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Have searched for answers to this issue but to no avail. Nothing happening when I try to bleed front brakes. Rear ones were fine. M/C is original and rebuilt by specialists PP. When brake pedal is pumped nothing much happens. A few small air bubbles appear in my ‘jar’ but in the reservoir nothing happens at all. Fluid level doesn't change, no bubbles, no leaks, nothing! 
Is this something to do with the tipping valve?
I wait with cautious optimism!

Many thanks

Tim

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You can either watch the tipping valve from the top without fluid and maybe without the plastic container. It must move a little bit when you touch the Brake pedal a little bit.

 

Better use the Gunsons brake bleeder. You can open the caliper bolt and let the fluid out. If nothing happens the tipping valve might be the culprit.

 

Gunsons or similar ist always my favorite system for bleeding. Nasty bubbles that stick somewhere will come out.

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Hi Tim,

friend of mine had the same problems with his TR250,

he told me the problem was the "tipping valve" inside the master,

also he assumed it was because his TR 250 has been jacked only on the front.

I don't know anymore what solved the problem - he perhaps also does not too, but his TR is back on the road.

Marco.

 

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17 hours ago, mtrehy said:

Check the rod position in the servo, probably no gap. Had that a few times. 

What do you mean by no gap?

Cheers,

Tim

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10 minutes ago, Tim T said:

What do you mean by no gap?

Cheers,

Tim

Gap between the servo push rod and the master cylinder piston end.

Stuart.

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Have played around with it all today. Have seen how it all works but have not sorted the issue yet!

I removed the M/C and reservoir, put some fluid in the reservoir and pushed the piston manually, travel was about 36mm. A good jet of fluid came out of the outlet.

I removed the reservoir and pushed the piston, the tipping valve closed as it should and returned to the open position on release of the piston. Put a small amount of fluid on top of the tipping valve and once again a good jet of fluid was expelled.

Put it all back on the car, fitted a short length of pipe to the outlet and into a bottle so that I could see what was going on. Answer - very little! everything appears fine off the car but not on it.

Does this point to an issue with the need for this gap between pushrod and piston that Stuart mentions? The pushrod travel is also 36mm.

How do I create a gap?

Thanks for your patience and help as ever,

Tim

 

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.... if I push the servo pushrod back into the servo unit I get a gap of 0.035. If I then depress the brake pedal and release again the pushrod does not return to its start position and finishes with no gap or even proud.

Thanks again,

Tim

IMG_6666s.thumb.JPG.37792eda236a849ad23fd8227a04230a.JPG

 

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23 minutes ago, Tim T said:

.... if I push the servo pushrod back into the servo unit I get a gap of 0.035. If I then depress the brake pedal and release again the pushrod does not return to its start position and finishes with no gap or even proud.

Thanks again,

Tim

IMG_6666s.thumb.JPG.37792eda236a849ad23fd8227a04230a.JPG

 

Thats your problem.

Stuart.

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Many thanks. Will report back tomorrow.

Cheers

Tim

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1 hour ago, Tim T said:

.... if I push the servo pushrod back into the servo unit I get a gap of 0.035. If I then depress the brake pedal and release again the pushrod does not return to its start position and finishes with no gap or even proud.

Thanks again,

Tim

IMG_6666s.thumb.JPG.37792eda236a849ad23fd8227a04230a.JPG

 

What do you mean by push it back? You have to screw it back and lock it in correct position

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I have recently learnt that it needs to be screwed back. But how is it locked in that position?

Tim

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When I rebuilt the brakes on my six I could get nothing at the front.

Filled a big 60ml syringe with fluid and primed up from the bleed screw, I soon found out why I was getting nowhere; there were a few nuts not quite tight enough that were letting air back into the system instead of fluid being sucked in from the reservoir.

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Reading this thread I'm now wondering if this gap between push rod & M/C could be the source of my braking issue.

Last year I fitted Wilwood calipers & discs on all four corners, at the same time I fitted the original servo & M/C which had just been refurbished by Past Parts. The brakes bled well with no issues, nice firm pedal feel and the car subsequently passed an MOT. However, the car does stop pretty well but just not as sharp as I would have expected, not as sharp as the original set-up, a braking system downgrade you might say.

It never occurred to me to check this gap, so needless to say no adjustment was made.

Could an incorrect gap be contributing to what I've described above?

Richard.

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If the pistons of the Wilwood calipers have a smaller surface than the pistons of the original Girling calipers you have less force on the brake pads.

I guess this is the issue, because I studied and calculated the surface of several "suitable" calipers.

And their surface has always been smaller than the surface of the Girling pistons.

Edited by Z320
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Everything is 100% standard and original here. Obviously discs and pads are new.

Tim

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From the BMW R 90S (a motorbike) I know,

if the piston does not move back in the correct position no brake fluid can flow from the reservoire to the piston.

On the R90S this flows through a simple drilling, on the TR5, 250, 6 this my be the "tipping valve",

I don't know, just an idea.

Good luck!

Edited by Z320
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Update time. The pushrod gap is good at 35 thou, so left alone. It also behaved exactly the same as another unit that I compared it to.

Next I bled the MC off the car. This worked fine, put it back on the car and bled the rest of the system.

Happy days.

Thanks for all input.

Tim

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 Hi

Be aware that 035" gap may be correct measuring against the servo face, but  the piston in the master cylinder can sit further in especially if not nos parts causing a bigger gap, I had a problem with long movement and trouble bleeding with new master cylinder checked against original one and piston was to far in, so adjusted nut to compensate.  The 035" wood have been bigger to tighten up gap. An expantion gap should be there between servo rod and piston , 

Richard

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Many thanks for all replies. Happily everything is now working well with no leaks!

Tim

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  • 4 weeks later...

 

On 1/26/2021 at 9:03 AM, Tim T said:

Many thanks for all replies. Happily everything is now working well with no leaks!

Tim

Spoke too soon, brakes are still spongy!!!!!!!
So today I thought that I would try to work through the system to see what works and what doesn’t. Bench bled the MC and all fine.Tipping valve working. Correct play on servo push rod.

Then blanked off MC outlets and tried the brake pedal, was nice and hard as it should be.

Connected front circuit only, bled, tried pedal and it was spongy again.

Blanked off the front circuit, reconnected rear circuit, bled, tried the pedal and it was spongy again!
There are no leaks at any of the pipe unions. Flexible pipes are Goodridge stainless. All components are original rebuilt by Past Parts except rear cylinders from Moss.

Where do I go from here, apart from the Samaritans!?
Any ideas very gratefully received.

Many thanks

Tim

 

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Yes and no air at all. Everything that I can see looks good. I did wonder if one of the calipers  or slave cylinders could be the problem but surely not one of each!

Tim

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