another brake problem

[Fast Ed]

Brake goes almost to the floor and is solid it will stop thee car. I've bled the brakes and there are no leaks. Does this indicate rotors too thin? What is the thickness required for a 76 rotors.
Thanx
Fast

 

[Tom Bryant]

brakes

Fast Ed,
I have noticed a reduction in pedal travel weith new pads and new rotors.
Tom

 

[Tims75]

Usually this means that you are pumping air at the calipers. This is very common for C3s.

This is caused by rotor runout. The tolerence for the rotor runout is very small, like a few thousandths.

Sometimes the rear bearings are loose and can cause this runout.

This happens because the type of calipers that Vettes use.

The pistons in the calipers, there are four in each caliper, cause the pads to be constantly in contact with the rotors. This is because there are springs behind the pistons pushing them out.

The seal design is more of a bellows type of seal and they allow air into the system if they move in and out too much due to the rotor not being true. Because air molecules are smaller them brake fluid the chance of fluid leaks to indicate this condition is less likely.

Several companies now make o-ring style calipers that help prevent this air pumping.

This is how I bleed my brakes:

Do you lose your pedal after driving a short while or do you never get a solid pedal?

If you never get a solid pedal I would check the master cylinder.

When I bleed my brakes I always use the gravity method followed by a quick two-man method. This is the method that the SSBC (I think it was SSBC, I can’t find the book) brake book recommends.

With the gravity method I jack up the end of the car I am gonna bleed to where the center of the axle, spindle, is about 15 inches above the ground and the other end is still on the tires.

Then I crack the bleeders a bit to get a slight flow of fluid. Making sure that the top is loose on the master cylinder and that the master cylinder never gets too low on fluid.

After about 10 or 15 minutes I close the bleeders then I use the two-man method to finish it off.

After that I check my brakes to see if they improved. If they did this tells me that this is the circuit with the air-pumping problem. I then repeat the procedure on the other end of the car.

Jacking only the end of the car I am bleeding makes the bleeder screws the highest part of the system so that the air works it’s way to the highest point.

This usually does it for me.

So I would go ahead and bleed your brakes and see how that works.

Also, on my 75 I had a problem with the stop light switch mounting bracket. It had bent up and allowed my brake pedal to travel to far back up. I noticed in the assembly manual that the brake pedal should only come up 4.6 inches from the floor board. Mine was coming up almost 7 inches. I remove the stop light switch, which is want stops the pedal in return, straightened the bracket and remounted and adjusted the switch. That helped a bunch.

Good luck.

Tims75

 

[Nut]

Me too

Ed,

I've got the same problem with my '81 and I'm dying to try out the O-ring piston fix. I have seen a VERY small leak under the inboard right front caliper. Only 66K miles so I doubt the rotors are worn that far and the pads are brand, spanking new organics. Stay tuned.......

...... Nut

 

[J Lance Miller]

All,
Here is the deal, Tim75 provided great info on gravity bleeding but I would also like to add that the order you bleed is equally important. Thier advice is to bleed the farthest brake from the master cylinder first, then the next farthest and so on. Usually this means RR, LR, RF, LF.
I had a similar problem with my '66 when I first picked it up - over time I was slowly accumulating air in the lines. In my case, it was compounded by a small, almost impercievable nick in the surface of one of the caliper cylinder walls. The nick had probably been there since the stainless steel inserts were installed but the seal took some time to get worn away in that spot - hence the slow deterioration of braking performance. I ran a hone over it to smooth it up ($5 Pep Boys), replaced the seal ($2.50 ea Zip), bled the brakes using gravity and the two-man (actually - one man one 12 year old) method and have enjoyed a firm, airless pedal for three years now.
I would suggest that you disassemble that leaky caliper and see if you can't find the cause of the leak - might just save yourself some money. As to the rotor minimum tolerance - if I remember right, it is written or stamped on the rotor.

Lance

 

[75corvette]

had same problem, a little lenthy.....

