Disc Brake Conversion Failing

[AJ/FormS]

Did anybody mention plumbing?
The front port feeds the Rear brakes. If you get it crossed up at the Combination valve, the front brakes will get the proportioning............ That's Bad News.

 

[RustyRatRod]

Did anybody mention plumbing?
The front port feeds the Rear brakes. If you get it crossed up, to the Combination valve, the front brakes will get the proportioning............ That's Bad News.

That's an interestin thought.

 

[tedsweet]

the left isnt for 4 wheel drum brakes

 

[RustyRatRod]

the left isnt for 4 wheel drum brakes

Those are my thoughts as well.

 

[1969383S]

Also the OP Stated a swap to 68 Disc's. This would imply Kelsey Hayes.

As a kinda less the happy KH owner since 1984 there are many issues that can be observed. 1" master is the best.

A "REAL" factory Master would be heaven! They have been remanufactured and given every "lie" in the book as to actual purpose.

If, one can purchase a 67-71 "True" A-body Disc/Drum master, more power to you!

Will they work? Well maybe, Will they fit correctly "Specifically BB Power Disc"? Doubtfully! Can you find one that will get it done? Yes!

My best response is go to the store and order every one of them listed for the application. Make them take each one out of the box and check for overall size, reservoir dimension and more before you buy it! Most of what is sold today is pure junk!

 

[RustyRatRod]

Cass at Dr Diff can get you one that works well. I plan on replacing mine when I do the swap. I've already made the proportioning valve and master cylinder swap. Going to put her down soon and do the front suspension and disc brake swap before long. It still stops very well with the 9" drums and disc master cylinder and proportioning valve though.

 

[GTX JOHN]

Save a LOT of problems and talk to Cass!!

 

[AJ/FormS]

My car has the KH 4-pots and 10x2s out back .
she runs a 15/16ths M/C and 15/16ths rear-wc's,
and a booster from a mid-70s Swinger or F-body (I forget which)
She runs 235/60-14s up front and 295/50-15s out back
with Zero Proportioning.
She is far and away, the Best stopping street car I have ever owned, in 53 years.
BFGs got nothing for traction in the forward direction, but they do pretty good for braking....
She burns the rear shoes up a lil faster than the front pads.

 

[Ironracer]

I did the drum to disc swap last summer. I haven’t gotten around to the proportioning valve. I bought an adjustable one but I’m hesitant to cut my line and make another potential place for a leak.
Here’s my question… Is a factory proportioning valve a direct replacement for the drum drum distribution block ?

View attachment 1715980703

Looks like the FMJ disc's that came on my Sat. Sway bar car, PO (big time Mopar guy) let it roll, without swapping calipers. Leaving Bleeder on the BOTTOM. what a Raw deal. So obvious..... yet Royally Rectally Annoying

 

[Dfr360cuda]

Looks like the FMJ disc's that came on my Sat. Sway bar car, PO (big time Mopar guy) let it roll, without swapping calipers. Leaving Bleeder on the BOTTOM. what a Raw deal. So obvious..... yet Royally Rectally Annoying

My bleeders are on top

 

[dodgedude37]

If the bleeders are on bottom the calipers are on the wrong side. How can you expect to get all the air out with bleeders on the bottom? As far as OP there has to be something wrong with the back brakes, maybe disassemble & inspect & reinstall with proper lubrication where required. Really inspect backing plate pads.

 

[Dfr360cuda]

The bleeders, which are not visible, are on top.

 

[chefmatty05]

Hey Fabo Fam's, it's been a long time and A LOT has been done to the Barricuda. I will post plenty of pics of whats been done and also post all of the parts that are up for grabs. But I do have a question for anyone that can help. The car is 67, I did a 68 disc brake conversion up front. the brakes were stopping but not locking and really doesn't feel much different from drum/drum application and the pedal does feel pressure. I replaced the drum/drum MC with a disc/drum MC and also replaced the stock distribution valve for what I think would be the correct proprtioning valve. Welp after all of this only one wheel is locking and it happens to a rear one at that. All of the wheel come to slow stop except the passenger rear. Pleeeeaaase help. MC was bench bleed, no air in the system (I've bleed and bleed the system) new shoes in the rear, new pads up front, new everything and no locking. Any suggestions?

