[2002TA]

I recently up-graded my 77 TA brakes to rear disc and dual piston fronts. I have a 400 engine running 16 psi vacum. After nearly 3 months of trouble shooting I'm very frustrated. I am getting 400 to 500 psi in both rear and 600 to 700 in both fronts. I have bleed and bleed and find both rear calipers are overheating. When bleeding the brakes I see all the fluid is "brown" like its burnt. I used dot 3 prestone and have went through over 2 quarts so I know its all new fluid. As for the rear caliper, it seems like not enough pressure to allow them to release. The wheels are so hot you can't grab them. SSBC told me it could be my proportioning vlalve so I replaced it with a unit from Summit made for these disc up-grades. After doing so I lost 50-100 psi in all lines. I'v been reading articles on here with others with same issues. I had no problems until going with this $2,000 up-grade. I get no more line pressure with car off/running. Master cylinder and Booster were re-built a few yrs ago. No kinked lines, all were replaced with lines from Russel or SSBC (Except) the hard lines running front to rear axle. I appreciate anyone and everyones help.

[kidd]

Did you replace the rubber line that connects the rear line to the 2 smaller steel lines at the rear axle? If not this could cause the calipers to stick. I had a similar issue on my 70, where the line swelled and blocked the return of the fluid. You could force fluid through under pressure, but as it did not return it hung the calipers up.

Mike

[2002TA]

Yes the kit came with new stainless lines for the rear. I guess I need to change out the main line to the rear and the rear line that runs from that line to both calipers.

[2002TA]

I hooked a guage directly up to the rear master cylinder line out and got 400 to 500 psi with the engine off. At idle i got the same if i got the RPM's up I got 700 ish. I think the brakes PSI should ber the same with engine off/on the Power booster only assist the foot pedal effort? My next step I guess would be to hook the guage to to the rear caliper and perform the same test to see if I have a line issue. am i on the right track . Master Power Brakes can sell me a new MS for 139 but I'm not sure if this is my problem. Any and all ideas/thoughts welcome...

[wrenchmen]

So your brakes are being applied without stepping on the brake pedal? or did I misunderstand you?

When you bolt the master cyl. to the booster, there is a plunger that protrudes
from the booster and contacts the master cyl. piston. This plunger must just touch
the master cyl. piston...if it protrudes out too far, than when you tighten the master cyl.
to the booster the plunger will start to press on the master cyl. piston and apply the brakes.

with your engine off and your pressure gauge installed indicating PSI.,
loosen the master cyl. mounting bolts and see if the psi drops.

With the engine running and good vacuum, while stepping on the pedal the booster will apply
more force to the master cyl. piston...and the psi. should increase.

[2002TA]

Thank you, I appreciate your response. I have zero PSI on my guage when car is off. My brakes worked fine until I up-graded to SSBC disc all the way around. I had front disc but went with the dual pistons in front and up-graded my rear drums to single piston. I am running 15 to 16 pis vacuum at idel. I'v changed Prop valve to a new one designed for this up-grade. SSBC are poor at customer service after the sell. The only thing I have not changed is the booster and master cylinder of which I purchased a few yrs ago and had chromed and built from the manufactorer. All lines are good stainless hoses from SSBC or Russell other than the origianl hard lines, no rubber. I am in a tizzy since its been 4 months since I went with Year One Bandit 18" billet Wheels and up-graded to SSBC brakes. No fun right now

[wrenchmen]

As for the rear caliper, it seems like not enough pressure to allow them to release.

....I'm not sure I understand you.

what exactly is the problem? or symptoms you are experiencing?

[runninwild]

If your wheels and calipers are overheating, then your pads are dragging from the systems failure to release pressure. Barring a plugged line or a cocked piston in the caliper, the problem is probably in the master cylinder. The piston in the master cylinder acts like a spool valve, applying pressure in one position, and releasing it in another position. Even without the assist of the vacuum your brakes would still work, but they would be very hard and unreliable. Since you have good vacuum, and have already replaced the portioning valve, my bet is the master cylinder. You might be able to verify this by bench bleeding. It could be that a very small piece of debris has worked its way through the system and is blocking all or part of the orfice. This would be my bet. Good Luck.

[2002TA]

Thank you I think I have the problem narrowed down to master cylinder or not enough vacuum. Depending on who I talk to I have been told I nee 16, 18 psi. I only have 16 at idel, I am guessing much less when I place the car in "Drive". I even sent one of the rear calipers back to SSBC to have it checked out due to "dragging" they returned it stating it was fine. I guess I have 2 issues
#1 Low line pressure, 400-500 in rear and 650-700 in front. I am told I need 600 in
rear and 1200 in front.
#2: Rear calipers not fully releasing. If the rear caliper issue is due to low line
pressure then hopefully a new MS would do the trick. I was also considering a
electronic vacuum pump to give me 18 PSI. I hope this info clears things up a
little. I appreciate your response.

