Brian's Bucket Build

[Hackerbilt]

Well I got out for a ride today and still no good. I jacked the rear of the car up and ran it in gear and I was unable to stop the wheels. The rear brakes are barely operating. I pulled the drums and stepped on the brakes and both wheel cylinders were expanding. I double and triple checked that the shoes and springs were installed correctly. Something aint right. Like I said all of the brake components were new when installed,bought from rock auto. So, I said the heck with it and went to advance auto and bought all new stuff. Tomorrow's another day, glad I'm retired.

Well you have everything you need to get good brakes now, so there is a mechanical issue somewhere.
"Island girl" made a good point about the adjusters...if you are running self adjusters...and so did "AusBucket" about the bench bleeding.
The rear shoes aren't some type of semi-metallic are they? There are some that need to get hot to get good stopping power.

Is the pedal firm and standing away from the firewall at full compression? Is the floor slot long enough?
Are you adjusting the shoes with the tire and wheel on? I'd adjust them to a noticeable drag as you rotate the tire and give that a test. Seems odd you get cylinder movement but still not enough clamping force to stop a jacked up wheel and tire!

 

[2old2fast]

W/o rereading this whole post , was the rear hose and tee block on the rearend replaced/ checked, the hoses collapse internally....

 

[Swampdog]

Are you sure that the rubber cup seals in the rear wheel cylinders are installed in the right direction. The cup side on the fluid side and the flat side against the piston.

 

[fletcherson]

Not to be insulting, but did you adjust the rear drum brakes? Like tighten them up so they are restricting (not preventing) wheel rotation? They will burn in in short order. If the shoes aren’t against the drums, the wheel cylinders will move the shoes but not apply pressure to the drums. Also, if the wheel cylinders are traveling back and forth, or if the fluid is freely flowing to and from the wheel cylinders, same thing. That’s the purpose of the residual valve, to prevent that. There shouldn’t be hardly any movement in the wheel cylinders or calipers, the pads/shoes should slightly contact the drums/rotors always, even when not applied. Even though cars came with dual resevour master cylinders from the factory, they still had proportioning valves to bias the brakes to that vehicle.

 

[DonnyRay]

General Motors disc to drum proportioning valve .

 

[Neshkoro]

I have to replace the leaking master cylinder on my bucket. Looking at the NAPA web site, they show 2 different master cylinders with different diameter pistons. One is 7/8" and the other is 1". The 7/8" piston is for metallic brake shoes and the 1" is for standard shoes. I'm assuming you need more pedal pressure for metallic shoes. My master cylinder is from a 1966 Chevy so that's what I'm replacing it with.
Maybe you have the wrong master cylinder.
I've never had any major problems with my setup. I did have a leaking wheel cylinder causing one front wheel to lock up due to the shoe being soaked with brake fluid. New shoes cured that problem.
The reason I ask about the master cylinder piston is that I never knew there was a difference.

 

[fletcherson]

I have to replace the leaking master cylinder on my bucket. Looking at the NAPA web site, they show 2 different master cylinders with different diameter pistons. One is 7/8" and the other is 1". The 7/8" piston is for metallic brake shoes and the 1" is for standard shoes. I'm assuming you need more pedal pressure for metallic shoes. My master cylinder is from a 1966 Chevy so that's what I'm replacing it with.
Maybe you have the wrong master cylinder.
I've never had any major problems with my setup. I did have a leaking wheel cylinder causing one front wheel to lock up due to the shoe being soaked with brake fluid. New shoes cured that problem.
The reason I ask about the master cylinder piston is that I never knew there was a difference.

The larger bore may have been for power assist also. (?)

 

[Hackerbilt]

General Motors disc to drum proportioning valve .View attachment 15319

That is to slightly restrict pressure to the REAR. Not what he needs.
T buckets have much better weight distribution than a regular sedan and can use a little more to the rear...especially with the larger rear tires and smaller front tires most use.
He just needs to figure out the issue with what he has now.

 

[Island Girl]

That is to slightly restrict pressure to the REAR. Not what he needs.
T buckets have much better weight distribution than a regular sedan and can use a little more to the rear...especially with the larger rear tires and smaller front tires most use.
He just needs to figure out the issue with what he has now.

I always thought that that proportioning valve was to restrict initial pressure to the front disk brakes for low need braking applications, as drum brakes need more pressure to overcome the retracting springs that are not present on a disk caliper. Once greater pedal pressure is applied, the front brakes are applied more equally.

Darlene

 

[Hackerbilt]

I always thought that that proportioning valve was to restrict initial pressure to the front disk brakes for low need braking applications, as drum brakes need more pressure to overcome the retracting springs that are not present on a disk caliper. Once greater pedal pressure is applied, the front brakes are applied more equally.

Darlene

Thats called, among other things, a hold off valve I believe. Those were used in some GM cars and were specific to each car model and individual years apparently. I dont know much about them. They are non adjustable though. What he has in the front line now is an adjustable proportioning valve. Its tuneable and will help balance things as needed. Once he finds out exactly whats happening to make his rear brakes so ineffective of course.

