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My very much better half has a 1990 R80 Monolever, single disc unfaired version, which we're trying to get back on the road - Rob Frankham had advised on a couple of matters previously some time ago, hence V2.0!. Health got in the way of bikes for Debs last year but she's back on the mend and determined to ride Otto again, so I have returned to sorting this bike.

The Master cylinder had seized with standing, so suspecting it was a mess we got a new one and at the same time new pads. Here is where it gets odd. One of my previous discussions with Rob was regarding the disc (solid, undrilled, looks original) does not seem to be quite centred with the caliper, and we didn't really come to any conclusions about that.

Now I have come to fit new pads, this mis-alignment will not let me fit a new pad to the inside, there isn't sufficient space (pistons and seals all new, fully retracted, not seized!). When looking at other Monos with single discs, I also note they are on the left - ours is on the right! The only RHS fitted one I can find is the black bike (with the purple background) in the brochure, so wouldn't guarantee that is an untouched image. Is this bike right? We have had it for years, but not from new, dealer bought but with one previous owner.

Looking at RealOEM having used the VIN to get to the hopefully correct pages, they show the brake on the left. Also they show the wheel spindle fitted from the right, whereas ours fits from the left.

What is going on here? Have I finally lost it? Is this bike a rebuild with wrong parts from some previous calamity?

My intention is to machine a little - I'd say 1mm is sufficient - off the wheel spacer to move the wheel and therefore the disc across to centre it in the caliper, I'll get a replacement one to do that with so I have the original the compare still. Is that a considered approach? What does the panel think, please!

Can you post a picture of the brake set and disc? They say pictures paint a 1,000 words. I'm no expert, but every 80's BMW I've seen has drilled front rotors, so I wonder if the disc is correct--could be wrong here.

Without photos for reference, I'm just throwing out some ideas.

I don't know if this is even possible, but you mentioned that that the caliper and spindle are on the opposite sides. So, I wonder if a PO switched/installed the sliders on the opposite sides. FWIW, early 80's BMW had Brembo calipers that attached on the front of the sliders while the later monoshock bikes have the calipers mounted to the rear.

With regards to narrowing the wheel spacer, just remember whatever you take off one side needs to be added to the other side. Otherwise, you could end up compressing the sliders too much together for proper operation.

Another option might be to purchase an aftermarket floating rotor, which might allow for better alignment.

Thank you for your reply.

Mono calipers are in front of the leg - always. It was the Brembo fitted twin shocks where the calipers moved to the rear. So that's not it! It is possible it has been assembled wrong sided, but then the caliper would not fit, I don't think.....I'm pretty sure the calipers are handed. I do wonder if it is a mash up after an accident, put together using whatever they could find.

I should be OK with shaving the spacer, the way Mono front wheel spindles work it is drawn in from one end while the other is left slack to slide through the other leg until it is all snugged up, then the fork lower is clamped down to the spindle. I think it'll work, I'll give it a coat of looking at though, I understand your point.

I'll photograph the brake, but not tonight.....it's cold and wet out, so I'm not going down to the garage just now!

Maybe something like this setup?

https://forums.bmwmoa.org/threads/weepi ... st-1345188

or this?

https://forums.bmwmoa.org/threads/1986- ... st-1096629

Kurt

New Haven Neil wrote: ↑Thu Jan 29, 2026 4:38 pm
Mono calipers are in front of the leg - always. It was the Brembo fitted twin shocks where the calipers moved to the rear. So that's not it! It is possible it has been assembled wrong sided, but then the caliper would not fit, I don't think.....I'm pretty sure the calipers are handed. I do wonder if it is a mash up after an accident, put together using whatever they could find.

Damn, brain fart and mixed things up.

New Haven Neil wrote: ↑Thu Jan 29, 2026 4:38 pm I should be OK with shaving the spacer, the way Mono front wheel spindles work it is drawn in from one end while the other is left slack to slide through the other leg until it is all snugged up, then the fork lower is clamped down to the spindle. I think it'll work, I'll give it a coat of looking at though, I understand your point.

My concern here was not with the wheel spinning, but rather creating stiction on the forks that they don't move up and down properly.

Kurt in S.A. wrote: ↑Thu Jan 29, 2026 5:17 pm Maybe something like this setup?

https://forums.bmwmoa.org/threads/weepi ... st-1345188

or this?

https://forums.bmwmoa.org/threads/1986- ... st-1096629

Kurt

Hi Kurt - yes, but single disc, with the RHS only. I'm beginning to wonder if it is parts from a twin disc, with the left caliper deleted. As it is 3c and chucking it down with rain I'm not venturing out to the garage just now! I winder if there are part numbers on the calipers anywhere. Will investigate!

Jeff in W.C. wrote: ↑Thu Jan 29, 2026 8:46 pm

New Haven Neil wrote: ↑Thu Jan 29, 2026 4:38 pm I should be OK with shaving the spacer, the way Mono front wheel spindles work it is drawn in from one end while the other is left slack to slide through the other leg until it is all snugged up, then the fork lower is clamped down to the spindle. I think it'll work, I'll give it a coat of looking at though, I understand your point.

My concern here was not with the wheel spinning, but rather creating stiction on the forks that they don't move up and down properly.

I get your concern Jeff, thank you, but when assembling it all the left fork leg is basically loose to float as the spindle is drawn to, and fixed into position by the right leg, the spindle is free to slide through the left leg at that stage. The left leg is only then tightened around the spindle, so as far as I can see has no fixed position. The step on the spindle goes against the wheel bearing via a spacer on the left side.......I think! Only then is the fork brace tightened after bouncing the forks a couple of times, so it should all be in line and free. When the weather improves I'll go down to the garage and check my supposition, these forks are completely different to the twinshock type. IIRC they are basically K75. I wish I'd kept my ST!

First point... BMW did mount single calipers on the right as well as on the left... not sure of the dates or models but, since all monos use the same components, it may even have been arbitrary dependant on what they had in stock at the time. There's no reason for it to make any difference.

I would have said that the spindle should be from the left but, looking at images, I can see some where the spindle definitely is in from the right... the bottom line is that the spindle can only fit one way as the clamps at the bottoms of the legs are different sizes so, unless someone has done something really radical (why???), if it fits from the right, that's the way it came from the factory.

The 'offset' disc in the caliper isn't new or unique. There are a few things to try/points to bear in mind...

First ensure that the legs are truly parallel. It's quite possible,especially if the brace isn't fitted, to pull the legs together at the bottom and this will move the caliper to one side. Tightening the clamp bolts at the bottoms of the legs before fitting the end cap to the wheel spindle and tightening it, will do it.

Also chedck that the bearings are set fully into the wheel. If one is offset, it will move the wheel to one side..

Finally, your plan of skimming the spacer isn't likely to cause any problems so go with it.

Discs slightly offset in the caliper are not unusual and not a problem as long as you can fit the pads.

Rob

Thank you once again, Rob.

I have now found another Mono with RHS brake, as you say it probably depends upon what stock was to hand at time of assembly.

I agree with all your comments, I was pretty sure that a little skim of the spacer would work as the registration of the wheel is totally dependent upon that side fork leg, the other side just clamps to wherever the spindle ends up as far as I could see. I'll go ahead with getting a used spacer 'from the usual place' and work on that, as the new pad will not go in.

Thank you Rob and everyone for your input - I'll try to remember to post the outcome when I get it sorted. Mrs H will be chomping at the bit to ride it as soon as the weather improves and her hamstring heals - lot of physiotherapy going on currently.