Had similar issues, the front brake line at the master has a residual pressure relief valve, make sure it has been removed for your front disc brakes, the valve is for disc brakes, even though I had replaced my master with disc front rear drum the remanufactured mac still had a residual valve, I cant recall who on here brought it to my attention, but I removed front line, screwed a sheet rock screw in and pulled the residual valve spring out, tah dah, fixed, when I tell you many dollars in new masters/ calipers/portioning valve and brake lines to get to a simple fix. Check it out, you may be pleasantly suprused!

 

[Swinger 340]

Looks like the FMJ disc's that came on my Sat. Sway bar car, PO (big time Mopar guy) let it roll, without swapping calipers. Leaving Bleeder on the BOTTOM. what a Raw deal. So obvious..... yet Royally Rectally Annoying

Bleeders must be at the top of the Calipers to bleed off any air. Calipers should be set to the rear of the rotors and not the front or the brakes lines could be in the way of turning. 3rd, install spindles on the correct side. As per the OP question, I believe if the lines are bled and clear than the shoes must be contaminated with some fluid or oil on the opposite side of the lock up brake. Check wheel cylinder for operation. Problem is at the "T" block and beyond, at the same side.

 

[Son2PopsCuda]

Update, I was able to find on eBay an NOS MC for disc/drum. Also made sure that it didn’t need rebuilding being that it is NOS. Seller said that all of the rubber is checked before shipping so rebuilding wouldn’t be necessary. I installed it and the brakes work as they should. It was the MC all along. I still have minor adjustments to the shoes in the rear but overall a major improvement. Thank you for all of your input and advice.

 

[Swinger 340]

Also the OP Stated a swap to 68 Disc's. This would imply Kelsey Hayes.

As a kinda less the happy KH owner since 1984 there are many issues that can be observed. 1" master is the best.

A "REAL" factory Master would be heaven! They have been remanufactured and given every "lie" in the book as to actual purpose.

If, one can purchase a 67-71 "True" A-body Disc/Drum master, more power to you!

Will they work? Well maybe, Will they fit correctly "Specifically BB Power Disc"? Doubtfully! Can you find one that will get it done? Yes!

My best response is go to the store and order every one of them listed for the application. Make them take each one out of the box and check for overall size, reservoir dimension and more before you buy it! Most of what is sold today is pure junk!

Flip over the MC and a 1" bore should have a 411 at the end of the part #. This has no barring to the rear brake lock up. Contamination of fluid in the line or on the shoes or a leak on that one side. When bleeding, you need a steady flow of fluid or you may have a blockage of some kind. Hint: When replacing any WC I always pump fluid through the lines before attaching new part.

 

[Son2PopsCuda]

I since replaced the MC with a factory coded disc/drum MC. Bench bleed it, re bleed the system, pressure was felt instantly and brakes work. I’m no mechanic and don’t pretend to be but I know my way around the garage. With that being said I’m definitely getting the brakes inspected and overhauled if necessary. It is a night and day difference though. Interesting thoughts on the subject. Thank you everyone that chimed in

 

[a-bodyguy]

I have the kh disks it had the rare 541 master the ebay master was silly money and could have been ng being old
i put a 56 dollar 15/16 on it with lifetime warranty
like the brake feel much better then the 1 inch master the big toe only stops the 3800 lb ragtop

 

[str12-340]

Had similar issues, the front brake line at the master has a residual pressure relief valve, make sure it has been removed for your front disc brakes, the valve is for disc brakes, even though I had replaced my master with disc front rear drum the remanufactured mac still had a residual valve, I cant recall who on here brought it to my attention, but I removed front line, screwed a sheet rock screw in and pulled the residual valve spring out, tah dah, fixed, when I tell you many dollars in new masters/ calipers/portioning valve and brake lines to get to a simple fix. Check it out, you may be pleasantly suprused!

OH!!! I really missed this - if the OP's replacement master really is a drum/drum MC, then it would come with residual pressure relief valves in both the front and back outlets which could be a great source of problems. So it's not just the reservoir size that is the issue - the unequal sized reservoirs are an indication that the MC is for a Disc/drum system with the residual valve only on the back brakes...