front disc drag - Team Camaro Tech
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post #1 of 13 (permalink) Old Aug 1st, 06, 01:30 PM Thread Starter
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Kurt
 
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front disc drag

Just got the car on the road and took it out for a ride. Every nut and bolt, component is new. During the ride the pedal became hard and you could smell brake lining. got it home and the front wheels were very hot. Let it cool down a couple hours and everything was OK. took it for another ride and the same thing happened. I search through the posts and found what seemed to be my exact symptoms. I removed the wheels and I had to use a small prybar to spin the rotor.I removed the caliper and pushed the piston back into it, and it went in no problem, In fact I left the lid of the MC and fluid shot all over the place (this was on the driver's side). the pass. side I could spin by hand although there was a good amount of drag. I pushed in on the brake pedal and the DS pison came out and it pushed right back in. That being said, I don't think it is a rod problem. I have some free play in the pedal and since the fluid returned to the MC, that would suggest the the push rod is the correct length. I put the caliper back on the rotor and as I was tightening it down the rotor became hard to turn again. I checked the pads and the inner (piston side) pad was not even making contact with the rotor. I continued tightening it and although there was not as much drag as before it was still hard to turn without using a bar of some kind. How much drag is supposed to be on the rotors? Can anyone give me an idea of what to try next? I did remove some of the fluid in the MC just in case it was overfilled, but it is too hot to work. or drive any more today.
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post #2 of 13 (permalink) Old Aug 1st, 06, 03:39 PM
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Re: front disc drag

Years ago a 68 Z I had did the same thing. I had tried rebuilding the original master and it didn't take so I had a Kragens(I know) master on the car and that turned out to be my problem, bad master. I had a hard time figuring it out but sounds alot like your issue. Good luck.
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post #3 of 13 (permalink) Old Aug 2nd, 06, 03:25 AM Thread Starter
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Re: front disc drag

You might be right. It seems like it takes a long time for the piston to retract back into the caliper. I press the pedal and go out side and the wheels are very hard to turn. after a few minutes they loosen up ab bit. Also, when I open up the bleeder after hitting the brake pedal I have fluid coming out of the bleeder. so there seems to be pressure in the system.
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post #4 of 13 (permalink) Old Aug 2nd, 06, 11:03 AM
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Re: front disc drag

Sounds like it, mine would even apply sometimes without touching the pedal while driving. Nobody could explain it either, try it and let us know.
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post #5 of 13 (permalink) Old Aug 2nd, 06, 11:38 AM
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Re: front disc drag

I'm sure you know about this and have checked - but,
Check to see if there is a residual pressure valve in the inlet of the master to the front side caliper hydraulic fitting.
GM disc's don't require (or want) any residual line pressure.
It's the only difference in some of the rebuilt masters and the 'smoe' that assembles them gets it wrong sometimes.
It should be a straight through shot to the master port.

If it is there, use a screw threaded into the insert and pull it out with a pair of plyers.
You can then get a disc style (no valve in it) or just remove the valve & spring from the original and reinstall it to furnish the seat for the hydraulic line fitting.

Worth a look anyway...

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post #6 of 13 (permalink) Old Aug 2nd, 06, 12:37 PM Thread Starter
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Re: front disc drag

I checked to see if there was a residual valve and there isn't one. I think I might have a couple problems. After really playing with it this morning I discovered that I could only push the piston in when the MC was loose. I used the long push rod (I have all original type components) and if I recall correctly the short rod was to short. also it appears that the piston in the DS caliper does not go all the way in. when I push the piston all the way in the rotor turns freely. as soon as I hit the brakes the driver side gets real tight (can't turn by hand), but the pass side is good. That being said I think I need to shim the MC out from the booster, and maybe replace the Driver side caliper. First though, I want to try shimming the MC. What do you use to do this? Do they make shims for this or do you make you own?
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post #7 of 13 (permalink) Old Aug 2nd, 06, 12:46 PM
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Re: front disc drag

Kurt;
Ok, just thought I'd mention that - helped a local kid out with that problem just a couple weeks ago...

You've checked David Pozzi's site for push-rod info haven't you? - http://www.pozziracing.com/brakes.htm#pushrods

A hanging-caliper is possible. I've done a couple retrofits with wreckin-yard parts and run into calipers that needed some rework to funtion correctly. Sometimes it's just a tight or stiff piston seal, that is not helping return the piston to rest (there are square cut v.s O-ring type, so they 'twist' as the piston is extended and then 'un-twist' when hydraulic pressure is released to retract the piston).

