86 Brakes
Thread Starter
Racer
Joined: Sep 2002
Posts: 420
Likes: 1
From: SAN DIEGO CA
86 Brakes
I still have about 3 to 4 inches of brake pedal play before the brakes start to work. I have changed out the MC, MC brake bias spring, Front calipers, and replaced all four brake lines with stainless steal. I see no leaks at the calipers or the brakes lines. I have bleed the system about 5 times in about 6 weeks. With the addition of the Bias spring i have noticed a nice improvement in braking but i am still displeased with the pedal travel. My last option now is to adjust that screw behind the MC. What tool do I need to use to get that screw to turn out a bit? It looks like a little nut with lots of tiny fins on it with a half round screw in it. I know i could grab some large pliers and tear the hell out of it while im trying to unscrew the screw but i was hoping that there was a tool i could buy. Ive read the posts about over turning the screw so i will try it 1 millimeter at a time. So is there a tool? Am Im missing something simple as far as my pedal travel is concerned? 
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
It's entirely the booster pushrod adjustment. I folded a rag around the pushrod and clamped it with minivisegrips. Used another set of minivisegrips or channellocks to unscrew the end. I think it has factory locktite on it.
You can sorta feel if the adjustment is too far when you put the mc back over it. I tried measuring it out, but the mc doesn't mount flush against the face of the booster.
You can sorta feel if the adjustment is too far when you put the mc back over it. I tried measuring it out, but the mc doesn't mount flush against the face of the booster.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
I agree; too much pushrod clearance.
I don't know if all the different power brake boosters on the market have adjustable rods but if yours doesn't, you can always add metal shims to take up the clearance.
Jake
I don't know if all the different power brake boosters on the market have adjustable rods but if yours doesn't, you can always add metal shims to take up the clearance.
Jake
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by JAKE
I agree; too much pushrod clearance.
I don't know if all the different power brake boosters on the market have adjustable rods but if yours doesn't, you can always add metal shims to take up the clearance.
Jake
I don't know if all the different power brake boosters on the market have adjustable rods but if yours doesn't, you can always add metal shims to take up the clearance.
Jake
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Originally Posted by CentralCoaster
I guess you could shim the master cyl away from it if the rod was too long, but you can't shim it closer.
I shimmed mine last year when I had to replace my booster and had the same pedal travel problem.
Jake
Le Mans Master
Joined: Oct 2003
Posts: 6,130
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From: seattle WA
Just a word of caution here-if you do adjust the rod and it seems to
resolve your problem, take it for an extended drive, get out and physicaly feel each wheel for heat.A friend adjusted the rod on an old Ford van I had and took it to far-if you go to far the brakes can actually have constant pressure on them-which causes them to over heat, and also causes the pads undue wear.
resolve your problem, take it for an extended drive, get out and physicaly feel each wheel for heat.A friend adjusted the rod on an old Ford van I had and took it to far-if you go to far the brakes can actually have constant pressure on them-which causes them to over heat, and also causes the pads undue wear.
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by JAKE
Sure you can. Just install shims between the booster rod and the master cylinder to take up the clearance.
I shimmed mine last year when I had to replace my booster and had the same pedal travel problem.
Jake
I shimmed mine last year when I had to replace my booster and had the same pedal travel problem.
Jake
Are you putting nickels inside the m/c against the piston or something? How did you add length to the pushrod or add length to the piston without causing more harm then good?
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Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
Originally Posted by CentralCoaster
Are you putting nickels inside the m/c against the piston or something? How did you add length to the pushrod or add length to the piston without causing more harm then good?
Small, flat metal discs did the trick for me. Even small metal washers can be used.
I shimmed mine well over a year ago and I've driven all over the country without a problem since then. Many thousands of miles: First from Texas to Indy for Super Chevy in 2004, then to Chicago, then to Mass, down to South Carolina, back to Texas, then to Denver, then back to Texas and now I'm back in Chicago again.
If I was to experience any "harm" it surely would have reared its ugly head by now.
Jake
Thread Starter
Racer
Joined: Sep 2002
Posts: 420
Likes: 1
From: SAN DIEGO CA
Rod Adjustment
I had played with the adjustment about 15 times before i got it to wear i think it felt right. One problem i encountered was when I got the adjustment where i wanted it I took the car out for a test drive and it worked great for the first 1/4 mile then i noticed the brake pedal getting extremely stiff and the brakes would almost lock up. I had to punch the gas to get it down the street to adjust it again. The pressure on the brakes seemed to be correct on low speeds but when i increased speed and the engine heated up (it gets ReaL HOT) thats when it seemed to lock up. This happened about 5 different times with different adjustments. Does engine heat have anything to do with the pressure on the Brake Booster? Is it time to change the booster? Its the original plastic booster but i see no cracks or hear any hissing. 
