front disc conv kits

[chopjake]

HELP> I need suggestions. Still have hard pedal after install of mbm disc brakes. Also installed vacuum pump, canister and new 8" booster and new dual diaphragm master cylinder and prop. valve. Pedal is still hard..doesn't seem to have any power assist. All parts were checked out and seem to be working properly. Rear has drums. Any advice would be greatly appreciated.
Mark

 

[rrTor-Red]

Did you bench bleed the M/C first?

 

[Bb70charger500]

Is your brake rod from your pedal to the booster the correct length?

 

[chopjake]

yes we did thanks

- - - Updated - - -

OK this I will have to recheck, thanks

 

[HEMI-ITIS]

You might also need to check line pressure.

 

[HT413]

SSBC makes an affordable line pressure gauge, like $45. I used it to diagnose poor brake performance and quickly narrowed it to a bad mc. Comes with fittings to hook it to each wheel cylinder / caliper or directly to the mc and anywhere in between. Well worth the price.

Btw, dr. Diff has a nice adjustable mc pushrod for like $45. Worked great for me.

 

[70GTX Texas]

I just finished my power drum conversion on my 70 GTX to 4 wheel discs using MBM. Got the install done, pedal was hard as hell. Called the supplier and explained my issue. When I ordered the kit, I was told my stock booster and master cyclinder would work.... it didn't..... I did more research and found out that the power drum master cyclinder had residual valves in it and I needed a 4 wheel disc brake master cyclinder and to by pass the prop valve on the fronts and the rear and install an adjustable prop valve for the rear.

I did all of that and still, hard pedal, and it feels like 0 power assist. Any ideas?

 

[70GTX Texas]

I'm going to get the line pressure gauge and see if that works..

 

[5.7 hemi]

What size m/c?

 

[70GTX Texas]

1 inch

 

[5.7 hemi]

That should work just fine with your set up.

 

[70GTX Texas]

correction, 1.125 inches....... and brake pedal is rock hard. No power assist at all. It stops pretty good but it feels like it is all or nothing on the braking.

 

[5.7 hemi]

If you have no power assist, then your pedal will feel as though you have a manual set up. Check for vacuum from the engine and then check the booster. My guess, the booster has failed.

 

[70GTX Texas]

booster checked out ok today. no issues there, its holding vacuum and I cannot force air back through it from the booster back to the engine so that check valve is still good. It does stop good but once you apply the brakes, there is nothing more there to go to in and emergency situation. I was on the phone with MBM brakes today going over all the components and checking out the booster. There were 4 or 5 different tests he had me do to it. He's doing some more research on his end and will get back to me tomorrow. Engine vacuum at idle is 15. I've had cars with 12 and still had good brakes.

 

[5.7 hemi]

Im out of idea's at the moment. Let us know what MBM has to say.