Rear proportioning valve (105)

[Chris1750]

My Series II 105 coupe, like everyone elses', is equipped with a hydraulic proportioning valve in the rear brake circuit.
During a recent overhaul, I removed and disassembled this component. It was so gummed up that the piston no longer moved, so presumably it had been jammed for years. I cleaned everything carefully, got it inspected by a local Engineering works and reassembled it with new O-rings, seals and gaskets.
Back on the car and the brakes are working well.
I was just wondering how I could tell if the valve is functioning. Most people I talked to said that they were basically useless and should be bypassed.
Chris

[benjoys02]

were your brakes malfunctioning that's why you overhauled the brake system? i'm currently working on a gtv that has brake problems. the system builds-up pressure and locks the brakes whenever i start the motor. i replaced the brake booster and master cylinder already. i will replace the hoses this weekend then bleed the system. i hope that i won't have any more problems then. otherwise, the prop valve is the next gadget that i will replace.

[Chris1750]

I had a leaky caliper and over a period of about 6 months I replaced or renewed every conceivable component in the brake system. I probably could have left the proportioning valve but it was suggested to me by the local hydraulic guys that I should remove it and clean it out so that I don't get a heap of crud washing into my rear calipers when I bleed the system. I did and was glad that I followed their advice. I found the correct size metric O-rings fairly easily and though the small cup seal took a bit more time, I eventually located it too.
Now the brakes work very well, but I'm just not sure what that valve is doing. Apparently there are better ones around but they require some rearrangement of the brake lines to get them to fit.
Chris

PS: If your brakes were locking when the engine was started, you more than likely had a sticking booster.

PPS: The only part missing from the photo is the square gasket that goes between the spring cover and the pressure chamber. I had to cut a new one.

[benjoys02]

i sure hope that it is in fact the booster.
thanks again!

[1750GT]

Can you tell me where you managed to find the cup seals? I'll be needing new ones on my BP valves as well.

[Farace]

I'd be interested as well. I've got one (I'm guessing it's the same; I'll have to compare) sitting in my tool box. Every so often I look at it and think I should take it apart to see what's inside. I've never looked for metric O-rings, and this being the US, I could see where that could be a problem. Do you know the sizes?

[velocedoc]

How about a rebuild kit for a nominal fee?

[Chris1750]

I did this about a year ago and didn't think to keep a record of the sizes - sorry. The guys at the Engineering works are mates and once I'd dissembled it and cleaned it, I gave to them to check. They had it for about a fortnight and during that time found all of the rubber components. When I got the piston and chamber back I photographed it, as I do for most bits that I pull apart.
I'll drop in this week and ask if they kept a record but I doubt it. No one made much of a fuss about it at the time, so I guess I assumed that the parts were all readily available.
It is, after all, an ATE part and ATE have been fitting hydraulic components to most European cars for 40 years, so you'd reckon that there should be a back catalogue somewhere. These were the same guys who rebuilt my ATE calipers and I know those parts are readily available.
If I ever get a hold of another proportioning valve, I'll get it measured up again and try to get some catalogue numbers for the seal and O-rings.
Once again, my apologies,
Chris

[1750GT]

Chris, although ATE have been a major brake component supplier for decades, their willingness to support their products on these albeit vintage cars has been very disappointing to say the least. We've been searching for replacement seals on other ATE components (specifically the DPWA brake switch manifold) and when Osso approached ATE they were willing to provide a new unit for a nominal fee of around $500.00!.This is not my idea of good product support.

Now with respect to the seals your guys at Engineering works found, if they are indeed of similar design to the original seals they will have more than a few dozen sales possibilities from members of this BB alone (I would by 2 sets immediately myself).

[Chris1750]

Rossano et al,
I'll follow this up this week and get back to you. As I said, they seemed to find the appropriate bits over about a fortnight and as I didn't think it was much of an issue, I didn't keep records of what they did or how they found the parts. I suspect that the O-rings will be standard metric parts and that the cup seal will be the bit that is hard to find.
If it comes to it, I'll just buy a second hand regulator, pull it apart and put the micrometer over it.
Also, I didn't realise that ATE were such pains in the a*se - very disappointing.
Regards,
Chris

[Anfanuts]

Two years ago, I took the adjustment cover off and brake fluid came out (69). Pretty grungy so it had been there for awhile. I found a salvage off a 73 and put it in and got a new one (pending install) from Alfaholics. I have no idea if the "setting" is the same. I'd think it would vary with the car, brakes and weight distribution??? It was suggested I get an adjustable racing PV valve and plumb it in (either where the original was or along the tunnel in the cockpit) but I wanted to stay as OE as possible. I've cleaned and flushed the old one but not taken it apart further yet.

[PSk]

These valves are very useful with the intension of reducing the likelihood of rear brake lock up under heavy braking (as the rear of the car gets lighter).

I used one of these on my Sud race car to further reduce rear brake pressure, worked well.

I suggest to test it you find a safe carpark and when it is raining do a few massive panic brakes and see if your car wants to swap ends or not. IMO it is easier to control a car that locks it's front brakes first than the opposite.

Nice work BTW .
Pete

[Rich]

Hi Chris,

Can you tell me which supplier you used to get the cup seal and the o-ring?
I am going to do the same thing this Thursday even though i was told not dismantle it, but i thought what the hell, if i stuff i will get another one. I did notice when i removed from the car that it was full dirty oil and something that looked like rust, I hope it wasn't rust. I was going to run some brake fluid before connecting to the rear calipers to clean it out, but thanks to you i will do the same.

Thanks
Rich

[Chris1750]

Rich,
It was CBC Bearings - they are very helpful and seem to have access to all manner of arcane bits and pieces, if not the original parts then usually others that are the same size.

If you pull the PV apart the only advice I have for you is not to alter the locknut/screw on the end of the spring cover as this adjusts the spring tension and is factory preset. Everything else looks like fair game and quite simple to service. The square gasket can be cut from standard 0.40mm gasket paper.
If possible, get the hydraulic part pressure tested prior to reinstallation to make sure it's not leaking brake fluid.

Chris

PS: Nice looking Duetto in the avatar - someday I'll get myself one

[VA_Alfa]

Rich,
Please photograph and document the seals, orings, etc that you use in the rebuild. There are many alfisti that will thank you for your efforts.