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Random brake pedal travel issue

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Old Sep 12th, 2021, 00:08   #21
Laird Scooby
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OK, I must admit I've never had need to change a P80 MC. Changed MCs on quite a few vehicles over the years, and never needed to bleed anything. Pour fluid back in thru' the top and be done. Air comes back up thru' MC. Worst case, I've a MityVac. Force fluid in from the the bottom and as it rises, see it pop out the MC.

Back in the day you could get coloured brake-fluids, red/blue or Green. That helped.

I've got the original MC on one 290K car. Should last the life of the car. Or replace 3-4 times more often than fluid, 'you pays your money'. See jammin's pix.

Unless a P80 is somehow different, the only reason I've ever done a bleed with an MC change,is because a flush is good practice... because we're on...
You've obviously been very lucky. Every MC i've ever changed has had upwards-pointing outlet ports so air will be present in the brake lines immediately after the MC and as you know, you should never reverse bleed them by pushing the brake pads away from the disc to expel the air into the MC as you force dirt backwards up the line to the ABS modulator and/or the MC which causes problems for the seals.

It is, as you hint at, best practice to always renew the fluid, especially when fitting a new MC as the warranty will probably be void if you don't renew the fluid. Same goes for new PAS racks and i wonder when anybody last changed their PAS fluid?

Just a thought - why are we even having this conversation? This is our safety and that of others, not to mention our cars that we've probably invested a lot of time, money and care in over the years in varying proportions.

We're pontifficating on the paltry amount of money to renew the fluid to preserve the braking system, why are we piffing about like this? It shouldn't need a discussion, we should just be changing the brake fluid at regular intervals instead. I recently bought a simple tester for about a fiver on ebay, it's a simple go/no-go tester with half a dozen LEDs, first shows it's working, next few show from 0% to 5% in 1% stages of contamination (presumably water as that will alter the intrinsic resistance of the fluid) and by the time it's reading 5% the last two LEDs are red - red for danger and the "suggestion" in the instructions is that 2% or more, change the fluid!

When i last checked my Volvo a few months ago it was 1-2% depending exactly where in the the reservoir i poked it in.

On my Rover last year it was off the scale - no surprise really, the plan was to change it immediately after getting it back from the MoT and i still adhered to that plan.

Thanks to the sheer incompetence of the garage doing the MoT it took 6 months to get it back and by then it had been sitting so the corrosion had time to take hold.

During changing the fluid, the MC popped but luckily i had a spare and plenty of fluid. I'd also managed to create a bespoke cap to fit the reservoir to use the Gunsons Easibleed thankfully so it took about 45 minutes in total to renew the pads and fluid all round after changing the MC and then readjust the handbrake.
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Old Sep 12th, 2021, 02:40   #22
Martin Cox
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Brake fluid is not expensive. The consequences of not changing it regularly, are.

Even the price charged by my local main dealer to do it makes me wonder why I'm even bothering to do it myself. Filling the fuel tank costs considerably more.

People on this forum generally care about their cars and keeping them in good order. This is why we discuss such things here.

it is a sobering thought that there must be many vehicles out there where the fluid is never given a thought and effectively lasts the life of the vehicle.

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Old Sep 12th, 2021, 09:39   #23
Luxobarge
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Even the price charged by my local main dealer to do it makes me wonder why I'm even bothering to do it myself.
Maybe it's because they don't do it properly? Have you ever observed what they actually do? I've been told by reliable sources that common practice in a dealer service is to suck out the fluid from the reservoir and replace with fresh fluid, which indeed would be quick and cheap. However, this is next to useless, as the most likely places for fluid contamination are the calipers and brake lines, and this method leaves the fluid in these components untouched.

I totally agree with your assertion that it's important and should be done regularly, but the only way to do it properly is to flush it out through all four bleed nipples, which is far more time consuming, and one of the main reasons that I always do it myself.

Next time you get a dealer to do it, check the bleed nipples afterwards, my money says that none of them will show any signs of having been touched.

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Old Sep 12th, 2021, 11:34   #24
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Maybe it's because they don't do it properly? Have you ever observed what they actually do? I've been told by reliable sources that common practice in a dealer service is to suck out the fluid from the reservoir and replace with fresh fluid, which indeed would be quick and cheap. However, this is next to useless, as the most likely places for fluid contamination are the calipers and brake lines, and this method leaves the fluid in these components untouched.

I totally agree with your assertion that it's important and should be done regularly, but the only way to do it properly is to flush it out through all four bleed nipples, which is far more time consuming, and one of the main reasons that I always do it myself.

Next time you get a dealer to do it, check the bleed nipples afterwards, my money says that none of them will show any signs of having been touched.

Cheers!
I have seen that done in a dealership, also oil/filter changes where the filter is wiped clean while the oil drains then cheap oil is used to refill the engine.

