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Brakes, Suspension & Steering Conversion questions & more.

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  #1  
Old Sep 9th, 12, 7:18 PM
Spang Spang is offline
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Default Spongy and low brake pedal

I have too much travel in my front disc one piston calipers, making brakepedal spongy and low.
I think my calipers is not parallell to the disc anymore, it seems like the outside pad sits a bit wedged so to speak.
When I release the brakes it is air between the disk and outside pad on the little diameter end, but full contact on the big diameter end.

Is this a known problem, and is there a quick fix to it?

When I clamp off the two hoses to the calipers the brakepedal sits very high and is rock solid.
Take either one clamp off and pedal goes too deep towards floor and is too spongy.
Take both clamps off and it gets worse.
The brake warning-light will not go on and pedal will not bottom out, but it is close.

It is a –69 Chevelle powerbrake front disc/rear drum.
I have worked on this issue two weeks now.
Bleeding brakes, changed and bench-bleed mastercylinder a few times, checked all hoses, bleed, bleed again and so on.
Not funny anymore.

A few years ago I had big problems with front brakes sucking in air thru the metering or hold-off valve mounted on the master cylinder.
I just deleted it and brakes was fine again.
Apart from that I think everything is standard Chevelle –69 on this car.
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  #2  
Old Sep 9th, 12, 10:59 PM
Schurkey Schurkey is offline
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Default Re: Spongy and low brake pedal

Bleeder screws on the TOP of the caliper, not the bottom?

Any chance you have low-drag calipers on the front? If so, they MUST be used with a quick-take-up master cylinder, or you'll have a low brake pedal.

Caliper mount bushings and O-rings still in acceptable condition? The bushings are brittle--will shatter if abused. Should be two bushings and four O-rings (two large, two small) per caliper, on the bolts that go through the steering knuckle/caliper mount.

Wheel bearings properly adjusted? Too much wheel bearing play will knock the pad and piston back into the caliper body.

Get another holdoff valve. Your front brakes will last longer.
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  #3  
Old Sep 10th, 12, 1:25 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

Yes, bleeder screws on the top.

I changed to new brake calipers a few years ago before I found out it was a faulty hold-off valve then.
Symptoms was almost identical as now.
Clamp the hoses - pedal ok - take away clamps - pedal to floor.
Same casting number on old and new calipers.
Brakes has almost always been good, exept when the hold-off valve was faulty.
No problems locking all four wheels at 60mph, rears requiring slightly more pressure on the pedal to lock.

Bushings, o-rings, pins, bolts, hoses looks good.
Was replaced at the same time as calipers.

Wheel bearings properly adjusted.
Had a mystery noice coming from the front wheels, everybody thought it was wheel bearings.
But it did not go away until I changed front wheels...

I picked up my old calipers today and thought i would give them a try again and see if that helps.
But I did not remember I took them apart when I changed calipers last time.
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  #4  
Old Sep 10th, 12, 3:50 PM
Jack Action Jack Action is offline
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Denny
 
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Default Re: Spongy and low brake pedal

Since you did not respond to Schurkey about the low-drag calipers, I will re-emphasis that comment. Read the last paragraph of this document; It is almost your post, word for word.
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  #5  
Old Sep 10th, 12, 6:14 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

Denny.
You are correct about my brakes feel just like i have low-drag calipers.
I have spent several hours on this Chevelle-forum, searching for an answer.
I found this link a few days ago, never heard of low-drag calipers before.


A few years ago I ordered new/remanufactured calipers to my Chevelle –69 and got same castingnumbers on them as the one sitting on the car then.
Brakes has almost always been great on this car.
This makes me belive I have the right calipers now, but who knows for sure?


It can be air in the calipers.
I have bleed them multiple times.
Gravity-bleed, pressure-bleed and vacuum-bleed.
Also have pushed pistons back in caliper a few times, just like when you change brakepads.
Two big bottles so far, 2 Litres (2quarters).
I am pretty convinced it is not air left in the calipers, but again who knows?


It can also be too much movement of the piston for some reason, making it act a bit like low-drag calipers?
The calipers is self-adjusting to aligment, but I start belive it is something wrong here making piston travel too long.


Is there anything I have overlooked so far?
It is only brakes, how hard can it be to fix!?
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  #6  
Old Sep 11th, 12, 2:18 PM
lowflyer lowflyer is offline
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Dan
 
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Default Re: Spongy and low brake pedal

Have you tried adjusting out the rear brakes?
I've had spongy brakes until I adjusted out the rears before.

