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Discussion Starter #1
I noticed my brake proportioning valve was looking a little strange today. It has a slight leak or seepage on the backside where there is a rubber boot or cover but I'm not sure what exactly is under the rubber piece and didn't want to touch it because I need to get the car inspected for registration. The seepage is the copper colored, milky substance in the pics. I replaced the master cylinder a few months ago and didn't notice anything so I'm assuming this is new.

Any ideas what's going on here? And what is the purpose of the rubber boot? What exactly is under the rubber boot?

Thanks....



 

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It's possible that with a new master you are getting more reliable and higher pressure through the prop valve and have disturbed a seal. If you're seeing seepage, it is leaking. It may not be urgent but you won't be able to tell until you're leaking fluid more readily.

The seepage is likely contaminated brake fluid mixed with water - the color is likely tinted from rust (valve body is cast iron). The prop valve has a valve and plunger and seals inside. Under the boot there is a threaded plug seal from memory. Depending on who you ask they are rebuildable but you'll need to take it apart in order to determine what seals you need (there are not kits available and I have never seen any dimensions posted for them anywhere). Others say they're not rebuildable. That valve was unique to the GTV6 in 85.5-86 and Milano Silver and Gold models as far as I know. A good used unit probably only will cost you a few bucks from Alfa Parts Exchange. Or, you could plumb in a new adjustable one like I did on my Mostro Milano.
 

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I'll second plumbing in a replacement that's adjustable. They aren't expensive and it's a fairly easy installation. I put a Wilwood valve on my car and it was fairly easy to do. There was some slight bending of existing brake pipes (I believe I had to move one of the steel lines to the front wheels 90 degrees) but in all, simple work.
 

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Discussion Starter #4
Thanks guys for the info. What part did you guys use for the new valve? I think Rob listed the part he used in one of my older threads about brakes but not sure. I was thinking the same thing about the new MC blowing out an aging seal. Also I remember dealing with a similar problem on my Alfetta with the proportioning valve or actually I think it was a safety valve which closed off a leaking circuit in case of brake failure but the milano valve is strictly a proportioning valve?

I guess I'll throw in an adjustable valve as it's not best to flirt with brake leakage problems. How is it as far as adjusting? Can you feel a big difference when adjusting from front to rear or do you have to lock them up to see which locks earlier?
 

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I thought that I would add my recent experience to this old thread. Working on a friends 85 GTV6, with 303K miles (!) I was tasked to perform a proper brake fluid flush and bleed. He said that that the pedal was getting spongy. I suctioned the old fluid out of the reservoir (fluid was many years old, and murky looking) and refilled it with new DOT4. No matter how much I bled, I continued to get large air bubbles from the rear calipers. The fronts bled quickly with no air. Upon inspection, I found a large fluid leak at the rear of the compensator (proportioning valve) and evidence of seepage at the rear of the brake master cylinder. Both parts looked very old. The owner stated that he seems to remember replacing the BMC once, many years ago, but no memory of replacing the compensator. The BMC is available from many suppliers for a reasonable price. The compensator was not so reasonably priced, IMO. Vick has one listed for $150. but he said that he doesn't have any, doesn't know when he will get more. Difatta was a bit cheaper than Centerline and is much closer to me. I bench-bled the master, installed it onto the booster, and then installed the compensator. I then bled the outlet lines at the compensator, then finally the calipers again. Finally, a good firm brake pedal. I disassembled the compensator, image below. The old unit was stamped Bendix Italy with Benditalia 1408355 on the rubber cap. The new unit is stamped Made Italy, 20293 with the same black cap.
 

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