Also on lease cars with servicing included, many lease companies will only pay for the absolute basics - no lube on the door hinges, locks and latches, no screenwash fluid just water in the reservoir - the penny-pinching goes on. Most of this doesn't impact the first owner/driver as the car is usually on a 3-5 year lease and changed for a new one, it's the second and subsequent owners that pay for this wilful neglect. Oh yeah, the penny-pinching extends to not changing the brake fluid properly!
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Old Sep 12th, 2021, 11:52   #25
CNGBiFuel
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I recently bought a simple tester for about a fiver on ebay, it's a simple go/no-go tester with half a dozen LEDs, first shows it's working, next few show from 0% to 5% in 1% stages of contamination (presumably water as that will alter the intrinsic resistance of the fluid) and by the time it's reading 5% the last two LEDs are red - red for danger and the "suggestion" in the instructions is that 2% or more, change the fluid!

If you prefer, yet a standard multimeter does the same. Spend the money on fluid, and at two years do it anyway. Leave race-fluids or so called high-performance stuff out of it. They suck-up water so well they want doing in months, or ideally each race. For road-use they're worse. And when they're not doing that, going to neat acid, all that water boils. Ouch. Cheap is actually best.

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I've been told by reliable sources that common practice in a dealer service is to suck out the fluid from the reservoir and replace with fresh fluid, which indeed would be quick and cheap.
Excuse my cynicism.... Told... told? Turkey-baster, 5 mins. and a bill. The public gets what the public wants. An hour's work, or five minutes? Well now, that's a hard one. Now, let me see...
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Old Sep 12th, 2021, 12:27   #26
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If you prefer, yet a standard multimeter does the same.


Excuse my cynicism.... Told... told? Turkey-baster, 5 mins. and a bill. The public gets what the public wants. An hour's work, or five minutes? Well now, that's a hard one. Now, let me see...
True but i prefer to keep my multimeter probes untouched by brake fluid!

A replacement brake fluid tester is still cheaper than a decent set of multimeter probes so i now which one i'm going with!



Most dealerships will always go for the quick, easy, cheap option. Most mechanics are (or at least were) on productivity bonus so they do the same. As our American counterparts say, go figure!
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Old Sep 12th, 2021, 12:34   #27
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....

Turkey-baster, 5 mins. and a bill. The public gets what the public wants. An hour's work, or five minutes? Well now, that's a hard one. Now, let me see...
If any garage quotes for a full brake fluid change then thats what you should get. All lines bled and with fresh brake fluid including all 4 calipers.

Anything less is a breach of the trades description act, not to mention making them a thief and dangerous B*stard.

Never assume anything with garages. Ask directly what they plan to do for the money & if in doubt ask for the old parts in a box and receipts for new parts as proof of works.

If they don't like it - tough - you can take your business elsewhere or get the spanners out yourself.

The actions of a few greedy idiots (or lot depending on which newspaper you read) tar the reputation of the true professionals - and that's just not in the mechanical trade either. Sad state of affairs.

Regarding the OP: Change the MC, change all the fluid and put 4 new bleed nipples in for the next guy.
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Old Sep 12th, 2021, 12:38   #28
CNGBiFuel
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In short, for road-use, the best brake-fluid is not the fluid sold with hog-wash about high wet or dry boil points. It's fluid you'll change most often. Fresh budget fluid will wipe the floor over pricey stuff that's six months older.

For most of us, brake-fluid is about change-interval, and the cheap stuff may have lower boil points, yet doesn't get wet so fast. For road-use you won't boil brake-fluid anyway, but you will boil the water in it. Water boils... and water makes that acid.

Cheap fluid and change it often.
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Old Sep 12th, 2021, 12:47   #29
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In short, for road-use, the best brake-fluid is not the fluid sold with hog-wash about high wet or dry boil points. It's fluid you'll change most often. Fresh budget fluid will wipe the floor over pricey stuff that's six months older.

For most of us, brake-fluid is about change-interval, and the cheap stuff may have lower boil points, yet doesn't get wet so fast. For road-use you won't boil brake-fluid anyway, but you will boil the water in it. Water boils... and water makes that acid.

Cheap fluid and change it often.
Going off at a slight tangent, i've often wondered why we still use brake fluid. After all, it's only hydraulic fluid. Some ATFs have a viscosity of SAE 32, the same as most hydraulic fluids/brake fluids. They are also not hygroscopic, kinder to rubber components, unlikely to boil in normal use and inside an auto box, function as hydraulic fluid to hold clutch packs engaged or in the case of traditional boxes, brake bands.
Also used to operate steering racks too - you see where i'm going with this? The one thing that i do have concerns about is localised boiling of the fluid under braking but that will take more research...................
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Old Sep 12th, 2021, 13:03   #30
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It's a complex subject. SWMBO is a chemist.

That's what the green stuff bunged in Citroen is... used in the military too. You want your military kit laid-up for years, hence green fluid. We use DOT4 etc stuff because the boil-point is high for its price. The classic brigade have alternatives, but pricey and awkward. Water-less coolants too.
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