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Hi

I need some help with my other car - an AH Sprite - the brake system is pretty much the same as my TR4 so hopefully someone can help.

Ive replaced the entire system - pipes, hoses, calipers, master and slave cylinders, pads and shoes.

i can only get a firm pedal if i give it a quick pump first, then its solid, but release it for a couple of seconds and i have to give it another quick pump to firm it up again.

The rear drums are adjusted correctly, and Ive squeezed off the rear hose to isolate the problem. There is no change with the hose squeezed off so the problem must be up front.

I'm 99% certain Ive got all the air out - using an eezibleed and bled it at quite a high pressure (using the eezibleed empty to avoid an disasters)

What i have noticed is that when the master cylinder is pressurised using the eezibleed the pedal is rock solid. I dont know if this is significant and telling me anything or not.

Ive checked and double checked everything and bled the system till im dizzy but with no progress, also left left the pedal wedged down for a period.

Next step is to replace the new master cylinder for another one and try again

Can anyone suggest anything - or confirm if the pressurised master cylinder making it work is significant

Thanks

Stuart

 

 

 

 

 

 

 

 

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Hi Stuart,

the pumping does indeed suggest there is still air in the system.

Have you tried bleeding it manually (throw the EeziBleed away).

 

What/which new calipers are you using.

There appears to be a problem with TR4 NEW calipers - in that they also do not bleed 100% of all the air.

 

Can you clamp the front pipes individually and together - if so do this. This will help localise the issue.

 

Roger

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Hi Stuart,

the pumping does indeed suggest there is still air in the system.

Have you tried bleeding it manually (throw the EeziBleed away).

 

What/which new calipers are you using.

There appears to be a problem with TR4 NEW calipers - in that they also do not bleed 100% of all the air.

 

Can you clamp the front pipes individually and together - if so do this. This will help localise the issue.

 

Roger

Whats the problem with the calipers as I havent come across any problems with them yet.

Stuart.

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Thanks for the replies - note its my Sprite, not my TR4 im struggling with

Ive got braided hoses on the front so cant clamp them, although if i cant solve it i may have to revert to rubber hoses while i investigate

I'll try bleeding with the pedal again, then change the braided hoses to rubber so i can clamp them, then try the master cylinder - or i might just take it to kwik fit and let them sort it.....

Regards

Stuart

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I've had problems with new 16P calipers recently and know of two others who've had exactly the same issue.

 

It manifests as a system that will apparently not fully bleed although Triumph systems (GT6 and Vitesse in these cases) are not normally problematic.

 

What's actually happening is that the calipers pistons are withdrawing too far when the pedal is released. Presumably this is because there is too much friction between the seal and piston causing the seal to roll too much (they are meant to roll a bit) before they slip.

 

The cure is to remove the anti-squeal shims, but leave the pads in place, then pump the brakes until you get a firm pedal and then release. At this point you should find there is just room to slip the shims back in and once they are refitted, you have a decent pedal. On our car we had to repeat the process after about 800 miles as the pedal got long again, but it seems to have settled as now over 2k miles and the brakes are still good.

 

Strangely enough, a week after the 16P problem I had the same issue with the rear calipers of my A6, which I'd overhauled myself using a genuine VAG seal kit. I've never encountered it before in 30 odd years.

 

Just possibly, if you have new/recon/overhauled calipers you have the same issue. Worth checking - and fairly easy to spot as it leaves the pads very slack in the calipers.

 

Nick

Edited by Nick Jones
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Brake operation comes about through rolling of the seals which allow the brakes to be released when the pressure is taken off. When the limit of roll is reached the pistons slide on the seals to take up wear on the pads.

Cheers Richard

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Brake operation comes about through rolling of the seals which allow the brakes to be released when the pressure is taken off. When the limit of roll is reached the pistons slide on the seals to take up wear on the pads.

Cheers Richard

Yeah, exactly....... but the problem with these new calipers is that they don't slip soon enough, so you get too much roll and too much piston return. I don't know why but I guess the options are:

- piston finish too rough

- Seals slightly over-size or rubber compound slightly different

- Seal groove in caliper slightly shallow or ramp angle slightly too steep.

- assembly lube not sufficiently lubricating

 

On the A6 calipers I rebuilt, the caliper castings were the originals (and I cleaned the seal grooves very thoroughly), the pistons were the originals and in good condition and I used Lockheed red rubber grease from the same tin I've been using for 15 years or so with good results..... so the seals would seem to be the only variation. Calipers were only dismantled to clean out and free-off the handbrake mechanism (acting up after a mere 21 years and 300k miles) and I had new seals in the overhaul kit. Once I'd managed to get the pistons to sit where they needed to be they've settled fine and no further issues. With the 16Ps, I think they've now settled but they are still on probation!

 

Nick

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It would seem to be the seals by the sound of it, Its highly likely that its not the same "Shore" of rubber i.e. the hardness of the rubber.

https://www.smooth-on.com/page/durometer-shore-hardness-scale/

Stuart.

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Hi Stuart,

so would decent seals sort the problem?

 

Roger

Provided the tolerances between piston and cylinder are in spec then yes.

Stuart.

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This sounds like a very similar problem back in my Standard Triumph days on the Triumph Herald/Spitfire it was always found that the front callipers where very difficult to bleed using all types of procedures, what we did find that if the front brake pads on one side where removed and both pistons pushed back to the bottom of the bores and the brakes bled in this situation all the air could be removed from the calliper, then replace the pads and very slowly push the brake pedal down to push the pads back into contact with the brake disc.repeat the procedure for the other calliper.

The conclusion was that it was possible that a small bubble of air was trapped under the piston and had great difficulty to escape during normal bleeding when the piston was part way up the calliper bore, but with the piston in the bottom position it was not possible for any air to be trapped on the underside of the piston, Worth a try.

Staffs Man .

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This sounds like a very similar problem back in my Standard Triumph days on the Triumph Herald/Spitfire it was always found that the front callipers where very difficult to bleed using all types of procedures, what we did find that if the front brake pads on one side where removed and both pistons pushed back to the bottom of the bores and the brakes bled in this situation all the air could be removed from the calliper, then replace the pads and very slowly push the brake pedal down to push the pads back into contact with the brake disc.repeat the procedure for the other calliper.

The conclusion was that it was possible that a small bubble of air was trapped under the piston and had great difficulty to escape during normal bleeding when the piston was part way up the calliper bore, but with the piston in the bottom position it was not possible for any air to be trapped on the underside of the piston, Worth a try.

Staffs Man .

We used to have a similar problem years ago on drum braked Jaguar MK1`s they had sprung cylinders and you had to clamp them shut right in or you couldnt get the last bit of air out. But its unusual to have this with 16P calipers.

Stuart.

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  • 2 months later...

Noticed slight weeping from the calipers but not sure where it was coming from though

replaced crush washers several times and went through 3 sets of banjo bolts when they sheared through overtightening

Still leaking / soft pedal

put the old calipers back on - bingo - no problem

I can only assume that the thread for the banjos is not square to the sealing face on the reproduction units.

Going to get the original units refurbished

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Noticed slight weeping from the calipers but not sure where it was coming from though

replaced crush washers several times and went through 3 sets of banjo bolts when they sheared through overtightening

Still leaking / soft pedal

put the old calipers back on - bingo - no problem

I can only assume that the thread for the banjos is not square to the sealing face on the reproduction units.

Going to get the original units refurbished

Banjo bolts arent used on TR`s so by the sound of it thats a machining problem.

Stuart.

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