help setting up booster delete and retain ABS

[Massive Lee]

As a very short technical note. If using OEM calipers and swapping the original differential bore MC, I strongly suggest to remove the OEM bias valve which is a pressure limiter. Otherwise the rear brakes will be very lazy on high pedal pressures, putting more than needed work on the front brakes and making the car unstable on hard braking. Here's the (probably) 10 years old graph that show what that valve does.

1 bar is roughly 15 psi



You can replace it by an adjustable one. But never put both in line. ;-)

[1990m3]

I’m reviving this old thread.

For those of you that track your cars, do you have any issues?

I have a Massive setup with Wilwoods up front and stock rear, both running off of an E32 25mm master cylinder and E21 booster. I’m very happy with this setup, but I’m considering going to ITBs, and this would interfere with my booster. I’m not a big guy, so I don’t have gorilla-legs. [emoji3]. Any recommendations on if it’s worth it and what MC I should use?

Thanks!


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I ran the massive boosterless setup with a 25mm master cylinder and it was very difficult for me to stop the car. I literally used all my leg power and couldn't get them to grab, I found myself coasting into brake zones at the track and had absolutely no confidence. I have the booster back in the car now and it's working well.

If you go boosterless you need to reduce the size of the MC, that was my mistake. This was a track only car BTW.

[digger]

Looks like I never updated after I sorted it all out... I actually returned to boosted brakes. New 944 booster feels really awesome. I was doing far more street driving than I intended, and never really got the strong brakes I wanted, especially for the street. Also I think I misunderstood the function of the bias valve when I initially installed it. It's only useful if you have MORE rear bias than you want, you can cut pressure to the rear to decrease it. At the very least, make sure the oem bias valve is removed.

If I understand correctly, there are two basic ways to increase rear bias; increasing mechanical advantage. Either decrease the size of the rear MC, or increase the total size of the rear caliper piston surface area.

That said, with my wilwood front kit, rear oem calipers/disks, and oem 17/22mm MC, bias is not that bad. ~67% front iirc.

I'm testing out a new setup soon though utilizing a Nissan z32 rear 2 piston caliper and a Toyota ma61 rear vented disc which ought to drop front bias to ~60%.

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do you think the massive twin M/C kit booster delete be better for the street?



or is the force/travel relationship going to be the same (all else equal)

[Beej '86 325es]

I’m reviving this old thread.

For those of you that track your cars, do you have any issues?

I have a Massive setup with Wilwoods up front and stock rear, both running off of an E32 25mm master cylinder and E21 booster. I’m very happy with this setup, but I’m considering going to ITBs, and this would interfere with my booster. I’m not a big guy, so I don’t have gorilla-legs. [emoji3]. Any recommendations on if it’s worth it and what MC I should use?

Thanks!


Sent from my iPhone using Tapatalk

[Sh3rpak!ng]

...from what I measured, claiming accuracy of more than one significant digit's just
not what happens in the real world.

So yes, the theory's good, and that's a good explanation, but it's not that repeatable-
sometimes it'll pull 50% of the pressure, but the next time (let's say you stab the brake
in a last of the great late- brakers attempt)
it'll pull 40%, or 60%.
I came from a bias- bar car that's dead- nuts stable to a Pro3 car where we can only
run a hydraulic bias adjuster.
I had lots of trouble getting the rears under control, because I kept trying to use rear brakes
as much as I could- and then, I'd get Brevilled- "just a bit more" and end up asswise.
Eventually, I backed them way off, and went faster...

t

Thanks for the real world feedback! this is good to know

Sooo. I've seen this thread for a bit but didn't engage. Why do you want to run abs? And why would you want to run abs after a BB delete? especially when you've changed MC, and are running prop valve?etc?

Well, mostly because I still street drive the car quite a bit and I don't trust people on the road in LA. I'm also not confident in my threshold braking skills. All that said, I've already returned to boosted brakes. And my purpose for the car has changed from a "daily" to a weekend only car, so if I were to do it again now I'd probably take a different approach.

[squidrope]

Sooo. I've seen this thread for a bit but didn't engage. Why do you want to run abs? And why would you want to run abs after a BB delete? especially when you've changed MC, and are running prop valve?etc?

[TobyB]

...from what I measured, claiming accuracy of more than one significant digit's just
not what happens in the real world.

