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I think I have an airleak in the braking system. Any ideas how to find it without doing a strip down? Handbrake nicely tight. No loss of fluid. No water in the fluid. No leaks/fluid at any joints/connections. No fluid around the pistons. Dual circuit system. Bled the system severtal times and after a relatively short time the brakes are soft again. Put a load on the brake pedal for a couple of days to exclude the air. What more can I do without going through a complete strip down?

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i had a very tricky to diagnose issue on a previous tr6, eventually traced to a cracked flare on one of the brake pipes coming out of the master cyl

this sucked in air but did not leak fluid, took weeks to find !

additionally some tr6 master cylinders have faulty reservoir to cylinder seals, causing leaks or again sucking in air.

so my suggestion is air is being sucked in somewhere

HTH

steve

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That is exactly what I am worried about, sucking air. Theorectically is everything new about 4000 miles. How do I find that air leak?

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Something else last week I tightened up the handbrake and after the brakes were so good I could lock them. A week later after standing in the garage, I took the car for a drive and the pedal went down a long way and pumping did help. I do not see any connection as I only touched the adjuster. When the brakes lock or nearly is there extreem pressure in the system?

Edited by Peter Douglas Winn
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it does sound like air is getting in to the system Peter

when i had air being sucked in through the flare, or if you have a dodgy reservoir seal, then i'd expect you to be able to see bubbles in the mc reservoir when the brakes are operated ( by an assistant!)

one other possibility is the rear wheel cylinders retracting under spring pressure from the shoes, hence the handbrake temp fixed the issue

this can be made worse if your rear brake cylinders are not 'floating' nicely, due to dirt or old 'grooved' backplates.

good luck tracking this down !

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OK the easy one is the brake cylinders. I don't quite understand what is happening. Are you saying air is getting in, through the rear cylinders or are you saying the movement of the cylinder, is making it feel like air in the system.

As I do everything alone, I have no help. No family or friends in the near (all dead) and on top a disabled wife. I will have to rig up a mirror system or a film camera to look into the reservoir.

How the hell did you find that cracked flair? I could have found it using the replacement technique. Out of that I don't know. If it was leaking that would be easy.

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hi Peter

i was meaning that the rear wheel cylinders might be retracting a little under return spring pressure, thus your first push on the brake pedal moves them out again but does no braking.

some people fit 'residual pressure valves' to alleviate this but i've never tried those.

with my leaky flare i had tiny air bubbles being drawn into the MC when the pedal was released, i replaced the brake lines to cure it.

I think you need a systematic approach to track the problem down Peter.

I'd consider isolating the problem by blanking off one of the MC outlets to determine which half of the system the problem is in.

Perhaps block off the rear circuit and test CAREFULLY! the braking system with only the fronts working?

Steve

 

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Now that is making sense. If I block off one MC orifice does anybody know what is the the thread for the unions? I do know mine is not metric.

Somewhere in the back of my mind is 1/4" UNF. I thought the car was basically UNF with the exception B.S.P was only for the fuel ystem. 1 or 2 threads are odities.

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On 11/8/2020 at 7:32 PM, Peter Douglas Winn said:

A week later after standing in the garage, I took the car for a drive and the pedal went down a long way and pumping did help.

Just a thought, but is it possible you're suffering front pad knock-back caused by worn or loose front wheel bearings or flex in the stub axle? If that were the cause, pumping the pedal would eliminate the problem until the next time you put plenty of load on the wheel bearings/ stub axles. I used to get a lot of pedal travel the first time I applied the brakes after reversing out of my driveway on full lock. A stub axle strengthening kit from Revington solved the problem. Of course, if the pedal gets soft just sitting in the garage, that isn't the problem!

JC

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I think the bearings and stub axles are OK. The front end was done about 5,000 miles ago. Also new Mintex brake linings from TR Enterprises and new Pistons from Rimmers.

The back end piping renewal must be finished but it was always OK.

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JohnC raises a valid point.

Peter, does you brake pedal 'go soft' with the car standing or only when you move/reverse it ?

i replaced the original stub axles with some beefy ones from Classic Driving Developments, but the 'anti knockback' kits work too.

steve

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On 11/7/2020 at 8:34 PM, Peter Douglas Winn said:

That is exactly what I am worried about, sucking air. Theorectically is everything new about 4000 miles. How do I find that air leak?

In the past there have been bad batches of TR6 Brake Master cylinders?? Have you got one of these?

Bruce.

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Steve I don't know I must try it.

I have heard about the MC problems but I don't know exactly what was wrong. So I don't know if I have got a bad . It was replaced about 4 years ago.

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55 minutes ago, Peter Douglas Winn said:

Steve I don't know I must try it.

I have heard about the MC problems but I don't know exactly what was wrong. So I don't know if I have got a bad . It was replaced about 4 years ago.

That time frame puts it into the area of the problem ones Im afraid. Though most didnt last as long as this.

Stuart.

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3 hours ago, Peter Douglas Winn said:

Steve I don't know I must try it.

I have heard about the MC problems but I don't know exactly what was wrong. So I don't know if I have got a bad . It was replaced about 4 years ago.

It will be at the end of the  line as Stuart posted, I strongly recommend you change it as they can fail without warning. 

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If it is the MC would a repair kit be OK or is it a metal/plastic problem? For various reasons I have not used the car that much. The MC could have been laying in stock for a long time. The reason I am concerned is, I found a tiny drop of fluid under the MC and also under a union. As it was so small I could not taste it to tell whether it was brake fluid or condense water. The garage is dry and underground so why condense water?

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1 hour ago, Peter Douglas Winn said:

If it is the MC would a repair kit be OK or is it a metal/plastic problem? For various reasons I have not used the car that much. The MC could have been laying in stock for a long time. The reason I am concerned is, I found a tiny drop of fluid under the MC and also under a union. As it was so small I could not taste it to tell whether it was brake fluid or condense water. The garage is dry and underground so why condense water?

Im afraid you do need to replace it, the problem wasnt only confined to internal parts.

Stuart.

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2 hours ago, Peter Douglas Winn said:

ok ist any supplier on the black list for this part?

I buy mine from TR Shop.

Stuart.

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Hi Peter

as others have said there were a lot of duff MCs being sold a few years ago.

for the modest cost i'd buy a new one, and i too recommend the TR Shop.

for bleeding the brakes, esp with a new MC i recommend the Gunsons Eezibleed pressure bleeder, but make sure you only have 10 psi in the tyre.

i have a special modified tr6 reservoir cap that you are welcome to borrow if you wish to take this route.

in fact i could post the whole kit to you if it helps as it's not heavy so wouldn't cost a lot.

steve

Edited by Steves_TR6
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The problem with that batch of master cylinders was with the casting/machining resulting in the seals failing to do just that or failing prematurely because of the machining.

As for bleeding the old fasioned 2 man bleed is hard to beat. Pump up, hold the pedal down, release the nipple until the pedal hits the deck, tighten nipple, top up and repeat until the pedal is rock hard.

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