Brake woes

[Divano Veloce]

I have interesting problems with the brakes on a 75 twin spark. Symptoms include:

Pedal sometimes super hard and brakes very ineffectual (definitely cant lock a wheel on wet asphalt)
Pedal sometimes pretty soft and brakes work better with rears locking well before fronts (front left never locks)
ARC brake and stop lights sometimes start flashing after taking foot off brake pedal and will go away after braking again

All of this started after i rebuilt the rear brakes. in that process the rear brake circuit was drained of fluid but the front circuit was not.

I have bled and adjusted the rear calipers and they seem to be working well. I have bled the front and this first seemed to make the pedal worse but with more bleeding has improved things a bit.

after some opinions on what to look for.... I suspect that the master cylinder isnt bled properly or is stuffed.

[Robert. Dale]

Hi I had a similiar problem about 25 years ago.
I had purchased a 1974 Alfetta 1.8 Sedan (the first model) and did a complete re-build.
I had all the brakes re-built by a very reputable Brake company at the time and after about 9 months I experienced a similiar problem to you.

It turned out that they had re-sleeved the master cylinder and it had come loose slightly and was occasionally moving and blocking either the front or rear circuits.

If in doubt buy a new master cylinder this should cure your problems.

Re-sleeving of brake components should be outlawed as it can be dangerous if problems arise.

Regards, Rob.

[VeeSix]

Verify your front and rear calipers are good, check the vacuum in your assistance unit, no air leaks and replace brake master cylinder and brake proportioning valve

[Divano Veloce]

Thanks Gents,

the PO told me the MC had been recently replaced/repaired so it could be suspect. The rear calipers are good, fronts i haven't checked but may be suspicious.

The brake fluid in the reservoir when i purchased the car had a distinctive oilyness about it and was dark. I didn't like the look of it...

I have noticed some photos of alfetta TS conversions without the brake bias valve, also some reference to bypassing it or replacing it with an adjustable unit. Any advice here? I would have thought that the weight distribution and front rear piston/disc diameter would have the brakes pretty close to balanced no?

The first thing I'll do is bleed a front and rear caliper at the same time, this seems to me to be the best way to bleed a tandem MC in situ.

[Divano Veloce]

Front left not locking up might be a clue... its supply from the MC is via the proportioning valve...

[GTVeloce]

Hi mate

I am inclined to think either M/C or proportioning valve. On my GTV TS I used the TS brakes but not the proportioning valve - I stuck with the original system which has a valve underneath the rear of the car just before the rear brakes.

I have no issues with either car's brakes but have been eyeing off an adjustable conversion similar to this:
http://www.alfabb.com/bb/forums/milano-75-1985-1993/265201-wilwood-brake-proportioning-valve.html

Changing the MC is a right royal pain in the a... It's hard in an Alfetta but worse in a 75 as the heater cock is also in the way. So, I would rule out the proportioning valve first. Is there someway you could bypass the valve altogether? Just temporarily, and to see what happens. I don't believe they are rebuildable so you would need to source a replacement. I have a spare Alfetta valve but its in Melbourne and I'm not...

The ARC light is a different issue although now that I think of it, maybe not. Perhaps the MC is not returning properly (i.e. the pedal spring is ineffective) and hence the light and possibly insufficient braking. Then again it could be just the light switch playing up. The switch on my 75 died not long after I got one and I had no rear lights and the ARC came on. New switch fixed.

I doubt it is the front callipers however, they are really easy to check out. It's a very easy job to remove the pads, push the pistons out and check out the condition of everything. Also easy to put new seals in (just two per side - a seal and a dust cap) and they are cheap. You will probably spend more time bleeding than the rest of it!

[Divano Veloce]

Thanks Julian. It seems the front left not working is somewhat common:

http://www.alfagtv6.com/discus/messages/205/1374.html?1093549896

With some careful bending the valve can be bypassed. According to google this will result in the rears locking up before the fronts.

So first thing will be to carefully re-bleed everything starting at the mc and proportioning valve.

Maybe by bleeding front circuit such that the bias valve is pressurised by the rear circuit somehow blocks flow to the front left circuit? I will bleed a front and rear simultaneously to see if this helps.

[rowan_bris]

Check that the brake lines have been put back in the right way when it was last apart in case the proportions get valve is preventing the left front working instead of preventing the rears locking!

[Divano Veloce]

Got some air out of the front left with a speed bleeder on one of the rear calipers.... Will test drive tomorrow.

I'm very curious as to how this pressure regulator works.... how the front brake hydraulic pressure is used to regulate the rear pressure.

Anyone know a good place for brake hoses? I dont think they're the culprit here but the dont look too good....

[Divano Veloce]

I know lots more about 75 brakes now...  Plumbing in the front left to the rear proportioning valve seems to introduce a single point of failure into the tandem brake system.

The proportioning valve piston is retained by a circlip (theres 2 actually, not sure how/what the second one does, maybe a backup?!). This circlip fails and out pops the piston and both front and rear circuits are connected to each other and to atmosphere!

Anyway, of my two cars, one had a sticking proportioning valve and the other was seized. One had a broken circlip...

Neither valve has any corrosion internally and are repairable

[Divano Veloce]

External corrosion and broken circlip


Proportioning valve (and MC) disassembled

[Divano Veloce]

Valve rod


cylinder bore


Red car looks like it had some custom plumbing. Front part of tandem cylinder goes to right front and rear wheels. Rear part of tandem cylinder goes to proportioning valve and front left...

[Divano Veloce]

So i got one regulator working and car passed RWC today!

A basic function test of one of these regulators is to put your finger on the rubber boot end and have someone press the brake pedal fairly hard. You should be able to feel the valve rod move out a bit. If yours is on the bench, the bush retained by the circlip should be able to be pushed in about 5mm. If it doesn't budge the rod is seized in this bush.


If it doesn't pass either of these tests it is seized and will make brake function poor and brake bleeding a nightmare. Pull it apart, you might be able to resurrect it.

The two valves I've disassembled both were seized on the atmosphere side of the seal, internally they were fine.

[Divano Veloce]

[GTVeloce]

Great news on the RWC! What's the status with both cars now? Still planning on making one a track car?