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Brakes

Daytrepper

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FBBO Gold Member
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Raleigh, NC
So I got my 66 Coronet on the road that I've been working on for a couple years.

Someone had installed an SSBC Front Disc Brake conversion kit. Nothing looked to be wrong with them, looked like they had hardly ever been used when I got the car.

I rebuilt and replaced all the parts on the rear drum brakes, as well as the master cylinder, as the old one had rust in it.

Flushed the system, power bled it; made sure the rears were adjusted correctly.

The car stops terribly. I smashed the brakes as if in a panic stop, couldn't get any of the wheels to lock up. The pedal is hard. Feels like you better plan your stops and hope nothing jumps out in front of you unexpectedly.

It doesn't pull or anything, it just doesn't seem to have the stopping power it should have, especially with the SSBC 4 piston calipers.

Rears seem to be working fine, proportioning valve is set all the way open, and they were good and warm when I got back to the shop after a 5~ mile test drive slamming on the brakes several times. Doesn't make a difference if I adjust the proportioning valve at all.

They are manual brakes.

Any suggestions? I am thinking maybe the disc kit that is on the car is not enough.
 
I suspect something is not optimized with the master cylinder.
What did you put in?
My 66 charger has Manual SSBC discs and it stops pretty well. I'm sure it's heavier as well
 
"Proportioning valve all the way open" is not a good thing....it should be partially or mostly closed to limit the fluid to the rears as they *should* lock faster than the discs.
Did you properly bench bleed the master cylinder? Easy stuff first...Re-bleed and re-adjust the drums. Check the pedal rod and verify that it's stroking the master all the way.

And...yours wouldn't be the first case of a crappy "new" master cylinder...

FWIW the "Right Stuff" manual front disc kit stops my 440/'68 car fine and the brakes will lock me into a skid if I jam the pedal.
 
What is the bore size of your master cyl? A 15/16" bore is used quite often on manual disc brakes.

I suspect something is not optimized with the master cylinder.
What did you put in?
My 66 charger has Manual SSBC discs and it stops pretty well. I'm sure it's heavier as well

I put in a replacement from SSBC that is for the kit that is on the car, 1-1/32" bore.

"Proportioning valve all the way open" is not a good thing....it should be partially or mostly closed to limit the fluid to the rears as they *should* lock faster than the discs.
Did you properly bench bleed the master cylinder? Easy stuff first...Re-bleed and re-adjust the drums. Check the pedal rod and verify that it's stroking the master all the way.

And...yours wouldn't be the first case of a crappy "new" master cylinder...

FWIW the "Right Stuff" manual front disc kit stops my 440/'68 car fine and the brakes will lock me into a skid if I jam the pedal.

Yep, was bench bled, and power bled. Instructions said to set the valve all the way closed, set to all the way open while counting the turns, and close 1/2 the number of turns needed from close to open -- then open as needed until rears lock up before front. I did this, never made a difference in the feel or stopping power. Rears never locked up. Last run it was all the way open.

The car sat for a long time before I got it; I'm not sure exactly when the SSBC kit may have been installed, but it was likely 5 plus years ago. I am wondering if any damage occurred to the calipers from sitting that long; rust/corrosion inside; etc; on the outside they look fine. I would think I'd have gotten a pull or some other symptom though.
 
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The masters from SSBC are for corvettes and personally I think they are ugly and out of place in a Mopar.
I'd suggest something like this
Screenshot_20230318-201210.png
 
Talked to a fellow Mopar friend that has been around these cars for 40 years or so; he says likely just the manual master cylinder alone doesn't have the balls to properly operate these 4 piston calipers. They'll work, but not like they need to. He also said the factory manual brakes sucked when they were new anyways, LOL.

If I stick with the current disc brakes, options are to put a power brake booster in and a proper proportioning valve --not the "regulator" valve that came with this kit when it was installed.

Because of the rust I found in the master cylinder I am wondering if any of it made it to the calipers as well; so I'm thinking an entirely new disc brake kit, with power boost; something with the 80's-90's style single piston caliper that they put on everything back then. Easy to get parts for and should have no problem stopping the car. Stay tuned.

This car is going to be doing alot of travelling and driving this year, and the last thing I want to worry about is stopping.
 
Talked to a fellow Mopar friend that has been around these cars for 40 years or so; he says likely just the manual master cylinder alone doesn't have the balls to properly operate these 4 piston calipers. They'll work, but not like they need to. He also said the factory manual brakes sucked when they were new anyways, LOL.

If I stick with the current disc brakes, options are to put a power brake booster in and a proper proportioning valve --not the "regulator" valve that came with this kit when it was installed.

Because of the rust I found in the master cylinder I am wondering if any of it made it to the calipers as well; so I'm thinking an entirely new disc brake kit, with power boost; something with the 80's-90's style single piston caliper that they put on everything back then. Easy to get parts for and should have no problem stopping the car. Stay tuned.

This car is going to be doing alot of travelling and driving this year, and the last thing I want to worry about is stopping.
Only difference on what you have going to power is your leg. If a power booster makes you happy then you were not pushing hard enough when it was manual. You can verify each caliper by removing them and having someone push the brake pedal. I use two c-visegrips to keep the pistons from going to far.
 
I agree push them out a bit and then take a c clamp and press them back. They should go back smoothly.
Again I'd put a $50 master on it before I did anything else.
 
Only difference on what you have going to power is your leg. If a power booster makes you happy then you were not pushing hard enough when it was manual. You can verify each caliper by removing them and having someone push the brake pedal. I use two c-visegrips to keep the pistons from going to far.

I'm kind of at the point where I don't want to mess with troubleshooting it anymore, especially since my friend said 4 piston calipers + manual master cylinder is not a good combo. There are too many questions due to the car sitting so long and the rust found in the master. I stood on the brakes with both feet at one point, and it didn't change the stopping power much; she did stop quicker, but nothing locked up, and I dont want to have to worry about that in heavy traffic, car shows, etc. More of a safety issue at this point.
 
I'm kind of at the point where I don't want to mess with troubleshooting it anymore, especially since my friend said 4 piston calipers + manual master cylinder is not a good combo. There are too many questions due to the car sitting so long and the rust found in the master. I stood on the brakes with both feet at one point, and it didn't change the stopping power much; she did stop quicker, but nothing locked up, and I dont want to have to worry about that in heavy traffic, car shows, etc. More of a safety issue at this point.
Then follow your friends advice and see where that leads you. Let us know how that turns out.
 
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