As for the crooked disc to pad, does the car shake when brakes are applied?
Remove, clean and ispect the inner races on the rotor. Make sure they haven't started to pull out and get crooked. Inspect the bearings while you have it apart. The rotor could be pushing the caliper piston back, but you would feel a heck of a vibration when braking. If the braking action is smooth, I would rule that out.

Make sure the caliper mount pins are parallel with the spindle when installed.

Did this problem just suddenly come up? Or did you change something and then this started?

I would start by replacing the hold off valve. Then inspect the calipers really well, to rule out the system sucking in air.

Bleed the master cylinder on the car. Push the pedal in, and then crack the line. Tighten before you let up on the pedal, then repeat. Could be a failing master cylinder...

Good luck and keep us posted.
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  #7  
Old Sep 11th, 12, 6:52 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

Dan.

I thought this issue gradually has getting worse over time, but I am not sure anymore.
It might be the owner (me) doing something wrong earlier or now.

I do not have the hold-off valve installed.

Rear brakes adjusted properly.

No shake when braking, wheel bearings ok.
Actually the car is on jackstands now, wheels removed.

I have tried a new and the old used master cylinder, bench-bleed it but I have not bleed it on the car as you describe.
I will try that.

How can I check that caliper mount pins are parallel with the spindle when installed?
Is it just to look at it, or is there a good way to measure it?

Last edited by Spang; Sep 11th, 12 at 7:09 PM.
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  #8  
Old Sep 11th, 12, 6:58 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

I tried to use C-clamps today, holding caliper pistons in the all in position.
Just like when you change brakepads.
I tried it to test the whole complete brake hydraulic system, eliminating any movement in the calipers.
No improvement, pedal still goes almost to floor.

I am pretty sure I do not have air in the system from the master-cylinder to the hoses.
But it seems to me now I have air still trapped in the calipers, what else could it be?
I will take calipers loose, hoses still connected.
Bleed and at the same time move calipers in different angels to get all air out.
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  #9  
Old Sep 12th, 12, 11:48 AM
lowflyer lowflyer is offline
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Dan
 
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Default Re: Spongy and low brake pedal

Have you replaced the brake hoses to the calipers? Sounds like they are ballooning somewhere... You may not see them actually ballooning, they do fail within the hose liner and you may never see it. Check the rear one too.

If you've clamped off the calipers at the piston and you are still getting spongy brakes, then you have eliminated the calipers or any air stuck in them as a problem.

Now you move onto clamping the rear brake hose now. While still having the front calipers clamped. Try to clamp as close to the master cylinder as possible.

If the problem goes away, then its in your rear brake system. Bad wheel cylinder sucking air, or a flexing rear brake hose, or your rear brakes way out of adjustment.

If it still goes to the floor, is either a bad master cylinder or a bad brake hose.

Don't replace with old, known bad parts. Replace them with new ones if you can. And while you are at it, replace that hold off/proportioning valve. It'll keep you from locking up the rears and crashing that freshly fixed car!!
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  #10  
Old Sep 23rd, 12, 5:20 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

Now I have changed almost all parts in the hydraulic system to the front brakes.
New mastercylinder, calipers, bushings and o-rings, hoses and brakepads.
Also eliminated the brake warning light block, bypassing it using tee fittings instead.
I am not using the hold off/proportioning valve at all.

I checked the push-rod length, and it seems to be ok.

NO IMPROVEMENT at all, I am totally lost on this issue now.

I have read a trouble-shooting section suggesting a bad power brake can give excessive pedal travel on Mopar cars.
Is this possible on GM cars too?
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  #11  
Old Sep 23rd, 12, 5:40 PM
Schurkey Schurkey is offline
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Default Re: Spongy and low brake pedal

Quote:
Originally Posted by Spang View Post
When I release the brakes it is air between the disk and outside pad on the little diameter end, but full contact on the big diameter end.
Photo, please.

Quote:
Originally Posted by Spang View Post
I checked the push-rod length, and it seems to be ok.
HOW did you check pushrod length? There are TWO pushrods--one from pedal to booster, one from booster to master cylinder. The one from pedal to booster should be in the LOWER hole in the brake pedal.

