[Jimbro727]

I've had a problem with the brakes on my 78 T/A since I bought it a little over a year ago. I initially had a mechanic replace the M/C, prop valve, and parts of the brake lines, but that didn't seem to help much. I then replaced the drums/shoes/cylinders and calipers/pads - no significant change. After chasing the problem around, I ended up replacing the booster and M/C (this is now the second M/C, and I also bled it). The problem persisted - the brakes don't stop the car from a roll until late in the pedal's travel. I then decided to replace all of the lines (including the rubber lines) and the proportioning valve (again). Now every single part in the brake system is new. I pressure bled today, having just finished installing the lines, and everything seemed to bleed fine - some bubbles, then solid fluid, from all four corners.

The problem is the same - although the pedal feels slightly different. The pedal is stiff when the engine is not running, and when it is running, it's feather light, there's almost no resistance. The car won't stop from a roll until the pedal is floored.

Anyone have any idea what the problem might be? Absolutely everything is new. Is there any kind of adjustment on the pedal? I know there's two holes - the booster rod is on the lower hole. The upper hole has a screw and a nut through it. How much fluid do I need to bleed after replacing all of the lines - maybe I didn't bleed enough?

Any help would be greatly appreciated - I'm at a total loss here. Thanks!

[67drake]

Since it seems you have been screwing around with this for a long time now,I'm sure you have tried this,but I have to ask since I didn't see you mention it.
Have you tried to adjust the rear brakes up tighter? If the rear drums are too far out of adjustment,it will have the same symptoms.
Just checking.

[Jimbro727]

Originally Posted by 67drake

Since it seems you have been screwing around with this for a long time now,I'm sure you have tried this,but I have to ask since I didn't see you mention it.
Have you tried to adjust the rear brakes up tighter? If the rear drums are too far out of adjustment,it will have the same symptoms.
Just checking.

Hey thanks for the reply-

I have done this a few times as I've chased this problem around - but I haven't done it recently, so I'll give it a shot.

How much would you tighten them? I've read all different ways to know when they're set. I think the method I used last was to tighten them until they drag, then back it off a little.

[quicksilver97ta]

Did you check the clearances between the master and booster? That could account for excessive pedal travel. Honestly though, my best guess, and it's only a guess, there is still an issue with bleeding the brakes.

[Jimbro727]

Originally Posted by quicksilver97ta

Did you check the clearances between the master and booster? That could account for excessive pedal travel. Honestly though, my best guess, and it's only a guess, there is still an issue with bleeding the brakes.

What clearances? How do I check that?

Do you know how much I should bleed the system before it's safe to assume there's no air anywhere? I agree that it sounds like air is somewhere - I just don't know where.. or how

[Hammertime Mike]

Pedal travel comes to mind.I believe there is an adjustment that you can make on the brake pedal rod.If for some reason the rod length has been messed with prior to your ownership this could throw everything out of whack!I'd first check the rod length to another rod from another bird.At least it would tell you if your rod length is OK.Goodluck!

[low63gp]

Well, I have been having the opposite problem, too soon of a pedal that will put your face in the dash but I do know that on my 63 GP, there is an adjusting screw on the end of the booster rod that sticks out and goes into the MC. It is a smal ball type end adjusting screw that takes a 1/4" wrench and the other (female) section takes a 5/16". I'm not sure if it is adjustable like mine or it may take a ball or something like that in between the MC and rod? Sounds like this is where your problem is?

[Jimbro727]

Thanks for the replies-

This is what throws me off: The pedal is stiff all the way from the beginning of its travel when the engine isn't running. I don't know much about the inner workings of the booster, so would the booster alone cause the pedal to be stiff when the engine isn't running? I've been assuming that it's stiff because the booster is making contact with the M/C.

If that is the case - the booster is making contact with the M/C from the start of the pedal's travel - then if I adjusted it, it would constantly be depressing the M/C piston - is this what should be happening, or should the booster come completely off of the M/C when there's no pressure on the pedal?

[quicksilver97ta]

Originally Posted by Jimbro727

Thanks for the replies-

This is what throws me off: The pedal is stiff all the way from the beginning of its travel when the engine isn't running. I don't know much about the inner workings of the booster, so would the booster alone cause the pedal to be stiff when the engine isn't running? I've been assuming that it's stiff because the booster is making contact with the M/C.

If that is the case - the booster is making contact with the M/C from the start of the pedal's travel - then if I adjusted it, it would constantly be depressing the M/C piston - is this what should be happening, or should the booster come completely off of the M/C when there's no pressure on the pedal?

There should be no contact between the booster rod and the master cylinder, only the slightest clearance to allow for heat expansion. If the booster rod is depressing the master cylinder just by being bolted together, the system may not bleed properly since the master cylinder is never fully at rest. Try loosening the bolts for the master, pull it forward from the booster just slightly, then bleed the brakes again using a vacuum pump at each wheel.

[4dblnkldude]

Sounds like it is definitely a rod problem. However it seems you still mdon't have them bled all the way too. Let that TA gravity bleed for a while. I imagine the second gens are similiar in fluid capacity, about two quarts. Bleed all the way through til you get nice clean fluid out the rear. Good luck

[Jimbro727]

Originally Posted by quicksilver97ta

There should be no contact between the booster rod and the master cylinder, only the slightest clearance to allow for heat expansion. If the booster rod is depressing the master cylinder just by being bolted together, the system may not bleed properly since the master cylinder is never fully at rest. Try loosening the bolts for the master, pull it forward from the booster just slightly, then bleed the brakes again using a vacuum pump at each wheel.

