Master cylinder?? Issue.

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E Satterfield

E Satterfield

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i own 2 Mopars a 72 Duster and a 69 Roadrunner. My question pertains to the B body. 2 years ago I did a disc brake conversion on it. This included all new components to include the master cylinder a dual compartment 15/16 bore.

Today I went for a drive and noticed the car did not coast like it did the last time I drove it a couple months ago. I immediately cane back home and found that I could barely turn one of the front wheels and could not turn the other.

I broke the line loose on the master cylinder going to the front brakes and the wheel was free. I checked the pedal pushrod adjustment. And also pushed the pedal down and disconnected the push rod from the pedal and the same thing. It will only free when the line is broken loose.

I had another new master cyl on the shelf from another project so I bench bled and installed it with the same results.

Somehow in the process of the conversion the lines were reversed at the master cylinder. Front pot small reservoir is feeding the front disc. Large rear pot (at firewall) feeding the rear drums. I know this is wrong but I would have thought I’d noticed extremely hot front brakes over the last couple of years if there was a residual valve issue etc due to it plumbed incorrectly?

Any ideas? Thanks as always
 
So before the lines were reversed and you didn't have this issue. Or you just now noticed them reversed?
 
I noticed today that the lines are reversed. I did the brake conversion a couple years ago and without going into details I was having a rough time of things in my life so I screwed up a few things .But as I said I’ve driven the car for 2 years like that and never noticed any heat issues with the front brakes.

I just finished an automatic to manual transmission conversion and today was the first day to do a road test. I thought at first maybe I had assembled the transmission wrong or something because there was such a noticeable drag
 
You swap out the pedals for the trans swap? Maybe the pushrod length has changed. Can you shim the MC away from the firewall a little or when its locked up, loosen the MC and see if it that frees the lines up.
 
Before I replaced the master cylinder. I loosened the 4 mounting bolts and then disconnected the rod from the pedal with no success. After I installed the new cylinder I pushed in the pedal and removed the rod from it and made no difference. The only thing I’ve found that works it to loosen the line
 
well I wanna say bad master cylinder, but two of them doing the same thing doesn't make sense. Someone smarter than me will come along soon...
 
If the master is a drum/ disk cylinder, it will have residual pressure valve on the drum connection, so if reversed, it might hold the disks in some
Determine where the pressure is releasing/ holding.

Might be a piston problem, or piston not returning. Some have claimed hose problems. Sometimes disks can wear tapered (non parallel) or worn caliper / bracket/ hardware can misalign the caliper
 
You can get rust/sediment in the brake hoses & lines that block the pressure. Try disconnecting the brake lines individually & blowing air through in both directions.
 
A little more info. I prefer shifting my own gears on a hobby/ muscle car but because I felt I got a great deal on this Roadrunner I was willing to purchase it with the automatic transmission . Plus it was newly rebuilt with an aftermarket stall convertor.

It ran well but I didn’t enjoy driving it as much as the manual cars and I don’t have any experience with stall convertors .

So I blamed any type of drivability issues slip etc on the convertor and couldn’t wait to get a 4spd in it.

I’m wondering if this has been a problem since the brake conversion and because I only drove the car once before I did the brakes.

it’s more noticeable now because of the manual trans driving style more coasting In neutral and free rolling with clutch in ?

But it doesn’t explain why I never noticed any extra heat on the front brakes? I would have thought they would have been smoking
 
Could make sense with not noticing before because you were never really "out of gear" with the automatic

what if it sits for a few hours does it bleed off. If you are disconnecting at the master cyl to get it to bleed off then you gotta assume everything forward from there is OK. Master cyl or pushrod.... Final answer and help bump to top... ;)
 
When I purchased the car it had all new IT factory style lines and a bolt on top dual master cylinder. The replacement master cylinder ( Right Stuff Detail) is basically reversed from the factory issue. Small pot in front 9/16 thread and large rear pot 1/2.

I hooked the lines up as were threaded and so with that the small pot 9/16th thread with residual valve was feeding the front brakes and large rear pot with 1/2 thread feeding the rear drums.

In other words the ports were as stock but the pots in the master are reversed from the stock 69

Why I didn’t consider all that at time of install who knows? As I said there were some bad times for a few years.

I still don’t understand why they didn’t smoke ? I may have been wasted but my wife wasn’t when she was riding with me and she’s knowledgeable enough to notice stuff like that.

Reversing the lines with the help of some adapters seems to have cured the problem just went for a short road test and it seems good.

Thanks to Everyone Again
 
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Not discounting this reservoir reversal or whatever your master is doing or not doing. Your front brakes not releasing, take a look at your distribution block. Had this happen to my rear brakes this past summer, had to get trailered home. Wish that I had never replaced and threw away my old nasty looking block. The new replacements are trash, my opinion. If you have replaced one, did you have issues trying to get your lines to seal ? The internals look different, they may do the same thing, but they look different. I believe that I had a seal failure, got another new one and couldn't get the top vertical line to seal, port was done at an angle. Got a third replacement, it looked worse than number two. Took the guts out or number two and put into number one. Haven't had an issue with things since, but I am waiting. As RRR says, Chinesium? I don't know who manufactures the block, but their machining is terrible, the nipples inside the ports of the ones I have, are not finished properly, another reason for leaking lines. The next time I have a failure, will probably throw the master and distribution block and go aftermarket.
 
For whatever reason, as mentioned, your brake fluid is not re-entering the master cylinder reservoirs.. It really is that simple.
But the reasons for not returning can be several, I think all of which have been mentioned.
 
The owners manuals used to suggest bleeding the brakes every two years. Hoses can collapse internally, restricting fluid flow.
 
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