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Brake Fade SS 253

Started by _BradleySS_ , Dec 01 2018 12:27 PM

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12 replies to this topic

#1 _BradleySS_

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Posted 01 December 2018 - 12:27 PM

Hi

I am having a problem with when I sit idling in the SS and the revs are low the brake pedal starts to slowing sink. Raising the revs fails to lift the brake pedal. When I freshened the motor up and put it back together the brake booster failed so I had it reconditioned. Also when you brake there is a fine line to a quick stop and locking it up.

I have the brake booster reconditioned 8 months ago and have changed out the vac pipe to the brake booster to ensure no vacuum leaks. Bled the brakes twice. Was thinking it can only be master cylinder or proportional valve. Anyone had this problem so I can tackle the correct part for replacement

Thanks

Edited by BradleySS, 01 December 2018 - 12:27 PM.

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#2 S pack

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Name:Dave
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Posted 01 December 2018 - 12:52 PM

I would take the booster back to the guys that recoed it and get them to check it for leaks.

The touchy brake pedal sounds like the reaction disc is missing from inside the booster.

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#3 _BradleySS_

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Posted 01 December 2018 - 03:26 PM

I hope not as thats a prick of a job getting the booster in and out.Not the master cylinder?

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#4 rodomo

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Posted 01 December 2018 - 04:59 PM

Foot dropping sounds more like master or other hydraulic leak.

"fine line to a quick stop and locking it up" could be reaction disc.

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#5 _BradleySS_

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Posted 01 December 2018 - 05:42 PM

No leaks been all over it and not losing any fluid

thanks

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#6 rodomo

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Posted 01 December 2018 - 09:43 PM

Master cylinder can by-pass internally which will make your foot drop.
Unbolt the master from the booster and check for fluid in that cavity.

Edited by rodomo, 01 December 2018 - 09:44 PM.

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#7 _BradleySS_

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Posted 02 December 2018 - 10:01 AM

Hi

Will look at that as i remember the brake man bench tested the master cylinder as said it was fine.Has to be the booster

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#8 S pack

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Posted 02 December 2018 - 11:14 AM

The master vac on our VS started sucking air in past the rear seal when the brake pedal was depressed and the pedal would also very very slowly drop away under foot.

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#9 _BradleySS_

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Posted 02 December 2018 - 11:17 AM

Inside brake booster?

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#10 _BradleySS_

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Posted 08 December 2018 - 02:16 PM

Hi

Thanks for the suggestions.To follow through I took the brake booster off and had it inspected by the brake man and all checked out fine visually.He suggested the same as above from rodomo ,that the master cylinder may be by-passing internally.I bought and fitted a new one and no brake fade.I had no problems with brakes until I pulled everything off for paint and had on the shelf for 6 months.But the booster and master looked original so cant complain after 40 years.Just threw me that after replacing the brake booster the master cylinder went shortly after.After I fitted the brake booster I had a little fade and thought it was air in the system but several bleeds didn't change it.As time went on it got worse.It would hold sometimes and 15-20 seconds latter would start dropping.Got there in the end

Regards

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#11 rexy

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Posted 08 December 2018 - 03:14 PM

Not an uncommon story with the master. The bleeding process using the full stroke of the master must upset the bore seal in some of them.

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#12 koalasprint

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Posted 11 December 2018 - 01:09 PM

If it was a "big nut" master cylinder don't throw it out. they are somewhat sought after these days.

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#13 Big_Red

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Posted 17 December 2018 - 09:08 PM

When replacing brake pads on old cars I was always taught not to use the full stroke of the pedal when 'pumping them up' for this very reason. Also can pay to flush old brake fluid threw with new before doing other brake work like replacing pads. Don't forget brake fluid should be replaced every 2years, or 1year in areas of high humidity. Something fairly small that often isn't done. Wet brake fluid boils easily with heavy braking and can also give a slightly more squishy feel.