Brake Pedal Feel Issue

[MasterKwan]

For subaru's, they sometimes remove the booster and use a spacer instead. In that way there's a direct connection between the pedal and the MC. That's why I was wondering about pedal effort with no booster.

You know, the fact your brakes rattle suggest your real problem is that the pistons are pulling back into the caliper too far.

http://www.summitracing.com/parts/WIL-260-1874

Residual pressure valve. Designed to keep the pistons pressing on the rotors slightly. Wonder if that might change the pedal travel thing.

[Brent 930]

^I was looking into that at one time. The easiest way to incorporate it into the system would be at the front brake lines someway. So you would need one for each corner.

[Nicklle36]

I'm having a similar problem here.
Setup is M3 MC, M3 front brakes, e46 328 rear brakes (294mm vented).
I'm using Brembo plain rotors all around, Calipers rebuilt both front and rear 4k miles ago, front calipers use stainless pistons from BW.
Fluid is ATE, alternating between 200 and superblue.
Boosted check-valve is new.

On the street I'm using PBR Metal Masters. Very hard pad compound, extremely long life. Pedal feel is ok, I would say less boosted than my gf's Mazda3, heel&toe goes well.

On the track I'm using PFC97 rears and on the front either PFC97s or 01s. They are fairly used, probably have 30% left, but I'm using them with spacers (old pad plates if that makes any difference).
The 97 fronts have more meat left than 01s, but the 01s produce a better pedal feel.
I have also once shimmed them to the point where the total thickness of pads+shims was equal to brand new pads and the piston was completely pushed in. This was actually no better, which leads me to believe the problem could be related to pad compound vs rotor?

Also I've read a number of posts pointing to the direction that the system might be over-assisted? Has anyone tried using a smaller booster hose? Not half the size, but maybe 30% smaller. Wouldn't that decrease the boost applied to the booster and improve pedal feel a bit?

[TXRFan]

Also I've read a number of posts pointing to the direction that the system might be over-assisted? Has anyone tried using a smaller booster hose? Not half the size, but maybe 30% smaller. Wouldn't that decrease the boost applied to the booster and improve pedal feel a bit?

I suspect the only thing that will do is hurt the booster recovery. If you stomp the pedal several times quickly you can run out of boost. If you make that hose smaller, it will take longer for the booster to recover from a pedal operation. Sadly, I believe the only way to alter the boost is to disconnect the booster completely or alter the internals.

-Mike

[LVP]

That's where I'm at - a smaller hose or valve on the line just cause you to run out of boost on subsequent pedal presses. With manual brakes, the travel is just the same, but the leg effort required is considerably higher.

I'll figure it out at some point, I just haven't had time to get a booster and rip it apart. I have two old sled motors to rebuild and steering rack to replace before I get into boosters. Whenever I do, I'll post what I find. Cheers.

[ScotcH]

Update on this, since I just worked on it in our e36.

Basically, the booster has a shitload of moving parts in it, all which contribute to a low pedal. There are joint, and interface, and in no way is the rod coming off the pedal connect to the rod pushing the piston on the MC. There was about 1/4" slop in the rod before anything happened on the MC side. Considering where the rod attaches to the pedal, that's probably a good 1-2" of travel before anything happens.

We got rid of the booster, and fabbed a bracket to hold the MC. Thereaded the clevis rod that attaches to the pedal, used a coupler nut (2" or so), and 3/8" hardened allthread on the other side to push the MC. It's adjustable, and directly connected between MC and pedal.

Now even with this setup, there is probably around 1" of travel in the pedal before the brakes start grabbing ... this seems to be internal to the MC, but it's significantly less than what was there before. Once the brakes start grabbing, there is no more pushing ... pedal just stops.

So, it seems that the booster can indeed be culprit ... for racing and assuming your class allows it, get rid of the booster and have happy brakes again

[NeilM]

Basically, the booster has a shitload of moving parts in it, all which contribute to a low pedal. There are joint, and interface, and in no way is the rod coming off the pedal connect to the rod pushing the piston on the MC. There was about 1/4" slop in the rod before anything happened on the MC side. Considering where the rod attaches to the pedal, that's probably a good 1-2" of travel before anything happens.

That's interesting. I've never looked inside a booster, and since it's an "it either works or you replace it" sort of a thing I'd bet not many people have. Is there any scope for tightening up that internal slop with replacement bushings or such?

Neil

[ScotcH]

That's interesting. I've never looked inside a booster, and since it's an "it either works or you replace it" sort of a thing I'd bet not many people have. Is there any scope for tightening up that internal slop with replacement bushings or such?

Neil

Possibly, but taking the booster apart is probably a "it's now garbage" type of operation ... You might be able to reassemble it, but I don't think I'd bother.

[LVP]

Have your got any pics of the install or what you fabricated? This is what I suspected. I didn't have time to pull out the booster and tear apart. You obviously have full manual brakes now.

