Still no brakes in the back

Topic: Still no brakes in the back (Read 1451 times) previous topic - next topic

Still no brakes in the back

September 15, 2009, 07:17:09 AM

I swapped in a TC rear and replaced the brake line that runs from the MC to the rear. Also swapped the TC prop valve along with new calipers, pads and rotors.

When bleeding the brakes, I can stand on the pedal while dad cracks the bleeders and we get hardly any fluid in the rear. Anytime you open a bleeder while on the pedal you will feel the pedal fade, then close the bleeder This is not the case when doing the rear. The fronts are fine.

Could the flex lines from the body to rear be collapsing? I've heard this can happen but does not make sense to me....when you pressurize a system, how does something collapse...it should expand.

I've read about gutting the prop valve....how does this help and how is it done??

Still no brakes in the back

Reply #1 – September 15, 2009, 08:04:03 AM

There a number of things which may cause the problem.

Start your diagnostic process by pulling the line at the rear end and pump the pedal. If you still have a hard pedal and very little fluid loss, it's likely your proportioning valve. If the pedal works normally and fluid flows, then move to the hoses, disconnect them at the caliper one at a time and see if you have fluid flow, if it's fine there, then the calipers are frozen.

The hoses can go bad, but it's not common as they are not in a position to get kinked easily (the fronts are more pr0ne as people let the caliper hang from hose when swapping pads). The resulting damage from the kink causes fluid to become trapped in the caliper causing the brakes to become locked. Based on your discription of the symtoms it's unlikely the hoses are the problem.

Gutting the proportioning valve and installing a remote adjuster is pretty simple and is outlined on COOLCATS site in the tech section on swapping in a Turbo Coupe rear.

Still no brakes in the back

Reply #2 – September 15, 2009, 08:43:36 AM

I'm thinking there is a problem in the prop valve. There is good fluid everywhere else. I'm getting VERY little fluid from the bleeders and a hard pedal. I thought the TC prop valve was supposed to be the cure to that problem?

Still no brakes in the back

Reply #3 – September 15, 2009, 11:13:44 AM

Clearly there is a restriction. Though the prop valve is the likely suspect, tracking the culprit should be pretty simple, it's just a matter a process of elimination.

Pull the line at the axle (before the flex line), if no fluid, pull the line at the prop valve to make sure there is no kink in the line going back to the axle. If still no fluid, gut the prop valve. If there is still nothing, check the line from the M/C and then finally that leaves the M/C itself.

Still no brakes in the back

Reply #4 – September 15, 2009, 12:17:19 PM

Are you getting flow out of the master cylinder for the rear brakes to the proportioning valve?

On my 86 standard the rear wasn't getting any fluid and the master cylinder was the culprit. No flow out of the rear portion of the master cylinder.

Still no brakes in the back

Reply #5 – September 15, 2009, 09:02:52 PM

I have good fluid from the MC lines...already checked that. I'll have the manifolds back on it tomorrow so it will be mobile again that I can get it over to my other garage and in the air for another eval.

Is gutting the prop vale a rather quick operation? Can it be done on the car? Guessing thats a big "no" but have to ask.

I hate messing with brakes........

Still no brakes in the back

Reply #6 – September 16, 2009, 03:50:11 PM

You can gut the prop valve in the car. I did it on mine, it's a bit tight.

This is the excerpt from the Cool Cats site:

Proportioning Valve Plug
(Used With Adjustable Prop Valve Only)
Currently available as a Motorsport part only under part number M-2450-A, this plug will reside on the end of your old proportioning valve. After the new master cylinder and prop valve are installed, and before you put in any fluid, you must essentially gut the stock prop valve. The end facing the front of the car must be removed and the spring and plunger inside must be taken out. The new plug will go on, and that's it. Be sure to save the old parts.

I know I ordered the Motorsport plug and used it, but it's been long enough ago, I don't recall why it was needed...

Still no brakes in the back

Reply #7 – October 04, 2009, 04:37:48 PM

Ever get this figured out Dan B? What was the problem.

Still no brakes in the back

Reply #8 – December 27, 2009, 09:31:14 PM

I would also be interested in the outcome. I have recently installed a disc rear on my 83 with all new line on the axle, plus a new master, and an adjustable prop valve and I do not believe the rear brakes are working well. I think I may have bent one of my caliper mounting brackets though, so I have to check that and then figure out how many turns is a good spot for the prop valve(Sitting about 50% right now). The Prop valve plug is required due to the valve being integral with the cap bolt, so one must be removed and replaced w/ the other.