How to diagnose a faulty proportion valve?

**Johnzoku** · 02-08-2007, 10:34 PM

Ive recently completed a S13 coil over front suspension upgrade with SR20det brakes (280mm one pot calipers), I also completely flushed out my system, replaced my rear calipers with ones of my spare car and disks that are 0.5mm undersized (as in TSRM 18mm min mine are 17.5mm) and I got some custom brake lines made where you keep the end going into the hard line, and the small length going from the strut to the caliper has now got a banjo joint on the end to fit the s13 calipers. And lastly had my master cylinder checked and its fine as well as the brake booster. I put it all together and bled the system. The rears seam to be fine but I have a problem with the fronts.

The problem is passenger side caliper doesn’t have much pressure so you can still spin the hub/disk freely but the drivers side has too much pressure going to the calipers that once you’ve bled it once you can’t move the hub/disk at all. I do get fluid out of both calipers as well? I check every line and there’s no leaking and also tried swapping the calipers over from passenger to driver side to see if it’s the calipers and its still the same problem on the same side (drivers)

The system runs like this - master cylinder - Line – T section – line – proportion valve – line – soft line – caliper. I’ve checked the underlined and there all fine and the fact that the problem occurs with the caliper on either side suggests that it isn’t them either.

So is the answer a faulty proportion valve or something?

The proportion valve is a AISIN 2K from my MZ11 and a AISIN 3R from my spare… I changed the 2K to the 3R a while ago since I was having problems with the 2K.

**lexsmaz** · 03-08-2007, 12:12 AM

Certainly sounds like you have residual line pressure issues on the drivers side calliper, but to be sure you need to pump up the brakes again, re-check that the disc doesn't turn & crack the bleeder nipple, if it is residual pressure the disc will now turn ... Now comes the fun part trying to work out why, the m/cyl is it the same one that you were using before? is there clearance between the brake booster / m/cyl pushrod & the m/cyl piston, ie brakes always on slightly?
I dont know what sort of car you have, & i'am having trouble following your layout of the lines, need some pics, Are you sure of all the plumbing you have done, no kinked or swapped lines, does your proportioning valve involve the rears as well ( it needs to )
The m/cyl is for a 4 wheel disc setup i pressume?
With the lack of braking on the passenger side the calliper has the bleeder at the top of the calliper i pressume, if not that explains the passenger side, but not the drivers side, as i said need more info & pics ...
Just on the proportioning valve, they usually do not control the pressure to the fronts it just
restricts the pressure to the rears only ..

**Johnzoku** · 03-08-2007, 09:11 AM

ok... i drive a MZ11 soarer that has 4 wheel disks, i had the m/cyl checked and its still the same one that i was using before... i put a new gasket in as the old one was ruined so if anything it might of increased the gap between the piston and pushrod since its new gasket paper (not proper gasket)

ive rebleed the brakes a few times and no change as well as when i crack the brake nipple the calipers does not release the disk... i have to remove the caliper and then use a caliper retractor to get it to move it back...

the proportion valve has both the rears running thru it as well as the front left hand side running thru it as well... i pulled the proportion valve apart and apart from some greasy build up in it but seams to be fine although im not sure of anyway to test the spring... might of hardened is all i can think of.

the only line ive swapped is to the rear and that seams to work fine and im pretty sure all other lines have no kinks... ive tested all lines in the front are working fine by blown air thru them and i seam to get good pressure out of it.

so the only things i could think off is the proportion valve, and i guess the m/cyl?

ill take some detailed pics tonight and post them if they help.

thanks.

**allencr** · 03-08-2007, 10:49 AM

Originally Posted by xcedricx

no change as well as when i crack the brake nipple the calipers does not release the disk... i have to remove the caliper and then use a caliper retractor to get it to move it back...

"brake nipple" is the bleeder valve, right, then there cannot be any hydraulic pressure unless the bleeder is one of those mickey mouse 'self bleeder' things that is F'd up.

With no residual hydraulic pressure, and the caliper swap, it has to be an install problem.

Alignment or too long a bolt hitting the disk.

**Johnzoku** · 03-08-2007, 10:54 AM

Originally Posted by allencr

With no residual hydraulic pressure, and the caliper swap, it has to be an install problem.

Alignment or too long a bolt hitting the disk.

how so? ive checked everything 4 times now and i cant see a fault so far.

by too long a bolt hitting the disk do you mean cailper piston?

**lexsmaz** · 03-08-2007, 04:32 PM

If when you crack the bleeder nipple & it doesn't release the calliper, you have a sticky / faulty calliper piston ....If it was residual pressure due to m/cyl etc, when you crack the bleeder nipple, fluid would expell through the bleeder & the disc would turn ...from your second explanation of the layout i now understand, & all sounds ok, the proportioning valve definately on your system does not control the fronts, because you only have the left hand side front runing through it, & its only there to help regulate the pressure to the rear's .. Sounds like you may have 2 dodgy front callipers, Thats the first area of address then go from there ......

**Hen** · 03-08-2007, 04:41 PM

I'd rebuild the calipers as a matter of course when changing brakes.

It may or may not be the cause of your problem, but I think it's a good idea and will either be a cure or rule out a cause.

Hen

**Johnzoku** · 03-08-2007, 08:41 PM

Originally Posted by lexsmaz

If when you crack the bleeder nipple & it doesn't release the calliper, you have a sticky / faulty calliper piston ....If it was residual pressure due to m/cyl etc, when you crack the bleeder nipple, fluid would expell through the bleeder & the disc would turn ...from your second explanation of the layout i now understand, & all sounds ok, the proportioning valve definately on your system does not control the fronts, because you only have the left hand side front runing through it, & its only there to help regulate the pressure to the rear's .. Sounds like you may have 2 dodgy front callipers, Thats the first area of address then go from there ......

it seams on my car that the proportion valve has a spring to regulate the pressure for the fronts. just a smaller version of the spring for the rear section of the unit.

well to tell you the truth ive had only one cailper rebuilt...

could this be the cause? uneven pressures due to one rebuilt cailper and one normal? but if that was the case when you changed it over wouldnt the problem change sides?

im going to have another look at my soft lines tomorrow and see if there blocked... but im pretty sure its no them either?

ive rung a few places and most of them have been stumped by whats happening to my car and im getting tired of hearing "can you bring it down so we can have a look" no i cant and if i could i wouldnt need too!!!

**Johnzoku** · 08-09-2007, 11:04 AM

sorted!!! it wasnt brake lines, proportion valve or anything else of the sort, seams when i got new lines i got new bolts as well to hold them on to the cailper which were too long, this was causing them to foul on the inside of the cailpers causing the problem.

its always the simplest things that cause the most problems