71 Braking

[Thomas H.]

After having my car for 3 years or so now, I find that I am still not impressed with the stopping power of the car. I thought that it would stop better then it does. In fact, I think that my 2001 Explorer with 110k miles stops better.

Over the time I have had the car I have;

-Rebuilt each brake caliper. They were sleeved prior to my ownership so all I did was upgrade to O-ring seals in the pistons.

- Rebuilt the original master cylinder, followed by bench bleeding.
- Replaced the front crossover brake line.
- Replaced all of the rubber lines going to the calipers.
- drained the system and filled with new DOT3 fluid.
- Bleed the brakes numerous times by gravity and pedal pumping.
- New pads, VBP ferro carbon.
- New rear rotors, front rotors are the originals
- I have NOT done anything with the vacuum booster.

I have a firm pedal and the car tracks straight when stopping, I'm just not impressed with the stopping power. I was sort of expecting that eyeballs coming out of their sockets feeling when I stand on the brakes. Instead I get the "holy cow I should have started braking earlier" feeling.

Don't get me wrong, the car stops and I feel safe driving it, I just thought it would stop better. Am I expecting too much?

LS5, 4spd, power brakes

Thanks,
Tom

[Joe L.]

Re: 71 Braking

Am I expecting too much?


Thanks,
Tom

Tom-----


I think so.

[William C.]

Re: 71 Braking

If you can "lock up" the tires, then the brakes are applying all the force that can be applied. The rest of the issue is simply coefficient of friction between the tires and the pavement vs the speed and mass of the vehicle (and driver)

[Thomas H.]

Re: 71 Braking

Tom-----


I think so.

I thought so...........

Joe, I must say, I look forward to your replies to peoples questions as I usually learn something from them but I do believe that this is the shortest response I have seen you post since I've been on the TDB

Thanks for the sanity check!

Tom

[Thomas H.]

Re: 71 Braking

If you can "lock up" the tires, then the brakes are applying all the force that can be applied. The rest of the issue is simply coefficient of friction between the tires and the pavement vs the speed and mass of the vehicle (and driver)

Bill,

I have never been able to lock the brakes up. I actually tried to one day in a parking lot, but was unable to. This was before I rebuilt the calipers and I have not tried it since. I may have to look into this again in the spring. I won't be doing too much driving (if any) for the next several months.

Thanks,
Tom

[Joe L.]

Re: 71 Braking

Bill,

I have never been able to lock the brakes up. I actually tried to one day in a parking lot, but was unable to. This was before I rebuilt the calipers and I have not tried it since. I may have to look into this again in the spring. I won't be doing too much driving (if any) for the next several months.

Thanks,
Tom

Tom-----


If you can't lock up the brakes, my suspicion would be that you have some air in the system. Bleeding ALL the air out of a 1965-82 Corvette brake system can be a real challenge.

[Terry M.]

Re: 71 Braking

Check the master cylinder. I once worked on a 1969 that had poor braking -- back in the days before we knew about master cylinder casting numbers. After all sorts of work and tests, it turned out that it was a standard brake car, but a power brake master cylinder had been installed.

[Thomas H.]

Re: 71 Braking

Joe,

I have been over them many times (I know, everybody says that, but really I have......). When I had the car in for the annual safety inspection last spring, we gravity bleed them while it was up on the lift. Filled up about an inch of fluid from each caliper into a container. No difference noted.

I used to have a 71 SS-454 Chevelle that was not the easiest car to stop even with the power disc brakes up front. I thought the Corvette would be better since it has 4 wheel disc and the Chevelle had rear drum brakes. I would say that the two cars are on par with each other in braking.

My expectations may be too high. In the spring maybe I'll try some stopping distance tests and see how they compare with whatever published specs I can find.

Regards,
Tom

[Thomas H.]

Re: 71 Braking

Check the master cylinder. I once worked on a 1969 that had poor braking -- back in the days before we knew about master cylinder casting numbers. After all sorts of work and tests, it turned out that it was a standard brake car, but a power brake master cylinder had been installed.

Terry,

Good thought, but.... the master cylinder and power brake booster are original to the car. I have a 5480346 master cylinder with the "PG" stamp on the machined flat edge.

Tom

[Michael W.]

Re: 71 Braking

Bill,

I have never been able to lock the brakes up.

Then there's something very wrong. PB cars can lock the wheels with even moderate pressure on the pedal.

Aside from the pads (I have no experience with those particular ones) I can only wonder if the booster is not functional. This will tend to give you a hard pedal but not much braking action.

[Jim T.]

Re: 71 Braking

Thomas with all you have done and having good pedal and your 71 not stopping like you think it should, it could be the disc brake pads. I have not used the disc brake pads you installed. My 70 with power brakes stops very well, has since it was new. Have used silicone DOT-5 for about 20 years. My very good brakes kept me from impacting a car that turned illegally in front of me a few years ago, I was doing about 55-60 and my 70's brakes did not lock up the tires, came real close though. My suspension has been modified so that weight is not transferred like it was when new, no nose diving under hard baking. Anyway my pads are Bendix brand over the counter similiar to original equipment type.
A memory from when my 70 was new. My passenger had a dress on and the material her dress was made from and my leather seats did not provide a lot of gripping. I had to make a quick stop in traffic, she was not wearing a seat belt and slid forward off the seat. She did not like the experience.

[Thomas H.]

Re: 71 Braking

Then there's something very wrong. PB cars can lock the wheels with even moderate pressure on the pedal.

Aside from the pads (I have no experience with those particular ones) I can only wonder if the booster is not functional. This will tend to give you a hard pedal but not much braking action.

Jim,

Is there any way to diagnose the booster? It is the original one. There is definitely a difference in pedal feel with the engine running, as there should be with a power brake car. I don't recall how long the booster holds vacuum after the engine is shut down. If I get a chance, I run the car tonight and see if it bleeds down after I turn the engine off.

Tom

[Michael W.]

Re: 71 Braking

Jim,

Is there any way to diagnose the booster? It is the original one. There is definitely a difference in pedal feel with the engine running, as there should be with a power brake car. I don't recall how long the booster holds vacuum after the engine is shut down. If I get a chance, I run the car tonight and see if it bleeds down after I turn the engine off.

Tom

I can't say that I know of a test beyond the rudimentary checks you've already mentioned. Bleed down time may not be fully indicative as a faulty check valve will shorten bleed down time but not affect brake perfomance with the engine running. Maybe others will have ideas.

Mike

[Bill M.]

Re: 71 Braking

Thomas with all you have done and having good pedal and your 71 not stopping like you think it should, it could be the disc brake pads.

I agree. I would call the pad supplier and ask about a pad with greater effectiveness (coefficient of friction). You should be able to slide the front tires, and then when you push harder, the rears tires.

[Terry M.]

Re: 71 Braking

I think there is something in the Chassis Service Manual on how to check the PB booster. It has been more than a few years since I looked though.