Booster check valve

[foolonthehill]

Where can I buy a brake booster check valve for a 1st gen? I'm having a tough time getting my brakes dialed in, really don't think its being effected much by the lack of a check valve, but want one on the truck anyway.
I've got the factory booster and M/C on the truck, with a Speedway proportioning valve. I've got Toyota hubs and rotors on it, with the Mitsu front calipers, and a Mopar 8.75 rear with Aerospace Components disc brakes out back.
I've got a really weak, low, pedal, even after repeatedly bleeding the system.
My brother thinks I may need an M/C with a bigger bore, but I note the Fordubishi is using the stock set up on his which has a big Ford 9 inch rear in it.
Any advice would be appreciated, and especially who carries the check valve...

[Fordubishi]

Upgraded to the 10X2.5" rear drums from an Areostar and still using the stock M/C, Hard lines and proportioning valve. Going to upgrade the M/C to a Wilwood this winter and the Wilwood 13" front rotors and 4 piston calipers. The M/C goes from a 13/16" bore to a 1" bore for higher line pressure.

http://wilwood.com/Images/MasterCylinders/Master%20Cylinder_Drawings-Large/260-8794_dwg-lg.jpg

[camoit]

If the pedal is low the rear brakes need to be adjusted up.

[foolonthehill]

Hummm, interesting point, comoit. Actually I've got the prop valve all the way off the rears right now, so they ought to be locking, but they're not. I was about to try going back to the beginning and re bleed the M/C again and just start from one end to the other all over again.
What Wilwood M/C were you going to use, Fordubishi? (part number) I had emailed Wilwood tech and they weren't too helpful. Are you going to have to make your own push rods to mate it up to the mitsu booster?

[camoit]

There just way out of adjustment. Go to pep Boys and use a safe set tool, it's free to use. If there out of adjustment then the pedal will need to go lower to push them to the drums. 1/4" out = 2/3 stroke.

This side goes over the shoes.

4039

This side goes inside the durum and you lock the set screw. Then use the other side to pre-set the shoes. Thats it. The adjuster will take it from there.


Oh one thing to look at. if you did run the master cylinder dry. You should try pushing the pedal about 1/4" in. just tapping it a crap load of times. This will bleed any air that is trapped in the top of it out the reservoir hoses.

A smaller MC piston will make more pressure but the delivery of oil is less. So this means that adjustment becomes more impotent. A larger piston will deliver more oil but make it harder to achieve the same pressure. To adjust that we make changes in pedal lengths. This is why many master cylinders have 2 different stroke bores. One large for the front disk, and smaller stroke for the rear drum.

[foolonthehill]

camoit, I've got Aerospace Component's disc brakes on the rear. The front's are stock mitsu calipers with slottted Toy hubs and discs.
What I found this afternoon was this, one, I had a little dribbling leak at the rear brake fitting down by the steering box. Fixed that. Also re-bled the m/c. RE-bled the rear brakes, and got a bit more pedal. However, while making test passes to adjust the proportioning valve, we ended up completely closing it, and the rear are still locking. This tells me that although I have fluid coming out of the front calipers, I must still have air trapped in them, because they are just plain not stopping the truck. So it appears that I just haven't worked hard enough to pass the air out of all the new lines yet.
I'll post up with what I find later this weekend. Thanks for all the advice folks! Also still looking for the m/c vacuum check valve, anyone know where to get one for the smaller vacuum lines the mitsu uses?

[Fordubishi]

This is the one I'm looking at.http://wilwood.com/MasterCylinders/MasterCylinderProd.aspx?itemno=260-8794 All the dimensions are very close to the first gens M/C. it comes with a push rod as well so might have to mod it or use the stock one.

[pennyman1]

I have a 1980 parts truck that has the check valve on it - I will check it to see if its good and get back to you.

[camoit]

Ah ok,,, so you have disk on the rear now. On the check valve you should be able to use any check valve with the same size line fittings as the line you have. If the fronts aren't working then there must be a high spot in the line somewhere trapping air. I would imagine you have new pads on this now? I was going to suggest you reverse bleed the calipers. Just squeeze them so all the fluid flows back to the reservoir. Then pump them up again.
Also you should have about 1/8" clearance between the master cylinder and the booster push rod. Then 1/8" between the pedal and the booster. If the push rod hits the master then you are not getting a full stroke.

[foolonthehill]

Thanks again, all. The pads aren't new, and everything was working pretty well until I put the proportioning valve in. I had to run new lines everywhere under the hood. All new lines from the wheels to the prop valve, and from the m/c to the prop valve, etc,etc. One thing I did a little different is that I ran both the left and right brake lines to the center of the crossmember so they'd each be equal length. I have a T fitting there where the line from the prop valve ties in. I did this on the advice of my chassis builder, who told me equal length lines do help controllablility on high speed stops.