So yes, the theory's good, and that's a good explanation, but it's not that repeatable-
sometimes it'll pull 50% of the pressure, but the next time (let's say you stab the brake
in a last of the great late- brakers attempt)
it'll pull 40%, or 60%.
I came from a bias- bar car that's dead- nuts stable to a Pro3 car where we can only
run a hydraulic bias adjuster.
I had lots of trouble getting the rears under control, because I kept trying to use rear brakes
as much as I could- and then, I'd get Brevilled- "just a bit more" and end up asswise.
Eventually, I backed them way off, and went faster...

t

[Sh3rpak!ng]

And just because it's both pertinent and not particularly obvious,
there is an early 318 master that has a slightly stepped bore (19/20? I forget).
It gives 'just a bit more' rear brake, if plumbed properly, and then the bias valve
can be used to prevent rear lockup, if needed.

I found different valves worked differently- some are pure pressure limiters, others
have a 'knee' above which they reduce pressure at a ratio, and few were particularly
consistent. As in, a stab at the brake got you a different rear pressure than a gentle
squeeze did.

hth,
t

That't good to know. Found the PN for the 19/20 MC 34311156273

And regarding the prop valve, this is a good explanation:

"one helpful thing to keep in mind when setting them up is the knob/lever adjusts the SPLIT POINT PRESSURE.

Before the split point rear pressure rises 1:1 with front pressure. After the split point, rear pressure rises 0.57:1 with front pressure (on all the common proportioning valves I've seen, Summit, Tilton, Wilwood etc.). So the least amount of bias you can have is the rear pressure being 57% the front pressure with the split point all the way down. As you raise it up you change where the "knee" occurs so your rear/front bias will be greater than 57%, but falling at increasing pressure. This is an inherently stable setup, since more brake pressure without a lockup means more weight transfer, so your bias moves in a "safe" direction for any setting that performs well in the dry."

[TobyB]

And just because it's both pertinent and not particularly obvious,
there is an early 318 master that has a slightly stepped bore (19/20? I forget).
It gives 'just a bit more' rear brake, if plumbed properly, and then the bias valve
can be used to prevent rear lockup, if needed.

I found different valves worked differently- some are pure pressure limiters, others
have a 'knee' above which they reduce pressure at a ratio, and few were particularly
consistent. As in, a stab at the brake got you a different rear pressure than a gentle
squeeze did.

hth,
t

[Sh3rpak!ng]

Looks like I never updated after I sorted it all out... I actually returned to boosted brakes. New 944 booster feels really awesome. I was doing far more street driving than I intended, and never really got the strong brakes I wanted, especially for the street. Also I think I misunderstood the function of the bias valve when I initially installed it. It's only useful if you have MORE rear bias than you want, you can cut pressure to the rear to decrease it. At the very least, make sure the oem bias valve is removed.

If I understand correctly, there are two basic ways to increase rear bias; increasing mechanical advantage. Either decrease the size of the rear MC, or increase the total size of the rear caliper piston surface area.

That said, with my wilwood front kit, rear oem calipers/disks, and oem 17/22mm MC, bias is not that bad. ~67% front iirc.

I'm testing out a new setup soon though utilizing a Nissan z32 rear 2 piston caliper and a Toyota ma61 rear vented disc which ought to drop front bias to ~60%.

Sent from my SM-G920T using Tapatalk

[potatomash]

How did you find the rear bias after all this? Do you think the prop valve actually allows more rear pressure? Got same setup and wondering if prop valve worth is going to help me or not

[Sh3rpak!ng]

https://www.amazon.com/Speed-Bleeder.../dp/B003TL2QNG

Track only: Raybestos ST-43 front/45 rear. The slightly more aggressive rear pad really helped the brake bias.

Thanks, figured it was track only

[e30_302]

https://www.amazon.com/Speed-Bleeder-Thread-length-Individually/dp/B003TL2QNG

Track only: Raybestos ST-43 front/45 rear. The slightly more aggressive rear pad really helped the brake bias.

[Sh3rpak!ng]

You can get the speed bleeders for a Wilwood caliper, I have them. Or figure out what size the bushing is and see if there's a speed bleeder to match.

But back to the master cylinder, I have a 20.6mm from a Fox Mustang and it's great. Don't even notice that it's un-boosted now.

hmmm any chance you have a part number or info? Here is the listing on the wilwood site for replacement wilwood bleeders: 220-0627 described as for "Calipers w/ 1/8-27 Bushing & 1/4-28 Bleed Screws". My concern is that since the caliper is aluminum, repeated tightening and loosening of a bleeder directly mounted into the aluminum would wear out the threads over time

What pads are you running? And do you drive on the street or only track?

[e30_302]

You can get the speed bleeders for a Wilwood caliper, I have them. Or figure out what size the bushing is and see if there's a speed bleeder to match.

But back to the master cylinder, I have a 20.6mm from a Fox Mustang and it's great. Don't even notice that it's un-boosted now.