Front brake failure

pcolbeck · Jul 19, 2021

So I've had my R850R for about six weeks or so and its been fine. Had a brand new MOT when I bought it with zero advisories.
On Saturday I went for a ride and about 60 miles in the front brake lever started pulling closer and closer to the bars. Took a flick with a finger to make it go back fully as well.
I could pump it up and get some pressure back when stopped but it only lasted a few minutes. Limped home very very carefully.
I cant see a leak anywhere but I think its on the original brake hoses and I have no idea how old the brake fluid is.
Also it was very very hot on Saturday (for the UK) and I was on a hilly single track road.
I have ordered some Venhill braided hoses and will fit those and bleed the system.
Is it likely to be anything else?

P.S No ABS on this bike.

DrFarkoff · Jul 19, 2021

could have been vapour locking

Are your brake calliper pistons moving freely in the callipers?

Does the master cylinder easily return to the outer position so your brake lever always has a little tension (Not Floppy) ??

Oh and you will need a standard M10 brake nipple and rubber cover for the right hand brake calliper There is "Usually" a fill point fitted there

Steptoe · Jul 19, 2021

Year of bike would help. There’s an enormous difference between the early 1995 onwards models and the post 2001 versions.

pcolbeck · Jul 20, 2021

Its a 1996 and the lever is floppy. There is no pressure at all in the first 1/2 of the travel and when released the lever only returns half way. If I push it back it will go back the rest of the way.
Pumping it worked a bit. There is pressure in the last bit of lever travel and the brakes do work. Doesn't seem to be a fluid leak that I can see.
This weekend I can start taking a closer look.

Ajay · Jul 20, 2021

As failure sudden & no leaks, I'd be looking at the master cylinder

Motorworks repair kit £41.40 (caveat re scratched original m/c)

If your m/c is damaged, consider a s/h unit, James Sherlock list them at £79, with 6 month warranty
I've bought several s/h items from JS, always pleased with condition.

pcolbeck · Jul 20, 2021

I can feel a complete front brake system strip down coming on ....

DrFarkoff · Jul 20, 2021

pcolbeck said:
I can feel a complete front brake system strip down coming on ....

One thing at a time Don;t dive in and start pulling everything apart

You will need the "Bobbin" (Piston and seals you will understand when you see it) for the master Cylinder as I suspect that it is stuck down the bore with crystals It happened on my Old R1100RS of the same era

And if there is a crust around the pistons in the callipers making them very stiff

Are your brake pistons sticking? May only be one of 4 per calliper but its quite dodgy and needs fixed

You will likely find that salts have built behind the outer wiper rings and have pushed them against the brake pistons and making them stick? Giving the calliper a boil in ordinary water a big pot for 20 mins or more with a couple of drops of fairy liquid can dissolve that and help to get the pistons out

blow any residual water out Clean the salts from behind the sealing rings and "wiggle" the pistons back in

One other thing I forgot Try and crack the bleed nipples before you start all this They may be galled in :rob

I think I have a pair of the correct callipers if you need some

pcolbeck · Jul 20, 2021

Thanks. DrFarkoff.

Just been out to the garage and the bikes been sat on the side stand for a few days so on a lean. Its now wet under the brake lever / master cylinder assembly so I'm guessing its the master cylinder that's blown a seal.

DrFarkoff · Jul 20, 2021

pcolbeck said:
so I'm guessing its the master cylinder that's blown a seal.

Very likely yes But Also Assume nothing! :rob

Check the rest when you are at it If you can't push a brake piston back in with decent finger pressure? Its kind of tight and needs further looking at

The design of the master cylinder is pretty good "But" The plastic on the brake lever pin can jam in the lever and you cant get the fecker out

You need to drop the lever out to get the brake "bobbin" out

There is a small allen bolt that is used at the pin to prevent the "bobbin" from travelling out of the master cylinder and it has a small alloy washer Make sure it goes back or you may get a leak!

And order a new rubber boot at the same time your one will likely come out like Jelly!

This should cover your bike

https://www.carlsalter.com/download.asp?p=833

donkeydoo · Jul 21, 2021

One tip if I remember rightly, assuming it's the same as GS, is to heat the pivot pin before removal with a soldering iron as I think it has thread lock on it and can be a pig, also make sure the kit you get comes with the spring as some used to not include it..

pcolbeck · Jul 21, 2021

Thanks all.

Might give the thing a respray while its off as its pretty scabby as these things often are. Looks like paint damage from spilt brake fluid.

Steptoe · Jul 21, 2021

pcolbeck said:
Thanks all.

Might give the thing a respray while its off as its pretty scabby as these things often are. Looks like paint damage from spilt brake fluid.

You don’t have to remove it on the early models. . Remove the lever and the new piston and seals can be fitted with it all in place ... 5 minute job. Just make sure you put the piston in the correct way. Have the bars turned to full left lock and if you know what you’re doing you won’t even have to bleed the brakes, just gently get the air to pop up through the M/C fluid reservoir

pcolbeck · Jul 21, 2021

Thanks. Might leave it in situ then as I plan on cleaning it up and respraying a few things over the winter anyway. The subframe could really do with sending to the powder coaters for a start.
I'm replacing the brake lines now anyway with some braided ones. Bleeding shouldn't be too bad as I have a vacuum pump brake bleeder.

Front brake failure

pcolbeck

Member

DrFarkoff

Grumpy Ole Git!!!

Steptoe

What a waste.

pcolbeck

Member

Ajay

Registered user

pcolbeck

Member

DrFarkoff

Grumpy Ole Git!!!

pcolbeck

Member

DrFarkoff

Grumpy Ole Git!!!

donkeydoo

Active member

pcolbeck

Member

Steptoe

What a waste.

pcolbeck

Member

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