Car: 93 LT1 auto with 12 inch stock factory brakes, 60K miles, about 4K on the front rotors and pads. The engine is a 396 stroker with a solid roller cam with a duration of 242/248 and a 110lsa. I currently have put 200 miles on the new combo.

Background info: When I first started driving the car after it sat for 4 months the brake pedal was hard and stiff. This went away after a few miles. I then went to stop when parking the car and the brake pedal went to the floor and there were almost no brakes. This went away and was problem free till now.

Problem: I went for a 20 mile ride on Saturday night and the brakes were fine until I was almost at my destination. There was some traffic and the car was a little hot (225*). I went to hit the brake pedal and it went straight to the floor. I pumped it a few time and it got better but the Brake light came on on the cluster and then went off a little while later.

When I went to drive the car home tonight, it was fine again until I hit traffic. It was bumper to bumper and the temp rose to 235*; I had no brakes. Pedal went to the floor and pumping did not help. I parked the car for a few minutes to let it cool. I then started driving again and when driving at a higher rate of speed the car cooled and the brakes seemed fine. I then got into town, car got hot, and brakes went to **** to the point where I had to push it into the garage because I was afraid of hitting something.

Now, I am not implying that engine temperature has anything to do with this but I figured I should mention it since it seems to go hand in hand, a fluke maybe but I don't know.

My ideas: This might be dumb but, maybe the car running hot is causing the fluid to thin out and not function correctly. The master cylinder is shot and something inside is hanging up.

And yes, I have checked the fluid and it is full. I have also semi-checked for vacuum leaks.

Any thoughts, comments or great ideas are appreciated,

Dave

 

I think it your master cylinder.

 

I did forget to mention that before these modifications the brakes were fine.

 

think of it this way:

a hard pedal = bad booster.

a soft pedal = bad master.

sitting for months could harm the fluid. I would try to bleed the system, if nothing else, it gets you close to the brakes and have a chance to see if a seal is bad.

Most importantly, don't drive this thing until you get this fixed.

 

I vote for a MC as well.

 

No leaks + no peddle = master cylinder
Unless the fluid is boiling?
Flush the system with fresh fluid and change the master cylinder to be safe.

 

I have no leaks and have not lost any fluid. As far as I know the fluid is what came in the car in 1993 minus what was added as was needed along the way.

Considering I'll have some stuff apart, what would be some things to change? I was thinking stainless steel lines and speedbleeders wouldn't hurt. I drive the car on the street and drag race it often. Eventually I know I'll have to upgrade to some kind of 13" brakes as these were a little scary even with the old combo.

 

Master Cylinder is expanding with the heat allowing Blow by.

Weak or hardened o-rings in the MC allowing Blow by.

Go get a new or rebuilt MC at Your auto parts store and swap it. This will continue to worsen with time.

Mine did the same thing last summer. Only wanted to fade when I really needed it in bumper to bumper traffic. Swapped it out and never looked back. And quite frankly, I set aside about 4 times as much time needed to do this job as I needed. It took me just over an hour to complete.

You may want to investigate the Filler cups being already attached to the replacement MC. Some have a lot of trouble removing them and replacing them onto the new MC. You can order the MC with new filler cups already attached.

 

Same thing has happened to me, I have changed MC, and flushed the system some times with different products and no luck yet.

I will be installing SS lines and a new MC and hope to solve this condition .

 

Sounds like the master cylinder. If you do go for one change the fluid while you are at it

 

Well, how can you not change the fluid when you replace the MC?

If you chase the bubble down the line....all the way....The old fluid should be out as well correct?

 

I would also check the vacuum going to the booster. Aftermarket cams tend to lower it.

 

Yes the vac would be lower at lower speed due to a bigger cam, but that wouldn't cause a mushy pedal, it would be like losing the the booster....the pedal would be hard correct?

 

I had that going on too. That is no where near as scary as having no brakes.

After doing some research, I found this will cost me a little bit..

GM list for a master cylinder is $611 and my cost is $360.
Corvette Central is the cheapest at $229.99
Mid America Motorworks lists at $359.99
Corvette America lists one at $519.99

Which one of these have you guys went with or would go with if you had to choose?

 

Me personally, I wouldn't go with any of them. I'd buy a rebuilt for $75. I don't even need a 2nd thought.

 

Holy smokes!! look at those prices!

Rebuilt from Kragen ~$50-$75 bux.

seems like every time I get a car I have to go through the brakes. Been using rebuilt MCs for almost 30 years now.

Had I ever had an issue I might rethink using a rebuilt MC.

back in the day, we used to rebuild the MC ourselves, as well as the Calipers.

Hone, replace seals, put it back together......

 

Update...

So I got the new MC, bench bled it, installed it, flushed and bled the brakes twice and I now have almost no brakes. There were no bubbles coming out when I bled the brakes.

I have noticed I only have about half of the pedal travel which feels a little softish. I cannot however get the pedal to go to the floor; it is like hitting a wall. From a slow roll I can get the front tires to lock up and screech on the garage floor, but the faster I go the less brakes I have. The other weird thing is when I mash the pedal with both feet, the car still rolls a little bit and then it stops, again from a slow roll, like there is a delay. I doubt I have any air in the lines because if that was the case, pumping the brakes should help, which it doesn't.

I'm thinking this may have something to do with the abs or the prime pipe that I didn't bleed.

Any thoughts or ideas? Anyone have tips on bleeding a 93?

Thanks,

Dave

 

I got a brand new MC in the box GM/AC Delco for $189 +$10 shipping from here:

http://motors.search.ebay.com/_W0QQsassZthepartsladi

They have some of the best prices on genuine GM parts around. Quick shipping and great prices.

I've not had good luck with rebuilt anything in the past so I go new if at all possible!

 

I like speed bleeders for bleeding the brakes! I can do it by myself- a few bucks well spent. I also used a long line and put a small loop in it like a sink drain then put it into a bottle with some fluid in it. I can see the bubbles this way. Also the FSM tells you which side to start bleeding from

 

Another update...

I have bled the prime pipe and the brakes are a little better but still not good. The pedal still only travels 1/2 way and even with a 2 foot press it does not stop well.

I checked the Chiltons and the FSM and it seems if my brakes are bled I shouldn't have to bleed them again after bleeding the prime pipe. I know the FSM says do the prime pipe first, but the Chiltons says you can do it either way. Any opinions on this?