'67 brake problem

[Tom L.]

Re: '67 brake problem

Prior to the problem, was the car stored without being driven for a while? If so and if you have determined that there are no air or fluid leaks, try flushing the system completely and thoroughly with new fluid. I have no real explanation but I've had two cars that sat for a while and the fluid was so contaminated/dirty I figured that I would start there before replacing parts. In both cases the pedal came back and I havn't had a problem since. Good luck!!

[Joe L.]

Re: '67 brake problem

Previous owner replaced both front rotors since he scored originals with improper placement of brake pads. Rear spindles only, not the rear rotors were redone by "place in FL"-name?, apparently separately from rear rotors.How do you set up a dial indicator to be square with rotor so it will give accurate reading of runout? Any and all other suggestions also appreciated regarding SIMPLEST way to correct problem. Do calipers with O ring seals prevent this air sucking even if rotors/hubs are slightly out of specs?
Thanks

It's a little hard to explain how to set up the dial indicator. However, the attached photo from the Chevrolet Service Manual shows one way to do it. There are several different ways to set it up. A flexible "gooseneck" type dial indicator stand can be especially helpful. But, it has to be a GOOD one that stays rigid when locked.

Using o-ring seals and associated pistons will eliminate the air pumping problem. However, if there is excessive runout on the discs there will also usually be created a "brake squeaking" syndrome caused by the rubbing of the brake disc backing plates against the ends of the caliper pad slot as the pad moves in and out. Also, for proper braking performance it's important to have the run out within specification. So, whatever you do to correct any air pumping problem you have, I'd recommend at least seeing where you're at with run-out. Besides, if it's within specification, then you know that your brake problems lie elsewhere than the air pumping syndrome. It's really pretty easy to do the run-out check. If the rotors are "rivet-less", make sure you fasten them up tight with the lug nuts before checking runout.

[John H.]

Re: '67 brake problem

Here's another way to set it up - note that the half-shaft must be disconnected from the spindle flange to get a true reading.

[Joe L.]

Re: '67 brake problem

Here's another way to set it up - note that the half-shaft must be disconnected from the spindle flange to get a true reading.

John------


Yes, the half shaft should be disconnected just as you say. However, there's one other issue that often doesn't get considered but I do not usually bring it up. Technically, one is supposed to determine the spindle end play and then subtract this from the total indicated runout and the result needs to be less than 0.002". However, I've never "bought that". As far as I'm concerned if the total indicated runout exceeds 0.005" with no correction for end play it's too much.

For the fronts, the spindle nut should be snugged up to take up all end play before the total indicated runout is measured and should also be 0.002", maximum. I don't buy that, either. For me, if the total indicated runout exceeds 0.005" with the front bearings properly adjusted it's too much.

Later in the C3 period (about 1974), even though there was basically no change in the disc brake system since 1965, the total indicated runout spec changed to 0.005" for both the fronts and the rears with the end play subtracted out for the rear and the end play taken up at the spindle nut at the fronts. I still go with 0.005" disregarding any correction for end play or taking up the end play prior to measuring.

[Dale S.]

Re: '67 brake problem

Great picture John H. Dale

[Gerard F.]

Re: '67 brake problem

Here's another method, but with the trailing arm off the car:



Yes, that is .003

[Gene M.]

Re: '67 brake problem

The .002" bearing end play will yield way more than .005" at the brake rotor edge. Do the math or just wobble the rotor side to side. Better results to set bearing clearance to .000" but not tight then measure rotor run out.

[William F.]

Re: '67 brake problem

All sounds like too much sugar for the nickel but I'll see what I can do.-why do you have to disconnect the half shafts?Are regular brake shops like Midas, etc. set up to measure runout?

[Joe L.]

Re: '67 brake problem

All sounds like too much sugar for the nickel but I'll see what I can do.-why do you have to disconnect the half shafts?Are regular brake shops like Midas, etc. set up to measure runout?

William------


Generally, yes.

[Joe L.]

Re: '67 brake problem

The .002" bearing end play will yield way more than .005" at the brake rotor edge. Do the math or just wobble the rotor side to side. Better results to set bearing clearance to .000" but not tight then measure rotor run out.

Gene-----


The runout measurement is supposed to be taken 1 inch inboard of the perimeter of the rotor, but I completely understand your point. However, I have found that if there exists much more than 0.005" total indicated runout regardless of where that runout originates, air pumping will occur. So this all means that the end play has to be minimal (0.001")and there has to be near zero runout on the rotor/hub or rotor/spindle assembly.

[Gerard F.]

Re: '67 brake problem

[quote=Gene Manno (8571);514438]The .002" bearing end play will yield way more than .005" at the brake rotor edge. Do the math or just wobble the rotor side to side. Better results to set bearing clearance to .000" but not tight then measure rotor run out.[/quote

Gene,

That's a total runout of .003 in the picture. I wobbled it in and out with the guage in place, and then picked it up by the rotor and turned it, with the gauge in place. It was actually just under .003.

The picture shows was a brand new (refurbed) trailing arm assembly with riveted on rotors from Ikerd's.

[Tom L.]

Re: '67 brake problem

A question about your measurements. When you measure runout is it measured from "true" in both directions or is it measured from the low spot to the high spot. If measured from low to high I think you could assume that it is only moving off "true" .0015 in either direction. Just a thought.

[Joe L.]

Re: '67 brake problem

A question about your measurements. When you measure runout is it measured from "true" in both directions or is it measured from the low spot to the high spot. If measured from low to high I think you could assume that it is only moving off "true" .0015 in either direction. Just a thought.

Lynn------


The way the set-up is done for this measurement, it's measuring from the high spot to the low spot. However, essentially, that's what the specification is based on rather than a measurement from "true".

[John H.]

Re: '67 brake problem

A question about your measurements. When you measure runout is it measured from "true" in both directions or is it measured from the low spot to the high spot. If measured from low to high I think you could assume that it is only moving off "true" .0015 in either direction. Just a thought.

Lynn -

As Joe noted, it's from the low to the high; runout is measured based on T.I.R. (Total Indicated Runout), which is the mathematical difference from the point of the lowest measurement to the point of the highest measurement.