I have most recently replaced the cast iron rear calipers with the aluminum PBR setup. Well my brakes still suck. The rear wheels still will not hold while in drive and on stands (pressing as hard as i can). Well I have heard that the master cylinder from the 88'(J65) and earlier disc brake setup was different from the 89' and later setup requiring a (J50) disc/drum master cylinder. I have just most recently purchased one. Well the question is while i am bench Bleeding the rear most (for the front) has plenty of fluid. The front port (for the rear) is the one which does not "squirt" hardly any fluid. Well is this the way these master cylinders were desinged? If anyone knows what i am missing here and might know what the hell is wrong with my brakes, please let me know. thnaks for any help.

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86',88',89' IROC-Z, 350 TPI, 700-R4

[This message has been edited by mystikkal_69 (edited September 23, 2001).]

 

Mystik,

If you study the design of the master cylinder, you'll understand that there must be some restriction on the rear discharge port (for the front brakes) to allow pressure to build at the front discharge port (for the rear brakes). The rear piston not only pumps fluid to the front brakes, but also uses the fluid column in the cylinder to depress the front piston. If you allow all the fluid to flow out the rear port, there will be very little piston travel on the front half of the cylinder and therefore very little fluid.

As for the rear brakes not holding, you may have an issue with the proportioning valve. The valve may be stuck in the rear position, blocking the rear brake port. The valve may also be designed to flow for rear calipers with smaller pistons (less fluid flow), so your rear brakes are going to be very sluggish at best. If the car was converted from rear drums, you need to check the valve to make sure it has been changed. The drum brake unit has a residual pressure check valve that will maintain a slight line pressure in the rear brake system. This is great for drum brakes with return springs, but will quickly overheat and wear rear discs.

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Later,
Vader
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Justice and Freedom will Prevail

 

Thanks Vader For The Info. As always a very informative response. I believe i have made a error on my post. oops. Well the rear most (for the front) has plenty of fluid. The front port (for the rear) is the one which does not "squirt" hardly any fluid.
I had disc brakes on it before just the sorry screw in type of calipers. The prop valve i have is for disc brakes but i guess i'll have to try another. I am at a loss.

Well I Guess Let The Bonfire Begin!!!

[This message has been edited by mystikkal_69 (edited September 23, 2001).]

[This message has been edited by mystikkal_69 (edited September 23, 2001).]