Air in brake system

[fallingoffalot]

Yes the kit recommends no more than 20psi, so I thought 18 would be OK, it was the original reservoir I think and old plastic like that is very brittle. I was bleeding the old way with my son pumping the pedal. It seemed very slow and laborious that's why I bought the kit. Anyway I've ordered a new reservoir from JK, looks like an easy install.

As far as the boot is concerned, I don't think I've got much choice. I'll see what Bigg Red come back with, but I'm not hopeful. When I took the calipers off, the n/s one had no sign of boots - this was the one that had seized. The o/s had one boot intact and the other hanging off, turns out this is the one that won't fit, so looks like the previous installer couldn't get it on either.



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[fallingoffalot]

So it turns out that the lip that holds the boot on the one that doesn't fit is ~70mm, the internal diameter of the boot is ~63MM!! WTF! After searching about on the net the only conclusion I can make is that this caliper has been refurbished/rebuilt from 2 slightly different ones.

Bigg Red have been extremely helpful and, after I described my issue, asked me to send photos and they're going to try and find a boot that will fit.

Great service from these guys, their rebuild kits are cheaper than the usual VW suppliers and they include shiny new pistons, the others don't seem to.

 

[ozziedog]

:shock: With all the good will in the world, if your reservoir gave up with that little bit of pressure, how long before it just collapsed anyway or if you had knocked it inadvertently whilst driving :shock: :shock: :shock:

Ozziedog,,,,,,,,could’ve been a real shocker, maybe got off light :mrgreen: :mrgreen:

 

[Coda]

Ozzie's got a good point (as usual), but when you put that all back together, why not consider using a vacuum pump to bleed the brakes? If you don't have one, I can lend you mine if you're anywhere near me.

 

[67westy]

I have been looking at vacuum pumps recently. Do they work well? I wasn't sure how quickly they would drain the reservoir as it's quite small

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[fallingoffalot]

Yeah, good point, luckily it was almost empty when it popped, so I didn't get fluid everywhere. For future reference, can you use the brakes if the reservoir has a hole, or no cap?

Thanks for the offer Coda, but I think I'll just do it the old fashioned way with my son pumping the pedal.

I got the new reservoir today and Bigg Red have found a boot that may fit, they are sending a couple to me.

Glad I'm doing this myself, if I'd given it to a garage, I may have never know about the abnormal boot size.

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[Moseley]

Yeah, good point, luckily it was almost empty when it popped, so I didn't get fluid everywhere. For future reference, can you use the brakes if the reservoir has a hole, or no cap?

Thanks for the offer Coda, but I think I'll just do it the old fashioned way with my son pumping the pedal.

I got the new reservoir today and Bigg Red have found a boot that may fit, they are sending a couple to me.

Glad I'm doing this myself, if I'd given it to a garage, I may have never know about the abnormal boot size.

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Yes, there will be no issue with the brakes until the bottom reservoir (on top of the master cylinder) runs empty on one of the two chambers. The top reservoir just serves the purpose to be an easy point to add fluid, but also as an easy location to act as a tell-tale for a leak somewhere underneath the bus.

 

[fallingoffalot]

Yes, there will be no issue with the brakes until the bottom reservoir (on top of the master cylinder) runs empty on one of the two chambers. The top reservoir just serves the purpose to be an easy point to add fluid, but also as an easy location to act as a tell-tale for a leak somewhere underneath the bus.

Oops I think I may have drained the bottom reservoir, maybe partially. At one point it seemed like the brake pedal wasn't pushing any fluid round at all. The confusion lay in the fact that I was asking my lad to top the fluid up when it was empty, we soon realised that it had been empty a while but looked like there was still a bit in there

Hopefully if I install the refurbed caliper, get that full of fluid, then bleed the system it should sort it.

 

[ozziedog]

Use you’re gunson now and you’ll be fine. If you don’t want it,I’ll have it off you as mines got quite a few bits missing here and there.

Ozziedog,,,,,,,,what dya want for it ? :mrgreen:

 

[fallingoffalot]

Oz you can be cryptic at times, but it's a bit early for this one!

