No Rear Brakes

[Jerry Clark]

This question pertains to a completely restored 1965 350 hp power brake car. I chose "O" ringed calipers, Stainless lines, White Post rebuilt M.C and Jerry MacNeish rebuilt booster.
This dual circuit M/C will bleed the front chamber, (although not easily), but nothing I can do will put fluid to the rear.
I have:
1. bench bleed the M/C several times, (fluid pressure from both outlets).
2. attached a vacuum pump to the rear at the caliper and it will hold 35 " of vacuum, (no leaks)
3. applied air pressure to the line while disconnected from both the M/C and the caliper, (no restrictions).
4. returned the M/C to White Post for a reassurance that all is working properly, (it is).
5. vacuum filled the rear lines from the M/C to the caliper
NO REAR BRAKES
I am out of ideas and any and all will be appreciated.
Hope all had a wonderful holiday
jer

[Patrick H.]

Re: No Rear Brakes

Jer,

I'm having a similar problem with my Cutlass. It turns out that the PB booster pushrod is slightly too long, and when I bolt them together, won't let me bleed them properly because it's depressing the MC piston AND as a result, I had no brakes - mostly front not working in my case.

Today I measured that the pushrod is 1/8" too long. I inserted two 1/16" thick washers between the MC and the booster at each stud, and I was able to bleed the system and the brakes work GREAT! The only problem is that now I've got to somehow adjust/fix the pushrod length, but at least I found the problem.

Don't be afraid to think "outside the box" a little in your case to see if it's something similar.

Patrick

[Verle R.]

Re: No Rear Brakes

Check for a mashed/pinched line.

Verle

[Mike McKown]

Re: No Rear Brakes

If the problem isn't what Patrick described then I would suggest it to be the master cylinder itself and as a long shot, both rear flex hoses could be shot. You did mean "no rear brakes, neither side" didn't you?

If as Patrick suggested, I would think you would not get fluid to front or rear.
If you had a pinched line, it could hold vacuum but not pass fluid. I wouldn't think the booster would have anything to do with it. So what does that leave?

The thing that sounds suspicious is you say the fronts don't bleed very well. I assume you mean by the pump the pedal method. This be the case, it takes you back to what Patrick said or faulty master cylinder.

Please post your cure when you find it. I'm really curious.

Mike

[Jerry Clark]

A Bit More Information

EVERYTHING in this restoration has been done. All suspension and brake components are new with the exception of the M/C and Booster
The brakes were functioning with this booster and actuator rod when the car arrived so it should be a safe assumption that those pieces should be of a correct configuration
White Post has double checked the M/C and they assure me it is fine.
Personally I believe that air is the culprit but for the life of me can't understand why vacuum bleeding will not overcome the air, if in fact that is the problem.
Doc is also correct in stating that I use Dot 5 but again I stress that the entire system is new and dry prior to the induction of fluid and the lines were subjected to air pressure and are FREE of obstructions.
I will pressure bleed the system if all else fails
Thanks again
jer

[Patrick H.]

Re: A Bit More Information

Jer,

On both the Cutlass and my Dad's 72 Corvette conv (both of which I bled today) I get a better pedal when I do the wife-pushes-pedal-to-provide-pressure method after I vacuum bleed. Both times I stiil got air out of the system AFTER I'd already done what I thought was a good vacuum bleed.

Even though you sent in the original parts, you don't think it was possible that the pushrods were changed or the configuration somehow altered? It can't hurt to just loosen the MC from the booster and check. I learned a lot when I did this. You can even bleed the system with the MC disconnected from the booster if necessary. I know this for a fact.

Patrick