While the car was in the shop I also had them replace the master cylinder. The master cyl. was a repro style of the original that looks exactly like the original but doesn't have the two bleeder valves. I bought it from D & R Classic Automotive (www.drclassic.com).

The pedal is now VERY sensative. All I have to do is give it a quick push when it's all the way up and it will fall all the way to where the brakes are stopping the car pretty quickly (this is hard to explain). The pedal will then pretty much stay down and keep the brakes on; sometimes I even have to use my foot to pull it back up to continue rolling to a stop sign, for example.

When the car is off I can pump the pedal all the way up and it will hold the pressure. My old master had the classic failure mode where it wouldn't hold any pumped up pressure, so I think the new one is working fine.

When the pedal doesn't go all the way down and stick down it is very touchy. If I put the breaks on quickly it will throw me toward the windshield while I'm yelling, "what the hell."

Any opinions on what the deal is? Like I said...my mechanic has disappeared and hasn't resurfaced yet so I can't really bring it back to him right now.

Thanks,
Dan

Let's start with some questions: Does it have power brakes? In other words, does it have a power booster? Is it drum or disc/drum? Also, do you mean that when you let off the brake pedal, the pedal doesn't return?

Oops, forgot to mention that. Yes, I have the factory power brakes with discs up front; yes to power booster.

Yes, when I let off the brake pedal it does not return.

I had something similar happen a while back after I replaced a master cylinder. Turned out the new master cylinder was bad. The first thing you need to do is bleed the brakes and see if there is any air in the lines. If you only had the master cylinder worked on it's probably the problem. One important clue would be how the brakes worked before the master cylinder was changed. If all these problems started after te master cylinder was changed it might be a bad rebuilt part.
Jim

It almost sounds like your power brake booster is malfunctioning, giving you a very sensitive pedal and holding itself down. I'm reluctant to suggest this, but one way to test this is to find a big empty parking lot and disconnect the vacuum line to the booster, and plug it on the engine side. Then try your brakes (carefully!-a lot more effort on the brake pedal will be required, so don't be close to anything, and be ready with the emergency brake-it does work, right?). If they don't seem sticky like before, the problem may be the booster. Find out from your mechanic (if you find him) if the power booster was replaced as well. I had one that would put me through the windshield if I looked at it wrong. It didn't hang up or pull itself down but it wasn't too far from doing that. When the car was running and stationary, I could push the pedal almost to the floor with very little effort, which would definitely have locked up the brakes and stood the car on its nose had I been moving. I hate to think of how my rubber brake lines looked when I did this! I replaced the booster and things went back to normal.
If they still feel sticky, then someone may have put the wrong seals in when they rebuilt the master cylinder, causing it to be sticky. This wouldn't explain the oversensitivity though, so my bet is still on the booster.

maybee he put the push rod in the wrong hole
on the petal or the bushings are worn out in the petal there is also a spring on it check these first

good luck bill :p

He says he just had them replace the master cylinder. Stands to reason the new master cylinder is the problem. I've bought a few bad remanufactured master cylinders.
Jim

This master cylinder is a brand new product. The only failure mode that I know of for the master is that it will leak down and not hold a firm pedal. I was seeing this and now that it is replaced it will hold a very firm pedal. I don't think it is the mc.

What are the signs of a failed power booster? The one I have is a remanufactured one and was replaced about 2000 miles ago. My best guess would be that if the power booster weren't working well it would result in having to press very hard to get the brakes to be engaged??? Anyone know about this?

I'm going to get under the dash tomorrow and check out to see if I have a spring on the pedal. I'm betting I don't have one the way this thing will go down and stay down...I don't think I have bad bushings because the pedal moves freely otherwise. A spring to bring it back up would fix most of my issues except for the sensitivity which might just be due to the new master.

I'll report what I find.

a bad booster can cause an extremely sensative pedal in some instances while still allowing boost, as stated earlier. i've never seen a sensative booster cause a pedal not to return, but it seems possible.

a master cyl can go bad in more than one way, and new does not always mean good. it may also not be matched to the pushrod length. a short pushrod might cause something like this.

the pedal return spring is coiled around the pivot rod, and may be hard to see. check those bushings too, even though the pedal moves freely. do not add an extra spring as a band-aid.

I have replaced a master cylinder and it did ALL of the things you are talking about. There are a LOT of bad NEW parts out there. Was your power booster acting up before?? If a mechanic changes a master cylinder did he hurt the booster?? I doubt it.
Jim