Front brake bias fix

[jfryjfry]

New here, and just started tracking my s13 (drift only before). it's a 180sx from japan and is fun, but i was having the worst front wheel lock up...

the car, i believe, originally came with abs but doesn't have it now and has a non-abs master. it's a 1" with the 2 front lines and one rear.

the rear brakes i believe are stock s14 brakes (it has the 5-lug conversion), and the fronts are nissan, but bigger than z32's.

I played with the idea of different master cylinders, but that would be an involved and expensive and unpredictable fiasco.

So I plumbed in two proportioning valves from summit racing.

I took it out and I ended up having to fully close the valves and still have a little premature front wheel lock up.

Which means that i am blocking about 57% of the braking to each front wheel and it's still a bit grabby up front.
I have hp+ pads up front and probably stock in rear (unsure), so maybe that has something to do with it, but it was a whole lot more fun on the track with bnrakes that actually work.

and the nice thing is i can dial them back for drifting.

[McCoy]

What front caliper do you have? I know that when I did the Z32 brakes up front and kept the S13 rears (using a Z32 1" BMC), the fronts locked up way to easily on the street and was terrible on track. After adding the Z32 rears and running the same pads F/R (hawk blues) the balance was SO much better.

If it were me, I'd upgrade the rears to Z32's, get the same pads F/R, and remove the prop valves as they shouldn't be needed if you have a properly matched brakes to the M/C.

[mmdb]

same problem here. it's a bad idea to trim your front braking power. I switched out my rear pads to a more aggressive track pad, but the obvious negative consequence is rotor wear. the best option in the long run is to get a new brake setup. sucks to hear it, unless you can somehow rigg the current cylinder or find someone that makes a new setup it's not so bueno.

[Seraphim38]

I have this exact same situation with Z32 brakes front and rear, exihibiting excessive tendency for front lockup in autox.

I am mentally preparing myself for an imminent brake upgrade requirement. The wilwood group buy being over, I am considering all options with a rear brake upgrade on the list scoring high for yielding improved braking balance and the front brake upgrade high on the list for weight reduction and improved braking.

[McCoy]

I have this exact same situation with Z32 brakes front and rear, exihibiting excessive tendency for front lockup in autox.

Are you using the Z32 BMC too? I remember this being the key on my setup for a good bias.

[mmdb]

I believe the z32 has more front bias than the 240sx bmc...

[Seraphim38]

I have the Z32 master cylinder...I think it is the larger of the 2 designs, which also contributes to the problem I think.

[McCoy]

I believe the z32 has more front bias than the 240sx bmc...

Looked back through a few of the other Z32 threads and you are right.

[CodyAce]

For me, switching from 1" one to the 15/16" Z31 MC and loved it.

[jfryjfry]

The fronts are probably some sort of skyline or similar as they are larger than the z32. But take the same pad...
Upgrading the rears is the best way to go and would probably fix my prob, but A. maybe it wouldn't and B. I need the ebrake for drifting and the mini drum brakes suck.

As far as playing with different bmc's, changing the diameter affects ALL brakes and I needed to reduce front pressure/increase rear. The prop valve would have more to do with that and I have found minimal info on it. All I read was that it stops I creasing pressure to the rear at a certain point. Who knows if that's even right.

As far as the comment that it is a bad idea to put a valve on the front, why? I haven't seen anything saying that. Certainly the front brakes are more important than the rears and do more work but if these valves had a habit of failing I believe we'd have heard about it. That being said, I'd rather be adjusting the rears but that's not possible.

All said and done, you can fix your problem for the price ($50ish) of one or two valves, 2 or 4 fittings (<$10) and the tool ($20-40) if you don't have one. Now you can surely fix your problem (instead of maybe/probably not by fitting different $80-$200 master cylinders AND be able to fine tune YOUR car. Different speeds, tires, pads, surfaces etc could mean you benefit from being able to dial in a little more or a little less front brake.

[Tower240sx]

...or you could do it right.

there are several discussions on here regarding brake bias and how best to deal with it, but you really should start with brakes that are closer to matched so you aren't doing so much playing with valves,

Someone mentioned using the front channels to feed all 4 corners then installing adj. prop. valve(one channel front one rear) this eliminates the valve built into the master that limits pressure to the rear brakes,

At the VERY least I'd suggest not running 2 valves for the front you could readily end up with different pressures at the front brakes and erratic handling under braking,

[Def]

The fronts are probably some sort of skyline or similar as they are larger than the z32. But take the same pad...
Upgrading the rears is the best way to go and would probably fix my prob, but A. maybe it wouldn't and B. I need the ebrake for drifting and the mini drum brakes suck.

As far as playing with different bmc's, changing the diameter affects ALL brakes and I needed to reduce front pressure/increase rear. The prop valve would have more to do with that and I have found minimal info on it. All I read was that it stops I creasing pressure to the rear at a certain point. Who knows if that's even right.

