MadaboutKitcars

Have now got to the stage of plumbing in the brakes on the M3 based Sportster me and the old man are cobbling together in the ever shrinking garage!! I appreciate this has been asked before, but would like your advice please guys on the Master cylinder conundrum. Have a Metro servo and brake master cylinder souced off the 'Bay for a good price, and would like to know what's the next step. I assume you don't just keep it as is as the master cylinder looks way too puny for the job. All the builds I've seen online seem to replace it with either an E30 one using an adaptor plate or have seen a Sierra one used also. Your advice as always would be greatly appreciated.
Also on hanbrake cable shortening, I would like to keep the cables in the rear hubs and shorten the lever end of the cables if I can, is this advisable? And if so what's the best method please?

Progress report: Rear end 95% there, all bolted in and looking lovely and hammeritey! Front end 95% there, using the new Marlin supplied uprights with integral mounted wing stays, had to buy new Wilwood 4 pot calipers though and use a 6mm spacer to accommodate the 28mm front discs off the donor M3!! Will try and post some piccies soon on here or on my Flikr account, keep getting to the end of the night, and forgetting to take photos.......Must try harder!!

As always, thanks in advance for your responses, things are gradually coming together (but not quick enough for the wife though!!! )

Rob

I used a standatd E30 master cylinder (new) along wih the Marlin supplied adapter plate for the Metro servo. I had to make up a spacer for the pushrod the same length as the adapter plate thicknes.

The problem I find with the brakes is that the original BMW has a 6:1 servo and the Metro is just 1.6:1 which means that you have to push pretty damn hard to get any real stopping power. I suspect that the brakes would be much better with softer pads than the standard E30 ones.

Robin

Hi Robin, thanks for the advice, seems to be the preferred method having looked at a few build diarys.
Terry at Marlin replied to my query with "P100 master cylinder (Ford). This will be fine. Yes we can supply an adapter plate no probs." So may go that route, but need to clarify if this needs the pushrod length adapting too.

Thanks

Rob

From Patrick Short's experience, then I think the answer is yes, you will need a pushrod lengthening adaptor, but its quite easy to make.
I think you should have been supplied the master cylinder adaptor as part of your kit.

http://www.flickr.com/photos/58068042@N07/6035878189/in/set-72157625905139194

Patrick and Robin's build sites show details for shortening handbrake cables at the lever end.
But, Ian has shortened his at the brake shoe end...

http://www.flickr.com/photos/58068042@N07/5964953585/in/set-72157626910079218

Rob,

I have used the P100 Master cylinder, and yes, I have had to make a small extension for the pushrod. You'll have to make a bigger one if you use the adaptor plate. I couldn't find any good reason to use the plate (assuming you are using a remote resevoir) so I have mounted the master cylinder straight on the servo.

You'll need some metal putty to form a smooth surface and a good seal between the master cylinder and the servo. Have a look at GOO's build site. He gives a good description there.

http://www.greatoldone.co.uk/Gooster/Build_Diary/Entries/2007/2/27_Plumbing_The_Front_2.html

Nigel

I was going to go down the route of a remote reservoir, but felt the Ford OEM reservoir mounted direct to the master cylinder would look neater.
I made my own adaptor plate, to rotate the master cylinder to vertical, and then fitted the Ford reservoir.
I had to add a spacer between the servo and master cylinder, and used another push rod to get the cup shaped end. I also welded an extension on to the rod that connects to the brake pedal as I was not keen on Marlin extension arrangement with a potential double pivot and acts in compression.

http://www.flickr.com/photos/mikes_bmw_marlin_cabrio/3736409890/in/photostream/

Following on from Mike's point about the double pivot - this actually happened to me, resulting in brake failure and a replacement servo. The opinion of the mechanic who fixed it for me was that it was a design fault.
Tim

Whoh ! - I bet that was scary! I think your mechanic is right. Having two pivots that are only loosely pinned,not bolted, acting in compression is a design fault and is asking for a problem. Marlin's whole pedal box assembly leaves a lot to be desired, with the accelerator and particularly the clutch pedals only being cantilever supported from a very thin gauge structure.

How did you/your mechanic deal with the problem?

Mike

Fortunately happened during testing so no harm done. Except to the servo rod of course

I believe my mechanic welded one end of the joining plate so it became a single pin system. Not very good for translating angular motion into linear motion but the tolerances are such that you can just about get away with it.

Tim

I found that the biggest problem was that the whole bulkhead flexed when standing on the brakes. It's only sheet metal with nothing in the way of re-reinforcement. I found a big improvement was to bolt a 1" box section accross the entire width of the top of the bulkhead picking up on two of the bolts used to mount the pedal box. I put it in such a position that the closing plate for the rear of the fibreglass dash top also picks up on it.



Robin

Thanks for all your tips guys. Will do my best to source a p100 master cylinder and will shorten the cables at the lever end as the rear is on so don't want to have to dismantle it if I can help it!! Will have a good look at the pedal box side of the servo and may well opt to remove the two pivot "design feature" AND look at strengthening the bulkhead too!! The list of jobs grows longer............