Do I need a proportioning valve?

Hemimad · Post by **Hemimad** » Tue Sep 24, 13 11:44 am

Looking for advice, I have a Wilwood disc brake conversion going on the 70 Runner to replace the drums (including disc spindles). The existing brakes are not power assisted but I am sure I've read somewhere that I need a proportioning valve to be fitted. If so, what type is commonly used and where do you normally mount them?

Thanks

Dave C

Pete · Post by **Pete** » Tue Sep 24, 13 12:07 pm

Proportioning valves are normally deployed where the rear brakes lock up first under Panic brake scenarios - take it from me - most Mopars have too much rear brake bias!

The valve isn't one - it is merely a manually adjustable restricter and reduces the line flow to the rears, a crude way of improving bias to the fronts (Drums operate before Discs do, which is why you need a different M/C - or mod your original one).

One of those suck it and see moment!

Dave-R · Post by **Dave-R** » Tue Sep 24, 13 12:18 pm

I had to fit an adjustable valve in the line to the rear 11" brakes as they were locking up bad.

When Chrysler fitted 11" heavy duty drum brakes you got 11x3 drums at the front and 11x2.5 at the rear to help balance the braking.

When you got the optional front disc brakes they fitted 10" drums on the rear to reduce the rear brake force even more.

They are simple to fit. Summit do a branded version of the Wilwood version. Fit it where it will be easy to reach under to adjust. On the chassis just behind the front wheel is a good place.

Hemimad · Post by **Hemimad** » Tue Sep 24, 13 1:46 pm

Thanks for the advice, I'll put one on the never-ending list of things to buy! The picture is a great help, looks like a good spot, not too on show but not inaccessible either.

Cheers

Dave C

Dave-R · Post by **Dave-R** » Tue Sep 24, 13 1:54 pm

If people ask what you are doing down there just tell them you are fiddling with your knob until it brakes.

Pete · Post by **Pete** » Tue Sep 24, 13 1:54 pm

A lot of people put them in the engine bay so they don't get covered in crap, or actually through the floor so you can adjust them in motion from the driving seat.....

Dave-R · Post by **Dave-R** » Tue Sep 24, 13 2:06 pm

But in reality, once adjusted so you brake right on a dry surface, they are usually never fiddled with again.

John · Post by **John** » Tue Sep 24, 13 6:28 pm

Mine is the opposite,

I have drums all round and when driving slowly the fronts lock real bad and nearly put you through the screen if your not really careful. So without looking my question is, would I have an adjustable bias for mine?

shovelheadrob · Post by **shovelheadrob** » Tue Sep 24, 13 6:36 pm

The other difference between discs & drums is that drums will have a residual pressure valve (usually in the master cylinder), because drum brake wheel cylinders use umbrella type seals they need a small amount of pressure to keep them sealing. The return springs are stronger so the brakes don't bind. If you don't remove this in the front brake circuit the disc pads will not release properly. Ideally you will change the master cylinder for a proper disc/drum one.

Dave-R · Post by **Dave-R** » Wed Sep 25, 13 8:47 am

Yeah you have to use a disc/drum master cylinder but I think the residual pressure valve can be removed from a drum MC. I seem to remember you remove teh pipe fitting from the MC and it is in there?

DaveBishop · Post by **DaveBishop** » Wed Sep 25, 13 9:20 am

Yep Dave a self tapping screw and two screw drivers to leaver it out:thumbright:

Pete · Post by **Pete** » Wed Sep 25, 13 12:31 pm

DaveBishop wrote:Yep Dave a self tapping screw and two screw drivers to leaver it out:thumbright:

Yes you can, but you will write off the taper that the pipes seat against so you will need an new one..........

DaveBishop · Post by **DaveBishop** » Wed Sep 25, 13 12:52 pm

Hi Pete
I thought that he was taking them out and not putting them back
Cheers Dave

Pete · Post by **Pete** » Wed Sep 25, 13 12:54 pm

Yes but if you take the valve out, it sits behind the boss that makes the seal with the pipe, and you have just destroyed the boss to get to the valve...........

DaveBishop · Post by **DaveBishop** » Wed Sep 25, 13 1:02 pm

Hi Pete when you used to get rebuild kits that is what the instructions told you to do. They supplied a new one in the kit you only put them back when you had drums. I remember doing this years ago when I changed to discs on the front