1989 BMW R100GS-Paris Dakar Restoration

Paul Rochdale said:

Another tip I was given was to ram the piston in (and out) using a large screwdriver as this would give more oomph (better leverage) than relying on the brake lever.

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This could prove difficult at 60mph IMO.

Well still no success bleeding the front brake. I have tried each and every method a number of times and still get air bubbles at first and when they go, no pressure at the lever. I wondered if I might have bought from Motorworks the wrong repair seals (kit) for the master cylinder so checked the number underneath the master cylinder (13) and yes, these were in fact what I fitted. Jim Cray suggested tapping the s/s lines with the handle of a screwdriver - I did but it no difference. Motorworks suggested my K1100 caliper was the problem as it's now fitted on the nearside ahead of the fork leg and back to front - but it worked OK before. He also suggested I undid the caliper and raised it a bit - I did but the s/s hose and steel brake pipe goes thought the mudguard and being rigid, I couldn't move it much.

It's getting very frustrating and whilst I've been successfully bleeding brakes on cars and bikes for years, I've never had this problem before. I know I'll go back tomorrow and find more air in the system. I always clamp the lever overnight too but with no pressure, that's bound not to work, and it doesn't.

Paul Rochdale said:

Well still no success bleeding the front brake. I have tried each and every method a number of times and still get air bubbles at first and when they go, no pressure at the lever. I wondered if I might have bought from Motorworks the wrong repair seals (kit) for the master cylinder so checked the number underneath the master cylinder (13) and yes, these were in fact what I fitted. Jim Cray suggested tapping the s/s lines with the handle of a screwdriver - I did but it no difference. Motorworks suggested my K1100 caliper was the problem as it's now fitted on the nearside ahead of the fork leg and back to front - but it worked OK before. He also suggested I undid the caliper and raised it a bit - I did but the s/s hose and steel brake pipe goes thought the mudguard and being rigid, I couldn't move it much.

It's getting very frustrating and whilst I've been successfully bleeding brakes on cars and bikes for years, I've never had this problem before. I know I'll go back tomorrow and find more air in the system. I always clamp the lever overnight too but with no pressure, that's bound not to work, and it doesn't.

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ok - i've been biting my tongue but it reckon you only have one choice. - The dreaded clamp method.

you won't like it - but it works.

maybe change the top ss pipe for an old rubber one - then swap out the bottom one etc etc.

get a pair of mole grips and clamp the pipe an inch out of the m/c.

pump until rock solid.

release and remove the mole grips and use a big pair of pliers down a couple of inches. Hold the pliers closed in one hand and pump with the other Then pump until you feel the pressure and use the pliers as a one way valve - pump against them and slowly let the fluid past by releasing them - clamp tight as you release the lever - and keep repeating.

keep going until you get to the caliper.

job done - 30 mins.

its a trade trick and last resort when no ones looking

But when the old rubber hose is replaced with the s/s one, air will get in and I'd be back to square one. I also thought about changing the s/s - steel pipe combination for a one piece s/s hose all the way to the caliper. This would at least allow me to swivel the caliper around a bit to extract that last air bubble.

I just can't believe that with all the pumping and various methods I've tried, there's still air in there. Perhaps as Motorworks said, "Non-standard fitment of the K1100 4-pot caliper, non-standard problems".

But thanks for your suggestion.

Last time I chased the problem it was a calliper seal which was drawing in air.

It wasn't leaking enough to drip on the floor, or wet the calliper bottom, but when I removed it for a good look one seal was just a bit moist, while the other was bone dry.

Time before that the calliper was drawing air at the bleed nipple thread - teflon thread tape sealed it temporally, and I fitted Speedbleeder niples which already have a sealant on the threads.

Speedbleeder nipples have always worked perfectly for me - worth every cent IMHO.

Paul Rochdale said:

But when the old rubber hose is replaced with the s/s one, air will get in and I'd be back to square one. I also thought about changing the s/s - steel pipe combination for a one piece s/s hose all the way to the caliper. This would at least allow me to swivel the caliper around a bit to extract that last air bubble.

I just can't believe that with all the pumping and various methods I've tried, there's still air in there. Perhaps as Motorworks said, "Non-standard fitment of the K1100 4-pot caliper, non-standard problems".

But thanks for your suggestion.

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just do it on the new ss / ptfe lined pipe then...works a treat...just feckin do it or i'll come over there and do it myself...

What and damage my shiny s/s brake hose? Don't you dare. One thought after what Beemerboff said, I did seperate the caliper halves so maybe the tiny O-ring (which I failed to replace) is at fault? Also the caliper pistons, even though well lubricated with brake fluid, were bloody tight to re-insert with new seals, in fact I needed to squeeze them in using the vice, another 'first' for me.

Paul Rochdale said:

. I wondered if I might have bought from Motorworks the wrong repair seals (kit) for the master cylinder so checked the number underneath the master cylinder (13) and yes, these were in fact what I fitted. . .

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You did put the brake master cylinder piston back the correct way around, didn't you...........

Well back to the grind stone today. I took the modified K1100 caliper apart using an airline as I had a hunch that fluid might have been leaking from there but there has been so many drips from the bleed nipple anyway, it was hard to tell. I seperated the halves of the caliper and got the pistins out using an airline, not easy as the interconnecting port needed block to build up the pressure. This is the horror story I found. When a rebuilt the caliper a few months ago, I refitted new seals and pistons, but the pistons were such a bugger to fit squarely in the bores. As I mentioned before I squeezed them in using the vice and this hamfistedness has hardly done the bores any favours. I've cleaned them up with a fine Dremelling so fingers crossed they will be OK. With even more cleaning and fresh brake fluid I managed this time to get them in with just thumb pressure (OK, and a slight squeeze for two in the vice). The tiny O-ring was fine so I had applied a tiny amount of Wellseal around it. Belt & braces.

