I converted my 68 Ragtop from front wheel drum to a rebuilt disc setup. With the upgrade, I also went from a manual to power with the use of a Masterpower Brakes Dual Diaphram 8" booster, Master Cylinder and their Prop/Combination Valve.

After the rebuild The brakes are way to sensitive. There is not much peddle difference between moderatly applying the brakes and an all-out panic stop. I need to always feather touch the brake pedal or lock up the wheels.

I've done brake rebuilds before, and I would assume it's not the disc conversion.

Is it possible the booster is way to powerfull? It's almost more enjoyable to drive with the vacuum disconected from the booster and having a hard pedal. At least I have a little more control over the brake effort applied.

Any Ideas?

Hi Jeff,

I remember after I replaced my booster and rebuild the calipers, surfaced rotors, blah blah, the brakes were REALLY grabby for a week or two. after about 50 miles, they settled in nicely, and the car was overall safer.

Plus, wiht a 496, I think you're gonna want all the brakes you can get smile.gif

Did you change the pivot point on the brake pedal? The drum brakes required more "throw" than the discs so there are two holes in the brake pedal arm.

correct me if im wrong but arent the two holes used for manual brakes or power brakes? the lower hole is for power because of the angle the booster is in, and the upper sits straight for the upper holes. If im wrong let me know because i just converted to power and im using the lower hole.

Originally posted by lev:
Hi Jeff,

I remember after I replaced my booster and rebuild the calipers, surfaced rotors, blah blah, the brakes were REALLY grabby for a week or two. after about 50 miles, they settled in nicely, and the car was overall safer.

Plus, wiht a 496, I think you're gonna want all the brakes you can get smile.gif I agree with this. I had my braking system completely redone a lil while ago, and I had the same problem as you, but, after about a week they softened up and work fine now.

Break-in of the pads and rotor is not the issue since I did this swap last year and the brakes feel the same.

I talked with a tech at MPBrakes, he thought the booster is providing too much power. They usually recommened the Dual diaphram on big-block cars only beause of the extra weight on the front end.

Another situation where more is not necessarly better I guess.

Was the prop/combo valve that came with the kit adjustable? Sounds like all the power is going to the front discs too fast and not proportioned right between the front and rear.

Had the same problem when i didn't have a proportioning valve, also this was caused by a BAD master cylinder. Things you might want to look into, but by all means give it a week or so of braking in if everything is new.

You didn't say if it was the front wheels or rear wheels that were locking. But I agree with in that it could be a problem related to the proportioning valve. The master cylinder push rod could be too long. If yours is adjustable, you can try shortening it just a bit.

Did you check the rear shoe adjustment? If they are too tight, or if there's a lot of brake shoe dust in the drums, it can also cause this problem.

When it locked up during a stop, it sounded like the front wheels.

The master cylinder and combination valve are also both new pieces from MP Brakes.

I think I'll give a different booster a try. I will also check the rear shoes for correct adjustment.

Front brakes rarely lock up like this, so you may be onto something in regards to the booster. Keep us up to speed and let us know what fixes it.

I read all the post's & you've got some good advice ... one thing thats been over looked is the material the pads are made of .... orginic pads are stock & alot softer ..using splintered steel pads which are harder will help with the touchy peddle your experecing plus's are better hot performance less fad ... down side they wear out rotors faster then orginic ones

Hi Jeff,
Sorry to butt in on your thread, but I've tried to contact you through your website about some pics but either missed your reply back or ????

Anyways, if you could e-mail me at diels1@aol.com I would greatly appreciate it.

BTW, very very very nice ragtop 'velle! graemlins/thumbsup.gif

Joe

I should be installing a MPBrakes 9" single diaphram booster this weekend and I'll report my results.

The pads are orgranic. The only other pad that was in stock was a $55 pair of Raybestos Ceramic. I've never really had a problem with pads in the past, so I'm hoping this booster will take care of the problem.

Joe, I'll shoot you an email tonight.

I bolted on the 9" single diaphram booster last night, and it solved the touchy brakes.

Now that I have more control, it's fun to drive again.

I think the dual diaphram would be better on a big-block car moving with more mass. The touchyness would probably not be there.

PS: Anyone want a deal on an almost new 8" Dual Diapram booster and a brand new MC.