Marlin BMW Cabrio Brake Master Issue

[P_Seabrook_Harris]

I urgently need help as my brake master cylinder needs replacing. Seems the standard Sierrs item is too short for marrying up to the servo snd pedal set up.Any ideas folks???

[danny_nelson]

If you have the standard Sierra servo fitted Then the master cylinder from the Sierra range should be fine Peter.

[danny_nelson]

Sorry Peter I should have asked which servo is fitted

[A_Hogg]

Hi Peter, have messaged you via facebook

[Neil Johm Kirk]

Hi Peter, have messaged you via facebook

Just out of interest, why has this thread moved to Facebook messages? I'm sure there are people out there who would have been interested in this issues resolution. I know I would.

[A_Hogg]

In answer to that - I owned the Cabrio prior to Peter and did a fair amount of work on that one and consequently Peter has stayed in touch via Facebook messenger. He contacted me over the origin of the BMC on the car which I thought was standard Sierra as I recalled changing one and found the purchase on my e bay account. However the timing was much later and the Cabrio was already in Peter's hand so deduced it was for my last Cabrio . It appears that both the items obtain by Peter were incorrect for different reasons and the garage doing the work have informed him that it's 23.8 mm bore NOT the standard 22.2mm .He has ordered a repair kit to suit . I think the 23.8 mm cylinder MAY be from an XR4i but at present unable to find web site to confirm. I'll update when more info is obtained so don't feel left out!

[A_Hogg]

I should also add that I upgraded the Cabrio to a dual diaphragm servo instead of the original Metro unit which was useless

[A_Hogg]

Bit more research and '82 - '86 Sierra xr4i and xr4x4 variants with bendix cylinder were 23.8 mm bore

[Neil Johm Kirk]

In answer to that - I owned the Cabrio prior to Peter and did a fair amount of work on that one and consequently Peter has stayed in touch via Facebook messenger. He contacted me over the origin of the BMC on the car which I thought was standard Sierra as I recalled changing one and found the purchase on my e bay account. However the timing was much later and the Cabrio was already in Peter's hand so deduced it was for my last Cabrio . It appears that both the items obtain by Peter were incorrect for different reasons and the garage doing the work have informed him that it's 23.8 mm bore NOT the standard 22.2mm .He has ordered a repair kit to suit . I think the 23.8 mm cylinder MAY be from an XR4i but at present unable to find web site to confirm. I'll update when more info is obtained so don't feel left out!

Thanks for all the detail, its appreciated.

Reason I'm so interested is I too own a BMW engined Hunter (Cabrio in all but name) which has a clutch where the pedal movement is the equivalent of standing on a brick. I'm looking for all the clues I can to resolve the issue. BMC is one potential area.

[A_Hogg]

Presume you have the Marlin pedal box with the master cylinder internal and above pedals?

[Neil Johm Kirk]

Presume you have the Marlin pedal box with the master cylinder internal and above pedals?

Exactly what I have. I also believe the gearbox is not a type 9 but some Land/Range Rover thing. I had heard that may people consider a Metro V6R4 MBC but have heard conflicting stories on whether it is actually suitable.

[A_Hogg]

Is the engine from E30 series 325i? Gearbox would probably be Getrag 5 speed or possibly ZF. On the Cabrio I had the clutch master cylinder was fed from a remote reservoir mounted on the engine side of the bulkhead and fed the cylinder via braided stainless hose - it was a pig to replace . I seem to recall using a Willwood cylinder of the same bore . If you go bigger on the bore size you'll displace more fluid but pedal effort increases and vice versa. Too small and it may not more the slave cylinder enough to disengage clutch. Slave cylinder on mine was standard BMW E30 series 325 and easy replacement. Try posting some photos of layout so we can see what you have.

[Neil Johm Kirk]

The engine is a 325i; believed to have been new when installed (2006). The build details say its an R380 box but the reverse gear position doesn't match for an R380. I will try to get down to garage and get some interesting piccies. I may take off the side panel and access plate anyway (needs doing to make progress). Then all will be revealed.......

[A_Hogg]

Not something I've tried but have you thought of adding a small servo [standalone type] to help with clutch pedal pressure? Guess finding somewhere to locate it might be a drawback!
Just to add - my wife never drove that cabrio due to heavy steering and clutch pressure but I never had an issue with either and at 5ft 9in at a push and maybe 10 stone wet through probably says all you need to know!

[martinclan56]

Nearly all of us that built Sportsters back in the day had a similar problem. As I recall the original BMW pedal box had a strange over centre arrangement with a massive helper spring for the clutch pedal. The Marlin pedal box of course doesn't have this.
Most of us got around the problem of needing to be Arnold Schwarzenegger to operate the clutch by some careful fettling of the Marlin pedal box. As I recall, amongst other things, I moved the point at which the push rod attaches to the pedal.
You still needed a good strong left leg though but at least it was doable!