Topic: ZX3 with rear discs adjustable proportioning valve question

Our team had a very successful first race at NJMP two weeks ago.  This was our first opportunity to run our newly built car in anger, and it performed very well.  However, we had some problems with our rear brakes. 

The ZX3 originally had rear drums, but we did some CL scrounging and were able to put in SVT rear discs.  These "cheaty" rear brakes ( in the words of Judge Steve) gave us problems with locking up before the fronts, which made for more excitement than we would have liked, especially in Saturday's rain! 

We decided an adjustable proportioning valve plumbed into the rear line was the best solution to reduce the rear's tendency to lock early.

Upon inspecting the ZX3 brake lines, it has separate left and  right rear lines running all the way from separate outlets on the master cylinder. Is there any reason we can't tee the two lines into a single line so we can use a simple single inlet/outlet proportioning valve? 

Master cylinder---two lines---tee---single line---proportioning valve---single line---tee---two lines---rear calipers

Thanks in advance for the help!

Re: ZX3 with rear discs adjustable proportioning valve question

How about the proportioning valve from the SVT focus that donated the rear discs?  That's what we did with the rear disc swap on our Civic, used the Integra valve along with the rear discs. 

Another option is to tune with brake pad compound.  Run a less aggressive compound in the back to change the brake bias through friction difference.  We do that too, with Raybestos ST43 in front and Porterfield R4E in the back.

Chris from 3 Pedal Mafia

Re: ZX3 with rear discs adjustable proportioning valve question

Our ZX3 actually doesn't have any external proportioning valve.  Just four individual lines coming from the master cylinder.  An SVT MC might be an answer, unless there is some fundamental difference due to it having ABS and the ZX3 not. 

We ended up running stock SVT pads after our R4E pads started ratting/banging after Friday practice.  The rotors were getting HOT, too--lots of blueing.  We swapped because the stockers had an anti-rattle clothespin spring on the ourboard pad.  Their worser friction helped somewhat with our lockup problem, but we still need less.  The stock pads still overheated and blued a new set of rotors we installed between Saturday and Sunday.

Re: ZX3 with rear discs adjustable proportioning valve question

It won't matter what kind of pads you run they will still run hot. The stock MC is sending to much pressure to the rear discs brakes. Drum brake wheel cylinders usually require more pressure then a caliper piston.
Reducing the pressure to the rear is what you need to do.  Taking the two feed lines and running them into a "T" with the third outlet to the rear into another "T" should work.
Not sure how Lemons thinks about it but I would route the brake line into the car and next to the driver so you can mount the proportioning
valve next to him. This way you can make adjustments while on track. Most likely once you find a "happy place" you won't need to mess with it. But on a club race car I ran I did make slight adjustment when starting a race with a full fuel cell of 20  gal. This was a Mustang with the cell located behind the rear axle.

Re: ZX3 with rear discs adjustable proportioning valve question

Or........  you can make the brake pad surface area smaller.......



Bill

2020 I.O.E. CT #36 The Rootes Of All Evil,1958 Sunbeam Rapier Convertible (YES 1958!!) & 2019 Judges Choice NJMP
2016 Thompson Speedway #36 Sabrina Duncan's Revenge, IOE Trophy, 5th Place 'C' Class 1977 Ford Pinto
2009 Stafford Motor Speedway #16 Team Teflon, 11th Place (overall) 1997 Saturn SL2

Re: ZX3 with rear discs adjustable proportioning valve question

-SDR- wrote:

Or........  you can make the brake pad surface area smaller.......



Bill


I like this idea, but I'd be concerned that the same clamping pressure with less pad material might result in much shortened pad life.

Re: ZX3 with rear discs adjustable proportioning valve question

David Eckel wrote:
-SDR- wrote:

Or........  you can make the brake pad surface area smaller.......



Bill


I like this idea, but I'd be concerned that the same clamping pressure with less pad material might result in much shortened pad life.

No "might" about it.......

An angle grinder can dish out a section down the middle, and the more it wears, the more pad is left.  Yea, your braking force will gradually increase, but depending on a few factors, if you swap out the pads between days, it might work. 

Not ideal, but I have used this method on a couple cars with success.



Bill

2020 I.O.E. CT #36 The Rootes Of All Evil,1958 Sunbeam Rapier Convertible (YES 1958!!) & 2019 Judges Choice NJMP
2016 Thompson Speedway #36 Sabrina Duncan's Revenge, IOE Trophy, 5th Place 'C' Class 1977 Ford Pinto
2009 Stafford Motor Speedway #16 Team Teflon, 11th Place (overall) 1997 Saturn SL2

Re: ZX3 with rear discs adjustable proportioning valve question

-SDR- wrote:

Or........  you can make the brake pad surface area smaller.......

Do not do this as a permanent solution to an ongoing problem.  Find a MC that works and plumb that in.

--Rob Leone Schumacher Taxi Service
We won the IOE at Southern Discomfort.
We got screwed at The Real Hoopties of New Jersey  and we took cars down with us.
We got the curse at Capitol Offense but they wouldn't let us destroy the car.