EDIT: Ah I see, all makes sense now! I am a bit nervous of the parts down stream of the reservoir, would hate to blow the m/s reservoir.

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[Moseley]

Yes, there will be no issue with the brakes until the bottom reservoir (on top of the master cylinder) runs empty on one of the two chambers. The top reservoir just serves the purpose to be an easy point to add fluid, but also as an easy location to act as a tell-tale for a leak somewhere underneath the bus.

Oops I think I may have drained the bottom reservoir, maybe partially. At one point it seemed like the brake pedal wasn't pushing any fluid round at all. The confusion lay in the fact that I was asking my lad to top the fluid up when it was empty, we soon realised that it had been empty a while but looked like there was still a bit in there

Hopefully if I install the refurbed caliper, get that full of fluid, then bleed the system it should sort it.

Partially emptied would be ok, the problem only arises when the level drops to the inlet port of the MC, as this is when air will be pulled into the system and all your hard work is undone.

However, the bottom reservoir level can be misleading - the dual circuit ones have a little wall inside them that acts as a weir. This means that a catastrophic leak on either the front or the back system will keep the other system functioning. When bleeding, if not paying attention to the upper reservoir, the lower reservoir can appear to be full, but the other side of the weir is empty. It’s not the easiest to see the level in, and either needs to be very clean, or a very bright light shining through it!

 

[fallingoffalot]

Got the new boots from Bigg Red, they're slightly bigger, but still too small. This caused me to have a brain wave, I'll glue it on!!! It's diameter is the same. So I was thinking contact adhesive, any other ideas on the glue front? I've just cleaned it up and it appears I'm not the first to have this idea, I scraped away some old glued on rubber. Gotta be the only option now.

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[67westy]

It might not be an issue depending on the mileage you do. I guess the best long term solution may be a new caliper?

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[fallingoffalot]

It might not be an issue depending on the mileage you do. I guess the best long term solution may be a new caliper?

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Yes I agree, I'll go with the glue idea then check it in a few miles. I'm sure it'll be fine.

One more question.......
If I remove the brake line for the fronts from the master cylinder to check whether there is a valve there preventing the calipers fully retracting, I'm guessing this is going to drain the master cylinder, will this be a problem in terms of bleeding the system when I reassemble it all?

Thanks

 

[67westy]

It might not be an issue depending on the mileage you do. I guess the best long term solution may be a new caliper?

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Yes I agree, I'll go with the glue idea then check it in a few miles. I'm sure it'll be fine.

One more question.......
If I remove the brake line for the fronts from the master cylinder to check whether there is a valve there preventing the calipers fully retracting, I'm guessing this is going to drain the master cylinder, will this be a problem in terms of bleeding the system when I reassemble it all?

Thanks

What I normally do is take the cap off the upper reservoir, wrap a few layers of cling film over the top and screw the top back on. This should form a vacuum and stop the fluid draining (assuming everything else is air tight). That way you should just need bleed the little bit of air that got in to the pipe

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[67westy]

Oh and remember to take the cling film out when done!

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[mike202]

Great idea ! [emoji108]


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[fallingoffalot]

Fantastic idea, thanks!

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[ozziedog]

What a lot of the pros do, is clamp the flexi to keep most of the fluid in. They have a special tool that’s sort of like a plastic set of mole grips. I’ve often wondered if they are responsible for flexis collapsing internally in later life, possibly if they’re near their sell by date. You could do similar with some mole grips and two pieces of plastic, something like window glazers packers or facia board off cuts. I like the cling film plan though, that’s great.

Ozziedog,,,,,,,,,,,lots of different ways , I’m sure. :mrgreen:

 

[fallingoffalot]

I've seen quite a few YouTube vids where they use mole grips, or even the plastic clamp things and yes I agree doesn't look like a good idea. The hose seems quite rigid. I have a plastic bleed nipple cover which I pop over the end, stops it dripping, but I guess wouldn't stand any pressure.

My plan was to put the whole lot back together, bleed, then look at the return valve in the m/s.

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