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Brake fluid leak


Busybee

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Hi guys. Been a while. Hope all's good in the world of IB.

My blue car (Alex's old car). I have a brake fluid leak. Reservoir level goes down after a hard session on the brakes. Topped it up maybe 5 times now but drops about 1/2". Can't see any leaks anywhere. Bled the old ATE blue brake fluid out earlier this week and filled with Motul racing dot 4, Calipers dry, under the pedal floorboard all dry, master cylinder dry, joint under the steering rack is dry. 

Took her to Castle Combe for a PCGB track day yesterday and she went well. Lovely torque laiden motor that just pulls if you floor it. But the brake fluid was going down between 15 minute sessions so topped it up. Never lost pedal firmness or brake efficiency. 

Spoke to a chap from Parr about it and he thinks its upstream of the pressure side of the system. Only the brake booster really?

Any ideas? 

Few pics of the cars at the TD to spice up the thread. Aga blue car is a Tuthills built 3.2 on carbs putting out 280hp. 

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Edited by Busybee
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1 hour ago, sopor said:

It could be leaking into the brake booster. Any white smoke out of the exhaust on hard cornering?

Not that I noticed. Had flames on the downshift though - apparently 😂

1 hour ago, sopor said:

It could be leaking into the brake booster. Any white smoke out of the exhaust on hard cornering?

Can you test the brake booster Felix? Quite an expensive part I think 

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I’m with Felix on this. When I bought my BM all of the brake fluid was in the servos. It won’t be the servo that’s at fault per se but could be the MC leaking into the servo (most likely). Easy to take the MC off and have a look.

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I had a mystery brake fluid leak on a Mk I Scirocco. Nothing visible but I once made sharp turn in a car park and there was a huge cloud of white smoke out of the exhaust. The MC was leaking into the servo and the sharp turn sloshed the fluid up to the vacuum port and it was sucked into the engine and burned off. New MC solved the problem.

Edited by sopor
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You might be able to take the vacuum hose off the servo and see if it’s wet inside? Or make some sort of dipstick to see if it’s an auxiliary brake fluid storage container? 

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37 minutes ago, sopor said:

You might be able to take the vacuum hose off the servo and see if it’s wet inside? Or make some sort of dipstick to see if it’s an auxiliary brake fluid storage container? 

Cheers Felix. Good idea. I’ll investigate. 

Regarding MC replacement, is it worth upgrading to the bigger bore turbo unit with standard calipers or stick with 91135501112? 

I have a new SC MC on the shelf 90135501202 on the shelf but I think that’s the 19mm bore. 
 

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There is no point in putting in a bigger MC if you are not going with bigger brakes, you will just upset your pedal length. If you are happy with it as it is then leave it. Bigger MC is only needed if you are pushing more fluid but even then not necessarily. 

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1 hour ago, Phill said:

There is no point in putting in a bigger MC if you are not going with bigger brakes, you will just upset your pedal length. If you are happy with it as it is then leave it. Bigger MC is only needed if you are pushing more fluid but even then not necessarily. 

Yep. Reading a few threads, larger diameter mc with standard brakes results in a harder pedal and less feel. I’ll stick as I am for now. 🙏🏼👍

Taken the vacuum pipe off. I can’t really poke anything in to see if it’s wet in the servo but this elbow joint connector to the servo has a metal pin at the bottom. Maybe a pressure actuated valve? The pin looks wet but no puddle of fluid in the elbow joint 

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Vacuum pipe itself is bone dry inside 🤔

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You been on an extended holiday?….If you cannot see any leakage anywhere Haith, the fluid must be going somewhere, (short of evaporation) only place I can think of is the servo if you have one? (big vacuum container).

Regards,

David

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3 minutes ago, David Gander said:

You been on an extended holiday?….If you cannot see any leakage anywhere Haith, the fluid must be going somewhere, (short of evaporation) only place I can think of is the servo if you have one? (big vacuum container).

Regards,

David

Hi David. Hope you’re well.

Just lurking. Lots of non air cooled driving. 

So I asked the same question somewhere else and quite a few people have said they’ve experienced similar with fluid coming out of the reservoir under spirited driving/tracking the car.

Solutions seem to be an upturn in the breather hose from the reservoir, using less fluid so as the reservoir isn’t full, a catch tank or combinations. 

I don’t know the hydraulics that would cause this but I’ve fitted an upward loop in the breather hose. Fingers crossed that’s the fix. Still no visible leaks in the system I can see. 

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Good luck with this Haith, cannot be too hard to eventually nail this down.

Regards,

David

PS How is the candle business going?, we’re still using one that you kindly gave me yonks ago as a night light for our two Lhasa Apso’s as their eyesight is now failing, really heartbreaking, they are our babies!

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  • 2 months later...
22 minutes ago, SurlySurdi said:

My 2 penny's worth, I had the same issue, turned out the clutch slave cylinder needed replacing, the fluid was leaking into the footwell and pooling under the carpet near the pedals. Easy place to check.

SS

master?

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10 hours ago, SurlySurdi said:

My 2 penny's worth, I had the same issue, turned out the clutch slave cylinder needed replacing, the fluid was leaking into the footwell and pooling under the carpet near the pedals. Easy place to check.

SS

Thanks SS. Checked under the drivers floor mat and inspected the pedal box area and it’s bone dry. Poked around in the booster and that’s dry too. 

Few guys have said the fluid can leak from the breather hose on the brake fluid reservoir under heavy braking. Needs an upturned kink in the hose to stop this. No idea what happens down stream in the booster but can that push fluid back into the reservoir I wonder. 

Not used the car since so not tested the theory (but have bought a small bowl filter to pop in-line on the breather hose to see if that collects any fluid). 

Edited by Busybee
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At least that's ruled out. Might be an idea to use some sort of tape or material that you can tape to various parts that changes colour when it gets wet and using that to work out where the fluid is going? Just thinking outside the box a little.

SS

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On 02/09/2023 at 07:08, Busybee said:

Thanks SS. Checked under the drivers floor mat and inspected the pedal box area and it’s bone dry. Poked around in the booster and that’s dry too. 

Few guys have said the fluid can leak from the breather hose on the brake fluid reservoir under heavy braking. Needs an upturned kink in the hose to stop this. No idea what happens down stream in the booster but can that push fluid back into the reservoir I wonder. 

Not used the car since so not tested the theory (but have bought a small bowl filter to pop in-line on the breather hose to see if that collects any fluid). 

Hi, I can't message you quite yet as I just signed up. Was the Guards Read 993 turbo sold?

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