Big Brake Kit Setup questions (line lock/prop valve/mast cyl upgrade)
 

Hey all,

I have some questions before I get everything installed on the car...

I just installed a Pettit Big Brake Kit on my 1995 FD with rebuilt rear calipers...all SS brake lines removed the OEM flex rubber parts...

My brake pedal goes much lower then stock due to larger piston sizes on these new calipers so I will be installing the 929 master cylinder upgrade hoping to correct that...

Also at the same time, I ordered a line lock solenoid some universal lines to work with the setup and a wilwood proportioning valve to help offset the big brake balance...

So here are some of my questions...

Where should I be placing the Brake Proportioning Valve? On Robinette's site where he also mentioned Fritz's install the BPV was installed inline to the Front Brake line from the Master Cylinder...and STOPTECH article states specifically not to do front, but rather do rear!!! So which is it...Pics and locations are greatly incouraged....

Also with the line lock, does it matter which location I should be using to put it inline as long as its in between master cylinder front output and the abs!!! (My concern is if i have to put it before or after the BPV) in this sequence (Master Cylinder->BPV->Line Lock->ABS)

Thanks...

I thought you couldn't do a proportioning valve unless you removed the ABS? Also, is a line lock really useful w/ a 5-speed?

The brake bias is fine with the Pettit kit. Why do you think you need to install a proportioning valve?

Your brake pedal is low probably b/c you have air in the system. Keep bleeding. I did a 4 wheel BBK and brake pedal was fine.

I will try it again...but im installing a brake prop valve because i may upgrade in the future...and since im doing a line redo for the 929 MC it just makes sense!!! Just need to know the specifics!!!

If you say so... I still don't see the sense in it. Like Ptrhahn said, the ABS pump controls brake bias.

Yeah I know...But you can still correct the bias to the more linear responce rather then speed dependant...

I installed stoptech fronts and 99 rears, pedal feel is much firmer without changing the master cylinder, yo may just have air in there, as far as the PV goes most people install it in the rear...

Yeah thats what i thought...its reading the robinettes site that made me confused as to why they put one in the front and with ABS intact!!!

Also the Outlaw calipers have much larger SS pistons that move more fluid then the StopTechs!!!

That's weird, I was sure the stoptech's were bigger than Pettit's but I guess I was wrong, I have the race version which uses 34/36 mm pistons versus the stock st40 caliper thaty uses 30/36 mm pistons...

But either way it is a good idea to change to the 929 master cylinder, I will be doing the same thing when I delete my ABS.

Good luck and I hope that you figure it out...

Yeah thanks man...I hope so too...My 929 arrived and now im waiting for the rest of the stuff, which should be here wed or thu!!!

Any help from the pro's or anyone that knows who did this with good results chime in!!!

I've been told that using a proportioning valve in these circumstances is a bit of a kludge.

The PV does not increase brake pressure to the rear brakes, it reduces pressure to the front brakes.

So your new front brake kit is being dialed back to help bias the now relatively weak rear brakes.

That's not a complete loss, as there is now a lot more brake rotor to absorb heat.

I have a Wilwood BBK on the front of my car, and stock brakes in the back.

They feel fine to me. There isn't a 929 MC, nor a PV.

The 929 MC might be nice, but last I tracked the car I never felt the pedal was going too low.

Ok so i will see about re-bleeding the brake system again...

Then on the part of the BPV, so if I were to upgrade to a 99 spec or a Racing Brake rear rotors (larger diameter rotors) upgrade, should I still install the valve to the front or the rear?

Again I am just lookig for a straight answer and back up as to why, as I am using robinettes site as he installed the BPV on the front with a brake kit and other say to install it in the rear? Im just getting confused :(

http://www.rx7.org/Robinette/mod_pro_con.htm
http://www.rx7.org/Robinette/brake_valve.htm

I think you are reading too much into Robinette's comments and over thinking things. Keep in mind that Rob was writing back in the mid/late 90s when there weren't as many brake options as today.

He seems to have written that from the perspective of adding a BBK that wasn't designed/engineered to work with the stock brakes. In that case, you MIGHT have incorrect brake bias front to rear b/c of the leverage effect of the large front brakes AND the sizing of the pistons in the calipers. The size of the brake rotor alone is not sufficient to add enough front bias that you NEED to change it. The size of the rotor together with the caliper piston sizes needs to be considered when determining brake bias.

The Pettit, StopTech, RacingBrake, M2/Wilwood and others ARE / WERE engineered to work with the stock rear brakes so that the bias change is negligible and a proportioning valve is not needed.

Thanks for the clarification on the matter!!! This seems to have stuck in my mind more...

Since i am planning on possibly changing the rear brakes I will be installing all the parts for the 929 swap and because i have to make new lines, I will install the parts as needed!!!

Thanks alot for all your help in the matter... Especially gracer7-rx7

Basically here is the answer, if you remove your ABS you need the PV but if you keep the ABS you dont need it as there is a stock PV that is hooked up with the ABS.

Do you know if the stock BPV mechanical or electronic or speed dependant(hydraulic)?

(Do you know if the stock BPV mechanical or electronic or speed dependant(hydraulic)?


I know Im Bringing this back from the dead but I would like to know this also.

I have a bbk in the front and stock rears would I need a pv or will the abs unit take care of it.

If the abs computer is removed will it effect the braking power or just the abs option

thanks for the help