Brake Problem

Stuart · #1 1st April 2006, 08:16

I have had a problem with the brakes on my Sporster build and thought i would share the results with you all just in case it happens to you.
I have used the standard bmw master cylinder with the adaptor plate,after bleeding i had little to no brake pedal basically 2 inch travel before any brake pedal!
After examining the system i found that the server actuating rod is 8mm short of the master cylinder piston.

I have resolved this by making a sleeve to fit over the actuating rod and make it 8mm longer now i have a full brake pedal

MartinClan · #2 1st April 2006, 19:46

Hi Stuart

Useful information - could save me hours when I get to that stage. I wonder if it is a "standard" problem or just the combination of bits that you used. Did you use a standard MBW master cylinder? If so what was the part number?

Cheers

Robin

MartinClan · #3 1st April 2006, 19:47

BMW master cylinder (Dyslexic keyboard...)

Stuart · #4 1st April 2006, 22:04

Martin it was the standard bmw master cylinder not sure of the part No. but it came from a 1989 325i Sport and i believe it is the later of the two different types. Looking at the autodata manual the insides of the two units have very much the same fitting to the servo so i guess the problem would be the same for both. To check yours with the adaptor plate fitted to the servo the servo rod should be flush with the outside edge of the plate mine was 8mm short and it looks as though its due to the thickness of the adaptor plate which by coinsidence is 8mm thick.

Patrick · #5 1st April 2006, 22:19

I'll let you know how it goes once I have my pedal box bolted in for the final time and everything connected up properly! I've got the marlin servo and master cylinder.

Stuart · #6 2nd April 2006, 08:14

Patrick
I dont think that you should have a problem as you have the Marlin master cylinder without the adaptor plate so yours should fit all ok.

Patrick · #7 5th September 2006, 21:43

Yes please, not sure why i have the problem as im not using an adapter!

Let me know how much

Thanks, Patrick

MartinClan · #8 6th September 2006, 09:03

Quote:

Originally Posted by Patrick

Yes please, not sure why i have the problem as im not using an adapter!

Let me know how much

Thanks, Patrick

Hi Patrick - are you sure you have this problem as you are not using the marlin adapter? I suggest you check first by measuring. If you use the little sleeve thingumajig and you don't need it the effect will be that the brakes are slightly but permanently on - not good. If you take the master cylinder off the servo you can measure the postion of the plunger in the master cylinder. The corresponding pin on the servo is flush with the flange (the same as the original BMW one). Not a very good explanation but if you take it to bits you will see what I mean.

Cheers

Robin

Patrick · #9 6th September 2006, 09:06

I see what you mean, I'll take a good look at it and let you know!

I've not had time to rebleed the brakes could just be some air int here I guess

Patrick · #10 7th September 2006, 19:50

I've pulled the master cylinder off today and had a good measure up. There is an 8mm gap between the pin and the contact area in the master cylinder. I measured the BMW and the contact area is exactly inline with the mounting flang. With that and the huge bit cut into the mounting flang area im starting to think this is a waste bin reject part...

Im close to buying a BMW master cylinder and using the adapter.

jeremy · #11 7th September 2006, 20:20

Patrick, R U using a metro servo and ford master cylinder presently, without an adaptor plate?

Patrick · #12 7th September 2006, 20:30

im using the servo and master cylinder I ordered from Marlin directly, I don't what the parts are from. Im not using an adapter plate.

Here is a picture: http://www.msportster.co.uk/data/construction224.jpg

Patrick · #13 8th September 2006, 13:16

I've decided to use the BMW master cylinder as my sealing solution on the marlin supplied one will mostly likely not last long and I'll end up with air leaks everywhere again and a bad running engine.

Robin yes please can you please get one made for me too.

jeremy · #14 8th September 2006, 14:32

Hi patrick, it looks like mine which is a rover/mini metro master cylinder and sierra master cylinder and I was told that there is a small area that woul.d need sealed at the cylinder servo junction.

Patrick · #15 8th September 2006, 14:37

Quote:

Originally Posted by jeremy

Hi patrick, it looks like mine which is a rover/mini metro master cylinder and sierra master cylinder and I was told that there is a small area that woul.d need sealed at the cylinder servo junction.

Not sure I would call a gash like that "small" the BMW part has a rubber ring round the flang to seal it, much better

The M20 runs like a dog that's been shot in both rear legs if there's a vacuum leak (no offence to the dog

).

MartinClan · #16 11th September 2006, 12:09

Quote:

Originally Posted by Patrick

Not sure I would call a gash like that "small" the BMW part has a rubber ring round the flang to seal it, much better

I am not sure that you can use the o-ring when using the Metro servo as it sits in a recess in the (BMW) servo - I am going to take a look at mine tonight as I am just getting to that stage. In any case the Metro servo, marlin adapter plate and BMW master cylinder all have flat faces and so it should be easy to seal with a gasket compound or even a paper gasket.

It would be intersting to know what other builders have done on this point?

Robin

holgate86 · #17 11th September 2006, 21:50

I would check your servo, it may have a leaky diaphragm. The master cylinder does not normally seal to servo, with the master cylinder totally removed it should not leak vacuum, ask your fellow builders to confirm it on there builds, it might save you some wasted time and cash.

Brian

MartinClan · #18 12th September 2006, 19:32

Quote:

Originally Posted by holgate86

I would check your servo, it may have a leaky diaphragm. The master cylinder does not normally seal to servo, with the master cylinder totally removed it should not leak vacuum, ask your fellow builders to confirm it on there builds, it might save you some wasted time and cash.

Brian

Just checked mine and the vacuum does pull on the master cylinder side on the Metro servo (has to when u think about it to amplify the force applied to the other side by the brake pedal which is open to the atmosphere). So that means the master cylinder has to seal to the servo or you will get unmetred air leaking into the manifold upsetting the mixture.

Robin

Patrick · #19 9th September 2006, 20:40

Does any one know what marlins solution to this problem is?

Patrick · #20 11th September 2006, 13:09

The hole in the metro server goes all the way in, version 3 of my attempted to seal it was silicon sealer and lump of rubber in the hole. That actually seemed to work for a bit. I had tried various gasket compounds but they all started leaking after a week or so. I run the engine approx 1 a week at the moment.

Im going to eBay the metro one and get a new BMW one.