As far as the comment that it is a bad idea to put a valve on the front, why? I haven't seen anything saying that. Certainly the front brakes are more important than the rears and do more work but if these valves had a habit of failing I believe we'd have heard about it. That being said, I'd rather be adjusting the rears but that's not possible.

All said and done, you can fix your problem for the price ($50ish) of one or two valves, 2 or 4 fittings (<$10) and the tool ($20-40) if you don't have one. Now you can surely fix your problem (instead of maybe/probably not by fitting different $80-$200 master cylinders AND be able to fine tune YOUR car. Different speeds, tires, pads, surfaces etc could mean you benefit from being able to dial in a little more or a little less front brake.

Different BMCs have different split points where the rear pressure starts diverging from the front.

The Z31 15/16" MC would give you better bias since you essentially have the same setup as some S14s/S15s had (iron Z32, sliding weeny calipers in the rear).


If I were really into drifting I'd have a dedicated hydraulic rear brake caliper (note I didn't call it an e-brake).

[jfryjfry]

...or you could do it right.

there are several discussions on here regarding brake bias and how best to deal with it, but you really should start with brakes that are closer to matched so you aren't doing so much playing with valves,

Someone mentioned using the front channels to feed all 4 corners then installing adj. prop. valve(one channel front one rear) this eliminates the valve built into the master that limits pressure to the rear brakes,

At the VERY least I'd suggest not running 2 valves for the front you could readily end up with different pressures at the front brakes and erratic handling under braking,

do it right? that would imply that i'm doing it wrong.... sure, i could do it more simply which i would say is better, but at a significantly higher cost. And I lose a benefit of my system which would cost another $250 to solve.

Funny that you say do it right and then offer to either get properly matched brakes (a good idea) OR re-route a stock system AND use a valve just like I've already installed. no logic there!

and your final suggestion is to at the least, put it back to how it was (a dangerous situation).
Why?
what's wrong with my set up? i mean really wrong, not proposing a different way?

thanks, but i just fixed my problem and am very happy!

[jfryjfry]

Different BMCs have different split points where the rear pressure starts diverging from the front.

The Z31 15/16" MC would give you better bias since you essentially have the same setup as some S14s/S15s had (iron Z32, sliding weeny calipers in the rear).


If I were really into drifting I'd have a dedicated hydraulic rear brake caliper (note I didn't call it an e-brake).

I have not heard anything definitive saying the 15/16"'s would work properly. In fact, since i had to decrease the fronts by such a large amount, i would say that a 15/16"'s would not increase the rears enough.

it might be better, but would it fix my problem? i have serious doubts.
Plus, to check, I would either have to source one with the proper middle fitting or destroy mine which would mean i couldn't go back to what I had. AND a bmc is probably going to be the same or more $$ than what I did.

As far as a hydraulic ebrake/parking brake/separatate system/whatever (manufacturers are calling them parking brakes now for legal reasons....), you're looking at a $1500-$3000 job if you source it out. I know because that's what I charge.

it would be a much better system, but why should I do that when mine works just fine?

you might be referring to a staging brake which is a much cheaper alternative, but still around $250 if I do it myself. The problem with these is they often don't work well. And, again, mine works fine.
If you were into drifting, you would put one in just to put one in even if your current set up worked fine?

I don't see the logic....


I have a set up that isn't much $$, and works great! Stops fast, works on the track wonderfully, good brake feel, good ebrake... What's the problem? I mean a REAL problem?
If someone else can solve their problems differently, then great! I'm just throwing out there my solution.
and if there is a real reason I shouldn't do it, please let me know.

[Def]

I have not heard anything definitive saying the 15/16"'s would work properly. In fact, since i had to decrease the fronts by such a large amount, i would say that a 15/16"'s would not increase the rears enough.

it might be better, but would it fix my problem? i have serious doubts.
Plus, to check, I would either have to source one with the proper middle fitting or destroy mine which would mean i couldn't go back to what I had. AND a bmc is probably going to be the same or more $$ than what I did.

As far as a hydraulic ebrake/parking brake/whatever (manufacturers are calling them parking brakes now for legal reasons....), I work with them a lot and can tell you that many times, they don't work well.
plus, you're looking at $250 ish to put one in.
Why should I do that when mine works just fine?
If you were into drifting, you would put one in just to put one in even if your current set up worked fine?

I don't see the logic....

The FSM would tell you it'd work if you'd read it. I already said your EXACT brake setup came on some JDM S14s/S15s. They had the a 15/16" MC with the same split point as a... yep, you guessed it, Z31 BMC.

Your setup with two prop valves on the front is janky because you almost surely have different brake pressure on each side of your front braking circuit, even if you set the proportioning valves "the same."

As for the hydraulic rear brake setup, there's a reason you don't have a cable going to all four corners of your car for braking. It's not progressive with force, it just controls pad movement. So yes, you can lock the rear wheels, but there's more to driving/drifting than on/off inputs. A hydraulic system can give a progressive amount of braking force. Working ok and working much better are two different things, but it doesn't seem like you understand the difference...