Caliper back on and more brake bleeding, both conventional and back flushing. Result? No damned difference.

Going back to Kaiser's method I squeezed the s/s line a few inches from the master cylinder using small Moles. Result? No difference. This suggests that the master cylinder isn't applying enough pressure yet it did when it was on the road and, yes Steptoe, the piston and it's seals are in the right way around.

I have finally lost patience with it all and will source a trailer and take her over to Jim Cray. Perhaps a fresh mind is needed? I am presuming I have the bleed nipple and brake pipe in the correct tapped holes - Bleed nipple on the inside, brake pipe on the outside - or does it even matter as the ports are linked?

the bleed nipel should be on the aut side !!!! if you need a new caliper I have plenty thier all as new no messing with skiming down or service kits and come with good pads in 2 or 4 piston setups

you just need to pump keep your reserver prity full dont let it go emty and after a few minues when you see no more big boobels in your fishtank hose pipe coming aut of your calliper tighten up your bleed srew pump a nother 3 or 4 times with the screw tight and your preshure should be thier

OhFUGG You should Never need to use a vice to put these in a pair of worn use a pair of old waterpump plyers with tape/cloth wrapped around the sharp bits

GENTLY catching outer couple of mill of the piston and rotate whilst inserting and gently pushing down with thumb

Works every time, as long as you have cleaned out the alloy corrosion gunk from behind the new seals

Searching on Google Images, I have to agree that I appear to have transposed the bleed nipple and brake pipe. Shit.

As for the use of my vice. I hated having to do it because it didn't seem right however the back of the caliper is not completely parallel with the faces of the pistons and it's SO EASY not to get them in straight. As I said, this time I did get two in with just thumb pressure, and the other two only halfway in with thumb pressure.

Thanks for the advice and I'm still kicking myself. Tomorrow I will swop them over.

macke shure you have a washer top and botom of your fittings to breaded hoses

Right swopped the brake pipe and nipple over, bled the front brake yet again, twice, and back flushed it twice, and the result? Still no pressure. I'm now going to fit a replacement master cylinder piston (13mm) as without any leaks, I've run out of ideas.

You could try the caliper with another master cylinder such as the rear one or one off another bike - that way you would know whether it was the caliper or MC that was the problem.

Viv

viv said:

You could try the caliper with another master cylinder such as the rear one or one off another bike - that way you would know whether it was the caliper or MC that was the problem.

Viv

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Or just ask a freind hu has bled brackes before to help you !!! if it is your master cylinder I have a good 13mm one thier you only need to swap the cylinder hause
not the holle thing but its normal after you bleed your brackes you need to pump it a few times first before it will work I now zum people dont pump brackes they just let them run throu and keep toping the reserf up till all the air is aut thats allso a fool proof way of doing it !!!

Today I fitted a new brake master cylinder piston and after bleeding, no difference whatsoever. Then using a torch - it's bloody dark in there - a careful examination of the 4-pot brake caliper revealed a tiny weep, not enough to prevent some sort of pressure I would have thought, but a tiny weep all the same. Now whether it's leaking from where the tiny O-ring seals between the two halves, or from the piston seals, I don't know but as I had badly scored the piston bores, I shall replace the entire caliper for another 4-pot caliper. This saga has gone on too long.

Litelfun, PM'd you. If he doesn't have the correct 16v K1100LT lefthand caliper, I shall be searching for one on here.

A great read.

Lots of info for an aspiring PD circa 1991 purchaser (just got to haggle the price down). If I do get it it will be going in for a major 'refit' and some of the 'stuff' mentioned here might find its way onto/into it.

Right, almost there. I'll take her for a test ride around the (private) estate when the rain stops.

Well the saga with the lack of brake pressure had a happy ending. After replacing the master cylinder piston and seals, and making no difference, I finally had to bite the bullet and buy another K1100 brake caliper and fortunately Litelfun had a nearly new one. Not cheap but this nonsense had gone on long enough. I got about 2mm machined of the top and bottom tabs and bolted the caliper onto the slider after repainting the slider. The fresh silver paint had been stripped in places by the brake fluid. Four or five minutes bleeding, and I got much welcomed pressure at the lever. Clamped overnight to remove the last vestiges of air. I've got a good brake at long last.

Fork legs. I decided to use the Howard Millichip Fork Oil Formula - which is as follows.
Left leg - 75% SAE15W and 25% SAE20W = 470ml (for completely dismantled forks).
Right leg - 100% SAE15W = 470ml

The copy of a Surefoot side stand which I bought some years ago was always held onto the rear engine bolt with the nut only using a few threads so I got hold of some 12mm stainless steel rod and made a longer bolt (stud). The M12 nyloc nuts now have a proper purchase on it. Incidentally the sidestand was a very hefty chunk of steel which I whittled down and drilled some lightening holes. Once I get the bike off the motorcycle bench and onto the ground, I'll be able to judge what angle to saw the end of the sidestand and to weld a foot on it.

Right about time to check the timing and the carbs. Using my old Gunson strobe, I could barely see anything in the tiny hole. I tried turning the bean can about 1/8" but the misfiring resulted in me replacing the bean can in it's original position.

Chris Tunbridge lent me his gauges to check the carb settings, easier said than done. The gauges fluttered like buggery and didn't settle down unless the engine was revved to 4000rpm where the needles were more or less OK. I tried altering the stops on the carbs to get them identical but it made no difference. It seems I must shell out for a pair of DAMPED Davida gauges.

So I am leaving the carbs and timing well alone and see what she's like on the road. I may well take her back to Jim Cray to have a final tweek if she needs it.