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I am having problems bleeding the brakes, l have followed the recommended procedure, starting with the front N/S followed by front O/S and  rear N/S. l get pedal pressure without the engine running but with the engine On no pressure.

Help!

Andy  

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Bit quiet on the TR7 forum isn't it.

Seems to be pointing to the servo. Was it working before / what have you replaced ?

Try bleeding with the engine running perhaps.

Jerry

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Hi Jerry

Thanks for your suggestion. Brakes were working, l decide to bleed the brakes prior to a MOT. I will try with the engine running and let you know the results.

Andy

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I gave up trying to bleed the brakes on my 3A and took it to the local garage. They managed it and never a problem since. I do not like to give up but sometimes it is successful.

Richard & B

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Seems weird.

Booster should have held vac even without the engine running. But assuming its lost vac that would make the pedal heavier without the engine not loose brake pressure.

With engine running it should be a lighter  pedal but still get pressure.

Are both brake circuits loosing pressure? I think they should be split diagonally. 

 

 

 

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Thanks for all the input. I tried bleeding with engine running, made no difference, pressure with the engine off, no pressure with the engine running, could the be a problem with the master cylinder?

 Any other suggestion welcome.

Andy

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It has been said with troublesome brakes that wedging the brake pedal down and leaving under pressure overnight sometimes clears difficult air locks.

Has the car been standing for a time before bleeding? Sounds as if something in the servo is not returning to it's proper position.

Jerry

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Do not buy a new master cylinder. They are not usable. Get your original overhauled by Past Parts and it will work properly. I had all those problems. Richard & B

Edited by Richardtr3a
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How did you bleed them? On/off at the pedal or a vacuum bleed? Did the reservoir run to low while doing it?

 

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I can't work out the logic but i think the issue is in the master cylinder. There is a mechanical link from the pedal through the booster so the only way that is going to go soft is if something deflects the pushrod. That's unlikely.

More likely either a seal has been damaged or a piston has got stuck when bleeding because you tend to push the piston further than normal so it goes into an unused (corroded) area. 

If you can push the slave cylinders in, the reverse flow may free it up but that obviously means getting to the brakes. You can try putting a pump on the nipples to push back from there but you will have to bleed the brakes again.

The first thing would be to tap the master cylinder with a hammer in the hope it frees up anything stuck.

I assume you are not sucking fluid past the seals with the engine running.

Are you getting the same pedal travel? The only thing that i can think off is that the pistons are not retracting fully (under spring pressure) and there is some air trapped somewhere. When the booster has vac its actually sucking the piston back so you have to press the pedal further before generating pressure.

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Having check through previous suggestions l am coming to the conclusion that the master cylinder is the problem. If l bleed starting with the N/S front, fluid passes  with no air bubbles  and l get some brake pedal pressure, with engine running the pedal just goes straight to the floor, no pedal pressure, just want to get the advice of 7 community before removing the master cylinder.

Regards

Andy 

 

 

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Andy, try a post in the general Technical section as not enough people look in here. i don't know anything about the 7 braking system, but it doesn't sound like the master cylinder to me, otherwise you wouldn't get any pressure under any circumstance.

Jerry

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  • 2 weeks later...

Continuing saga of my TR7 brakes. l decided to rebuild the brake master cylinder, l remove the main pistons, clean the bore and re-sealed, the only problem l have, l can't remove the warning light valve to replace the O rings. As far as l can work out this only works the warning light so would it affect the brake operation if not re-seal.

Regards

Andy

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I have bled TR7/8 brakes manually and with a vacuum system - it appears not to make any difference if you remove the warning light valve thingy!

 

Cheers

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I know this might sound odd , but I had a problem of not getting a pedal, after much head scratching I found I tiny and I mean tiny pin whole in a brand new brake pipe.

Before you go to far, just run your hands along all the pipe work, to see if you feel any leakage, I could not see it until after I made a new pipe and replaced it, but I did feel the brake fluid on the faulty pipe

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Sounds like a big air lock to me.

I have resorted in the past to pressurising the master cylinder reservoir with  a low pressure air line and a wheel cylinder bleed nipple undone.

The fluid from the m/c should be forced through with any air that might be present.

Repeat on all wheel cylinders.

You will need to modify a reservoir cap to fit an air line.

Careful with the pressure, if the pressure is released quickly brake fluid is blown all over the place!

David

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On 7/22/2020 at 12:44 PM, David James said:

Sounds like a big air lock to me.

Me too.

Andy,

Try bleeding the brakes again and this time start from the brake furthest from the M/C and work towards it, i.e. first NSR. then OSR etc. Edit: assuming the M/C on the TR7 is fitted OSF, if not then Vicky-Verky.

Cheers, Andrew

Edited by Andrew Smith
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  • 1 month later...

Thanks to all for the input, after a delay in playing with the 7 the brake bleeding problem solved. After talking to Steve of S&S Preparations fix was easy, in a previous rebuild the front calipers had been fitted wrong way round ( right left, left right) so thew bleed nipples were on the bottom, change over, bleed nipples top and the aid of a pressurised bleed system the problem solved.

Cheers.   

 

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