does at least suggest that tighter fitting pins may be worth pursuing.
Regards,
John.
If we took the "cocking" of each caliper to be 1mm to nothing at worst case, it's fair to average this at 0.5mm of clearance or travel before full contact between piston, pads and disc.
With 54mm diameter front caliper pistons and 38mm diameter rear caliper pistons, I then make the total displaced fluid volume 3.424ml.
To displace this volume in a 22.2mm bore master cylinder requires specific travel of approx. 8.9mm.
If your leverage on the pedal is approximately 4/1 (rough guess, not gone out to measure the relay linkage accurately) that's anything up to 36mm of travel before full brake contact is achieved.
Aren't we forgetting any wear & tear movement in the pedal assembly?
Or did I miss that part in the info above?
I deliberately omitted any consideration of that, as it's not impacted by any misalignment of the calipers. :) Same for free motion in the master cylinder before fluid displacement starts.
Yes, but we are not talking about that here, the original question was that of the inability to properly "heal-toe" due to free/dead movement in the brake pedal. I just would have thought that would have been the first thing to consider, that's all.
CB,
the amount of "cocking" is important insofar as how much piston push back it allows to happen. Some of the 'push back' will actually be 'pull back' caused by the hysterisis in the piston seal (a designed characteristic of square section piston seals, eliminating pad drag by slightly withdrawing the piston when system pressure drops to effective zero). Some of the push back seems to be caused by the caliper body wobbling on the loose pins with vibration and impact (potholes / bumps). Rotating the piston to create a tighter clearance (actully zero clearance) between the piston and the inner pad will prevent (or at least substantially lessen) both 'push' and 'pull' back. Some push back may be caused by compliance in the wheel bearings etc, but in this case I suspect this is minimal.
With my front calipers there is some slight manually feelable freedom to 'cock', but there is no easily detectible in / out motion at the caliper body (relative to the caliper bracket, disc). Having said that, there probably is at least some in / out motion in use, but not a lot I would expect. It was different at the rear calipers (prior to rotating the pistons), much more significant 'cocking' was easy to produce by manually wiggling the caliper body, and somewhere between about 0.5mm and 1mm of in/out caliper body movement was easy to feel, and to see. This could also be felt (with hands as the caliper body was pushed / pulled) as a slight 'clunk' as the pads contacted the disc with each in and out push and pull on the caliper body. The great majority of the unwanted pedal travel seems to be generated in the rear calipers, with not much (if any?) at the front calipers.
The free motion at the pedal is now much less than it was, but was initially (prior to piston rotation) still significantly less than your 36mm guessalculation (not that I actually measured it, it was Xmm statically, but often X+ dynamically, and it was not consitent). It was still enough to be a problem for heel / toe, and inconsistency in the pedal feel. There is still some pedal free motion, but significantly less than before, and the pedal feel, consistency and braking responsiveness are quite noticably improved even when just braking 'normally'. The brakes are now more confidence inspring in general.
Eliminating caliper body wobble at the front calipers would probably have some affect on pedal free play, but I think not much because the pins are not all that loose. It's the substantlly greater looseness of the rear caliper pins that I think was creating the great majority of the somewhat erratic free play at the pedal. I think further improvement is probably achievable (over and above what the piston rotation has created), with tighter pin clearance in the rear caliper pins. It would be interesting to fit residual pressure valves at all four brakes...
Apparently there is a bronze bushing / machined pin and bushing kit available for BMWs, which replaces rubber mounted stock pin bushes (the pins are a close fit in the bushes). The reports are that this kit significantly improves the braking performance (pedal feel, motion, consistency, pad wear), but in this case it is a 'race only' modification because the BMW calipers have rubber pin bushes and don't have an effective dirt exclusion device (i.e. rubber bellows), and the bushes are exposed to road dirt, water etc.
Regards,
John.
Quote from: bazzbazz on May 02, 2018, 06:51:13 PM
Aren't we forgetting any wear & tear movement in the pedal assembly?
Or did I miss that part in the info above?
I don't think that pedal assembly wear is a significant issue here, though some probably exists. If such wear were the primary problem here, then the rotational adjustment of the rear pistons would not have had as significant positive affect as it has had...
Regards,
John.
I think you should go and have a look at how much pedal movement free play you have with the pedal movement assembly.
I have yet to work on any 147/156 that doesn't have some.
Baz,
I'd more than half expect to find at least some pedal pivot wear, but I can't see how it could be significant to this since it was a change at the rear calipers affecting an obvious piston clearance issue that has improved things so much (still not perfect though, much improved).
Of course some free pay at the pedal itself is necessary (i.e. at the push rod). If play is zero here then this can cause the hydraulic circuit to be shut off from the reservoir, so, as the fluid heats up and expands the resulting pressure cannot 'escape' into the reservoir, so the pistons move out instead. This causes the brakes to 'auto-apply', and when this happens the fluid gets hotter, the pressure increases, the brakes auto-apply harder, the fluid gets hotter, the pressure increases more, etc. This gets worse and worse until you can feel the car 'losing' power, and to smell very hot pads. Don't ask me how I know this, but it does involve a Honda Accord.
I've seen an identical problem with a friends racing kart when he adjusted the pedal free play to zero (the brake disc went black from the heat, then the brake stopped working entirely because of all the smoke coming off the pads).
While I'm here; it's not 'ideal' that there is now some amount of pad drag at the rear brakes, but it doesn't appear to be causing any problems. If the drag were excessive then I'd expect to encounter a fairly substantial heat build up in the rear brakes, but this doesn't occur. I checked this the other day, after a long stretch of straightish road I gradually pulled over and felt for heat coming from the brakes, the rears were about as warm as the front brakes (i.e. I could hold my fingers on both front and rear discs for a few seconds before the pain began...).
Regards,
John.
I have here, a set of MY05 147 rear calipers and yokes, approx 130K on them. Make me a cheeky offer and you can build up a set to your ideal specs that will readily exchange with the present items. :)
CB,
Thanks for the offer. I'd be interested were I not so embarrasingly impecunious at present (just gave all my money to the ATO, who are adamant that it was their money...). Maybe later...
Regards,
John.