504 parts identification

Only GRs & SRs (model 1980 & up) have rear live axles.
GLs up till 1979 have independent rear suspension.
According to the parts' catalogue, GRs & SRs do have a brake compensator PN 4861.20
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Beano said:
Don't forget that Doush is in Africa....it may be for an Egyptian 504...They usually have drum rear brakes so will have a 'live' rear axle.

Come to think of it, do rear drum brakes even NEED a rear brake compensator ??????
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If memory serves correctly, any car with discs on one end and drums on the other needs a proportioning valve so that the correct pressure is applied to the discs and drums. Discs need a higher pressure applied than drums do. 504s with discs all round have a load compensating valve to allow for possible higher weight at the rear. Feel free to say I don't know what I'm talking about.
 
Peter C said:
If memory serves correctly, any car with discs on one end and drums on the other needs a proportioning valve so that the correct pressure is applied to the discs and drums. Discs need a higher pressure applied than drums do. 504s with discs all round have a load compensating valve to allow for possible higher weight at the rear. Feel free to say I don't know what I'm talking about.
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I am pretty sure that you know what you're saying ;)
Just saying that all models seem to have the compensator. even the 404 which - I think - have rear drum brakes like the 504 GR/SR.
It's the exact function of the compensator that I don't quite understand (heard that in case the rear wheels leave the ground for some reason, it applies pressure to the rear brakes. I don't know if this is correct.
 
I think there are two different devices. One is a proportioning valve that reduces the pressure to the drum brakes as drumes require less pressure to operate than discs. The other is a load compensating valve that increases the braking effort applied to the rear if the rear is loaded up with people and luggage, etc. Anyone able to verify this?
 
Yes, that is correct. I was getting mixed up between the compensating valve and the proportining valve. I must be getting old.:rolleyes:

And I can verify that it is essential to have a correctly functioning one. When they get old they leak. But sometimes they do not leak...they just freeze up, and you don't know they are not operating properly. But when you put on the brakes HARD, the rear brakes lock up and the car skids forward instead of braking correctly.
This happened to me and I crashed into the back of someone. AAAARGH !

After that I bought one of Ian Robbo's reconditioned stainless steel-sleeved valves.
 
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