Gary

Folks,

I've got my new valve and some spare time at the weekend (for once!). It's the 928 valve (33).

A quick question : it's looks a really simple job to change the valve - will I have to bleed the clutch as well as the brakes?

Michael Weinstein

Yes, the job is very easy to do. The port that the proportioning valve screws into is closed when you remove the old valve. So there is no need to bleed the system. Just unscrew the old valve, screw in the new one and you should be good to go. That was my experience anyway.

ninefiveone

You shouldn't need to bleed the clutch unless your brake fluid drops below the pickup where the clutch draws its fluid.

You should, however, bleed the brakes. The port will be closed when you remove the old valve but the new valve will be empty of fluid so it'll introduce some air into the system.

Michael Weinstein

Good point! Bleed the brakes.

zucker

Is this required when big reds are installed?

Danno

yeah, you would need a higher-pressure prop. valve when you install Big Reds because of their larger piston diameters. With hydraulic amplification, this would increase the proportion of braking force to the front, exacerbating the stock condition of having too little braking in the rear as it is. So a higher-pressure prop. valve would restore that balance somewhat.



Even better would be to get an adjustable brake-proportioning valve. Tilton makes a 7-position one with a large handle that can be mounted on the tranmission tunnel for in-car fine-tuning. Or there's a smaller unit with a little **** to adjust the balance:



<a href="https://secure.vbcomm.net/store/detail.asp?part=A0707+BLACK" target="_blank">https://secure.vbcomm.net/store/detail.asp?part=A0707+BLACK</a>

Gary

[quote]Originally posted by Michael Weinstein:
<strong>Yes, the job is very easy to do. The port that the proportioning valve screws into is closed when you remove the old valve. So there is no need to bleed the system. Just unscrew the old valve, screw in the new one and you should be good to go. That was my experience anyway.</strong><hr></blockquote>

Really appreciate the feedback guys - that's going to make my weekend easier as well as allow more time for other things on the car!

I will actually be changing pads to MM's (thanks Jason!) as well so will probably bleed as a matter of course.

One comment : if the valve introduces a little air, I will basically have to bleed all the way through the system, right?

Sloth

[quote]Originally posted by Danno:
<strong>yeah, you would need a higher-pressure prop. valve when you install Big Reds because of their larger piston diameters. With hydraulic amplification, this would increase the proportion of braking force to the front, exacerbating the stock condition of having too little braking in the rear as it is. So a higher-pressure prop. valve would restore that balance somewhat.

Even better would be to get an adjustable brake-proportioning valve. Tilton makes a 7-position one with a large handle that can be mounted on the tranmission tunnel for in-car fine-tuning. Or there's a smaller unit with a little **** to adjust the balance:</strong><hr></blockquote>

Is that with Big Reds on all four corners or just up front. My experience with Big Reds on all four corners is that the rear brakes to much (locks up before the front). This was evidenced to me by the dancing around of the rear during hard braking and the mild flat spots on the rear tires. Thoughts???

Right now I have the stock valve and m cylinder, but plan on getting an adjustable valve.

TIA

Danno

"Is that with Big Reds on all four corners or just up front. My experience with Big Reds on all four corners is that the rear brakes to much (locks up before the front). This was evidenced to me by the dancing around of the rear during hard braking and the mild flat spots on the rear tires."

My example was with just Big Reds in front. Having them on all four corners would be creating the opposite problem as the stock brakes. Now you've got way too much braking force on the rears instead of not enough.

In stock trim the '86 951 has what looks like identical brake calipers. But the pistons inside were different. The front had 40/36mm pistons while the rears had 30/28mm ones.

If you work out the hydraulics, that gives the front brakes 72% more power than the rear ones with identical input pressure. Then add a prop. valve and you've got like 110% more braking power in front for F/R balance of something like 70/30%. By using a higher-pressure prop. valve you can adjust this to be closer to 60/40% for more work from the rears.

By putting the same BR calipers on all four corners you've taken this to another extreme with 50/50% F/R braking. Now the rears are doing TOO much braking because of the weight shift to the front under deceleration.

Sloth

[quote]Originally posted by Danno:
<strong>By putting the same BR calipers on all four corners you've taken this to another extreme with 50/50% F/R braking. Now the rears are doing TOO much braking because of the weight shift to the front under deceleration.</strong><hr></blockquote>

I thought I was going nuts when I kept hearing that the front brakes lock up before the rears, which was totaly contrary to my own experience.

Thanks for the insight.
<img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />

Alan C.

I have Big Reds in the front with stock rears and NO bias valve. The proportioning valve is adjusted to the min. Max braking to the rear and I have a little too much front brake.

Not real bad but it makes life interesting when you dive in just that little bit deeper

Danno hits on a good point about piston size. I will probably update to a set of stock fronts in the rear as a first shot. If that doesn't work I might try a set of 94 3.6 turbo rears. I used that combo on my RSA with really good results.

Alan

Gary

[quote]Originally posted by Michael Weinstein:
<strong>Yes, the job is very easy to do. The port that the proportioning valve screws into is closed when you remove the old valve. So there is no need to bleed the system. Just unscrew the old valve, screw in the new one and you should be good to go. That was my experience anyway.</strong><hr></blockquote>

Michael,

I had a closer a look at things today and can't work something out. I understand that the master cylinder will automatically close but what about at the brake line end when you unscrew that? Is there some kind of valve on the end of that too (i.e. does it close also)?

<img src="confused.gif" border="0">

Michael Weinstein

Ok, I need to qualify my experience here. When I did the changeover, I had an '88 951 with ABS. Although I just bought an '86 951, I have not made the switch to the new regulator yet.

I checked the factory manuals, and I can see that there is a difference between the cars with ABS and those without. So, to give you a perfectly terrible answer - I don't know. Hopefully someone else can give us both the answer we need on this. <img src="graemlins/c.gif" border="0" alt="[ouch]" />

Gary

[quote]Originally posted by Michael Weinstein:
<strong>Ok, I need to qualify my experience here. When I did the changeover, I had an '88 951 with ABS. Although I just bought an '86 951, I have not made the switch to the new regulator yet.

I checked the factory manuals, and I can see that there is a difference between the cars with ABS and those without. So, to give you a perfectly terrible answer - I don't know. Hopefully someone else can give us both the answer we need on this. <img src="graemlins/c.gif" border="0" alt="[ouch]" /> </strong><hr></blockquote>

I have the factory manuals also and the only reference is to the differences and how to screw/unscrew the valve. It says very little about anything else related (including how to change it, which side to do first, what parts will need bleeding, whether on the '86 the master cylinder blocks the port when you unscrew the valve etc. etc.).

I'd really like to hear from someone who's done this ... please (?)

<img src="graemlins/yltype.gif" border="0" alt="[typing]" />

eugene

On a Non ABS car the valve screws onto the brake master cylinder. The bias valve(male end) screws onto the master and the metal brake line( line that goes to the caliper) screws onto the bias valve.

Non ABS car
Step(1) Unscrew nut to remove brake line from the Bias Valve( cylinder about 2.5" long)

Step(2) Unscrew bias valve.
Step(3) Screw in " New " bias valve.
Step(4) Reinstall brake line onto the bias valve

Complete flush/bleed brakes.

On a ABS car, the Bias valve is screwd onto the ABS Unit in the passenger side fender well towards the door( need to remove the plastic fender inner lining) A bit of a PITA to remove/install the bias vlave due to the confined space.

The bias valve screws onto the ABS unit and the brake line from the Master cylinder screws into the bias valve.