found a perfect master cylinder for our swap boosters and stock brakes

[2.5-12]

I was digging through my parts pile and found a brake booster that looked very similar to the BMW 530i/540i/740i unit that so many of us use in this swap, but that V8 booster isnt sized correctly for the smaller pistons of the stock E30 brakes, giving a very short and hard pedal travel with somewhat poor threshold power.

this master cylinder i found fits perfectly in this Lucas BMW V8 booster and not only has two M10x1 fittings instead of one M10x1 and one M12x1 like the 540 master, it also is sized perfectly for E30 stock brakes.

it is a Mercedes-Benz Girling master cylinder found in the early 1990's 190E 2.6 (1992 for example here).

pictures show fitment. its EXCELLENT and its CHEAP.

the equivelant piece on BMW is the 325iX master cylinder and those range from 60-100 to buy. these are about $25 shipped for a nice one.

530i master left, Mercedes 190 master right.


530i master left 190E right


Mercedes 190 master on the 530i lucas booster


BMW remote reservoir plugged in to the 190E master and bolted up.



fitment in the car is great too fits perfectly between both headlights, plenty of room for the line.

this master also has a cast block built in to it for a second Front line to be drilled and tapped for non-ABS cars, but I opted to just run a single hard line to a T fitting (from the back of an E30) to split up the front brake pressure back at stock location.

hope this helps some of you! (especially those of you on budget builds)

[Ether-D]

That looks effing great. Good job.

[bmk]

What are the chances this will work on the massive booster delete?

[2.5-12]

its the same dimension where it counts as a 540i or iX master, so it should work for a booster delete just the same.

[M3 euro ltw]

Image is not posting: It is centric part number 130.35007
It states master cylinder bore is 25/19mm, pushrod 1.91 (the feature you like I suspect), and both ports 10mm

The centric website is awesome for looking up specs on different masters.

These are the specs for the master you're suggesting. Just a quick look at 325is examples of masters show some were 24/24 and some were 23/20. I would be very reluctant to use this particular master on a car that started with a 24/24

Working the math on a stock E36 M3 95 for example, they start with a 25/25... and the bias to the brakes mechanically is 68% to the front... excellent front bias, the ABS is designed to work with that and expects to make corrections and see certain results. Throwing the Merc master on there with a 25/19 bias changes the mechanical bias VERY much to the rear and it ends up 55% front bias only! That is a huge difference and one should not be surprised if they start increasing their braking distances, locking up the rears prematurely and not getting effective ABS function.

If you started with a 23/20 (likely 61.6% front bias), it still drops to 55%... a big change.

These things matter and can really screw up a car's braking.

Without having specifics about a 1992 190E brake set up, knowing that they used this master, it speaks towards probably having a small rotor on the rear or poorly chosen calliper, so they had to increase the bias to the rear of the car via the master to get the car to brake well. I'm quite certain the math for the 190 did not yield a 55% front bias back in 1992. It is only recently that the advanced systems move the bias back for a variety of reasons, in particular advanced EBD capabilities. But your E30 doesn't have that and you should seek to preserve the front bias to brake safely and operate within the parameters of ABS if you have it. If you don't have ABS, then all the more reason to preserve that front bias.

out of curiosity, I checked the 190 2.3 master for same year, it is a 7/8 front and back, basically 22.2 mm. It would not mess up your bias if you started with a 24/24... but it would be a softer pedal, more travel. Still would stop more effectively than 55% bias though, and fit at least.

Oddly enough, looking up 325ix it seems that was a 22/22 master.... so maybe just look for the 7/8 version from the 190 2.3 cars and it will in fact be fine given that most 325ix brakes seem ok.

[2.5-12]

the 2.6 190E master is working very well in the car for me. I have a 2.3 master as well I could try I suppose.

89 560 SEL master also fits, but thats a MUCH larger bore.