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When I got my car 20 yrs ago the PO had installed a second stock caliper on each rear wheel. I suspect as a result the car has always had more brake pad drag, evidenced by resistance to rotating the wheel by hand or pushing the car. (The rotors are not warped-- the resistance is steady.)

I believe the cars came with a brake proportioning valve, which was removed when the aftermarket (GM I think) master cylinder was installed. (Again, by the PO). My understanding is that said proportioning valves are to prevent rear wheel lockup.

I would like to remove the redundant rear calipers to eliminate the extra drag, and my question is whether I have to reinstall a proportioning valve if I do that.

I am running 285/40-17 and front 215/45-17 front tires, Goodyear Eagle F1. Looking at that puny rear pad I find it hard to believe that it will lock up that wide tire before the larger front pads will lock up the much narrower front tire.

So I'm thinking removing the extra rear caliper will not require a proportioning valve. Does that sound logical?

I'll disassemble the calipers also to check their condition after 20 yrs of silicone fluid use.
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There is no dial giving front or rear ratio a numeric value. It is all done by tests and feel at various speeds and adjusting the knob to your liking. That way you dial your own car in based on its individual braking ability.

I just made sure that my ratio didn't cause the rear to come around on a full 4 wheel panic lockup. I use the Porterfield pads so it is necessary to make sure they are correctly "glazed" during the tests.
The caliper that seemed to be binding the most was the right rear, so I took it apart. Attached is a photo of the WORST area of corrosion on the piston.
Actually it was just discoloration that wiped off the entire piston literally with 30 seconds of light wiping.
There was some black granular mud stuff in the caliper bore that just wiped away - there was no rust beneath it.
The reservoir is made of metal and there is absolutely no sign of corrosion in it or the fluid in it, the latter being crystal clear.

I took off the forward caliper on that side, turned it upside down, and bled the fluid out using a suction device. It was crystal clear without any sign of rust. So it seems there was no water in that caliper.


Images (1)
  • IMG_3395_Pant_RRR_brake_piston_sm
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