Rear master cylinder query.

My rear master cylinder which I have rebuilt with a kit, looks wrong to me. There is a gap between the lever that actuates the piston assembly and the piston. I thought it was incorrect, but have referred back to my “dismantling photos,” and it appears that it was the same prior to being dismantled. Therefore, is it right or wrong?

Is it fully filled with brake fluid ?
i had this on a rebuilt one i just adjusted the spanof the linkage and found it worked fine

You can adjust the clearance by rotating one of the fixings shown in the picture, just can’t remember which one of the top of my head. It is the one the arm pivots on and is actually eccentric. There should be just a little clearance.

There’s no fluid in at the moment.I’ll have a look tomorrow evening to see if I can see which is the eccentric adjuster.Thanks.

Best done finally when it is all filled up with fluid then you will be sure the piston is fully out. The spring should do that now but best to make a final check later.

Brake fluid will be going in in a few weeks. Thanks.

I just did mine this morning on my LM3, the old one was sitting as in your photo, the new one is flush with the end of the M/C. Perhaps 4mm further out, that is without the adjuster and lever in place. I guess adjusting the eccentric will find the correst clearance when the arm is fitted. Mine has an allen key and lock nut on the adjuster, which is where the forward bolt head is in your photo. Had to make up a little tool 19.9mm od, 14mm hole to press the retaining ring in.
Alan.bison2012-11-20 14:15:34

Alan, thanks for that info. It’s interesting that it’s not unusual for there to be a gap between the lever arm and the piston head.I’ve had a look for the eccentric adjuster and there isn’t one. The most forward stud/ bolt is a straight shouldered bolt for the lever to pivot on, and the small (10mm head) bolt behind, has a narrow rod /pin type structure which appears to be there to stop the lever/arm wearing the m/cyl body away. If necessary, I’ll either buy a new arm (£29…ouch) or get the exsisting arm/lever altered with some alloy welding and file it so that the lever sits closer to the piston.

ReggieV2012-11-20 22:13:27

This is mine, 1978 Spada looks like someone might of changed the pivot bolt at some time in the past or the Mk1 leMans doesn’t have the eccentric adjuster?

Yep, mine looks axactly the same as Don-Spadas’.
I assembled the lever and eccentric last night, the lever is only just touching the end of the piston.
Might be cheaper trying to buy/make an eccentric adjuster rather than modifying your lever arm?, or adjust the rod coming from the pedal to take up the play?, not quite good engineering practise but would probably do the job.
bison2012-11-22 08:03:13

Are you sure you do not have the eccentric adjuster somewhere but swapped it for a stainless bolt in a fit of enthusiastic renewal?

Hi Don and Alan, Firstly, I cannot find an eccentric adjuster in my box of bits, and on the S.D. site, it apprears to list a standard M6 X 20mm bolt where the eccentric adjuster fits on yours, for the LM1?Conversely, when I have looked on the SP3 spares list, I cannot find the above bolt or an eccentric adjuster listed.When I have looked again at the bolt head with a rod shank on my M/cyl, it does look “home made” now, but this is what was in the caliper that came with the bike. Also the lever I have fitted is a different shape to the one’s on your Spadas, but I do have a spare lever with an attachment that somebody has bolted on, which looks the same as yours. I am going to see about fitting this (with the attachment removed) either later today or tomorrow to see if it makes a difference? Alan, fashioning an eccentric adjuster may be the way to go.Thanks for your help.

ReggieV2012-11-22 13:38:44

If you were to cut the head off a 6mm (I think) bolt, use a junior hacksaw to cut a slot in one end for screwdriver adjustment, and file the centre part of the shaft to about roughly half of the diameter, offset of course, that would be a good start. When fitted use a self locking nut to hold it in place.


Well it’s now fixed I have fitted my other lever that I had and is pictured earlier in the thread which is the same as fitted to Dons Spada and Alans LM3, and it now fits the M/cyl spot on. I have to say that without the picture that Don put up, and realising that I also had one the same knocking about(albeit with an attachment for some reason…now removed) I probably wouldn’t have thought to try it. There is now a very small clearance between the lever and piston, possibly 10 thou, and all that’s left to do is make the bolt slightly eccentric so that I am able to adjust it if reuired at a later date. It sort of begs the uestion, where does the lever that I fitted and was previously come from? So thanks to you both, another problem resolved, a few to go.

ReggieV2012-11-23 13:40:41

I wonder if that other arm is off a California as the brake arm angles a lot further forward on those models.