Daveg
NT & VTS Council member
I believe I am perfect, but others may differ in opinion?
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Post by Daveg on Jan 9, 2010 14:18:40 GMT
I thought this was interesting to mention. Customer arrives in reception a good few months ago and says he has just been advised by a Vauxhall Technician that his brake fluid required changing. The customer advised us he had never heard of this before and he said he could not understand why because he said his brake pedal felt OK? One of our Tech's said to him; The guy was trying to get money out of you for nothing, brake fluid never needs changing? I have been in the trade 28 years, he has been in the trade over 30 years. people talk about experience and say that when you have got it you must know what you are doing? Two days ago we recovered a Vauxhall Astra G from the road side which had been parked there for soem time, the nearside rear brake was binding. We carried out a visually inspection and the parking brake lever functioned as normal, no other visual inspection indicated a fault so I completed a roller brake test were the nearside rear brake recorded 50Kgf without the foot brake or park brake being applied. I dismantled the brake and manually tested the caliper operation with a pressure gauge between the piston and brake disc faces were I found the operation satisfactory. I checked the parking brake operation the same way and found the operation satisfactory. I removed the brake pads and found no faults present, i.e. sticking seized pads, so I reinstalled them and primed the brakes and they functioned normally. The boiling point of the brake fluid was below 100*C. Could this have been the problem? Dave
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graham
Nominated Tester
Posts: 331
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Post by graham on Jan 9, 2010 15:51:59 GMT
I assume you put him right........
Brake fluid is hygroscopic and therefore absorbs water, lowering the boiling point. The usual symptoms are loss of brake pedal after extensive braking. I doubt that is your problem on the Astra. In theory once the brake pedal is released there should not be any pressure in the system therefore any change in the brake fluid/vapor density would be irrelevant. The system is to all intents and purposes open at the master cylinder end
Ok one thing that springs to mind would be a collapsed brake hose intermittently stopping return pressure or a faulty load/pressure valve.
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Daveg
NT & VTS Council member
I believe I am perfect, but others may differ in opinion?
Posts: 1,549
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Post by Daveg on Jan 9, 2010 21:38:59 GMT
I assume you put him right........ Brake fluid is hygroscopic and therefore absorbs water, lowering the boiling point. The usual symptoms are loss of brake pedal after extensive braking. I doubt that is your problem on the Astra. In theory once the brake pedal is released there should not be any pressure in the system therefore any change in the brake fluid/vapor density would be irrelevant. The system is to all intents and purposes open at the master cylinder end Ok one thing that springs to mind would be a collapsed brake hose intermittently stopping return pressure or a faulty load/pressure valve. The problem I have is that people believe what they choose to believe, so even when I advised about hydroscopic problems the reply came back, yes but air brakes suffer the same problem and they don't have fluid in? To me it seems the motor trade have a major problem with regards vehicle systems, how they work and what causes the faults to appear? Getting back to my problem with the astra you mentioned load valve or collapsed hose. Taking each in turn, the load valve would effect both rear brakes and my problem was only the nearside rear. The brake hose in my experience normally when it collapses internally stops the brake being applied, this brake could not be released. My colleague levered the parking brake lever on the brake caliper back to its rest position, which then released the brake OK, so we knew it had to be something along the lines of the cable or the caliper. I removed the cable from the caliper and found no restriction of free movment, although this was both tested under load and not under load I found no problem. I removed the caliper pads and tested the caliper as explained previously were i found no fault, I removed the caliper completely and manually tested by hand, the parking brake lever operated the piston out of the caliper and it was easy to turn it back in with the brake tool, I didn't feel I had concluded a fault present with the caliper. The brakes as explained previously were also roller brake tested were initially 050Kgf was present, then after dismantling and cleaning a re-inspection on the rollers showed the brake functioned OK. I was wondering whether it was possible for the caliper to have frozen and cause the problem I was experiencing. My colleague also mentioned something about the ice truckers on TV were they had blow lamps on their brakes as they were frozen. I have not experienced this before, but them we have not had weather this severe for a long long time, and I was a lot younger then David
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graham
Nominated Tester
Posts: 331
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Post by graham on Jan 9, 2010 22:41:04 GMT
We have certainly had hose failure that held the brake on, bit like a flap valve, could be working either way. re the load valve well not too sure about the Astra but some vehicles have 2 pressure limiters to the rear (dual circuit / diagonal split) brakes IIRC.
Very much doubt it was frozen in the UK.