Hey Fast-ed, I have had the exact same problem with mine.
I bought my car in july 00. with the same symptoms as you described. I took it to a mechanic to trouble shoot my brakes. he said they looked fine and bled the system. cost me about $50. I had a great pedal when I left the his shop for about 6-7 miles. I came to a red-light and they went right to the floor. the car did stop but the brake pedal was on the rug. I took it back the next day and he replaced the master cylander, booster, and two new brakes on the front. Cost me $400.00+. On the way home the same thing occured.
Called him the next day and told him to shove it. but I figured o.k. I have some new parts I'll take it to another mechanic. this new guy services all our trucks and said he was familiar with vette brakes. He does the same thing as the other guy, replaces the booster and master cylander, power bleeds the brakes and calls me to pick up the car. 6-7 miles from his shop the same thing occurs. this all happensd within 2 months of owning the car. TALK ABOUT BEING FRUSTRATED. o.k. I called him a idiot and took the truck contract away from him. I was really PIS--D. NEXT WENT TO THE PROPORTIONING VALVE AND NEW LINES with another mechanic who was recommended by a friend. another cost of $200 to no avail. now it's the end of summer and my brakes are still not working properly. I was still driving the car with a low petal, I was getting used to the feel of the brakes and I down-shifted alot to slow it up. NOT RECOMMENDED. I posted my dilemma to the corvette forum (member there first) and got a great response. and one in perticular from TIMS75, WHO WAS RIGHT ON THE MONEY. I printed his post and the others that responded and gave it to my new mechanic who did trouble shoot and found out that the rear rotors were no good. so I replace the rotors and rear calipers and now my car stops on a dime. I still don't know a whole lot about brakes and I hope you don't go through what I did.
GOOD LUCK AND THANKS TIMS75 FOR YOU HELP.
JOE
SAVE THE WAVE AND ALL VETTE FORUMS !!!!!!


[Edited by 75corvette on 03-06-2001 at 07:09 PM]

 

[Tims75]

Anytime guys.

I had the same thing as Joe when I bought my car a few years ago.

I replaced the booster, master cylinder, ( 3 times, last one new Delco), all the hoses; the rears twice, one spindle, all of the calipers; some twice, and rebuilt the rear suspension.

This over a period of months. Three or four mechanics plus my bro in law and myself. Now, I just do the work myself with my bro in law. It seemed that NOONE knows enough about Vette brakes.

For awhile I just went to the local Midas once a month and had them bleed them for $20. Worth the price. Then one day I went in and a newer mechanic wanted to sell me the whole package. Before he even looked at it. Said he couldn't just bleed them. I got ****ed and walked out. In retrospect I could have had them do the lifetime warranty thing and it would have cost about the same. Then everytime I had a problem I could have just gone back to them. Boy, would they have gotten tired of seeing me!

Finally my bro and I went through the whole system and now I get a good pedal.

Tims75

 

[chuck]

Re: Me too

Ed,

I've got the same problem with my '81 and I'm dying to try out the O-ring piston fix. I have seen a VERY small leak under the inboard right front caliper. Only 66K miles so I doubt the rotors are worn that far and the pads are brand, spanking new organics. Stay tuned.......

...... Nut

Nut,are you talking about zero tolerance pistons? A friend of mine installed them in his 74 worked real good. Hope you have S.S. sleeved calibers,with that combo you can't miss. Chuck

 

[Nut]

SS Calipers

Chuck,

Calipers are definitely SS. The guy I bought her from put nothing but the very best money could buy when replacing anything. However, the SS calipers were put on in '86, long before I brought her. I won't know for sure until I take them off. That's why I was originally interested in just replacing both front to be sure. Crossfire CE (Dave) got me fired up ove the O-ring replacements. Stay tuned.

Regards...... Nut

 

[vigman]

A twist on the bleed

I had the same problems, but I did powerbleeding with the KD device that straps on top of the master cylinder 9 pressurizing to 12 psi, and BADA-BING I got a stiffie ( pedal that is ) and it's a 1 guy job! The nice thing about that is the bleeders are regular thread and not pipe which means the bleeders leak thru the threads. The bad news... when you depressurize you can spray brake fluid mist everywhere! make sure that your fenders are covered!!!!

