Brake pedal drops during burnout
Thread Starter
Drifting
Joined: Oct 2009
Posts: 1,385
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From: San Diego CA.
Brake pedal drops during burnout
I was in a parade in 2019. The car has a 700R4. The onlookers loved burnouts. The sheriffs didn’t care. I had my foot on the brake and began. I’m smoking the tires when the pedal dropped half way down. The pedal always engaged a couple of inches down. Always firm. Perfect. I’ve replaced every brake part except the calipers. No leaks from any of them. Bled perfectly. The last thing to check is the pedal assembly itself. I was thinking I bent the mount? Is that possible? I can’t really see it, but I can feel it. Again, everything is new and adjusted properly including the rod between the master cylinder and the booster. I’m stumped. Any ideas?
Race Director
Joined: Mar 2017
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From: Virginia
You know what happens when you do burnouts like that, right?
The proper way is to isolate the rear lines. This video shows an example of a C3 that has done the mod to keep pressure in the front lines only.
The proper way is to isolate the rear lines. This video shows an example of a C3 that has done the mod to keep pressure in the front lines only.
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Burnouts holding the brake??? really? When I lived in the states I did a few 4th of July parade burnouts. spun um all the way down the street. Never , never touched the brake!
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Michael S. Palmer
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If you have power brakes.... (which are activated with engine vacuum)...it would not be a surprise that the brake pedal would be affected when the engine was making almost NO vacuum.
P.S. Doing that kind of burnout in a parade without a Line-Loc (or equivalent method of activating only the front brakes) would be risky...if not downright dangerous.
P.S. Doing that kind of burnout in a parade without a Line-Loc (or equivalent method of activating only the front brakes) would be risky...if not downright dangerous.
Last edited by 7T1vette; Feb 8, 2021 at 09:46 PM.
Thread Starter
Drifting
Joined: Oct 2009
Posts: 1,385
Likes: 86
From: San Diego CA.
Thread Starter
Drifting
Joined: Oct 2009
Posts: 1,385
Likes: 86
From: San Diego CA.
Thank you. I didn’t want to hit the folks in front of me. The pads are ceramic. I’ve checked every pad for signs of anything. The brake fluid in the reservoir wasn’t low. That pedal mount looks pretty strong. A mechanic told me he’s seen the base bend the thin metal it’s mounted to. I checked that.
Race Director
Joined: Mar 2017
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From: Virginia
But did you check the runout? You could have cooked the rear discs. Or the calipers. Or both.
Use a tool like this or with a magnetic base.
When I rebuilt my trailing arms, both rear caliper mounts were bent/broken. The skid rigs I've seen often have their rear calipers removed.
Use a tool like this or with a magnetic base.
When I rebuilt my trailing arms, both rear caliper mounts were bent/broken. The skid rigs I've seen often have their rear calipers removed.
Last edited by Bikespace; Feb 9, 2021 at 08:33 PM.
Thread Starter
Drifting
Joined: Oct 2009
Posts: 1,385
Likes: 86
From: San Diego CA.
i thought that it must be in the calipers. All pistons show no signs of anything. No oil leak. All brakes have stainless steel lines. I’ve not checked the proportioning valve. It’s the only thing I’ve not looked at.
Last edited by vetten76; Feb 9, 2021 at 08:39 PM.
Thread Starter
Drifting
Joined: Oct 2009
Posts: 1,385
Likes: 86
From: San Diego CA.
Thread Starter
Drifting
Joined: Oct 2009
Posts: 1,385
Likes: 86
From: San Diego CA.
But did you check the runout? You could have cooked the rear discs. Or the calipers. Or both.
Use a tool like this or with a magnetic base.
When I rebuilt my trailing arms, both rear caliper mounts were bent/broken. The skid rigs I've seen often have their rear calipers removed.
Use a tool like this or with a magnetic base.
When I rebuilt my trailing arms, both rear caliper mounts were bent/broken. The skid rigs I've seen often have their rear calipers removed.
Race Director
Joined: Mar 2017
Posts: 11,960
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From: Virginia
Also, just to be clear, did you replace everything AFTER the burnout and partial brake failure, or before?
Last edited by Bikespace; Feb 9, 2021 at 08:55 PM.