Back brake woes

621Andy · Sep 7, 2020

Evening People :bow

I'm normally lurking over on the Oilheads bit, however my boss has inherited a '79 R100 from Switzerland. It last ran 12 years ago and has been garaged ever since. The previous owner wasn't that hot on maintenance so it's proving a bit of a challenge...

We're making progress with it and hope to have it running by the end of the week :nenau

(Ever the optimist

)

Front forks have been rebuilt, as have the front calipers(Twin disc) and master cylinder. Master cylinder is fitted and calipers should go on tomorrow.

The big problem at the moment is the back brake system; I'm not an expert on this bleeding lark by any means and can't seem to get any fluid to flow through the system. The master cylinder has been rebuilt with a new piston, but still has the old plastic inlet on the top. The caliper has been rebuilt. The hose from the reservoir to the inlet is new, however the metal line between the cylinder and caliper is old as is the short length of flexible pipe at the caliper.
I'm assuming air is getting in somewhere but have no way of knowing where :nenau

Any ideas anyone please :confused:

barny · Sep 7, 2020

You could buy a reverse bleeder which sucks the oil through https://www.youtube.com/watch?v=bjXHUy6wojA they are not that expensive. You could also try removing the caliper or master-cylinder from the mountings and try moving them around to let the air pockets move back into the fluid.

Neil W · Sep 7, 2020

Get hold of a large 150 ml ish plastic syringe and a length of clear pipe that fits onto both the syringe and bleed nipple, take off the master cylinder lid attach the pipe from the syringe to the cracked off bleed nipple and back fill the caliper/ line/master cylinder and reservoir from the bottom end . It usually works fine with a stubborn system

621Andy · Sep 8, 2020

Many thanks. I'll try the syringe first, then look at bleeding kits if that doesn't work.

I was assuming there was a leak in the system but if this works I/we will be very happy as we're doing this soon a shoestring!

NeilDD · Sep 8, 2020

Another thing to bare in mind is that the flexi rubber section is around 41 years old, and could have failed internally.
Try the flush with a syringe and if that fails you may need a new brake line

Gelandestrasse · Sep 8, 2020

The back brake systems are tricky to bleed. You could take the caliper off and raise it up high to force any airlocks in the 'tube that always has airlocks' through as you bleed. I tend to use a vacuum bleeder. If the brake performs marginally when you have done, you haven't finished! They do work when all bits are in good condition and well bled.

Colin · Sep 8, 2020

have just replaced the rear flexy pipe on my R100rs 1977. couldn't bleed any fluid through. the original one had collapsed internally. got a nice new goodridge pipe from a gentleman near Salisbury. (thanks Mike)

621Andy · Sep 8, 2020

Hi All

Thanks for the tips! We've got working front brakes now!

However the back one is leaking at the back end of the master cylinder so we need to give some thought to how to seal it; PTFE tape?? Otherwise the syringe worked as it at least got fluid into the system...

I'll upload some pics as I know you're all dying to see what it looks like

. Any info on what model it is exactly would be great. It did have a screen at one time and it comes with leather(?) panniers too...

621Andy · Sep 8, 2020

Pics...

Here are some pics...

621Andy · Sep 8, 2020

The problem child...

621Andy · Sep 8, 2020

More...

621Andy · Sep 8, 2020

Some from its arrival from Switzerland with the previous owners son...

621Andy · Sep 8, 2020

Some more...

621Andy · Sep 8, 2020

Final oddsies

Gelandestrasse · Sep 8, 2020

621Andy said:
Hi All

Any info on what model it is exactly would be great.

From the frame number (what we can see of it), it is an Apr/May 1979 BMW R100RS 51 Kw. If the engine number matches, there you are. If it doesn't, look on these pages http://bmbikes.co.uk/chassispages/enginechassis1000.htm

Gelandestrasse · Sep 8, 2020

Colin said:
have just replaced the rear flexy pipe on my R100rs 1977. couldn't bleed any fluid through. the original one had collapsed internally. got a nice new goodridge pipe from a gentleman near Salisbury. (thanks Mike)

That'll be me, Colin! But my name isn't Mike! ;-)

621Andy · Sep 9, 2020

Gelandestrasse said:
From the frame number (what we can see of it), it is an Apr/May 1979 BMW R100RS 51 Kw. If the engine number matches, there you are. If it doesn't, look on these pages http://bmbikes.co.uk/chassispages/enginechassis1000.htm

Interestingly, the engine number doesn't match and appears to come from a 4/77 full power model (60814...); this fits with the fact that the 'Carte Grise'(papers) show it as having 70kW. The chassis number fits with it being registered in may '79.

