[GTOGreg]

There are two possible pedal considerations: 1.) the positioning of the swivel connector (that takes the pin), and the proper hole in the pedal arm, and 2.) the length of the pushrod that sits between the booster and the master cylinder...there are usually two pre-fit sizes and then an adjustable unit when you buy a new booster. I'm thinking it might be that you have too short of a pushrod in there or your prop valve is frozen or misadjusted.

[SteveGTO]

I had a horrible time when I replaced my MC and booster last year. Hopefully something in my story will help.

After the swap, with everything else unchanged, my pedal would get stiff and travel would become very short after a qhick drive. Ended up the front brakes also started to drag so badly that I couldn't even turn the tire by and after jacking it up. After it cooled down everything was fine. Pedal travel was adjusted all the way out but I couldn't give it enough not to run out of travel. I thought it was air in the MC, brake lines too close to headers, etc.

Read another post that ponted to some shoddy clearances between the MC and booster, specifically the rod. Ended up the MC was being engaging on me. Try this. Loosen the two MC to booster bolts. The MC should just sit there. In my case the MC wanted to pop off the face slightly. Nothing that made me think there was a problem. I threw some washers on the two mouting posts and I never had a problem again. Ended up the piston was being depressed slightly and after the brake fluid heated up I was getting enough engagement to drag the front brakes.

[Bandit79403Dave]

My problem has to do with a DSE booster/master cylinder combo...the pushrod comes with already installed in the assembly. I am going to try something tonight with regards to the brake bleeding/pushrod length and see if it works.

Thanks,
Dave

[Jimbro727]

Hey sorry I haven't checked on this thread in a while - I'm in my last two weeks of college, so I haven't had much pontiac-time.

I missed too much to respond individually, but I carefully read everyone's post. As many of you mentioned, there's just not that much to the system. I'm going to take the M/C off, bench bleed it again, and measure the rod length while it's off. That should eliminate two things. If that doesn't pan out, then I'm leaning towards two bad masters in a row. I've read a few people's stories of receiving two bad masters in a row, and it really throws you off, because after replacing it twice, you just assume that's not the problem.

Someone mentioned that the vac line could be wrong and collapsing or the valve could be malfunctioning, wouldn't that cause a lack of vacuum to the booster, thus making the pedal hard? This is an issue that I keep hearing in various forms - particularly when talking about my cam - that low vacuum can cause issues like this. Can someone with knowledge of these power boosters clear this up for me? I was under the impression that low/no vac would just cause a stiff, but still working, brake pedal, since the power assist wouldn't be operating. If I'm mistaken, then that introduces a few other possible causes for my problems.

Dave: I'm glad you're on your way to solving this! Definitely keep us updated!

[THEGTOCHISM]

i just mentioned the valve and hose as a area for you to inspect to be sure they are functioning properly. i don't believe that is your problem. If you have trouble finding booster hose, just ask for air brake hose like the trucks use. I am still leaning toward master cylinder hole debt, and booster rod length. A lot of the books now only list one master cylinder for power/none power brakes for the old cars. In the old days there were two different master cylinders listed on most models. These kids behind the counter now are too young to know that. They just go by what the computer says. also have you checked for any tight bends in the lines from the master cylinder to the prop. valve? You stated the brakes worked, just late in the pedal trave. and like gtogreg said pin location on the two pre drilled holes on the pedal. providing your car has that.

[Jimbro727]

Originally Posted by THEGTOCHISM

i just mentioned the valve and hose as a area for you to inspect to be sure they are functioning properly. i don't believe that is your problem. If you have trouble finding booster hose, just ask for air brake hose like the trucks use. I am still leaning toward master cylinder hole debt, and booster rod length. A lot of the books now only list one master cylinder for power/none power brakes for the old cars. In the old days there were two different master cylinders listed on most models. These kids behind the counter now are too young to know that. They just go by what the computer says. also have you checked for any tight bends in the lines from the master cylinder to the prop. valve? You stated the brakes worked, just late in the pedal trave. and like gtogreg said pin location on the two pre drilled holes on the pedal. providing your car has that.

OK no problem - I wasn't sure if that was just additional advice, or if I was misunderstanding how the booster functions. The lines are all new from inline tube, but I did have to play with the M/C -> prop valve lines to get them to fit. I was careful to only make big bends, but I'll double check.