Mike

 

[Tims75]

Hey Vigman, what is the name of this tool and who makes it?

I would like to check this thing out.

Tims75

 

[Tom Bryant]

pressure bleeders

The GM dealer where my wife works pressure bleeds brakes. Seems to do a good job.

Tom

 

[Fast Ed]

Thanx

As usual great info! Did any one notice CAC is griwing on a parabolic curve?

Fast

 

[vigman]

KD Tools

I have to look it up... but in the KD catalog it's a flat metal plate with a hole for a compressor fitting & rubber gasket on the bottom with two chains holding this down the top of the master cylinder. I purchased a seperate adjustable regulator to put in line with the air feed to limit the psi down to 12 ( 150 psi made a huge mess lol) KD also has the same devices for c4 style brakes ( which as an added bonus works for the clutch master) I wonder if KD is online??Hmmmm the tool was about $45.00. The other cool thing is you leave the system under pressure and any leaks show up quickly.

Mike

 

[vigman]

Vac bleed

If anybody suggests that you vacumme bleed a corvette system, run for your lives..... a vac bleed will pull all your pistons IN and you will never get a good pedal!!!! plus the bleeder screws will leak... and your brake "professional" will show you that have Bad calipers!!!! I had that SCAM pulled on me at Pep Boys in Canyon Country, I had to show THEM how to do a conventional bleed, just to get my car out of there... Then they asked me to pay for 2 quarts of Brake fluid that they used (wasted) trying to bleed my system. I will not post my responce to that .....person.... but it had something to do with a finger.

Mike

 

[Glassman]

I have some pictures of my cheep power bleeder. Any one can make it and is simple to use. Just email me for them.

 

[BobbyBJr]

Oh my, our 75 had great brakes when we first bought it, but a caliper started leaking. They haven't been right since I replaced that rear caliper. I have bleed and bleed and I still have a soft pedal and a pull to the left when the brakes are applied hard. I am planning to order a complete brake set from Vette Brakes in the next day or so with the SS sleeves and o-ring pistons and keep my fingers crossed that solves the problem. To compound my problem, one of my bleeder ports broke off the last time I bleed the brakes and I haven't been able to get it out so far. I am thinking I need to at the very least replace the other rear caliper and then do something about the broken bleeder on the front. That might mean replacing those calipers too, so I am going to just go ahead and replace the whole system with the o-ring style and hopfully be done with it for a while.

Bobby

 

[Glassman]

Before you buy from them checkout these guys I have been using them for years.
http://www.muskegonbrake.com/

Don't forget the hoses they also have the Teflon ones that will make your stopping distance shorter.

It looks like you need to go a little deeper into your problem you must have run out or a loose bearing assembly and if you read my other post you will see the only way you can make sure of getting a good reading of either is to disconnect the Half shafts from the axel.
There is nothing wrong with the o ring pistons but it may be a cover up for a more dangerous problem.
If you need more info let me know I have done this job a lot of times.

 

[BobbyBJr]

Before you buy from them checkout these guys I have been using them for years.
http://www.muskegonbrake.com/

Don't forget the hoses they also have the Teflon ones that will make your stopping distance shorter.

It looks like you need to go a little deeper into your problem you must have run out or a loose bearing assembly and if you read my other post you will see the only way you can make sure of getting a good reading of either is to disconnect the Half shafts from the axel.
There is nothing wrong with the o ring pistons but it may be a cover up for a more dangerous problem.
If you need more info let me know I have done this job a lot of times.

Thanks for the link. I will give them a call and talk to them before I order, but I have pretty much decided to go with Vette Brakes. I have pulled all the tires several times and checked everything. I do have a noisy wheel bearing, but can't detect any play or run out in it. The wife and I are discussing going ahead and replacing it too while we have it apart if we are going to keep the car. I don't do alot of mechanicing, but I have all the tools I need for those jobs. I used to build and overhaul machinery. Anyway, I think my problem is a caliber either leaking a small amount on a rotor or maybe one is sticking causing the pulling. Someone told me I should have replaced the rear ones in pairs instead of just the one, but it was too easy at the time to just put the one on.

thanks for the advice,
Bobby