Sometimes, especially in stop and go traffic, when I put my foot on the brake it will depress at least 3-4 inches more than normal before I feel the brakes. It scares me every time because I think I lost my brakes, but they still work fine if I keep pressing the extra 3-4 inches. If I take my foot of the pedal and then right back on again the brake feel goes back to normal. I'm thinking it's a vacuum or brake booster problem. Any suggestions?

I have an '86 N/A.

 

It may be an air bubble in the lines. I would bleed the whole system and double check both of the rubber hoses used for the brake booster. There's a piece at either end of the metal hardline on the firewall.

 

1. Brake Booster failure will only make the pedal harder and will cause a huge vaccum leak.
2. Hydraulic failure will make the pedal softer/spoungy, this includes air in the lines.
3. Caliper seizing will cause vehicle to pull or a slightly stiffer pedal
4. As RotaryRocket 88 said, make sure your brakes are bled properly and the fluid level is where it always is, you should never be losing fluid at any rate or you do have leak somewhere either internally in the master or somewhere in the system.

Check List:
1. All 4 Calipers for any visible leaks, drips, or wet grime on the caliper itself where everything else is dry.
2. Check all flexible hoses for leaks, drips or wet grime. As well make sure they are not uber dry and cracked.
3. Check under the brake master on the body of the vaccum booster for rust or wet grime as a leaking master can leak fluid through the back and either get into the booster and cause it to fail or leak out between the two and eat away at the paint on the booster body.
4. If all others check out and you can still massage the pedal slowly and it falls to the floor, your brake master is likely the issue and is the result of an internal failure.

 

Sounds like you have a bad master cylinder, But DarrenTRS is spot on with his checklist.

If you haven't expereinced complete failure i'd say your are leaking interally in the master cylinder. Only way to fix that is to Remove and replace the cylinder.

If you do, MAKE SURE YOU BENCH BLEED THE MASTER CYLINDER BEFORE YOU INSTALL IT..! I can't stess that enough. lol.

 

i would bet it's the master cylinder. but i'd give it a good bleeding out first.

 

I've been checking the fluid level and it's stayed full for about a week and a half now so I know I'm not loosing fluid. When the pedal goes, it's not spongy at all it just drops with the slightest push until I feel the brakes. The car is not pulling at all and brakes are still effective. Internal leak sounds spot on, I'll be figuring it out for sure very soon.

 

What could this mean: When the car is stopped with the engine off, if I suddenly apply the brakes I feel good pressure, but if I slowly apply them the pedal drops to the floor.

 

It's likely the master then [if you have no leaks], pushing it hard just means your applying enough pressure to force the seal out and allow you to apply the brakes but if you apply them slowly the fluid works its way around and back into the reservoir.

Same thing happened to me when my master went out but you kinda had to slowly massage it and it would go to the floor or if I slowly applied the brakes when the car was running or at a stop light I could feel it slowly drop.

 

out of curiosity how do you bench bleed a brake master cylinder?

 

clamp it down or someone hold it, put fluid in it and attach those little hoses(if the master cylinder comes with them), otherwise u'll have to make some, to pump that fluid back into the reservoir. stick a phillips screwdriver in the end of the cylinder and push it in and out to bleed out the air in it. this can be done on the car before the brake lines r connected. that's how i do it. when u rarely have help u find ways to do things by urself.

 

lol i had the same prob and just replaced master bAM there u go. but i didnt bench bleed so now i need to bleed my brakes badly. they grip right at the end right tight. good luck.

 

I bought a new brake master cylinder and bled the system. Brakes have been perfect since. Problem solved.

 

I had this problem just start up as I stop driving it for about a week. im changing the brake master cylinder so i hope that is the problem

 

Old thread revival here.

I had the same brake problem that zecc81 had.
Cam Pettit replaced the MC and it was better but still not perfect.
He's not happy with it and I'm not either.

I guess the replacement MC could be bad.

Any other thoughts?

 

sounds like air in the lines to me. bleed the whole system front to rear.

 

Just wanted to add my end of problem story and hopefully it will benefit other members.

My mechanic is Cam Pettit (ten minutes away, lucky me!)

Low brake pedal / MC passed Cam’s bad MC test / even though, we replaced MC with new MC / still had the same problem, maybe just a bit better / bought Zoom Zoom’s 929 (great price and thanks ZZ) / brakes are worse / Pettit felt the only other component was the ABS system / Pettit rebuilt the ABS unit / brakes are awesome, better then ever which he attributes to the 929.

The ABS was full of 23 years of crap to where the system could not function correctly.

I try to keep the mileage down and generally only drive it during cold fronts here in FL.
Not driving it keeps the mileage down but is not good for brake systems and probably other reasons.
And it turns your tires into stones.

Hope this helps.