I did check the pin location, and it's in the lower hole - which I *think* is the correct one, please let me know if it isn't. The upper hole has a bolt and a nut through it, which appears to serve no purpose other than to fill the hole (it's tough to get myself in to a position where I can easily see the holes).

[Bandit79403Dave]

Hey Guys,

I think I am on to something...I bench bled the master...again. No change...

Replaced the booster and and there is definitely a change for the better. I have to rebleed the system again and check it but I will keep you posted for tonight. It just got too late last night and I had to go to bed...I know...big baby.

Stay tuned...
Dave

[Jimbro727]

Originally Posted by Bandit79403Dave

Hey Guys,

I think I am on to something...I bench bled the master...again. No change...

Replaced the booster and and there is definitely a change for the better. I have to rebleed the system again and check it but I will keep you posted for tonight. It just got too late last night and I had to go to bed...I know...big baby.

Stay tuned...
Dave

Hey Dave,

Did you ever make any progress with this? I haven't had any time to look at mine, but I'll finally have time to work on it a lot next week.

Jim

[Jimbro727]

UPDATE: I took the M/C off to bench bleed again. While I had it off, I took a look at the booster rod length - it looks fine. I also pressed the pedal all the way down and measured how far the rod comes out of the booster. That length is also roughly the same as how far I can manually push the piston in the M/C.

I bench bled the master, and got some bubbles. I kept getting small bubbles out of the front reservoir if I let it sit for a few minutes, then bled again. I decided to bolt it on, but leave the hoses attached to the two ports and running back in to the reservoirs. I then pumped the pedal, and the rear reservoir was fine, no bubbles whatsoever, but very small bubbles kept coming out of the front port. When I pressed the brake pedal all the way down and held it there, little bubbles would continue coming out of the front port for a few seconds. I kept pumping to try to bleed that air out, but I couldn't get to the point where there were no bubbles.

I decided to hook the lines back up, bleed the system, and see if there was a change. While I was bleeding the rears, I also adjusted the shoes so that they make a good amount of contact with the drums (I'd have to tap the drum with a mallet to get it off). Either the bleeding or the rear adjustment caused the pedal to be a LOT more stiff when the engine isn't running. It feels exactly as it should - so tough that I feel as though I might break the pedal if I press it all the way down - but it still goes down, just with a lot of force.

Unfortunately, with the engine running, the pedal is still feather light, and I'm still having the exact same problem. The car doesn't stop until the brake pedal is almost completely on the floor.

What do you guys think? Bad M/C? I'm pretty sure I covered all of my bases. I pressure bled the brakes for a l-o-n-g time, there's no air in the lines.

[hectore3]

Replace the master. Is it one of the part store specials? If so try to get one from a reputable manufacturer.

[Jimbro727]

Originally Posted by hectore3

Replace the master. Is it one of the part store specials? If so try to get one from a reputable manufacturer.

It's a new unit that I purchased at Advance Auto, I forget who actually manufactured it. I don't know if that makes it a part store special or not. When I bought it, I wasn't aware that there was much difference if I was just replacing the original master.

Can you recommend any manufacturers?

[Jimbro727]

I've still been trying to solve this problem, but haven't had much luck.

While looking in to something else, I came across a diagram of how a front disc/rear drum brake system should be plumbed, and it showed a residual valve for the rear brakes, and said it's very important. I just replaced all of my brake lines, and didn't see any residual valve. Is that built in to the combination valve, or is it something I need? Does anyone know?

[69Goat1]

Change the booster...

[Jimbro727]

Originally Posted by 69Goat1

Change the booster...

I've already replaced it. Could the booster cause these symptoms? I'd replace it again, but I thought a bad booster would cause a hard pedal?

[GREATGTO]

also check to see what bore size master cylinder you have, the small bore 1'' or smaller are for manual brakes, yours should be the larger more than 1'' for power brakes

[Jimbro727]

Originally Posted by GREATGTO

also check to see what bore size master cylinder you have, the small bore 1'' or smaller are for manual brakes, yours should be the larger more than 1'' for power brakes

Yep, I thought (was hoping) that was the problem, but I measured the bore size of my previous master, and it was 1 1/8", which I believe is the correct size. I then called Cardone for the bore size of the master that I currently have installed, and they said that it's 1 1/8".