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wally
Nominated Tester
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Post by wally on Jan 9, 2010 22:51:05 GMT
Hi David, A few points i have noticed - It is quite possible the Vauhall tech had tested the brake fluid, I usually do any chance I get. You also said the boiling point was less than 100 - that is the lowest I have ever heard ! Usually around 150 is the lowest I have recorded.
I have seen quite a few collapsed hoses and when the brakes are applied there is one hell of a pressure going to the caliper which can force it's way past any restriction but when released although some pressure will be released it can be quite a lot that is retained, releasing the bleed nipple will elliminate any retained pressure and prove if this was a problem.
It is a possibility that the brake had frozen, with 100 deg boiling point the fluid must have been almost pure water! Regarding the air brakes freezing, several times over the years I have had no air in the workshop due to water/condensation in the airlines at the low points freezing and blocking the pipes completely, air brake systems do create a lot of condensation from the compressors that could be in the pipes.
One other possibility is has the vehicle got abs? Sticking valve in the valve block may be?
Wally
PS - All the best for the new year to everybody.
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Daveg
NT & VTS Council member
I believe I am perfect, but others may differ in opinion?
Posts: 1,549
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Post by Daveg on Jan 9, 2010 23:19:07 GMT
I can't say that the hose was at fault on this brake, surely if it was the brake would be faulty in operation all the time? The brake was binding before I touched it, the only thing I did to free it off was push back the brake lever on the caliper and the wheel was free, surely the brake hose would have no effect there?
On the astra when fitted there is normally only one valve to regulate both rear brakes, nissan sometimes have two fitted, i.e. the primeria.
This brake fault was interesting, i may never know the actual cause as i couldn't really prove the cause in the first place. Because I couldn't find any mechanical problem I suspected freezing of the caliper/hydraulics inside the caliper, I may now never know unless I find some really old aged brake fluid and put it in the freezer and see what temperature it freezes at.
Dave
Hope everyone has a happy new year
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Rob
Nominated Tester
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Post by Rob on Jan 10, 2010 10:36:18 GMT
One of our Tech's said to him; The guy was trying to get money out of you for nothing, brake fluid never needs changing?Oh dear. We had a 1985 Jaguar XJ-S in a few months ago for MOT. The guy that owns it has it tested, insures and taxes it but leaves it in his garage until it's next MOT is due, something to do with sentimentality as it was the first decent car he bought after starting his business. It's got 9,000 on the clock from new. This year he complained that the brakes were really poor on his three mile trip to us so we checked the brake efficiency on the roller brake tester, we got a reading of 38% for the service brake but the readings were all even so there wasn't one brake or one side of the braking system faulty. The linings were ok so we tried to bleed the system, what came out looked like jelly, so we sucked out all the fluid from the brake fluid reservoir and it was like tapioca. The fluid had absorbed so much water it had turned into this horrible jellified mush. On bleeding the system profusely the brakes were back to normal. Brake fluid never needs changing? Rubbish. On another note there was a recall on the Astra F years ago, because the offside washer jet which was positioned above the brake fluid reservoir had a habit of leaking into the brake fluid, it wasn't widespread but enough for GM to recall all models to have a kit fitted which would prevent it happening again. I took my Astra into our local dealer to have the job done, they were supposed to have fitted the kit and completely bled the system replacing all the fluid. When I got the car back I checked it out on our ramp, all the bleed nipples were completely dry, so I took it back and asked them to do the job properly. ;D On making a few enquiries in the trade (someone I knew worked for Vauxhalls) apparently the mechanics weren't on a very good bonus for doing recall work, so they skimped the job by just replacing the rubbers and checking the boiling point of the fluid, if it was ok they didn't bother changing it even though it was part of the recall procedure. Changing brake fluid is very common in all manufacturers service schedules (at extra cost ) these days, it's obviously done for a good reason, who are we to argue when there's money to be earned. We'd look pretty incompetent if a car had a fault or God forbid an accident, and the problem was caused by dodgy brake fluid because it hadn't been changed.
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Post by jonesy1975 on Jan 10, 2010 15:19:32 GMT
A few years ago my brother had a problem with the brakes on a cavalier , he was towing a caravan & was coming down a hill in 3rd gear with a touch of brake to keep it steady , then the pedal went to the floor . He managed to get the car into a layby & phoned the RAC , they came out & checked the car & then left saying they could find no fault with it . I decided to check the fluid as i was convinced this was the problem , the fluid that came out of the rear brakes was basically rusty water with a small amount of brake fluid in it . He never had any more problems with the car after this was done . this is one of the reasons why i change the fluid on my car every 2 years without fail .
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