The Master cylinder is off at our local mechanical genius' workshop to have him possibly work his magic and get it to seal...I suspect we'll end up having to try and find a reconditioned one, but this bloke can work wonders...

The new battery is on charge so maybe we can concentrate on that side of things tomorrow. I leave here Sunday morning so I'm determined to have it at least running if not on the road by then :green gri

Thanks again everyone!

Steptoe · Sep 9, 2020

621Andy said:
Evening People

I'm normally lurking over on the Oilheads bit, however my boss has inherited a '79 R100 from Switzerland. It last ran 12 years ago and has been garaged ever since. The previous owner wasn't that hot on maintenance so it's proving a bit of a challenge...

We're making progress with it and hope to have it running by the end of the week (Ever the optimist)

Front forks have been rebuilt, as have the front calipers(Twin disc) and master cylinder. Master cylinder is fitted and calipers should go on tomorrow.

The big problem at the moment is the back brake system; I'm not an expert on this bleeding lark by any means and can't seem to get any fluid to flow through the system. The master cylinder has been rebuilt with a new piston, but still has the old plastic inlet on the top. The caliper has been rebuilt. The hose from the reservoir to the inlet is new, however the metal line between the cylinder and caliper is old as is the short length of flexible pipe at the caliper.
I'm assuming air is getting in somewhere but have no way of knowing where

Any ideas anyone please

The old airhead rear disc brake was always a bastard to bleed, even when new.

The trick used to be to undo the rear caliper, wedge something inbetween the pads keeping the caliper pistons fully retracted and hold it up higher than the master cylinder.

621Andy · Sep 10, 2020

Thanks Steptoe, I'll remember that hopefully when I'm back down here next year...

A quick update...

Basically our maestro gently bored out the back end of the master cylinder but to no avail. Basically we'd farked it trying to knock the old piston out by using too big a diameter rod which damaged the seal face :blast

We reassembled everything and tried everything to get a seal but no luck...So if anyone has a spare for a '79 R100RS we'd be happy to take it off your hands

I also cleaned out all the old gopping grease out of the throttle linkage and grip cog and remembered to line the marks up when I reassembled it

.

More progress was made at the noisy end; The carbs were basically OK. I had a look at the diaphragms and decided I'd leave them for now and just replaced the cork bowl seals rather than bugger around inside them and knacker any previous settings(Bearing in mind it was basically running when the owner shuffled off his mortal coil beside his bike).
The new battery proved to be a bit taller(not a problem), but a bit wider(bit of a problem) so some metalsmithing with a cold chisel and hammer was involved to widen the plate a tad

and eventually it shuffled into place.
The tank went back on and a couple of litres of essence tipped in and fingers crossed...Nothing leaked out again which was a good start, so choke on and hit the button; Nothing....

Ahh, kill switch :blast

5 seconds on the button and it spluttered into life!

621Andy · Sep 10, 2020

So after letting it idle a bit to burn off all the crap from the pipes and block it became clear that the carbs need balancing but that's a minor issue. The next problem was the clutch which worked enough to get it into neutral but was obviously seized such that trying to put it into gear caused it to stall...Bugger.
Anyway a few minutes of trying to start it in gear and something went clunk and the clutch suddenly worked! Oh shit, that means I'd better take it for a test ride then

I was suitably dressed in shorts and sandals and bearing in mind our workshop is on top of a hill with a loose gravel track around it I set off rather timidly for a circuit of the yard in 1st gear- no back brake remember!
That all seemed to go well, so the only thing for it was a potter down the hill and back up again! Into second and take the left hand fork up to the main farmhouse. Turn around and back down the slope to the workshop which luckily is up the right fork; As I headed down the slope the front brake decided it didn't want to be one any more

so some rapid pumping on the lever restored enough pressure, combined with the uphill bit to the workshop ensured I survived unscathed...

The boss kindly took me to lunch and afterwards I re-bled the front brakes, repositioned the handlebars and levers and generally farted about a bit.

Soo, basically mission completed; To have it running before I head home to Germany on Sunday. However lack of funds and time will ensure that it'll sit now until I'm back sometime next year. The carbs were run dry again and everything reassembled so that we at least know where it all should be in 6 months time!
Once we've got it sorted, then it's just a Controle Technique(MOT) and the paperwork conversion from Swiss to French which isn't my problem

We've rescued a little bit of history as the owner was quite infamous in our line of work and was quite a character, so that's quite pleasing

And to have done it in the limited time I had available is also nice too.

Back brake woes

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