Thanks for sharing!

[E36forever]

Update on this, since I just worked on it in our e36.

Basically, the booster has a shitload of moving parts in it, all which contribute to a low pedal. There are joint, and interface, and in no way is the rod coming off the pedal connect to the rod pushing the piston on the MC. There was about 1/4" slop in the rod before anything happened on the MC side. Considering where the rod attaches to the pedal, that's probably a good 1-2" of travel before anything happens.

We got rid of the booster, and fabbed a bracket to hold the MC. Thereaded the clevis rod that attaches to the pedal, used a coupler nut (2" or so), and 3/8" hardened allthread on the other side to push the MC. It's adjustable, and directly connected between MC and pedal.

Now even with this setup, there is probably around 1" of travel in the pedal before the brakes start grabbing ... this seems to be internal to the MC, but it's significantly less than what was there before. Once the brakes start grabbing, there is no more pushing ... pedal just stops.

So, it seems that the booster can indeed be culprit ... for racing and assuming your class allows it, get rid of the booster and have happy brakes again

This is what Lee did from Massive for the E30. Makes sense.

[ScotcH]

Have your got any pics of the install or what you fabricated? This is what I suspected. I didn't have time to pull out the booster and tear apart. You obviously have full manual brakes now.

Thanks for sharing!

I can get some pics, but it's nothing special. I cut the flat suqare part from the booster that bolts to the firewall, welded 4 ~3" tubes at each corner to make a spacer, and a flat plate on the other end to bolt the MC to. The rod is about 5" long total, resued the clevis part that clips on to the pedal, and added about 3" 3/8" all-thread rod coupled with a coupler nut.

Would be way prettier to have a piece machined, but this was free and took about an hour to fab.

[TOOLEAN]

I can machine up a small batch of parts for us, if we can collaborate on the design, or if I can get my hands on a unwanted booster I can do the design work....

Just trying to help out. Let me know, Nate.

[=BA=]

Would be nice to know any track results actually.

Since it will require a very high amount of pedal pressure to brake I would think.

When my car is not running the pedal is rock solid, but you get more travel as you start the car (as it is now assisted obviously) but as you are not getting travel you are not building much pressure either, I would think.

[LVP]

I'm trying to get my hands on a donor booster so I can dissect it to see if it is fixable, or else, design something up that can be replicated. I posted on the max forum in Ontario, but I'm looking for a donor booster in Southern Ontario for this experiment. I have a couple of months to sort it out, but the sooner I can get into it, the better. I'll keep this thread updated with any progress I make as well.

I put a valve in the vacuum line to the booster, so I know what non-boosted brakes feel like. Seeing as my track car is street legal and drives to/from the track, this poses a slight issue. Worse case, I'll eliminate the booster, as this has been the only thing on my car that really pisses me off. For the rest, the car handles like it's on rails . My e30 M3 friends really dig me for my crappy brakes. I have often considered trading my e36 for an e30 just because of my brakes. That pisses me off even more, so I have vowed to fix them. But I still love the e30 M3's......

Cheers!

[Demon Speed]

Maybe I missed it somewhere in the 7 pages but has anyone adapter a brake booster from an E46 to an E36? Jags that Run site has some info stating that the e36 boost has a lot of flesh due to how it's bolted to the firewall, translating into spongy pedal.

[ScotcH]

Update after Sebring winterfest. The un-Boosted setup is FANTASTIC!!!! I don't know why this isn't a popular mod. The pedal feel, perfroamce, and general braking system was about 95% as good as a full tilton setup in the other car. We were blown away. Very easy to modulate, almost impossible to lock up (you have to really stand on the pedal), and perfect pedal feel ... no slop at all. you put your foot on it, and the brakes start working. Simple, cheap (free, except time), and easy to do. This would also very likely work perfectly well with the ABS still intact for rain or whatever.

Anyway, if your rules allow it, do it. Do it now. Ditch the booser and enjoy proper race car brakes finally!

[flink]

The un-Boosted setup is FANTASTIC!!!!

hm, that's interesting. I feared the pedal effort might be too high because the master cyl is sized assuming that assist is available. Do you happen to know what diameter is used on the stock master cylinder?

[E36forever]

Again this is what Lee from Massive did for the E30. Maybe he can make one for the E36 and E46.

In the mean time what was the break down of parts to do the conversion?

Thanks

[VengeanceM3]

2 years after my initial post it sounds like we may actually have a viable solution! Is the feel with booster removed substantially better than with vacuum to the booster shut off? I imagine so as your now removing all the crap between the pedal and master. I have my original booster i would be willing to donate for some further r&d of a solution...

[E36forever]

^It must be a sizeable difference in feel.

Only other idea I had was to do a stand alone vacuum pump for the booster. Say 10 in/Hg.

Note: I sent Lee an email so he can check this page out and chime in if wishes.