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
Last time I suggested it was the booster I got really flamed-but it did turn out to be the booster-so all ended well.May I give my thoughts, if you feel stiffness in the brake pedal-it could be a sign the booster has deteriorated-remember there plastic and plastic is subject to deterioration from the constant hot cold cycles. Have you sat in the car and watched the tach display while idiling and noticed any change in RPMs while depressing and releasing the brake pedal? if so, it could indicate the booster is leaking, or a bad vac line to the booster. And as the last member found out, it's not always possible to see a crack without
removing the booster-IF it turns out to be the booster-and because of your prior post, and this one-that would be MYnext move-there are metal after market boosters available for our C4s, and when I do mine-that's what I will replace it with.
removing the booster-IF it turns out to be the booster-and because of your prior post, and this one-that would be MYnext move-there are metal after market boosters available for our C4s, and when I do mine-that's what I will replace it with.
Last edited by rick lambert; Nov 26, 2005 at 10:03 AM.
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by JAKE
Small, flat metal discs did the trick for me. Even small metal washers can be used.
I hope I'm just not reading this right.
Team Owner
Joined: May 2002
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by PMARTINEZ92126
I had played with the adjustment about 15 times before i got it to wear i think it felt right. One problem i encountered was when I got the adjustment where i wanted it I took the car out for a test drive and it worked great for the first 1/4 mile then i noticed the brake pedal getting extremely stiff and the brakes would almost lock up.
Anybody know how suceptible to damage these booster are while fiddling wiith the push rod?
Or.. if they can 'self-adjust' themselves somehow?
All i can think of is you have the booster rod too far out, which was ok with the air in the brake lines, but after driving it and pumping the brakes a bit you forced some air out into the reservoir, and now the brakes are binding. If you had a bad booster you wouldn't be able to get lockup at any speed IMO.
When you say the pedal is getting very stiff, are you sure the brakes are close to locking up, or does it just seem that way because of the pedal force?
Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
Originally Posted by CentralCoaster
Whether or not it's worked so far, you've got pieces of steel sliding inside your master cylinder and in contact with a finely machined/ground aluminum hydraulic surface, with trace amounts of brake fluid and moist air. And the mc piston has a divot to locate the booster rod. Once you put a flat disc in, you lose that ability to center the rod, and it adjusts it out to the 'divot' depth plus the thickness of your shim, which is a bunch more adjustment than should be needed.
I hope I'm just not reading this right.
I hope I'm just not reading this right.
So let's just agree to disagree and drop it.
Jake
Racer
Joined: Feb 2004
Posts: 265
Likes: 1
From: Irwindale Ca
umm, my brakes would do the same thing , lock up that is. I noticed my pedal was not releasing. I just replaced the booster and master. It had a lifetime warranty and no problems ever since. Something fishy if you have to use shims and stuff. Shims werent used when it left the factory. If you have the funds pull that booster and master out and junk it.
Safety Car
Joined: Apr 2004
Posts: 4,532
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From: Lahaina Hi
Remove the master cyl nuts ,move it to the side.
Take a streight edge and lay it across the plastic on the brake booster where the master cylender bolts to. Measure about 1/4 inch in from the
streight edge you have across the brake booster,to the end of the nut that is black and hold the silver part with a pair of long nose vice grips.
Turn the black nut in or out to obtain the clearence you need.
The black nut will turn hard at first, but it will losen up after you break the lock tight lose.I used a 8mm socket on the little black nut.
You have a lot of peddle travel so the nut needs to be turned counter clock wise to bring it closer to the master cylender.I used a 5/64 th allen wrench to get the distance between the black nut and a streigh edge across the two big studs sticking out of the booster,works for me.
After you adjust it drive it for atleast 5 miles,if the brakes dragg then you need to do it all over again and turn the nut in about a 1/16 at a time to get it closer.Clock wise will give you more play and counter clock wise and you will have less travel.
Take a streight edge and lay it across the plastic on the brake booster where the master cylender bolts to. Measure about 1/4 inch in from the
streight edge you have across the brake booster,to the end of the nut that is black and hold the silver part with a pair of long nose vice grips.
Turn the black nut in or out to obtain the clearence you need.
The black nut will turn hard at first, but it will losen up after you break the lock tight lose.I used a 8mm socket on the little black nut.
You have a lot of peddle travel so the nut needs to be turned counter clock wise to bring it closer to the master cylender.I used a 5/64 th allen wrench to get the distance between the black nut and a streigh edge across the two big studs sticking out of the booster,works for me.
After you adjust it drive it for atleast 5 miles,if the brakes dragg then you need to do it all over again and turn the nut in about a 1/16 at a time to get it closer.Clock wise will give you more play and counter clock wise and you will have less travel.
Last edited by REDC4CORVETTE; Nov 28, 2005 at 02:27 AM.
