Removing proportioning valve on Master cylinder?

Furai · Post by **Furai** » Fri Oct 25, 2013 5:26 pm

So I need to improve rear brakes. My car is firm and low and for my Certificate test in NZ it locked the fronts too easily and barely worked on the back.

I have checked everything is working properly and it is, I had the brakes properly tested and its all normal for an MX5 but Im running 12/10Kg springs so I dont have much if any dive.

So has any tried removing the proportioning valve? I could get an adjustable one but it takes too long and I will run out of time to get my cert(Has to happen withing 2 months and I have about a week).

The other option is upgrading the rear brake calipers or bigger discs but it seems to be clamp pressure when using the pedal is the problem(Use the handbrake with the footbrake and it slows better and you can feel the back working)

siren676 · Post by **siren676** » Fri Oct 25, 2013 6:14 pm

Could you get away with better rear pads?

Furai · Post by **Furai** » Fri Oct 25, 2013 6:32 pm

Its the rear clamping pressure, would pads help that much in this situation?

warrior · Post by **warrior** » Fri Oct 25, 2013 6:34 pm

They are worth a try

siren676 · Post by **siren676** » Fri Oct 25, 2013 6:40 pm

Its not really a pressure issue if they are in good working condition, they will give the rear more bite which will give you more rear braking strength

2low2c · Post by **2low2c** » Fri Oct 25, 2013 9:04 pm

chances are because you use the hand brake for drifting that you have glazed the rear discs so they may just need a skim to clean them up and improve the bite .if you remove the factory proportioning you would have to replace it with an ajustable one(wilwood)

Furai · Post by **Furai** » Sat Oct 26, 2013 7:24 am

Who sells wilwood in NZ?

marcellarius · Post by **marcellarius** » Sat Oct 26, 2013 7:54 am

A proportioning valve seems like it would be trying to work around an underlying issue -- whether mechanical or questionable testing methods.

I'd look at new pads, skim the discs. Are you running the same type of pads front and back?

You will still be getting load transfer even if you made the suspension completely rigid, so long as the centre of mass isn't on the ground.

Snapfrozen · Post by **Snapfrozen** » Mon Oct 28, 2013 12:25 pm

Furai wrote:Who sells wilwood in NZ?

If you are heading down the direction I think you are then give Cardwells a call. They do a Willwood one and if I remember someone has found a part you can use to remote it...

http://www.flyinmiata.com/support/instr ... _valve.pdf

Snapfrozen · Post by **Snapfrozen** » Mon Oct 28, 2013 12:26 pm

And it is a known problem with MX5's in racing that they lock the fronts easily. The bias is great for a road car..

Here Furai - What I was looking for...

I believe "Thepass" also has one in his car but cant find the thread.

http://www.miataturbo.net/race-prep-75/ ... all-37313/

SLYDIT · Post by **SLYDIT** » Mon Oct 28, 2013 9:15 pm

a proportioning valve will only lessen the raer brakes though not make them better??

Snapfrozen · Post by **Snapfrozen** » Tue Oct 29, 2013 8:40 am

An adjustable prop valve will change the front rear bias allowing you to move it closer from the 7x : 2x ratio that it is from factory.

Born_disturbed · Post by **Born_disturbed** » Tue Oct 29, 2013 12:29 pm

I you can convince me to install my NB prop valve and help me bleed it after you can have my NA one

Mad Kiwi · Post by **Mad Kiwi** » Thu Nov 07, 2013 2:45 pm

Was there any solution to this problem?

I have read the valve only reduces the bias to the rear so it makes the problem worse....

Furai · Post by **Furai** » Thu Nov 07, 2013 4:05 pm

I removed the internals of it and the braking force didnt even change. Im going to try make the front brakes smoother and check them over but I cant seem to make it better. Replaced heaps and checked everything!

marcellarius · Post by **marcellarius** » Thu Nov 07, 2013 4:48 pm

I'd be looking at the rear calipers -- have you done a full R&R on them? If they are jamming up then that could cause a brake balance issue.

Do you have numbers that show the problem, like from a brake tester used at some WOF places?

SLYDIT · Post by **SLYDIT** » Thu Nov 07, 2013 5:00 pm

Mad Kiwi wrote:Was there any solution to this problem?

I have read the valve only reduces the bias to the rear so it makes the problem worse....

thats my point...many of the bias valves only reduce the rears not make them better. most race cars are over braked in the rear and you tune them down with the bias valve but not increase them compared to the front..

Furai · Post by **Furai** » Thu Nov 07, 2013 5:52 pm

marcellarius wrote:I'd be looking at the rear calipers -- have you done a full R&R on them? If they are jamming up then that could cause a brake balance issue.

Do you have numbers that show the problem, like from a brake tester used at some WOF places?

Yes and yes, Bought new calipers for the rears ages ago and overhauled before putting in.

WOF Machine said its pulling 1000NM which is fine.

But if you slam the brakes it locks the front more passenger side so we are thinking sticking caliper. Thats the cert issue.

siren676 · Post by **siren676** » Thu Nov 07, 2013 6:02 pm

Are you still going through with the cert even though your making it a dedicated track car?

Furai · Post by **Furai** » Thu Nov 07, 2013 6:16 pm

Well I still need to drive it places until I get a trailer

marcellarius · Post by **marcellarius** » Thu Nov 07, 2013 6:31 pm

The lower CoG is going to give you more of a front bias under deceleration, I'm not sure how significant this effect would be; it's not that low.

Could it be weight distribution related? Does it still lock up with a passenger in the car? 12/10 springs are pretty hard, could that be putting your corner weights out enough to cause that?

2low2c · Post by **2low2c** » Thu Nov 07, 2013 8:30 pm

SLYDIT wrote
thats my point...many of the bias valves only reduce the rears not make them better. most race cars are over braked in the rear and you tune them down with the bias valve but not increase them compared to the front..
that is actually incorrect the fatory valve is set at 50 percent of the front pressure a willwood valve can be ajusted between 43 and 100 percent of the front pressure so you can infact increase the rear brakeing over factory.

Furai · Post by **Furai** » Thu Nov 07, 2013 8:35 pm

Eliminated weight, tried with/without passeger, different rake, dampening, compsating for weight, Its the brake system.

I just replaced front pads and after a drive the side that isnt locking is leaking fluid so another thing to fix that could be the issue.

Moral of the story is ever since going for cert EVERYTHING has gone wrong. Dont go for cert

marcellarius · Post by **marcellarius** » Thu Nov 07, 2013 8:41 pm

Well, a fluid leak could definitely explain some things

My car has been running fine, which I guess can only be attributed to not having gone for a cert yet.

Angreal · Post by **Angreal** » Thu Nov 07, 2013 8:59 pm

Furai wrote:Moral of the story is ever since going for cert EVERYTHING has gone wrong. Dont go for cert

My clutch died a week after cert