I'm going to start isolating parts of the system today, starting with plugging the master, and seeing if the pedal stiffens up, that way I'll know if it's the booster/master, or something else, and I'll move around the system in that fashion, hopefully until I figure out the problem. If anyone has any suggestions, I'd be happy to hear them - I'm getting desperate! It's getting nice out, and I need my T/A to stop as well as it starts!

[GREATGTO]

maybe the proportioning valve is out of adjustment, most likely its going to be something simple. The other thing I would do is find someone who has the exact same car as you , take a look how everything is setup on theirs then verify it with yours.

[HWYSTR455]

Yeah, I'll take a shot, since there's a couple of grey areas still.

On the rear brakes, adjust them all the way to the drum, with it up on jack stands, and try the pedal with the car running, see if it's the same. Drums, adjusted, drag. If the shoes aren't centered properly on the backing plate, or there's something else out of whack back there, it can have this type of an effect. Take a pick of both sides with the drums off and post them.

You verified the booster push rod and MC plunger distance? What is it? It's supposed to be something like < 3/16s, not something you can eye-ball. You should be using the ears of the MC mounting area as a reference, and that suface on the booster. If there's a question, use a small piece of wax or something on the end of the rod, tighen the MC up, take it off, and see how far it's compacted.

MC bleeding. NO bubbles should come out, and you keep pumping that b*tch until there are NO bubbles. It takes a while, but you do get there. Don't even bother putting the thing on the car if you still see bubbles. You can tap the side with a wrech lightly in between pumps, it helps a little. You don't have to depress the punger all the way, and in fact, think you're not supposed to bottom it out.

MC sizing, yup, you'll probably have a 1 1/8 MC. Those are the type with shallow rod pucks. The 1" manual MCs ONLY come in deep rod puck/hole, which is what some people want, and they still don't make any. Some people have used spacers to use a 1" on a booster. Regardless, you have a 1 1/8, and if it's a 78 T/A, it's the typical GM large/small reservoir type MC. Take a pic, post it.

MC line placement. You say you replaced the prop valve? Which line do the rear brakes plumb to on the master? Usually, the front port on the MC goes to the rear brakes, and the rear ports go to the front brakes. If there's a question if this is correct or not, check the factory service manual. You say you had to 'bend' the MC to prop lines as shipped from Inline to make them work? Sounds like you might have them mixed up. Take a pic and post it.

Prop valve- Does the brake light in the dash come on when you hit the brakes all the way? If so, your prop valve brake bias rod may be all the way to one side, which generally, only effects your rear brakes. Do a search on pro-touring for 'brake bias switch'.

System bleeding- A quick note on this, gravity is ok, but usually on a fresh system, it's hard to get started. In general, however you bleed the system, always start from the furthest wheel from the MC, then the next furthest, etc. Never let the MC go dry, since you'll be re-entering air into the system, and that bubble will have to travel the entire distance to remove.

Booster replacement - You can unbolt and move the MC out of the way enough to where you don't have to take the lines off and re-bleed.


.

[Jimbro727]

Originally Posted by HWYSTR455

Yeah, I'll take a shot, since there's a couple of grey areas still.

On the rear brakes, adjust them all the way to the drum, with it up on jack stands, and try the pedal with the car running, see if it's the same. Drums, adjusted, drag. If the shoes aren't centered properly on the backing plate, or there's something else out of whack back there, it can have this type of an effect. Take a pick of both sides with the drums off and post them.

You verified the booster push rod and MC plunger distance? What is it? It's supposed to be something like < 3/16s, not something you can eye-ball. You should be using the ears of the MC mounting area as a reference, and that suface on the booster. If there's a question, use a small piece of wax or something on the end of the rod, tighen the MC up, take it off, and see how far it's compacted.

MC bleeding. NO bubbles should come out, and you keep pumping that b*tch until there are NO bubbles. It takes a while, but you do get there. Don't even bother putting the thing on the car if you still see bubbles. You can tap the side with a wrech lightly in between pumps, it helps a little. You don't have to depress the punger all the way, and in fact, think you're not supposed to bottom it out.

