E30 BMW brake servo..

[djw113uk]

A reasonably common 'upgrade' on the stag is to fit the BMW 3-series brake master and servo. You need to dent the inner wing to get it in.

Since the brakes on my mk2 PI have never been particularly good. (They work okay, but pedal is a bit wooden) and since I acquired a BMW servo for my 'one day' stag, I thought I might fit it to my saloon.

Before I pull out a perfectly serviceable setup, and just a few weeks before we take it on the RBRR, I thought I would see if anyone has already tried it on a saloon, or why it might not fit?

PS - The original master and servo has already been removed and replaced with a Sherpa tandem line setup, so plumbing should be relatively straight forward? Sherpa was 'new old stock', so I just assumed it was in no better order than the PI original. It has nothing to do with the PI vacuum tank as that is long gone too. Now rover v8.

David

[sprint95m]

or why it might not fit?

People always quote E numbers for BMWs, which are meaningless to me, but anyhow
what bore is the master cylinder you have David and what brakes are you using?

Standard Stag BMC is 7/8" bore (22.2mm).

Before going for LDV Sherpa I did consider BMW 5 series (I knew where quite a few rotten ones were lying) but discounted these without even looking at one
because their BMCs are 25.4mm (1").
They Lockheed BMCs fitted to Sherpas were very long-lasting indeed. My friend with the minibus business is dreading the day when they cannot
run their LDVs anymore because they are so much better than the (newer) Fords he has.

[djw113uk]

I have stag rear brakes, Jag 4 pot fronts, and originally standard 2000 master cyl and servo, and then Sherpa master and servo. I think it is a servo rather than master cylinder problem, but unless I raid the 2500s I am not going to get hold of another Sherpa servo very easily.

I understand that the BMW servo has a higher boost ratio, and they are ore readily available. I also assume that as they can be fitted to the stag relatively easily they should be simple to fit to the 2000 too.

I should probably mention that it has always run with silicone brake fluid, so I am thinking I will fit new 4 pot callipers, new rear wheel cyls and the 2nd hand BMW servo and master cylinder all with mineral fluid, then I am not swapping fluid type in anything but the lines.

[sprint95m]

I am thinking you could end up with rather a lot of pedal travel if you use a standard BMW 3 series master cylinder David?

This came up on Google:
Lucky for E30 owners there is a larger master cylinder that bolts right in: The 25.4-mm master from the E32 7-series shares the same bolt pattern as the E30. This is a significant upgrade from the factory 325 and 318is master cylinders, with their 20-or 22-mm bore depending on the year. The factory M3 master cylinder has a 23.8-mm bore, so the 7-series master is an improvement. The larger master bolts right into non-M3 cars, but the M3 requires a slightly different fitting (10 vs. 12 mm) for the master cylinder end of the rear brake line.
This was in relation to fitting huge discs and callipers (for racing?).

Helpfully, master cylinders usually have their bore size visible on the outside.

[djw113uk]

Hmmmm. Thank you for that. I need to find my BMW servo, it is in a box somewhere after the move. Hopefully it will say on it what the diameter is. I think I would prefer long travel with feel, over wooden pedal which I have currently, but perhaps I should look again. The 2500s has very sharp brakes with the Sherpa unit, and the only difference is stag rears and silicone fluid.