How to Install a Wilwood Brake Proportioning Valve for C4 Corvette Brakes in an 87 GT (Page 1/1)
Brian A MAR 16, 06:20 PM
Removing the factory brake combination valve and replacing it with a Wilwood Combination Proportioning Valve (Part Number 260-11179) was more complicated than I expected so I thought I’d document the war here. Note that I have Corvette C4 rotors and calipers front and rear in my 1987 GT.

The needed various connections are as follows:

Master Cylinder Front brake – SAE 9/16”-18 inverted flare (female)
Master cylinder rear brake – SAE 1/2"-20 inverted flare (female)

Brake line front right brake – DIN 10 mm-1.0 bubble flare (male)
Brake line front left brake – DIN 10 mm-1.0 bubble flare (male)
Brake line rear single line for both brakes – DIN 14 mm-1.5 bubble flare (male) (#%$*!)

Wilwood proportioning valve, all brake fittings – SAE 3/8-24 inverted flare
Wilwood proportioning valve, front brake light switch port – 1/8-27 NPT

A big problem is that GM used a rare 14mm bubble flare connector to the rear brake line. A union for this connector is virtually unavailable. The common bubble flare fittings are 10mm and 12mm.

Adding to this complication, there is no room to cut and reflare the rear brake line in the front compartment. Adding to this addition, the brake line is thick hard steel, so is impossible to flare without using heat, and there is no room for that. There is more: the rear brake line itself is 6mm NOT 1/4 inch (6.3mm) which means most flaring tools can’t flare 6 mm anyway.

Even though GM used both metric and SAE brake line fittings for the brakes, material for all the other connections are readily available so as long as you can double flare (“inverted flare”) and bubble flare (“DIN flare”). Connecting everything else is easy.

If I were to do it again, I would rip out the factory rear brake line from the front trunk all the way to the right rear of the car and replace it with handmade one using that easy-to-bend-and-flare nickel/copper brake line. A new tee fitting would be needed at the back with three 10mm bubble flare ports. The end in the front trunk could go directly to the proportioning valve using SAE 3/8 inch-24 double flare fitting.

The way I did it, after two weeks of banging my head on a wall, was to pirate the factory tee fitting from the back of a wrecked Fiero. It has two 10mm bubble flare fittings and one 14mm bubble flare fitting. I bought a plug for one of the 10mm fittings, hooked the 14mm fitting to that cursed rear brake line in the front trunk and flared a 3/16 inch tubing with a 10mm nut and a bubble flare for the other port. That, I hooked up to the proportioning valve back brake port with an SAE 3/8-24 inverted flare nut.

The good news is that I can appropriately proportion the brakes (I can selectively lock the rear or the front based on the proportioning valve setting). For my car's configuration, backing the proportioning valve 5 rotations off of "full rear pressure" causes the front brakes to lock and the rear wheels to still keep rolling but nearing their threshold.

Here are photos:
Patrick MAR 17, 12:35 AM

I have no plans to do such a conversion myself, but I appreciate the informative post nonetheless. Nice job!
PePe-LePu_For_2 MAR 17, 06:01 PM
Well done sir! I look forward to a demonstration!
jdv MAR 27, 05:48 PM
The bracket you have that says" Made in the USA" looks like it was made to fit the Fiero.
Brian A MAR 29, 05:50 PM

quote
Originally posted by jdv:
The bracket you have that says" Made in the USA" looks like it was made to fit the Fiero.



Ha! The bracket was indeed "Made in the USA" ... by ME ... in the USA.

Here is the cardboard pattern I made and used (note that I added a bit more metal to the left side where the two mounting holes are) (good luck) :



As for the sticker, well, I had it on my shelf and that large patch of blank metal was just begging for something to be put there.
Signupacct AUG 28, 11:33 AM


Thank you for posting your work. I am trying to accomplish the same. I want to replace the combination valve with the Wilwood. I have read this post and trying to piece together the parts you used and not sure I have been able to come up with a good list to move forward. Any way that you could reach out by email ? Mine is Signipacct "AT" outlook.com


I get that you adapted a three way that is used in the rear to split the rear brake line coming of the wilwood.

but coming off the master cylinder to the wilwood front and rear how are you getting from the Master Cylinder outlets to the Wilwood inputs ? I found some adapters that convert 9/16 18 1/4 to 3/8 24mm that will change the MC front resovoir outlet to 3/8 24mm and the same for the MC rear resovoir 1/2 20 to 3/8 24mm so that lines can go from MC to Wilwood But what line diameter are you using from MC front and rear resovoirs to the Wilwood 3/8 24mm inputs ?


What is the union and conversion for the fronts ?
Brian A AUG 28, 07:02 PM

quote
Originally posted by Signupacct:...coming off the master cylinder to the wilwood front and rear how are you getting from the Master Cylinder outlets to the Wilwood inputs ?...?



The connectors I used to terminate each short brake line are listed at the top of my first post.

I apologize for not pointing out that I custom made all of these short lines (there are five) with plain 3/16 inch nickel-copper brake line. (Buy a lot, like 15 feet, because it takes a lot of trial and error to bend the various lines into the correct and attractive shapes.)

[This message has been edited by Brian A (edited 08-28-2024).]

Brian A AUG 28, 07:14 PM

quote
Originally posted by Signupacct:... I get that you adapted a three way that is used in the rear to split the rear brake line coming of the wilwood...


I did not "split" the rear brake line at the front of the car. I just used a single rear brake line coming from the master cylinder into the single rear brake port of the Willwood valve and then a single brake line to connect to the single brake line that goes to the rear right side of the car. (The rear brake lines split to left and right at the rear of the car.)

[This message has been edited by Brian A (edited 08-28-2024).]

Signupacct AUG 29, 12:33 AM

ok I got the MC to the Wilwood figured out


Now trying to figure out the best way to get the wilwood connected to the two front lines and the single rear line going to the back

one of the two front lines is bubble flare and the other is inverted flare and the rear is bubble flare

how exactly did you convert these