[myckee]

It sounds to me like the master is bad also. I have less than 16" of vacuum and my 4 wheel discs (not ssbc) work fine.

[Skip Fix]

So where do you all get a brake pressure gauge to sandwich in the line?

[wrenchmen]

#2: Rear calipers not fully releasing. If the rear caliper issue is due to low line
pressure then hopefully a new MS would do the trick.

you want low line psi to release brakes...correct?...probably less than 2 psi, high psi has nothing to due with allowing the rear brakes to release.

You have to determine what is causing your rear brakes to drag, you have already
had the calipers checked for dragging/stuck pistons, you should be able to look at the caliper while someone is applying and releasing the brake and see the piston/brake pads
and caliper move when released. You also have to rule out a mecanical interference
between the caliper and its mounting bracket, it must be able to move freely.

If all above is good than you have hyd. psi not releasing and causing the brakes to drag.
with the brake pedal released, crack a bleeder open at the rear caliper and see if the brake releases. If it does than residual psi. is your problem and you must figure out what is causing that.
A. problem with brake line internally which allows fluid under psi to pass thru but not release.
B. faulty master cyl. or incorrect master cyl....some drum brake designed masters
have an internal residual psi valve which was designed to retain a small amount of psi in the rear brake lines to compensate for excessive movement of mechanical brake components/wheel cylinders.
C. faulty proportional valve. But you had the problem before you added the new proportional valve.

Low vacuum will also have nothing to due with the brake releasing...fix you rear brake drag problem first.

[2002TA]

Originally Posted by Skip Fix

So where do you all get a brake pressure gauge to sandwich in the line?

SSBC and all I did was capped the end going into the prop valve and screwed the guage into the MS. When testing rear lines just scre directly into the caliper.

Lester

[2002TA]

I think its "B" the MS has a residual psi valve plus its old and not designed for 4 wheel disc, so I just ordered a new MS for Master Performance Brakes.

Thanks to eveyone who responded and provided input to my situation I'll post a note once I get it on and see where I'm at.

[2002TA]

Originally Posted by 2002TA

I think its "B" the MS has a residual psi valve plus its old and not designed for 4 wheel disc, so I just ordered a new MS for Master Performance Brakes.

Thanks to eveyone who responded and provided input to my situation I'll post a note once I get it on and see where I'm at.

Just intalled new MS, still not enough power to stop the car properly. So its new calipers all the ways around from SSBC, new propertioning valve from summit, new MS from Master Power Brakes and still lack of power to stop the car in a panic situation. MPB tell me I can't run a Russell Stainless line from Ms to prop valve? However I have good pedal feel and the lines are High pressure and no longer do i have rear brakes dragging on me. any ideas?

[Goin' Topless]

With all the stuff you've changed, do you have the correct length pedal rod in the booster? Your pedal ratio may be off. Does your pedal rod have to go into the m/c an inch or two or is there a solid machined counterbore at the back of the m/c?

Sounds like you have all the right parts now.

[Skip Fix]

If it was an old Disc/drum MC it may have a residual pressure valve in the rear line under the flare fitting for the brake line. That would keep a disc from releasing if it is just doing that in the rear. Sounds like you got that figured out as a possibility.

[2002TA]

Originally Posted by Goin' Topless

With all the stuff you've changed, do you have the correct length pedal rod in the booster? Your pedal ratio may be off. Does your pedal rod have to go into the m/c an inch or two or is there a solid machined counterbore at the back of the m/c?

Sounds like you have all the right parts now.

Yes, the pedal rod seemed to be exactly the same as before I changed my MS. I just changed all the braided steel rubber lines coming off the MS and put new hard lines on the entire front of the car. Going to bleed the system today and this should be it

[2002TA]

Originally Posted by Skip Fix

If it was an old Disc/drum MC it may have a residual pressure valve in the rear line under the flare fitting for the brake line. That would keep a disc from releasing if it is just doing that in the rear. Sounds like you got that figured out as a possibility.

Yes, thanks please read my reply to "Going topless" hopefully today it will be done.

[2002TA]

Now after changing all my front braided hose lines to hard lines. And from replacing the lines from the MS to and from the proportioning valve and the front line, the car will stop but not hard/skid stop. Line pressure was good 1,100-1,200 front and 600 ish in rear. The only 2 things that i have not replaced is the booster and the main brake line that runs from the front to the rear axela nd the rear axle line.