Just out of curiosity, for those that have broken their transaxle, usually the diff. Under what conditions did it happen? And if anyone can remember, what gear where you in when it broke?
Ben
You mean when the spider gears strip? When people are pulling donuts all over the place :). Or at a motorkhana on a hard surface...bang!! Lots of lurvly metal bits in the bottom of the box....
CV's can go as well but gather you're talking about the internal bits.
Hi Aggie, yeah I'm more thinking what breaks inside, I've heard that diff pinion breaks but not actually spoke to anyone who has broken one.
Have heard of a few higher HP cars stripping the teeth off the pinion on hard launches.
My understanding of the transaxle weakness is the actual case moving under torque, misaligning the gear tooth mesh and shredding/wearing excessively.
That was my thinking too, just thinking of ways to add some strength if at all possible.
No real problems with late model transaxles. Reliability would max out at 300bhp. Custom clutch would be mandatory for that sort of power. Standing start big power launches will kill any box eg. hill climbs. However power shifts on the move should not be an issue.
I'd be more concerned about shredding donuts...
Well, in the gearbox, most of the forces are spreading the 2 gear shafts away from each other. A gearbox strengthening plate works here, to a point. Here's a link showing good pictures [conveniently I googled a Alfa 164 gearbox haha]. This can be applied to the transaxle gearbox too.
If the plate is 3mm thick, then you have 3mm removed from the case join faces so everything internal still lines up.
http://www.turbonutter.net/gearbox
The diff though is harder, with the diff having more axial load the strengthening plate doesn't work here.
I've seen people build exoskeletons for the transaxle before. More recently I seen someone make a clutch housing brace/exoskeleton for the transaxle. I can't find the threads via google right now, but I'll keep looking for a bit. They're interesting conversation pictures at the least...
Heres the clutch exo'.
(http://i42.servimg.com/u/f42/17/52/20/30/75_agn26.jpg)
Link to the thread here-
http://alfagtv6.com/phpBB3/viewtopic.php?f=9&t=4354&p=45019
Hi MD and Jazig. Yeah the clutch housing bracing is a known mod. I think the problem with the transaxle is the distance between and type of bearings used. The main pinion bearing is a needle roller type which offers no pre load for the shaft or immediate support at the pinion other than for radial loads. The next bearing is at the intermediate flange at the other end of the gearbox which also sets the pinion depth/height. Which was fine for its original purpose being a 1.8l 4cyl. And it holds up quite well for most applications, including low boost v6's. I'm just thinking of ways to add reliability. Depending on cost of course!
Well... You seem fairly aware of the 'problem'... Time to get out the SKF book, do some cross referencing and measuring.
Yeah I've already been all over reading about preload benefits and setup.
Looking for as much info as I can get about the issues with the gearbox so as hopefully not to miss anything.
Ben
I was using an Alfa 75 1800 INDY in the Netherlands during my race license training. On the 2nd 5 hour session the whole tooth of the Crown Wheel cleanly grinded off leaving me with no drive. Engine was practically std. Only sport air filter added and exhaust
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That's freaky and a condition I have never heard of before. I have been pounding transaxles for thirty years and the typical issues are much like any gearbox. Synchro sets , LSD packs and oil seals.
Just thinking out loud, but if case flex is an issue, how about vacuuming resin enfusing some carbon fiber cloth around (a thoroughly cleaned and slightly etched) case? Basically a carbon fiber exo-skeleton.
Steel like strength, bugger all weight penalty and apparently CF is pretty reasonable conductor of heat (no that you wouldn't have an external oil cooler at this stage).
Doing some lateral thinking of your CF concept, if it was possible to source a billet of CF, I dare say you could machine out the casing and make the entire casing components from CF.
At this point I am looking over my shoulder for a couple of guys in white coats moving a mobile stretcher with long tie down straps and if I am not mistaken, one of them is carrying a large hypodermic labelled "sedative". I'll keep you posted on my 4G network connection while I make a bolt for it.....
..to be continued.
Haha MD, I think few should all be looking over our shoulders just owning there cars :/
Duk, I have already been thinking if a similar process for other parts of the car but in the case of the trans I have concerns bout the expansion rate of the alloy and the vastly differing temps at which it works. From my experience of the carbon fibre I have worked with it really really really I mean REALLY!! Does not like to flex, bend or move in any way. A great idea i agree. It used in the same way to strengthen bridges and other structural items with great success but only in items the have a slow, steady and minimal rate of expansion. My issue would be on a usual day in Brisbane the case would be say 15deg and working in a relatively short time could reach 100deg. With alloy's expansion rate it would be pushing the limits of the carbon's resin. Once it cracked it would then become a costly, time consuming but very cool looking heat containing cover around the gearbox.
It may work but would need to confirm with an plastics engineer to confirm.
Ben
Aluminium's rate of expansion (please note that there are heaps of ALLOY steels) is considerable. But rember, the alloy block engines use cast iron sleeves and the rate of thermal expansion is still kept safe enough that gaskets and seals stay in 1 piece. And if it is that bad, then the growth of the parts of the case that locate the shafts relative to each other, would cause enough change (and probably can) that the contact between the gears would change. In this case, both reduction (by temperature control) and restraint of the the thermal expansion should be considered.
High temperature resin would still be a good idea, to maintain stability. As would an alloy steel centre plate.
And as mentioned, CF is a pretty good thermal conductor and you should already have an external oil cooler by this stage.
I get what you mean Duk. In the case of the engine having cast iron liners with an alloy/aluminium case, the liners are machined to actually stick proud of the block. Even though the liners are cast iron with a relatively low expansion, they are also subjected to a few hundred degrees more heat than the cylinder block. Combustion temps exposed to the liners compared to the block which only sees the coolant temp, yet it as still required to have the liners longer than the block to maintain an acceptable sealing surface at operating temp due to the blocks growth in length compared to the liners growth in length.
As for the shafts moving away from each other.. They do. Even though there is only approx a couple of millimeters between the the bearings, but more so because of the axial forces involved and the bearings being so far apart on the same shaft. Int flange at one end and pinion bearing so far away. Leaving long shafts with no real support in midway. That in itself there is a cure well 2 actually.
So strengthening the case will have little to no effect for that issue.