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I am putting together a car that I didn't disassemble. Working on brake system now and am confused by something.

In the diagram below it seems there are 2 proportioning valves...one in the engine bay and the usual one under the car. Is that correct?

I think I have the one highlighted in the red box (attached picture), but seem to be missing the under car one. The under car one seems pretty spendy to purchase new. If I actually need one of these for this car (i.e. it is a required component on this car), is there any reason I shouldn't just source a used one?
 

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The front one was to meet U.S. specs for brake warning lights.

You can do away with it. Alfa got rid of it sometime in the late 70's or early 80's.

If you can find a used one from that era. There is a guy on ebay that had the seals made and is selling kits.

The style in the link is the one that came on the rear of your car.

 

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a link to the seals, nice guy and great service

 

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I just got my 4 sets that I ordered several weeks ago. They look to be very high quality.
 

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Jim, as you know, I have hard lines on my checklist to-do. How would one know if the rear prop valve is malfunctioning other than uneven braking....then the question is why have it anyway? It can't be a safety issue is it?
 

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Keeps the rear brakes from locking up everytime you push the brake pedal.
 

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I am putting together a car that I didn't disassemble. Working on brake system now and am confused by something. In the diagram below it seems there are 2 proportioning valves...one in the engine bay and the usual one under the car. Is that correct?
Not exactly. Yes, there are two hydraulic devices in the braking system - one at the front and one at the rear. But only one of these is a "proportioning valve" - the one at the rear. As Jim G explains, the thing at the front doesn't influence brakeline pressure; it just lights a warning light on the dash if the F and R line pressures become different (it also houses the switch for the exterior brake lights).

Your Alfa would stop just fine without that front device. It always struck me as silly to devote all that hardware just to support a signal light on the dash telling the driver when he had lost half his braking system. If you can't figure out that something is wrong when you've lost half your braking, then maybe you shouldn't have a license!

The proportioning valve at the rear is essential. As Jim G explains, the rear calipers would lock the wheels under hard braking without that.

crackie said:
The under car one seems pretty spendy to purchase new. If I actually need one of these for this car (i.e. it is a required component on this car), is there any reason I shouldn't just source a used one?
Sure, install a used one. These tend to be long-lived, so a used one will probably work OK. As long as it doesn't leak fluid to the outside, it will probably be fine.
 

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[QUOTE="Alfajay, post: 8583435, member: 2539" (it also houses the switch for the exterior brake lights).


[/QUOTE]

Thats on the floor pedal cars.

Hanging pedal cars. Brake light switch is under the dash.
 

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Hanging pedal cars. Brake light switch is under the dash.
Ah, right you are. So eliminating it would only require a couple of unions.
 

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Discussion Starter #10
Ah ok, this solves the mystery. I saw the spade connector on the front one but couldn’t figure out what it could possibly be signaling. Definitely seems unnecessary.

Thanks for guidance on the (rear) proportioning valve. Think I’ll find a used one and rebuild. Mine is not in the boxes of parts I got with the car.

Thanks all!
 

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Discussion Starter #11
The BB thread suggestion algorithm has gotten pretty good. Suggested the thread below on replacing both of these units with a Wilwood unit. Thought I’d post here as it might be useful to someone on this topic in the future.
 

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Think I’ll find a used one and rebuild.
I'm not sure that rebuild parts are available. I think you need to either buy a complete, new unit, or install a used one as-is.
 

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Discussion Starter #13
I'm not sure that rebuild parts are available. I think you need to either buy a complete, new unit, or install a used one as-is.
A
I'm not sure that rebuild parts are available. I think you need to either buy a complete, new unit, or install a used one as-is.
Above in this thread is a post for a rebuild kit that folks seem happy with.
 

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You could also use this one. If your not going for original.

 

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Ah ok, this solves the mystery. I saw the spade connector on the front one but couldn’t figure out what it could possibly be signaling. Definitely seems unnecessary.

Thanks for guidance on the (rear) proportioning valve. Think I’ll find a used one and rebuild. Mine is not in the boxes of parts I got with the car.

Thanks all!
I'm not sure you deciphered the message.. The spade connector is your brake light switch.. the warning light on the dash has nothing to do with that. It is controlled by a switch in the brake reservoir that trips when it is low on fluid.... then the issue is what model and year you have which perhaps is muddled. I wouldn't rule out the value of that spade connection as a warning light on the dash.
 

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I'm not sure you deciphered the message.. The spade connector is your brake light switch.. the warning light on the dash has nothing to do with that. It is controlled by a switch in the brake reservoir that trips when it is low on fluid.... then the issue is what model and year you have which perhaps is muddled. I wouldn't rule out the value of that spade connection as a warning light on the dash.
No. That is the differential brake pressure valve. That connector grounds and lights the warning light if there is an imbalance in pressure between the front and rear brakes (indicating a leak).

His car is a '74 with hanging pedals. The brake light switch will be at the brake pedal in the footwell.
 

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Ah, sorry .. I didn't realize it ( the warning light and switch) was part of a multi-functional warning and not related to the brake lights.
 

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I have a 1973 Berlina. The proportioning valve on my car was made by Bonaldi. It is identical to one used on a Pantera. Repair kits are available from www.musclecarresearch.com. They have a tech article on their site showing how to rebuild it.
 

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Discussion Starter #19
I have a 1973 Berlina. The proportioning valve on my car was made by Bonaldi. It is identical to one used on a Pantera. Repair kits are available from www.musclecarresearch.com. They have a tech article on their site showing how to rebuild it.
Guessing this it the tech article you are referring to?

1971 - 1974 Pantera Brake Pressure Control Valve Rebuild | Muscle Car Research LLC and this 1971 - 1974 Pantera Brake Pressure Control Valve Autopsy | Muscle Car Research LLC

And the rebuild kit: Bonaldi Brake Pressure Control Valve Seal Kit | Muscle Car Research LLC
 

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Yes, that is the tech article. There are two differences between the Pantera valve shown in the tech article and mine. The Pantera valve has two outlet ports and the Alfa valve has one. The outlet from the Alfa valve goes to a tee and from there to each wheel. The Pantera valve is mounted in the front of the car and feeds the two front brake calipers with one line each. The other difference which I just saw is that the number of the casting on the Alfa Valve is 6211. On the Pantera Valve it is 5211. If you are considering buying a kit you may want to confirm a few things with the seller about the Pantera valve:
  1. The diameter of the piston where the small seal fits is 14mm
  2. The inside diameter of the valve is 28mm
  3. The I.D and O.D of the copper ring are 30mm &36mm
Best of luck with the project.
Jim
 
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