OK thanks - I'll give that a try. I don't think the booster is depressing the M/C just by being bolted together, but I'm not 100% sure. If I do determine that the booster is depressing the M/C, what should I do to fix that?

Originally Posted by 4dblnkldude

Sounds like it is definitely a rod problem. However it seems you still mdon't have them bled all the way too. Let that TA gravity bleed for a while. I imagine the second gens are similiar in fluid capacity, about two quarts. Bleed all the way through til you get nice clean fluid out the rear. Good luck

I'll give gravity bleeding a shot if the above doesn't work. I've heard mixed opinions on gravity bleeding - but at this point I'll try anything. Is there an advantage to gravity bleeding over pressure bleeding? One of the problems is it's hard for me to see when I've bled the entire system, since it's all new fluid.

[4dblnkldude]

Gravity bleeding is a pain, especially now, when you want to be driving it not chasing down bugs. I've just always jacked the car up level and cracked all four bleeders and let her go. Fill up master and wait an hour, come back and pour more fluid in. It takes all day but then your manual bleeding takes a half hour. Then do it again after a couple of days, the manual bleeding that is. Good luck, hope ya get squared away.

[Bandit79403Dave]

I am having the exact same problem with my '78 TA except I have a totally new system in there: '99 TA Rear brakes up front on 1LE rotors and '86 GN front disc brakes on the back...no E-brake. I have a Detroit Speed master/booster combo and no matter how much I bleed it as soon as I fired it up there is basically no pedal. EXACTLY like yours...hard when off, nothing when running.

GREAT to hear from someone else having the same problem...at least I am not crazy. I will try and adjust the push rod length and see what I get.

Dave

[Jimbro727]

Originally Posted by Bandit79403Dave

I am having the exact same problem with my '78 TA except I have a totally new system in there: '99 TA Rear brakes up front on 1LE rotors and '86 GN front disc brakes on the back...no E-brake. I have a Detroit Speed master/booster combo and no matter how much I bleed it as soon as I fired it up there is basically no pedal. EXACTLY like yours...hard when off, nothing when running.

GREAT to hear from someone else having the same problem...at least I am not crazy. I will try and adjust the push rod length and see what I get.

Dave

I feel the same way! I'm glad I'm not the only one out there. It's such a frustrating problem. My old mech couldn't even figure it out - he told me my cam was too big, so my vacuum was too low - but wouldn't that make the pedal hard??

Anyway, if you do end up solving it, PLEASE let me know, and I'll be sure to do the same.

Do your brakes work a little? With the car running, when I floor the pedal, I can stop it from a roll.

EDIT: I was just reading another thread, and someone mentioned that he's seen a lot of brand new M/Cs that are bad right out of the box - I've actually heard that a few times. Maybe it's possible that's my problem? Two bad M/Cs in a row? Are my symptoms indicative of a bad M/C?

-Jimmy

[chipster]

You still have air in the master cylinder. Either take it off and bench bleed it properly, or find a hill steep enough that the master cylinder is level when the car is parked nose-down and do short-stroke pumps on it for a while. The bubbles will come up from the holes in the floor of the master cylinder reservoir.

[Bandit79403Dave]

Hey Jim,

I hear ya! I have been working with Detroit Speed and they have been awesome...they went back to their manufacturer and after a day or two they sent me a new booster.

My car stops without the booster hooked up but as soon as I hook the booster up it takes virtually no pressure and the pedal goes to the floor. Too afraid to try and stop it with the booster hooked up.

I will try, once again to bench bleed the master. I am going to install speed bleeders as well to see if I can luck out there as well.

I'll let you know,
Dave

[Bandit79403Dave]

Well...I tried to bleed the brakes again. I did get a few big bubbles from the front passenger side but no change in vacuum assist issue. I tried plugging the master and bench bleeding and no change again...at this point it has turned into a full blown quest!!!

I am not sure at this point if the booster is really bad. I still think there is air hidden in the system somewhere. I will try and completely remove the master cylinder to try and bench bleed it while being level.

I used a mitivac to bleed it and I am still having no luck...anybody got any ideas for us???

Thanks,
Dave

[THEGTOCHISM]

i had a similar problem on a vehicle. turned out the master cylinder was wrong for the car. the dept of the rear of the master cylinder where the brake booster rod goes was deeper than the original. drove me crazy for a week. i thought it was trapped air. Remove the master cylinder and measure the dept of the rear hole. Now measure the extending rod end from the booster where the master cylinder will bolt on. it should be real close. check your manuel for the exact measurment needed. most booster rods have a adjustment on the end to lengthen or shorten them. mine was off darn near 1/2"

[Bandit79403Dave]

I am going to try something similar this evening...Detroit Speed and Engineering sent me a brand new booster so i would have to take off the master anyway...

I figure I will measure the pushrod while I have the opportunity.

Keep you all posted!
Dave

[THEGTOCHISM]

well it is more or less a process of elimination. if you have air in the lines you will see boubbles in the fluid when you bleed them. if you check the dept of the rear master cylinder against the lengh of the rod into that hole where it makes contact then that is eliminated. do you have the correct kind of hose from the intake to booster. a lot of people use gas line hose, instead of the heavier booster hose. That can collapse when the brakes are applied. also check the vacume one way valve on that line at the booster and make sure it is working properly.