When you have a helper push the brake pedal (less than one inch) there should be TWO "geysers" --one in each of the reservoirs--as fluid is pumped out of the compensating ports of the master cylinder.

That assures that the pushrods are not too LONG.

If the pushrod(s) were too SHORT, one inch of brake pedal travel might not provide any movement at the master cylinder, and you'd have no geysers until the pedal was pushed farther. Or, you'd have problems adjusting the brake light switch because the pedal was already too low.

Any chance you've got a master cylinder with a deep pushrod socket, and a booster/booster pushrod that's intended for a shallow pushrod socket master cylinder? You'd maybe have an inch or three of brake pedal travel that provided NO stopping power, then you might feel the brakes engage as the pedal dropped farther. What brand of booster do you have, and what brand of master cylinder? Delco master cylinder goes with Delco booster, Bendix master cylinder goes with Bendix booster. PHOTOS would be welcome.

Schurkey's Rule Of Thumb for brake pedal height: The brake pedal, on a NORMAL, ORDINARY GRADUAL STOP should STILL be HIGHER than the gas pedal in it's "idle" position. Level with the gas pedal is somewhat acceptable. Lower than the gas pedal is unacceptable. The difficulty here is describing a normal, ordinary stop.

Quote:
Originally Posted by Spang View Post
I have read a trouble-shooting section suggesting a bad power brake can give excessive pedal travel on Mopar cars.
Is this possible on GM cars too?
Not that I've ever witnessed. I'm prepared to learn something here, but so far as I know, a defective booster can cause a HARD pedal, but not a LOW pedal. The pedal may drop a little bit as vacuum is applied to a booster that's been drained of vacuum--but the pedal travel isn't that much.
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  #12  
Old Sep 23rd, 12, 6:35 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

I checked pedal to booster pushrod length by loosen the clevis at the brakepedal.
Pushed pedal to stop full-up position.
Was approx 1/16 free play.
Lower hole on the brakepedal, upper is used by the brake light switch I think.

I also tried to measure the pushrod length comming out of the booster.
It was difficult to measure, but it is within + or - .020” compared to my deep bore master cylinder.
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  #13  
Old Sep 23rd, 12, 7:27 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

I don´t know how to post photos here, do I need to upgrade my membership?

I will try to explain it in words instead.
When I release the brakes the outer pads had contact with the disc at the outer diameter.
On the inner diameter I could insert a .016 feeler gauge between the pad and disc.

I think I have a Delco-Moraine power brake booster according to my overhaul manual.
Non-adjustable push-rod in booster.

My mastercylinder looks like this one.
It has 11/8 bore
http://www.summitracing.com/parts/DHB-M89160/?rtype=10

I will do the “geyser” test.
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  #14  
Old Sep 23rd, 12, 9:29 PM
Schurkey Schurkey is offline
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Default Re: Spongy and low brake pedal

Quote:
Originally Posted by Spang View Post
I don´t know how to post photos here, do I need to upgrade my membership?
No. Upload the photo to a hosting site. I use my own web page provider, but Picassa or any of the dozens of other sites--OR--the Showroom feature of THIS web site will also work.

Once the photo is on the 'web, you use the picture icon in the text box for typing replies--it's the postcard-looking icon (two mountains and a postage stamp) in yellow and grey. Add the link to your photos in the drop-down box, and click "ok".

Quote:
Originally Posted by Spang View Post
My mastercylinder looks like this one.
It has 11/8 bore
http://www.summitracing.com/parts/DHB-M89160/?rtype=10

I will do the “geyser” test.


I'd have expected the other style. More like this one:

but as long as it is a proper match to your booster...I guess...it should be fine.
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  #15  
Old Sep 24th, 12, 3:02 PM
Spang Spang is offline
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Default Re: Spongy and low brake pedal

Today we did the “geyser” test.
It is two geysers appearing directly when brakepedal is depressed.

I can hear a “hissing” sound when the brakepedal is depressed.
But I can not tell where it comes from.
It can be from behind the mastercylinder, the gasket between mastercylinder and power brake.
Or the reservoir cover.
Can it still be air in the mastercylinder making this noice?
I will crack the nuts holding the brakelines open when pressure-bleeding to get rid of all possible air.

I may try posting a photo in a few days.
Seems to be many small steps to get it right.
Take a photo, transform it to the computer, use the right format, upload it somewhere and post it in this forum.
It may take as long as it takes to fix my brakes, 3-4 weeks now?!
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