 

[BrianD]

Ok, here we go again. Replaced everything again in the rear, still very little to no stopping power from the rear. I have an APV on the fronts, with the valve open all the way it stops ok. With the APV closed all the way (about 50% less pressure) I could barely stop with both feet on the pedal. I just ordered a pressure gauge to see what my pressures are front vs rear. Am I correct in assuming that when braking hard at say 40-50mph that all 4 wheels should be locking up if adjusted properly? Also should the pressures from the m/c be the same front and rear? It's a good thing that I'm independently wealthy, LOL. I appreciate all of the help and ideas you guy's,and gal (island girl)have been giving me, after I resolve this issue I'll be the forums new brake expert. I'll keep you posted, we will fix this.

 

[Spanky]

I hate to beat a dead horse, but have you adjusted the little star wheel on the self adjusters until the shoes make contact with the drums?

 

[Hackerbilt]

You will beat it...and it will be some silly little thing that will make us all feel stupid in hindsight! Hahaha
Thats how this stuff usually works out. Its very difficult to diagnose things long distance for all of us...but one thing about this board is everyone honestly tries to help...and most have been down the same or a similar road. We're all rootin' for ya! We want to see you out enjoying that little bucket!!! All the best!

 

[AusBucket]

Having read this thread from the start, I am of the opinion you have a combination of too small a wheel cylinder for the Master Cylinder bore. Reason I say this is because we face the same problem with the rear ends we use on the Clubman cars I've been building. We increase the size of the wheel cylinders (17 up to 21mm) and reduce the master cylinder to 5/8" bore for the rear. We use an 11/16" (.7") master cylinder for the front. This is using duel masters with balance bar. The Clubman can use quite a bit more braking in the rear like the Bucket can. I would look to see if there were any larger wheel cylinders for that series diff that would swap in, and I would reduce the master cylinder bore to 7/8" or smaller, maybe 3/4" if possible. This will give more braking effort to the rear and introduce compliance into the feel of the brake pedal, allowing modulation of the brakes that you have when the system is boosted. In the old days the pedal ratio was a minimum of 6-1, and a lot were 7-1. Your current setup is cancelling out the ratio advantage of the pedal reducing rear pressures by a lot.
Trust this is helpful.
Regards,

 

[Hackerbilt]

Having read this thread from the start, I am of the opinion you have a combination of too small a wheel cylinder for the Master Cylinder bore. Reason I say this is because we face the same problem with the rear ends we use on the Clubman cars I've been building. We increase the size of the wheel cylinders (17 up to 21mm) and reduce the master cylinder to 5/8" bore for the rear. We use an 11/16" (.7") master cylinder for the front. This is using duel masters with balance bar. The Clubman can use quite a bit more braking in the rear like the Bucket can. I would look to see if there were any larger wheel cylinders for that series diff that would swap in, and I would reduce the master cylinder bore to 7/8" or smaller, maybe 3/4" if possible. This will give more braking effort to the rear and introduce compliance into the feel of the brake pedal, allowing modulation of the brakes that you have when the system is boosted. In the old days the pedal ratio was a minimum of 6-1, and a lot were 7-1. Your current setup is cancelling out the ratio advantage of the pedal reducing rear pressures by a lot.
Trust this is helpful.
Regards,

I believe you are onto something there.
I know for a fact that the later S10's with the bolt on wheel cylinders had two sizes available.
When I bought my used drum brake setup from the pickapart I also bought NEW wheel cylinders in the larger size.
OP might have the smaller size on his setup.

Definately worth investigating!

 

[BrianD]

Well I got my pressure gauge and here's what I got. Front and rear pressures are the same, and pressures are the same if measured at the calipers/wheel cyl. and the master cylinder. With what I would call "normal" braking pressure I have around 4-500psi, If I stand on the pedal real hard, like in a panic stop I have about 700psi. If what I'm reading on the web is correct with my set up I should have 7-800psi with normal braking and almost 1000psi standing on the pedal. So, is this normal and I'm trying to fix something that isn't broke? I'm just not happy with the way this thing brakes. I guess my next step will be be either rear disc conversion or a power booster. I give up!!!!

 

[old round fart]

Think I would try a smaller bore master cylinder first. With a disk conversion you still have the same pressure. How about more pedal ratio?

 

[2old2fast]

This will sound .wackey.....sit in a position where you can push against the opposite wall....put the bathroom scale against the wall and push on it....100# pressure ??? ...x pedal ratio, 6:1=600#,. If you're not getting that , something wrong with pedal or m/C .,.

 

[Indycars]

With what I would call "normal" braking pressure I have around 4-500psi, If I stand on the pedal real hard, like in a panic stop I have about 700psi.

Well that tells the story very clearly!!!

Like ORF said, you need to change a smaller MC or the greater pedal ratio to generate the required
pressures. The only other thing that will increase the pressures would be to change all 4 wheel
cylinders to a larger diameter, but that would be considerably more work than changing the MC.

Some photos of the test equipment would be nice!

 

[AusBucket]

Next step is definitely a smaller bore master Cyl as suggested by ORF, there's nothing wrong with boosting the system as is either. Either way will give you a positive result.
Regards,