Happy 4th Vetteheads, Have a brake problem that does not seem to want to go away. Last year I replace: all calipers with SS lined Delco cored calipers,all rubber lines,MC,rotors,front wheel bearings, flushed lines out and replaced with DOT 5. Bled according to GM rotation schedule in shop manual. My problem since last year is that about every 3 days my pedal becomes soft, I bleed my right front caliper for a minute get a few bubbles and the pedal is hard again for a few more days. It is only the right front that I have to bleed to help out the soft pedal condition, can anyone shed some light on this? starting to get old if you know what I mean.

Thank You in Advance :flag :confused:

 

Sounds like there might be some runout in that rotor causing the cylinder to pulse and suck air. Common problem,

 

It is possible to have rotor runout in the front rotors. You said you replaced them, did you check them for runout?

 

No I did not, is that something a Midas or other can do as I do not have the knowledge or equiptment.

 

Don't know if a midas can help you. Good mechanics are hard to find these days, and midas usually doesn't attract the good ones.

What has to be done is to clamp a dial indicator to the rotor while it is still on the car. Rotate the rotor and measure the runout. Then shims are placed between the rotor and hub until runout is no more than 0.005" (I prefer 0.002" or less. It is doable).

 

Zwede stupid question, I have a feeling but is the caliper still on the Vette and if not how is the rotor attached? with the wheel nuts snugged up??? :flag :confused:


[Modified by Bond007, 3:07 AM 7/5/2003]

 

If this loss of pedal and bubbles started when you replaced the lines then it's a good chance that it's just a leaky connection. Loosen all the line nuts and hose nuts in the right front brake system and retighten them. Don't use any sealant on them since they are new and should seal up without any help. If this doesn't solve the problem then you may need to use some Permatex part B non-hardening in the threads. Don't use teflon tape cause the brake fluid will eat it up.

Oh, and in my opinion rotor runnout that is sufficient to cause the wheel cylinder to "pump" would be felt in the pedal. If you don't feel a pulsing that varies in synch with your speed then I doubt that you have rotor runnout. In fact I have another car that has serious rotor runnout, probably a warped rotor too; but, it has no problems braking and holds brake fluid nicely. The pedal throbs when applying the brake. But, since it's just a parts runner I ignore it.

 

I kinda have the same problem and was thinking it was the master cylinder. I get air in the fronts and eventually only have brake pressure in the rears. Anyone care to comment?
Weasle :D

 

Well, the problem is usually the caliper since there's mechanical movement and more stress than any other part in the system. The brake system can suck air into the lines through leaks which are large enough for air, even if the leaks are too small for fluid to leak out. The easiest way to determine which caliper is leaking is to attach a clear hose to the bleeder, slick the other end of the hose into a clear jar, open the bleeder about 1/4 turn, then pump the brake pedal just like in normal operation of the system. If you continue to see small air bubbles come out after about 2 minutes of pumping (stopping to refill reservoir and replacing cover) then you should replace the caliper. Leaks in the hoses are normally large enough to allow fluid to leak out as well as let air in, so only replace hoses if you see fluid leaking out.

Another point I should make is that sometimes even a new caliper will have a leak large enough for air to get sucked in, so sometimes replacing the caliper doesn't fix the problem, but it may still be the fault of the caliper. I usually figure if I encounter two new/rebuilt calipers that don't fix the problem then I begin looking elsewhere. But, replacing the caliper has always worked for me. The only time a new/rebuilt brake part failed on me was a m/c which didn't pass the bench bleeding; in other words, one of the outlets failed to pump out any fluid.