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post #8 of 13 (permalink) Old Aug 2nd, 06, 02:49 PM Thread Starter
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Re: front disc drag

Thanks for the info. I haven't gone to Pozzi's site for this problem, but have been there with the other problems I have had with this thing. I thought I had the right push rod in (long), but just for the heck of it I tried the short one I have and the brakes work perfect on the passenger side, but the driver's side still has considerable drag on it unless I push the piston in, which I am now able to do with the MC tight to the booster, now that I am using the short Rod. I'm going to ride it around for a while and see if that cured the problem, if not I will try a new caliper. Just for the sake of asking another question, I took the caliper off, removed the pads, and placed a block of wood were the pads go and hit the brake pedal the piston only came out about a half inch, is this normal or should it have come out further? been a while sincie I messed with brakes.
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post #9 of 13 (permalink) Old Aug 2nd, 06, 04:53 PM Thread Starter
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Re: front disc drag

Well, I wint out and pulled the MC and measured the depth and it is the 1 5/8 deep version with means I should be using the 4" pushrod and not the 2 1/2, so I guess I'm back to shimming the MC.
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post #10 of 13 (permalink) Old Aug 2nd, 06, 05:15 PM
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Re: front disc drag

Yes you need the short pushrod. The pedal pad height should be 4" to 4 3/4" from the floor, this is lower than the clutch pedal height.
The rod from the pedal should have a little free play, and the booser should control pedal height, not a rubber stop or brake light switch. The rod connects to the lower hole in the brake pedal and a spacer tab is bolted to the upper hole that contacts the brake light switch. Don't set the switch so it bottoms out and prevents full pedal return.

If the RF caliper only releases fully when you open the bleeder, there is pressure trapped somewhere in the line. Either a bad hose or line, or some restriction at the proportioning or distritubition block. You might find it by cracking open the line farther up the same way you did the bleeder and if you get beyond the problem area, breaking loose the line won't make a difference.

If cracking the RF bleeder doesn't help release the LF caliper, then the problem is below the point where the lines split RF/LF.

Also check the outboard pad for pressure against the rotor. If the caliper bracket is positioned too far inboard relative to the rotor, the caliper can't move more outboard to release the pad. You would have to shim the caliper bracket outboard to correct this. Also check the caliper anchor bolts and sleeves for binding. The caliper should have O rings inboard and outboard to guide it, these are lubed with silicone grease.
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post #11 of 13 (permalink) Old Aug 2nd, 06, 06:46 PM Thread Starter
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Re: front disc drag

Thanks for coming in Dave. Let me get this straight. I have the MC that has the 1 5/8 deep hole. Are you saying I need the short push rod (2 1/2)? My other car used the same MC and it has the 4" push rod. If I use the short Rod the RF brake works perfect (normal drag) the LF has alot of drag but not as bad as with the 4" rod (this is done by turning the rotor by hand and not actually driving the car. I don't know how good the brakes will work when driving). But if I use the long rod both sides bind up, the LF I can't even turn and I cant press the piston back into the caliper unless I loosen the MC from the booster. Once I loosen the MC the RF is good and the LF is still dragging but not as bad as when the MC was tight to the booster. I have free play at the pedal and my pedal is about were you say it should be (lower than the clutch). What do you think about the fact that I can't get the piston to come out of the bore more than a 1/4 inch or so. Do you think the caliper could be bad?
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post #12 of 13 (permalink) Old Aug 2nd, 06, 08:59 PM
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Re: front disc drag

My mistake, you have the deep master cyl and should use the long pushrod. I reciently put a new booster on a car that used the long pushrod and still had to grind a bit off the end of the pushrod to make it work right.

Before working over the pushrod or shimming the master cyl, make sure the pedal pushrod is not being held in.

The caliper piston should push out more with repeated pedal applications. If the booster pushrod to master cyl is a bit too long, the MC can't replenish itself and will limit how far you can pump the piston out.
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post #13 of 13 (permalink) Old Aug 9th, 06, 07:03 PM Thread Starter
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Re: front disc drag

Just to let you guys know the problem was that the MC pushrod was 1/16 to long. I just ground it down and it works perfectly now.
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