MC sizing, yup, you'll probably have a 1 1/8 MC. Those are the type with shallow rod pucks. The 1" manual MCs ONLY come in deep rod puck/hole, which is what some people want, and they still don't make any. Some people have used spacers to use a 1" on a booster. Regardless, you have a 1 1/8, and if it's a 78 T/A, it's the typical GM large/small reservoir type MC. Take a pic, post it.

MC line placement. You say you replaced the prop valve? Which line do the rear brakes plumb to on the master? Usually, the front port on the MC goes to the rear brakes, and the rear ports go to the front brakes. If there's a question if this is correct or not, check the factory service manual. You say you had to 'bend' the MC to prop lines as shipped from Inline to make them work? Sounds like you might have them mixed up. Take a pic and post it.

Prop valve- Does the brake light in the dash come on when you hit the brakes all the way? If so, your prop valve brake bias rod may be all the way to one side, which generally, only effects your rear brakes. Do a search on pro-touring for 'brake bias switch'.

System bleeding- A quick note on this, gravity is ok, but usually on a fresh system, it's hard to get started. In general, however you bleed the system, always start from the furthest wheel from the MC, then the next furthest, etc. Never let the MC go dry, since you'll be re-entering air into the system, and that bubble will have to travel the entire distance to remove.

Booster replacement - You can unbolt and move the MC out of the way enough to where you don't have to take the lines off and re-bleed.


.

THANK YOU for your informative response!

I got very excited, because I thought that the lines from my M/C to the combo valve might be wrong, because I have seen many cars with the lines crossed, but I verified in my manual that the rear (closest to the firewall) port on the M/C is for the rear brakes, and the front (closest to the front of the car) port is for the front brakes. The lines from the M/C are two sizes - the thinner one goes from the front port to the left (facing the firewall) port on the combo valve (the one for the front brakes), the thicker one goes from the rear port to the right port on the combo valve (for the rear brakes). Does that sound correct? I can post a picture if that helps.

I have adjusted the rear drums until they drag, but I will take pictures some time today.

I have not verified the booster pushrod distance. Is there a way I can measure this, or should I use wax or something as you described?

I haven't actually been able to get the warning switch connected. It seems as though the rod is too high for the connector to fit, but I hadn't played with it very much. The valve is new from inline tubes.

I've bled the brakes every possible way - traditional (using the pedal), vacuum, gravity, and most recently, pressure.


I do recall there being a change in the feel of the pedal once I replaced the booster. I hadn't thought about it, because I was under the impression that a bad booster would cause a stiff pedal. However, I've read recently that a bad booster can cause a low pedal, too. Is that true? If so, is there any way that I can test the booster?

Thanks again for your reply - I really appreciate the help. I'm getting very frustrated with this problem.

[HWYSTR455]

Yeah, I honestly can't remember the orientation of the lines/ports on the 2nd gen F-bodies, I ditched mine years ago for an adjustable. If you looked at the factory service manual, and it's clear which goes where, then obviously you're good with that.

On the rear adjustment, crank those things out there until you feel resistence in the adjuster, like with it applying brakes. This is just for troubleshooting to see if the pedal changes. If it does make a diff, you know where the problem may lay.

Pushrod measurement, well, may sound cheesy, but I used a paperclip bent from the flange to the cup, then measured the paperclip. Worked for me. If there's an issue with the pedal as you're talking about, it's going to be obvious. I kinda don't think that's it, because you say there's no 'loose' or 'free' travel of the pedal. You can take the MC cover off, and as you depress the pedal, you should see fluid movement, can try that as a general indicator.

Power/pressure bleed is the best, period. If you've got a rig for it, that's the way to go. Same thing, start at the furthest wheel, and make sure the tank is full.

Warning switch, that will tell you if the prop is boogered, in most cases. If it's a bias rod problem, the light will come on.

On the pedal, in the car, the upper hole is for manual brakes, the lower for power, or that's how I remember it. Wouldn't hurt to try a different one I guess. For a manual setup, using the power hole will make the pedal hard.

Hm, a bad booster causing a low pedal, not sure on that one. I know when there's no/low assist, due to a bad booster, the pedal is hard. Someone once told me that when you have your foot lightly on the pedal, and you start the car, the pedal should slowly go down, which indicates a good booster, but don't know how true that is. Do you have the original factory booster still? Might be able to try it. If you bought the booster from DSE, they should be troubleshooting it with you. Call them.