Posted By: dvw
hard brake pedal ,no stop - 08/02/11 03:14 AM
I did a disc conversion on my friends 70 Coronet R/T. Stock 70 pin type calipers and master. Car doesn't want to stop even at idle. Pedal feels normal until its about half way down. Then it feels like a brick is under the pedal. You can't move it further. All stock stuff. Pedal linkage is correct,tried 2 boosters,2 master cylinders(1 1/8" and 1"). Rear wheels can be turned by hand with brake applied unless it has extreme pressure is applied. I actually have this same condition with a 66 coronet. It has 4 wheel drum with a converted dual master. Otherwise all stock.
Any ideas?
Doug
Posted By: calrobb2000
Re: hard brake pedal ,no stop - 08/02/11 03:59 AM
hi
on the 66 i think you need a master cyl from a c body to get the correct preasure to the wheel cyl .
and maby some larger wheel cyl .
does the 70 have a proportioning valve ?
also old hoses cause problems !get new !
Posted By: DAYCLONA
Re: hard brake pedal ,no stop - 08/02/11 04:08 AM
Did you adjust the threaded pushrod on the booster before installing the master cylinder,...clearance should be approx .060....you may bottoming the pedal, but if the airgap between the pushrod and the master's piston is a "mile' away, it's just not moving enough fluid to create pressure
Posted By: peter
Re: hard brake pedal ,no stop - 08/02/11 11:38 AM
i have just done the same thing and have the same problem
ive in stall hemi style brake booster and disc brakes
when i drive the car ive got use both feet to try and get it
to pull up
pete
Posted By: dvw
Re: hard brake pedal ,no stop - 08/03/11 02:08 AM
The push rod adjustment has been to long,to short,and right on. Pads are not the issue,it won't even stop well at an idle. I believe the booster is bottomed before the master has enough travel. Could a drum booster have shorter travel than a disc booster? Come to think of it this is the 3rd car I've known of with this problem. The 3rd car was a 69 Hemi Charger Originally power drum brakes converted to disc. The booster was removed and converted back to manual disc. Problem solved. Removing the power brakes on this car is not an option.
Doug
Posted By: phantomx
Re: hard brake pedal ,no stop - 08/03/11 09:35 AM
After what my brother just went through with his drum brakes on his Barracuda, I wouldn't overlook the pads depending on where they came from. He put new drums and shoes on the front of his 65 and it would not stop, like scary not stop. He pulled them back down and the shoes still looked new, he slapped his old shoes back on just to see and voila, stopping on a dime. A new set of Wagner shoes and he's good to go. The offending shoes were from Autozone.
Travis..
Posted By: 1969RR
Re: hard brake pedal ,no stop - 08/03/11 07:42 PM
Hello, Did a 70 Challenger last year, and just today, finished a 71 Cuda...exact issue you are having!! 1st the Challenger. If you are using the valves from a 70 (two separate valves) make darn sure the lines are hooked correctly. Believe me, you can hook them up wrong! That was my problem. Could not get the car to bleed. Had a hard pedal tho. Switched the lines to the correct positions, problem solved. Now, the 71 Cuda from today. Kit came from Inline. It is to use the 70 valves. Shouldn't make a difference tho. Anyway, couldn't for the life of me get fluid to the rear. Bled, and bled..no luck. Ended up being a collapsed rear hose. Why it worked with the drum...I don't know. Replaced hose, all's good.
When you are bleeding, crack open fitting closest to master and work your way back. I bet you'll find the problem. Take care, Jeff
Posted By: RapidRobert
Re: hard brake pedal ,no stop - 08/04/11 12:17 AM
At this point, me I'd hookup a 1500-2000 psi gauge to the 4 corners & see if it's a psi or a pad/lining prob. You can get a 5" round gauge in that range for 10-$15 plus need several fittings to adapt it (I think the gauge is 1/4" male NPT)
Posted By: dvw
Re: hard brake pedal ,no stop - 08/04/11 02:47 AM
Cam is very mild,218@.050". Has well over 12" vacuum. There is plenty of fluid flow out of the rear bleeders. Pads were switched last summer with no improvement. I'm going to rig up a pressure gauge this weekend. It does have the stock drum brake valves. I may rig a temporary line from the master to the rear axle as well.
Doug
Posted By: dvw
Re: hard brake pedal ,no stop - 08/05/11 03:26 AM
I've tried both. 1 1/8" disc master. Also 1" drum master. And yes I removed the residual check valve 1st. Both felt the same. But your right the drum valve may be an issue. However car #2 with this problem was converted from a single master to a dual master, the original drum brakes are still on that car. So this is not a disc only problem.
Doug
Posted By: TheRamMan
Re: hard brake pedal ,no stop - 08/05/11 06:26 AM
CORRECT HEMI POWER BRAKE UNITS WORK VERY VERY WELL
Posted By: TheRamMan
Re: hard brake pedal ,no stop - 08/05/11 06:31 AM
you must have the correct parts ,functioning correctly ,for it to work correctly..i will help you 817 691 5996
wayne TRM
Posted By: TheRamMan
Re: hard brake pedal ,no stop - 08/05/11 06:34 AM
VERY SMART ...YOUR HOSE REASONING
Posted By: BradD
Re: hard brake pedal ,no stop - 08/05/11 06:50 PM
A POWER DRUM booster will not work with disc brakes!
We just went through this on a 68 Charger R/T. We put all of the disc brake parts on the car except for the original Power drum booster that was originally on the car. We had a hard pedal but the car was not stopping well. Changed to a Power Disk booster and stops great now.
Brad
Dorn Restorations
Posted By: 71X-mark
Re: hard brake pedal ,no stop - 08/07/11 01:34 PM
How can you tell the difference between the drum and disc boosters? Don't they look the same?
Posted By: dvw
Re: hard brake pedal ,no stop - 08/08/11 02:45 AM
The replacement booster was ordered for disc brakes. It looks exactly like the drum booster. The owner of the R/T was out of town this weekend and forgot to leave me the keys. I'll chase the problem this week.\
Doug