Re: ZX3 with rear discs adjustable proportioning valve question

jimbbski wrote:

It won't matter what kind of pads you run they will still run hot. The stock MC is sending to much pressure to the rear discs brakes. Drum brake wheel cylinders usually require more pressure then a caliper piston.
Reducing the pressure to the rear is what you need to do.  Taking the two feed lines and running them into a "T" with the third outlet to the rear into another "T" should work.
Not sure how Lemons thinks about it but I would route the brake line into the car and next to the driver so you can mount the proportioning
valve next to him. This way you can make adjustments while on track. Most likely once you find a "happy place" you won't need to mess with it. But on a club race car I ran I did make slight adjustment when starting a race with a full fuel cell of 20  gal. This was a Mustang with the cell located behind the rear axle.


FWIW, we have a rear proportioning valve in the cockpit, next to the driver, and its never been noticed/mentioned at tech (6 Lemons races on the east coast). However, the stock brake line routing is inside the car, we just interrupted the lines in a convenient location. Might be different if an inspector sees a home-brew routing of brake lines.

We Audi Be Faster
'85 Audi Coupe G(in &) T(onic)

10 (edited by VKZ24 2017-05-23 09:59 AM)

Re: ZX3 with rear discs adjustable proportioning valve question

David Eckel wrote:

The ZX3 originally had rear drums, but we did some CL scrounging and were able to put in SVT rear discs.  These "cheaty" rear brakes ( in the words of Judge Steve)

Since brake components are exempt per the rules, I'm not sure how adding rear discs would be considered 'cheaty'.

Captain
Team Super Westerfield Bros.
'93 Acura Integra - No VTEC Yo!

Re: ZX3 with rear discs adjustable proportioning valve question

The words "brakes are exempt" was floated briefly by us at BS, but when given the choice between A and B with 25 laps, we chose laps. 

Receipts were not referenced.  We didn't put up a fight.

We suspect we were hit with some laps to see how we would react--to get a feeling of whether we were combative douche nozzles who would be getting black flags all weekend. 

Hopefully we become a known quantity after a few races and the laps go away. 

Judge Steve mentioned he is building a Focus--maybe some choice cheaty Focus parts will happen to fall out of our hatch at the next BS inspection... wink

Re: ZX3 with rear discs adjustable proportioning valve question

To answer the original question and to clarify what RSB says, we have two proportioning valves in our cockpit.  One for each line to each rear wheel.  The reason being I wanted to keep the stock "diagonal"plumbing arrangement with the dual master cylinder.  I've seen guys block one rear brake line and tee the other one to have one proportioning valve control both rear wheels, thereby keeping the rear brakes balanced.  The down side is that now one piston in the M/C controls one front brake and the other piston controls one front brake and two rears.  It seems to work, but I wanted to keep the "normal" arrangement.  If I lose one piston in the M/C, I'm losing front left and right rear or vise versa.  I'm a little leering of losing three of four wheels at once. 

The car originally had and still has drum brakes.  The factory proportioning valve was a variable unit mounted to the trailing arm which reduced rear brake bias as the trailing arm swung up as the nose dived under braking.  It didn't work with the suspension lowered and running stiff spring.  I was locking rear brakes at the slightest touch.  So I dumped the stock unit and put in the two single line proportioning valves.  I did this a long, long time ago when the car was an SCCA IT car.  A little bit of tweaking the bias and got it balanced pretty well.  That was around 1998.  I haven't touched it since.  My instructions to my drivers is simple:  DON'T YOU DARE TOUCH THE BRAKE BIAS!!!

13

Re: ZX3 with rear discs adjustable proportioning valve question

Snuffy didn't explicitly say it, but your original idea is NFG - the configuration you suggest will tie both brake circuits together and will eliminate the isolation that is purposely created by the dual piston master cylinder setup. If you do this you will loose all braking with a single point failure since all brakes are now tied together in a single circuit.

Either use the 2 valve method like we have (one for each rear), or block off the source of one of the rears and then use a single valve on the remaining rear source and tee it downstream to both rears. As mentioned, the downside to the second setup to this is that it will put 3 brakes on one circuit, and 1 brake on the other.

We Audi Be Faster
'85 Audi Coupe G(in &) T(onic)

Re: ZX3 with rear discs adjustable proportioning valve question

Get on of these
https://www.summitracing.com/parts/wil- … oCixbw_wcB

and tee the rear lines together.  I have mine under the hood where the stock proportioning valve used to be.  Did a little testing and slowly turned in more rear brake until it was too much.  Backed it out a turn and now it is perfect.

If it doesn't have 2 doors, 3 pedals, and 5 lug nuts per wheel - It isn't a real race car

Re: ZX3 with rear discs adjustable proportioning valve question

I re-plumbed the MC from diagonal to front/back, then put a prop valve inline, I think with the rear. I left it under the hood; once we got it where it feels good, we don't mess with it any more.

Everybody grab your brooms, it's shenanigans!