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Old 10-22-2018, 08:19 AM   #1
Digitalwave
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E30 M3 5 lug conversion - Brake Bias

I'm running E30 M3 brakes on a non-M, with the original-to-the-car 22/17mm master cylinder. As I understand, E30 M3's had 23/23mm MC's. I am running PFC 08 pads all the way around. If I am understanding MC sizing correctly, then I am running much more pressure in the rear than intended for M3 brakes, correct?

My car gets a little squirrelly in the rear end under heavy braking. The back end starts to dance around a little bit, making trail braking difficult.

Could I try staggered pad compounds, or do I need to switch to a matched MC sizes f/r? I am happy with the pedal travel and modulation as-is, but would like to balance out the braking f/r better than it is now.

PFC makes 01, 06, and 08 for the front, and 08 and 11 for the rear. I think my only option for more bite in the front or less bite in the rear would be to move to 01's in the front, as I think the 11's are more aggressive than the 08's for the rear.
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Old 10-24-2018, 10:34 AM   #2
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Do you still have the ABS hooked up?

If not, yeah, I'd go to a straight master (and it doesn't HAVE to be 23/23- 22/22 might
give better modulation, at the cost of pedal travel. It's a 'feel' thing)

I'd get the hydraulic ratios right, rather than mess with pads, as different pads
will respond differently to different amounts of heat, and you run the real chance
of getting brake bias that changes with how hot your brakes are.
(this also happens with uneven cooling, too, which is always something to pay attention to)

hth

t
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Old 10-24-2018, 10:43 AM   #3
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Thanks for the input Toby. I am running ABS still. The M3 MC is 23.8mm, seems the closest I will get to that is likely the E32 25mm MC. I'm weary of the increased pedal firmness, but I would say my pedal travel is pretty long as is, so it might be beneficial.
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Old 10-25-2018, 08:20 PM   #4
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My experience has been that on paper, the master makes a big difference.
On the track, though, while it's noticeable, it's just not a big deal once it's
'not too soft'.

So unless I'm way off, here, the stock later ABS system uses the smaller master
on the fronts, giving more front bias before ABS kicks in. Once the fronts start to slip,
you usually have a lot of rear left.
Oddly, the earlier abs (until 88 or so- realOEM's numbers for masters seem to be accurate)
on an e30 had a matched 22.5/22.5 bore, and yet, the early and late ABS seem to
perform about the same.
So you COULD try the early master, and see if the late ABS handles it ok.
Or any other matched f/r master.
I have to use stock calipers, but use an early
318 master- it has a slightly stepped bore, and that works well to get
a little more initial brake bite to the rear, then a proportioning valve
to help with premature lockup,
because
an e30 does tend to instability under braking, as it loses camber as it loses rear dive.
This has been true since the 2002- the trailing arms just aren't ideal suspension elements.

hth,
t
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Old 10-29-2018, 06:20 PM   #5
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FWIW when you start going fast in a non-aero e30, the rear gets squirrely no matter what you do. Just learn how to counter steer it and you will be'aight as they say down in the south. Dont blow too much money chasing a byproduct of actually going fast (most people think they are going fast but get scared when they start to feel the e30 move around, and assume thats the limit).
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Old 11-03-2018, 05:14 AM   #6
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Quote:
Originally Posted by Skafrog View Post
FWIW when you start going fast in a non-aero e30, the rear gets squirrely no matter what you do. Just learn how to counter steer it and you will be'aight as they say down in the south. Dont blow too much money chasing a byproduct of actually going fast (most people think they are going fast but get scared when they start to feel the e30 move around, and assume thats the limit).
In general I agree, the rear is always a bit squirrelly in my e30 race car. Iíve been trying to tune it out but havenít been successful yet. 15 years of racing an e30...
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Old 11-04-2018, 09:56 AM   #7
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Rake plays a significant part in the squirrel behavior, we've found up here...
...but if your back brakes lock first, it's always bad!

heh
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Old 11-04-2018, 04:45 PM   #8
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Have you gotten rid of the little rear brake bias valve thing? Or atleast replace it with an adjustable willwood valve
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Old 11-05-2018, 01:18 PM   #9
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I reduced the rake in my car, and it helped some. And I understand and agree that the back end of an E30 is inherently going to be squirrelly, and I have noticed more as I've gotten faster. I do suspect there is still a bias issue, since the M3 calipers were intended to be used with a 23/23 MC. I am still running the stock bias valve in the rear.
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Old 04-26-2019, 09:22 AM   #10
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Just wanted to update this thread now that I have had the car on the track for 3 events with the 25mm E32 master cylinder. The brake bias is MUCH better, and it really transformed the braking on the car. I can brake much more aggressively overall, and it especially increased the ability to trail brake. If you have a non-M with an E30 M3 5-lug swap, I highly recommend changing to this master cylinder.
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