[NeilM]

hm, that's interesting. I feared the pedal effort might be too high because the master cyl is sized assuming that assist is available. Do you happen to know what diameter is used on the stock master cylinder?

In the E36 chassis the M3 that has the largest diameter M/C bore at 25.4mm, whereas the 325/328 uses 23.81mm. Other things being equal, pedal effort is proportional to the square of piston diameter, so the smaller 325/328 M/C would require about 12% lower effort than the M3 version. (Pedal travel would of course increase by the same proportion.)

Not huge, but noticeable, I'd think.

Neil

[Massive Lee]

Hi guys

Brent told me about that thread.

The e30 booster delete kit was a huge success and close to 80 units were installed. I shall have in three weeks a similar (yet improved) version for the e36 chassis, which will probably also fit the e46 chassis. The kit will be adjustable in ratio and allow to locate the MC to align with the original mounting hole on the pedal stem for a stock 4:1 ratio if a smaller (than stock) MC is mounted (which is my recommendation). The MC can be slid up by about 20mm in infinite increments to align for another clevis hole (that you must drill) for a higher pedal ratio (up to 6:1). I am currently deciding between a sliding MC, or only two fixed positions (4:1 and 6:1 ratios)

For that kit, despite trying hard, I couldn't (technically speaking) use an e36 MC with the diagonal mouting and the very deep recess. Therefore it will require an MC with horizontally located bolts (like "older" BMWs). It portrudes 3/4" less in the cockpit and allows for a much better rod angle change (when braking), being further away from the pedal stem. The good news is that those MCs are available in all sizes, starting from 17mm. The other good news is that they are available with three outlets if needed (two front lines, one rear), and differential piston sizes.

[ScotcH]

Hi guys

Brent told me about that thread.

The e30 booster delete kit was a huge success and close to 80 units were installed. I shall have in three weeks a similar (yet improved) version for the e36 chassis, which will probably also fit the e46 chassis. The kit will be adjustable in ratio and allow to locate the MC to align with the original mounting hole on the pedal stem for a stock 4:1 ratio if a smaller (than stock) MC is mounted (which is my recommendation). The MC can be slid up by about 20mm in infinite increments to align for another clevis hole (that you must drill) for a higher pedal ratio (up to 6:1). I am currently deciding between a sliding MC, or only two fixed positions (4:1 and 6:1 ratios)

For that kit, despite trying hard, I couldn't (technically speaking) use an e36 MC with the diagonal mouting and the very deep recess. Therefore it will require an MC with horizontally located bolts (like "older" BMWs). It portrudes 3/4" less in the cockpit and allows for a much better rod angle change (when braking), being further away from the pedal stem. The good news is that those MCs are available in all sizes, starting from 17mm. The other good news is that they are available with three outlets if needed (two front lines, one rear), and differential piston sizes.

That's awesome Lee! Too bad you didn't have this done in time for us to test last week, but I'm definitely happy with our (somewhat crappy) solution. I'm sure yours will be a much cleaner solution, and if it performs anything like in our car, I recommend this to everyone!

Will you also supply the rod, or can the OE rod be used? We found that it was too short in our application so we had to extend it.

2 years after my initial post it sounds like we may actually have a viable solution! Is the feel with booster removed substantially better than with vacuum to the booster shut off? I imagine so as your now removing all the crap between the pedal and master. I have my original booster i would be willing to donate for some further r&d of a solution...

The issue is not the boost ... it's all the moving parts in the booster itself. Just disconnecting the boost will not remove the slop, since it's all in the linkege. There are like 5 parts between the pedal and the MC ... all the slop in there is multiplied by the pedal ratio into a huge movement before you actually engage the brakes!

My solution (and Lee's I assume) is very simple ... you get rid of the booster, mout the MC to an adapter (we welded ours up from scrap steel), and extend the rod to push the MC from the pedal. Exactly ONE part between the pedal and MC, and absolutely no slop.

This solution is also ideal when you're not running ABS ... the booster is WAY too powerful for the brakes when you have no ABS, resulting in a very un-feeling brake pedal. It goes from 0 to lock up with very little pressure, and is hard to modulate. With the booster removed, the pressure:braking force is very propotional. You push harder, you brake harder. To lock it up, you really have to push hard, so ruining of tires is a thing of the past

Anyway, Lee does good work with plenty of reseach ... buy his product and be happy!

[Massive Lee]

Hi Scott

Clevis and threaded rod included. The clevis is a machined part while the rod is a 12.9 grade cap screw with the head shopped off. You can't bend that ;-) I was using a rod end that bolted on to the pedal stem fore the e30 kit, but it will not work on the e36 kit.

[odortiz]

the craftsmanship looks amazing on the e30 booster delete kit. does anybody use it on the street with street pads?
will there be a provision to set up the pedal travel sensor on some e36s to retain ABS?