 

Rnr, How can I possibly have a leak when I see no fluid anywhere. :confused: :flag

 

Hi

I had the same problem on a aft brake.
No external leak, but always air in the caliper.
This is the lip seal setup, that does it. When pushing the brake pedal, the lip seal will be pressed by the fluid pressure against the cylinder wall, hence sealing everything well off. With rotor runout and brakes released, the piston springs will pump the piston out and the warped rotor will push it back in. Due to the speed and fluid viscosity , the fluid can not travel fast enough in the lines to make up and air will be sucked passed the lip seal into the caliper.
If air is found in the caliper, it will not come from the master cylinder as air travels up in the fluid and not down, unless you have a fluid leak at the caliper.
I installed O-ring type caliper pistons and they don't suck any air .
The lip seal setup is middle age technology. Forget about it.
Get the VB&P O-ring kit for around 100 $ and forget about brake problems .

Good luck Gunther

 

After spending the money for a total brake job last year it is hard to dish out some more, however because I was not smart enough to ask the question of whether the calipers I purchased were lip seal or O-ring seals that is what I get. When not if, I purchase this conversion kit from VBP about how long would it take per wheel to do or should I just do the one I'am having trouble with?? Can they be mixed on the same car?? :confused: :flag

 

Because the runout actually causes a vacuum condition on the inside of the piston - sucking air in, but holding the fluid in also.

 

If you feel adventurous, I would suggest you pull off one or both of the rotors and see if the hub or hub surface of the rotor is rusty or has a "snot" that is causing the runout condition. Clean up the surfaces real good (I even put a thin coat of paint on them once I got them real clean and straight). You can pick up a decent Dial Indicator with a Magnetic Base pretty cheap and check the runout yourself. Grizzley has some pretty good, inexpensive sets. For example, G9849 "Magnetic Base/Dial Indicator Combo - President's Special" is only $19.95 and is DEFINATELY accurate enough for measuring brake rotor runout - I use them in my mini machine shop for more precise stuff than rotors! Go for it! You CAN do it.

Plus you can save yourself a LOT more than the cost of the indicator setup!



[Modified by pws69, 3:15 PM 7/7/2003]

 

New to me, can you briefly explain how to set this procedure up? :flag :confused:

 

Set the magnetic base against a fixed point on the suspension - the side of the caliper or the spindle (tire is removed of course car on jackstand) adjust the dial indicator so that is is perpendicular to the face fo the rotor about halfway between the outer edge of the rotor and the inside edge of the rotor (optimumly you would want to measure at the midpoint of pad contact which will be visible as the shiney area of the rotor.

Adjust the dial indicator so that is is very slightly in contact with the rotor and set one of the outer ring pointers so that it points to the needle inside the dial.(or zero your dial indicator if it has such an option)

Slowly rotate the rotor being careful not to disturb the dial indicator or its mount - watch the needle - any movement of the needle will indicate runout - either positive (past the pointer) or negative (behind the pointer) the total runout is the sum of adding how much below the pointer it moved to the amount above the pointer it moved.

Not sure what total runout should be though.

 

Thanks alot fauxrs and the rest of you VETTEHEADS I have a couple of days off, will try and borrow the dial indicator from a friend and go for it.

 

Hi

Once you have the caliper removed, it's very easy to repl the old lip seal pistons with the new O-ring pistons. I guess 1/2 Hour per caliper.
I guess, you could mix both types, but I would at least do them in sets, meaning at least both front or both rear together.
Since you need to remove the caliper anyway for the dial indicator measurement, I suggest you do this O-ring conversion in the mean time.
I left the piston springs out with the O-ring pistons and until now, all is still OK.

Good luck. Gunther

 

I just posted on this in another brake problem. The lip seals in the calipers are designed for .010 maximum pumping action. No more. If the bearings are not adjusted properly they can have that much clearnace, then the rotor if not trued can also have that much run out.
Set the bearings first and that is not just tighten them up and loosen to the nearest cotter pin hole, It is a bit more complicated then that, Then with the rotor installed with the 5 lug nuts torqued to specs start indicating the rotor and add shims as required to get the run out in the .001-.003 range.
Pop cans can yield shims cut with a sissors.
It is not hard just time consumming. An indicator and magnet base are cheap and a nice addition to your tool box.

 

Thanks WESCH and norvalwilhelm, this gives me some direction, norv, how exactly do you SET a front wheel bearing?? :flag :confused: