Brake failure?

Brake failure?

Author
Discussion

taylormj4

Original Poster:

1,563 posts

265 months

Wednesday 19th July 2017
quotequote all
Checking fluids in the engine bay yesterday I noticed paint on the inner wing around the master cylinder has gone all wrinkly and bubbled up. It looks like brake fluid has for some reason flooded out of the master cylinder lid. I checked the level in the master and it seems normal.

Then on the way to work this morning, had to brake hard at a junction and felt like I only had partial braking force, meaning I couldn't quite stop at the give way line.

Immediately following that, I found a safe area and made some brake tests and found that I now had full braking force.

Are these two occurences linked ?

Aussie John

1,014 posts

230 months

Wednesday 19th July 2017
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Haven't had new pads in lately?

taylormj4

Original Poster:

1,563 posts

265 months

Wednesday 19th July 2017
quotequote all
Good thinking, yes that could push the fluid out but no, no new pads. It hasn't had a service for around a year.

Can heat in the engine bay cause the brake fluid to expand so much that it comes out of the master cylinder ?

Classic Chim

12,424 posts

148 months

Wednesday 19th July 2017
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Yes. If it's topped upto the top it will spill out. Brake failure. The least I'd do is bleed any air oout the lines. Over time it gets well used near the calipers from brake heat and is well worth removing anyway so a good practice. Take the clutch cyl cover off and check for leaks around the brake master and servo.

blaze_away

1,502 posts

212 months

Wednesday 19th July 2017
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DOT3 and DOT 4 Brake fluid is hygroscopic ie it absorbs water. So over time the water content rises and the boiling point decreases significantly. If the car is left running with 'wet' fluid the master cylinder could boil over. I would suggest a full fuid flush as precautionary measure.

DOT 5 is silicon based and does not absorb water.

Edited by blaze_away on Wednesday 19th July 19:09

Classic Chim

12,424 posts

148 months

Wednesday 19th July 2017
quotequote all
blaze_away said:
DOT3 and DOT 4 Brake fluid is hygroscopic ie it absorbs water. So over time the water content rises and the boiling point decreases significantly. If the car is left running with 'wet' fluid the master cylinder could boil over. I would suggest a full fuid flush as precautionary measure.

DOT 5 is silicon based and does not absorb water.

Edited by blaze_away on Wednesday 19th July 19:09
Excellent stuff. I'm on Dot 5 for at least three years now and no boiling and still very consistent pedal feel.

RobXjcoupe

3,151 posts

90 months

Thursday 20th July 2017
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Dot 5 or dot 5.1?
Dot 5.1 is compatible with dot 3 and 4.
Dot 5 when mixed with the others will produce a gel which isn't good! :s

blaze_away

1,502 posts

212 months

Thursday 20th July 2017
quotequote all
RobXjcoupe said:
Dot 5 or dot 5.1?
Dot 5.1 is compatible with dot 3 and 4.
Dot 5 when mixed with the others will produce a gel which isn't good! :s
Good points. I dont think the OP has 5 or 5.1 though because there is evidence of blistering of the paint which dot 3 and 4 will do and 5 or 5.1 will not.

Steve_D

13,737 posts

257 months

Thursday 20th July 2017
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blaze_away said:
RobXjcoupe said:
Dot 5 or dot 5.1?
Dot 5.1 is compatible with dot 3 and 4.
Dot 5 when mixed with the others will produce a gel which isn't good! :s
Good points. I dont think the OP has 5 or 5.1 though because there is evidence of blistering of the paint which dot 3 and 4 will do and 5 or 5.1 will not.
I stand to be corrected but I think 5.1 will blister paint.
It is very confusing because 5 and 5.1 are significantly different chemically with 5.1 (i believe) being not very different from 3 & 4.

Steve

blaze_away

1,502 posts

212 months

Thursday 20th July 2017
quotequote all
Steve_D said:
I stand to be corrected but I think 5.1 will blister paint.
It is very confusing because 5 and 5.1 are significantly different chemically with 5.1 (i believe) being not very different from 3 & 4.

Steve
Steve, I didnt know that thank you

TwinKam

2,936 posts

94 months

Thursday 20th July 2017
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Steve_D said:
blaze_away said:
RobXjcoupe said:
Dot 5 or dot 5.1?
Dot 5.1 is compatible with dot 3 and 4.
Dot 5 when mixed with the others will produce a gel which isn't good! :s
Good points. I dont think the OP has 5 or 5.1 though because there is evidence of blistering of the paint which dot 3 and 4 will do and 5 or 5.1 will not.
I stand to be corrected but I think 5.1 will blister paint.
It is very confusing because 5 and 5.1 are significantly different chemically with 5.1 (i believe) being not very different from 3 & 4.

Steve
Steve, you are correct.
Whoever was responsible for naming silicon fluid 'DOT5' should be shot, it should have been given a very clearly different name outside of the DOT nomenclature, such as 'Silicon Brake Fluid Do Not Mix With Anything'.
And to the OP, I would be starting with a complete renewal and flush with new brake fluid, bleeding through about a litre. If you can vac out the old fluid from the reservoir first, so much the better.

Edited by TwinKam on Thursday 20th July 14:42

ou sont les biscuits

5,086 posts

194 months

Thursday 20th July 2017
quotequote all
FWIW I have wrinkly paint on the inner wing due to fluid spill.

The cause in my case was a duff master cylinder cap seal. It wasn't that expensive to replace.

The re-paint of the inner wing might be a bit more costly though.

RobXjcoupe

3,151 posts

90 months

Thursday 20th July 2017
quotequote all
Basically dot 5.1 is a high temp fluid compatible with dot 3 and 4 and it's an easy upgrade just by bleeding through the fluid.
Dot 5 is more a race car fluid which I believe needs complete fluid changes every 12 months. That isn't an issue but it doesn't mix with the other types of fluid

TwinKam

2,936 posts

94 months

Thursday 20th July 2017
quotequote all
RobXjcoupe said:
Basically dot 5.1 is a high temp fluid compatible with dot 3 and 4 and it's an easy upgrade just by bleeding through the fluid.
Dot 5 is more a race car fluid which I believe needs complete fluid changes every 12 months. That isn't an issue but it doesn't mix with the other types of fluid
Sorry to correct you, Rob, but DOT5 (the silicone one) has in fact longer life than DOT3. 4 or 5.1 as it is hydrophobic ie it does not absorb water. It does not attack cellulose paint either.
DOT 3, 4 & 5.1 (the ones in common use) degrade over time by absorbing moisture and should therefore be changed (ie flushed through and bled at each nipple) every two to three years.

Boosted LS1

21,165 posts

259 months

Thursday 20th July 2017
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Op, it may be the seals in the master cylinder are failing. It happened to me once and led me a merry dance.

RobXjcoupe

3,151 posts

90 months

Thursday 20th July 2017
quotequote all
No probs, no offence taken smile
I've been put off using silicon brake fluid because what I've read it's only suitable on brand new clean braking systems that haven't seen a glycol fluid.
Has anyone actually mixed the two fluid types?

MisterT

322 posts

225 months

Thursday 20th July 2017
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I've never mixed the two types but did put silicon fluid into a brand new braking system when I rebuilt my TR6. All new components and a firm pedal mostly, however on occasions the pedal would go to the floor and no stopping power, especially when driving hard which is just when you least need a brake failure. There hadn't been time for any moisture to affect the system so put it down to aeration of the fluid which silicon is apparently prone to do.

I dismantled and cleaned the whole system and used dot 4, never had another problem.

The theory about silicon brake systems not absorbing moisture is I think wrong, the moisture still gets into the system but isn't absorbed by the silicon fluid unlike the dot 3, 4 or 5.1 fluids. As a result tiny droplets of moisture in the fluid will boil and turn to compressible gas again causing the pedal to go to the floor.

In a lightly used classic car the problem may never be experienced but I would never again use silicon fluid in a performance (or any other for that matter) braking system.

I'm sure there are plenty of folk out there who use silicon fluid and haven't experienced a problem, but following my near misses with silicon in the TR6, never again.

taylormj4

Original Poster:

1,563 posts

265 months

Monday 24th July 2017
quotequote all
Thanks all for the replies.
It's only around a year since the last service when I presume they would change the brake fluid. Correct ?

Hedgehopper

1,537 posts

243 months

Monday 24th July 2017
quotequote all
taylormj4 said:
Thanks all for the replies.
It's only around a year since the last service when I presume they would change the brake fluid. Correct ?
I wouldn't bet on it!

TwinKam

2,936 posts

94 months

Monday 24th July 2017
quotequote all
Hedgehopper said:
taylormj4 said:
Thanks all for the replies.
It's only around a year since the last service when I presume they would change the brake fluid. Correct ?
I wouldn't bet on it!
I would bet on it NOT having been done. Even main dealers don't do it on newish cars in their care despite it being stipulated every 2 or 3 years (depending on the marque); it's an 'occasional extra' that it seems you have to ask for (as if most people even realise rolleyes) and so it tends to be overlooked.