T25 Brakes Issue / Question.....

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SiVWW
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T25 Brakes Issue / Question.....

Post by SiVWW »

This weekend i have to continue trying to identify where my"intermitant" brake problems is coming from.... Im only a weekend mechanic who tinkers so im about to start hardcore learning so i can work on my van in a layby emergency if needs be.... Id love if anyone could share some knowledge with me.

As you know, i lost my brakes..... brake pedal went "soft"with a lot of travel on first press, then to the floor loosing all braking. It then recovered momentarily, then going "soft" again.... and then to the floor once more. Was able to nurse it home by constant pumping of the pedal. It has sat for 2 weeks since, and on starting, the pedal is hard and normal again.

Having researched a lot about the brake master cylinders so far ( my previous thread ) and seeing that these characteristics can be related to this, i started pulling things apart for a deeper look and to learn.

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I checked round the brake master cylinder, fluid pot, servo and seals etc for leaks... all dry as a bone, and the brake fluid level still perfectly at max. I then had my head in my engine bay with a cuppa last night ( the joy of accessing your engine from under the dining table inside lol )

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on the phone to my chum who had his head in his engine bay ( sharing the same 2.0 CU unit ) and he was telling me to check the air piping from the bottom of the carb upto the brake servo at the dash.... I then tried to start Bert so i could check the suction from the carb and the battery was flat, so couldnt check and charging the battery for the morning.

So in forward planning of the mornings tests, could someone please share their knowledge with me, and everyone else on loss of suction to the brake servo, and how an air leak would affect the braking... and could this be intermittent through a small leak??

Many thanks in advance...

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toomanytoys
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Re: T25 Brakes Issue / Question.....

Post by toomanytoys »

Soft pedal cant be to do with vacuum and servo..
If you have no vacuum/leak/faulty non return valve, then the pedal will be hard and no assistance will be given.. it will also be much harder to stop as you will need to stand on the brakes to create the same hydraulic pressure on the master cyl..

A soft pedal would normall be attributed to air in the system, but yet you say the level hasnt dropped.. I would presume you have checked the rear wheel cyls for leakage as these tend to go before any issues with the calipers arise and may let a small amount of air in before problems are evident.

Another option is the seals in the master cyl are bypassing.. not common at all.. and i would expect to see some leakage (onto your shoes) at some point..

A flexi hose has damage and is balooning.. but this would be consistant and WOULD fail at some point.. leaking fluid away...

If the fluid is old and absobed water, then it will boil at a much much lower temperature giving the same symptoms as air in the system and a soft pedal..

Can you say under what conditions the pedal failed?? were you coming down a hill with the brakes on all the way?? (VERY bad practice)
Do you have a sticky caliper causing the brake to heat up, thus boiling the fluid?

California Dreamin
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Re: T25 Brakes Issue / Question.....

Post by California Dreamin »

soft brakes, pedal to the floor, pumping brakes.

Vapour lock.....when the brake fluid starts to boil with massive heat resulting in gas bubbles which are compressable. This could be caused by several things....excessive amounts of water in the brake fluid (brake fluid has a very undesirable property, it absorbs moisture from surrounding air (Hygroscopic) it HAS to be changed every two years regardless of mileage.
Sticking seizing calipers....leading to over heating and vapour lock (as described above)
Master cylinder seal failure: normally has the symptom of a slow progressive wander downwards of the pedal (pedal creep) as fluid forces it's way past the master cylinder.
Total master cylinder failure where seals fold back on themselves (extremely rare) but can happen after vigourous brake bleeding where the old worn master cylinder seals have been forced over the worn ridge (where the seals would normally travel up to) during old fashioned pedal bleeding (working the brake pedal through it's full stroke)

flexi brake pipe ballooning: where the internal structure of the flexi pipes has been compromised causing fluid to escape into the outter layer of the flexi causing a 'balloon' to appear.
Fluid leak: from rear wheel cylinders, front calipers or burst pipe...this would be permanent.
Air in the system: would also be permanent.
Martin
1989 California 2.1MV

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Hacksawbob
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Re: T25 Brakes Issue / Question.....

Post by Hacksawbob »

wiki'd
member 1168

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CovKid
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Re: T25 Brakes Issue / Question.....

Post by CovKid »

And if you do decide to remove rear brake hubs, go and buy new rear brake cylinders before you even start. I have yet to ever do that job and not find a need to replace them. Weakest part of the system usually.
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Shaundon
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Re: T25 Brakes Issue / Question.....

Post by Shaundon »

Hi

Did you find out what was causing this ? I have a similar issue and want to find out the cause....

see https://club8090.co.uk/forum/viewtopic.p ... 7#p7891497
1984 1.9 petrol wbx DH with a pierburg carb , LHD westfalia club joker.

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