Front brake operation

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chips01
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Front brake operation

Post by chips01 » Sat Oct 26, 2019 7:44 am

What would the group feeling be of the amount of movement in front brake caliper piston when brake pedal is depressed ?

I am at my wits end. New lockheed master cylinder (bled), new caliper pistons and seals, new brake flexis, new brake fluid, all brake line blown out, replacement brake balance valve with free fluid flow and no leaks. When system bled pedal still travels to floor, with pedal depressed fully front wheels still free to rotate. Brakes only operate when emergency stop brake pedal technique used, rapid and harsh press of the pedal. When brake pads removed and brake pedal pressed piston only advances in small increments.

My only remaining thought can be is that the new master cylinder is at fault. Do anyone of my more knowledgeable friends have an opinion?

Thanks to all.

Keith



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Front brake operation

Post by gtcse8 » Sat Oct 26, 2019 8:45 am

Is the engine running and can the servo be heard operating from inside the car??.


Mark Wilson. See the Beast on youtube under" RELIANT SCIMITAR CONVERSION LOL.,Se5,Se5a, Se6a, Two Se6b`s,1 & 1/2 GTC`s, SST 1800Ti & not a lot of sense

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Front brake operation

Post by scimjim » Sat Oct 26, 2019 8:50 am

Are the rear wheels locking?

Does the amount of pedal travel reduce if you pump it?


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chips01
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Front brake operation

Post by chips01 » Sat Oct 26, 2019 9:19 am

gtcse8 wrote:
Sat Oct 26, 2019 8:45 am
Is the engine running and can the servo be heard operating from inside the car??.
gtcse8 wrote:
Sat Oct 26, 2019 8:45 am
Is the engine running and can the servo be heard operating from inside the car??.
Have a replacement servo which appears to be working fine but all brake work is being done with engine stationary as carb is undergoing rebuild.



chips01
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Front brake operation

Post by chips01 » Sat Oct 26, 2019 9:21 am

scimjim wrote:
Sat Oct 26, 2019 8:50 am
Are the rear wheels locking? Rear wheels appear fine.

Does the amount of pedal travel reduce if you pump it?
After 10/15 pumps pressure does seem to build but only raises pedal by about 1-2 inches.



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Front brake operation

Post by gtcse8 » Sat Oct 26, 2019 9:26 am

chips01 wrote:
Sat Oct 26, 2019 9:19 am
all brake work is being done with engine stationary as carb is undergoing rebuild.
I think you have just found the problem :lol:
The system will not bleed fully unless the servo is working and the full pedal travel allowed, especially if all the system is renewed.
Been there before.


Mark Wilson. See the Beast on youtube under" RELIANT SCIMITAR CONVERSION LOL.,Se5,Se5a, Se6a, Two Se6b`s,1 & 1/2 GTC`s, SST 1800Ti & not a lot of sense

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Front brake operation

Post by chips01 » Sat Oct 26, 2019 9:30 am

Noooo. I cannot believe it. So the brakes can only be bled if the engine is running and the servo is operating correctly?



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Front brake operation

Post by ard126k » Sat Oct 26, 2019 11:01 am

When you say the m/c was bled do you mean bled on the bench, before fitting?
Alex.


1971 SE5 1977 SE6 1982 GTC

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Front brake operation

Post by gtcse8 » Sat Oct 26, 2019 11:32 am

chips01 wrote:
Sat Oct 26, 2019 9:30 am
So the brakes can only be bled if the engine is running and the servo is operating correctly?
Correct Keith, up to the point that the servo operating will help push any stray pockets of air out of the system, which is why when you stamp on the brakes you get some operation.
Without the servo operating the MC piston will only be allowed to travel part of its full stroke.
One tip I learned years ago is to pull the handbrake on as hard as you can when bleeding the rears and ONLY let it off when your certain there is No Air left in the rear system.
When you release the brake a small amount of fluid is pushed back into the master and it helps shift any stray pockets of air.
I also use a Vacuum type of bleeder which sucks the fluid etc through the system.


Mark Wilson. See the Beast on youtube under" RELIANT SCIMITAR CONVERSION LOL.,Se5,Se5a, Se6a, Two Se6b`s,1 & 1/2 GTC`s, SST 1800Ti & not a lot of sense

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Front brake operation

Post by halfpenny » Sat Oct 26, 2019 12:46 pm

The system should bleed perfectly well with the servo non-operational, but take care that air is not trapped in the upper end of the servo cylinder. Try bleeding here by slackening the tube nut. I assume the servo is correctly orientated. You may have a very stiff (new?) master cylinder seal which is slipping on the cylinder bore, rather than sealing to generate pressure. You describe getting pressure when stamping on the pedal, which would fit this scenario.



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Front brake operation

Post by chips01 » Sat Oct 26, 2019 12:57 pm

ard126k wrote:
Sat Oct 26, 2019 11:01 am
When you say the m/c was bled do you mean bled on the bench, before fitting?
Alex.
Yes bled on the bench and has also been bled separately in the car.



chips01
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Front brake operation

Post by chips01 » Sat Oct 26, 2019 1:05 pm

gtcse8 wrote:
Sat Oct 26, 2019 11:32 am
chips01 wrote:
Sat Oct 26, 2019 9:30 am
So the brakes can only be bled if the engine is running and the servo is operating correctly?
Correct Keith, up to the point that the servo operating will help push any stray pockets of air out of the system, which is why when you stamp on the brakes you get some operation.
Without the servo operating the MC piston will only be allowed to travel part of its full stroke.
One tip I learned years ago is to pull the handbrake on as hard as you can when bleeding the rears and ONLY let it off when your certain there is No Air left in the rear system.
When you release the brake a small amount of fluid is pushed back into the master and it helps shift any stray pockets of air.
I also use a Vacuum type of bleeder which sucks the fluid etc through the system.
I have tried pressure bleed, two person and vacuum. Once carb recon is finished (awaiting manifold gaskets) I will power her up and do all full bleed again. If that doesn't solve the problem it can only be a fault with the MC which is brand new.
Many thanks to all who have helped with this and my other problems. Vast wealth of knowledge and friendly members here.



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Front brake operation

Post by gtcse8 » Sat Oct 26, 2019 1:10 pm

chips01 wrote:
Sat Oct 26, 2019 1:05 pm
(awaiting manifold gaskets)
Which ones Keith?.
The large inlet to heads gasket or the Oblong Carb to Manifold ?.

I have large stock of gaskets and kits if I can be of help.
Mark


Mark Wilson. See the Beast on youtube under" RELIANT SCIMITAR CONVERSION LOL.,Se5,Se5a, Se6a, Two Se6b`s,1 & 1/2 GTC`s, SST 1800Ti & not a lot of sense

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Front brake operation

Post by derekoss » Sat Oct 26, 2019 1:20 pm

The solution to no engine vacuum is, well, a vacuum cleaner. Don't ask how I know !!

Derek



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Front brake operation

Post by efi_sprintgte » Sat Oct 26, 2019 1:31 pm

I bought a 6a that had refurbed everything but no pedal to speak of, the dual circuit lines were connected the wrong way around...


JC

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