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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
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?
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.
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.
I am going to have alook at mine. My car donor car had ABS so it means the master cylinder has two ports. I beleive non ABS cars have a master cylinder with three ports - not that this makes any differnece but it means there must be at least two differnt types.
Stuart - please could you tell me how you connected up the remote reservior? Did you get some bits from Marlin or what did you do?
Stuart,
I seem to have the same amount of free play in mine, but have not filled the system with brake fliud so it's a little difficult to tell. I am using a BL metro servo, BMW master cylinder and the Marlin supplied adaptor plate.
I think I will wait untill the barkes are bled before taking any further action.
Patrick,
I have fitted the rear brake compensator removed from my donor, but no idea if this is correct. (My logic was to replicate the BMW system)
I also have rear drums, not discs, as my donor was a 320i.
You don't want your rear wheels locking up before the fronts!
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.
Its turned out that i have the exact same problem. Servo & master cylinder from Marlin. Additionally the master cylinder has not form of O ring or seal - in fact it has a big hole between it and the servo. This cause very rough idle on the M20 as the vacuum system is not sealed. I'm now on my 3rd gasket atempt so make is seal. I'm getting close to sending the marlin cylinder to parts bin heaven and getting a BMW one.
EDIT:
Before ripping things to bits (now that i have a decent vacuum seal) im going to re-bleed the system. I found a small leak at the T piece and think there may be some air in there. After that hopefully the pedal will feel better.
How are you finding the E30 stock brakes on the Sportster? I keep having the little voice in the back of my head telling me to upgrade the fronts to wilwood and get some new calipers for the back
Just checked mine - same problem. I need a sleeve/spacer to add about the same thickness as the Marlin adapter plate - about 6mm in my case. Looks like a trip to the welder I use who also has a small engineering workshop. Anyone else want one while I am at it?
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.
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.
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.
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.
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 ).
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?
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.
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