CJ/ Commando brake question

uglyjeepoffroad

uglyjeepoffroad

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Joined
Mar 20, 2005
Location
Hickory, NC
I have '78 CJ front discs on the Commando. They stop really well, but when I was doing the swap, I let the master run dry. I replaced it with a '78 cj master and went through about a week of bleeding to get it to work. The rear never really did bleed, but I was able to drive it a little.
Now, I swapped in a new (rebuilt) '72 master to get back to the original that seemed to work better.
It bled great and the pedal firmed up nicely. I took it for a little ride and the pedal kept getting firmer with every stop. It tightened up to the point that the front brakes are dragging. I got it back to the house and, with it out of gear, I can't push it.
The front brakes are locked up totally.
I ASSume there is a residual pressure valve for the original drum setup, but I am not sure how to remove it.
Does this sound like what is happening?
 
Did you "bench bleed" the new master? You have to bench bleed it before hooking up the lines and bleeding the lines or you're pissing in the wind, so to speak.

You didn't mention it, so I assume it wasn't done...forgive me if that was a given
 
Did bench bleed. I am thinking now that I may have extended the rod a little too long and the master is not returning all the way. I had shortened the rod to put in a '78 CJ master and had to re-lengthen it for the original.
 
uglyjeepoffroad said:
Did bench bleed. I am thinking now that I may have extended the rod a little too long and the master is not returning all the way. I had shortened the rod to put in a '78 CJ master and had to re-lengthen it for the original.
Click to expand...


I think you have your own answer -
There needs to be some freeplay in the linkage or constant pressure will cause heat & expand the fluid and make the calipers drag - causing more heat causing more expansion = vicious cycle.

Another possability is kinked or collapsed brake hose(s) - can give similar symptom. You can press hard enough to force fluid through, but the fluid can't return. Effectively creating a "one way valve"
A way to check this is (with pedal up i.e. at rest) crack the bleeders loose. See if there is pressure. Like as if someone was pushing on the pedal. That is a good indication that pressure is not releasing.

HTH,
 
I am thinking I goofed on the length. Wow, that is the first time...































...today.:D
 
I know on the Ford MC's that if the push rod going into the MC is adjusted too long--that when you drive it and the vaccume increases in the motor--it will apply the brake as if you put your foot on the pedal. Looks like you may have already realized that---this was just an FYI responce.
Good luck with it, because I know from personal experience that having brakes that work good enough to feel safe on the road/trail is ok, but I don't like wondering all the time, "could they be better" or "is something going to go wrong at a time I need them most".
---Sty
 
uglyjeepoffroad said:
The front brakes are locked up totally.
I ASSume there is a residual pressure valve for the original drum setup, but I am not sure how to remove it.
Click to expand...
To remove a Residual Valve...
-remove both brakelines from the master...
-then check to see if you actually HAVE them! (most are brass, so if you only have cast, they're gone already)...
-if you do have them, find a couple of nice sheetmetal screws...
-insert them into the brass fittings seat a thread or so and pry them out...
-you'll probably want to rebleed the system afterwards.

FWIW, the last drum-drum MC I put on the Moss was missing the RPV on both ends... guess they were running short that day in Guatemala! :shaking:
 
Did you put the prop. valve for the disc brakes on there also, an good point on the Resi. valves a lot of people over look this master cyl. feature when doing a disc brake conv., not realising that these valves preload lines. Can very well be locking you up.
 
No proportioning valve, but I did find that the rod is not allowing any play at all. I think it is just a little too long. It is not allowing the master to fully retract, thereby building pressure.

I ran it for a few months before I replaced the master and it was fine.
 
Let me know what you find...

I know my drum-drum master absolutely SUCKS (well, could be pushrod length also), but I plan to go with a disc-drum master soon. BTW, take a couple of digis of the brake linkage underneath the dash... I'm thinking of ditching the booster (too many pucker factor stops! :( ) and I'm pretty sure the linkage is different....
 
Chris, I had the EXACT same thing on My CJ when I swapped MC's. I took the Push rod out and put it to the grinding wheel and knocked off about 1/4" That was too much.... Now I have to pump my brakes once real quick to get good pressure. Take little off the new rod, about 1/8".
 
Caver,
The linkage is only a rod that goes straight into the master. It has a post on the pedal, and the rod has a "ring" on the end that fits over the post. I'll see if I can contort under the dash and get a pic.
Brent,
I hear you on the length. I am going to take a little at a time, until I have just a little play before it engages.
 
Shortened the rod about 1/4" and took it for a test drive. Nailed the brakes at about 40 mph and locked up all 4 35's.:D
Drove it for about another 3 or 4 miles and the pedal stayed where it was supposed to be.
 
uglyjeepoffroad said:
Caver,
The linkage is only a rod that goes straight into the master. It has a post on the pedal, and the rod has a "ring" on the end that fits over the post. I'll see if I can contort under the dash and get a pic.
Click to expand...

No joke Sherlock! :flipoff2:

I wanted a picture to compare with mine that is setup for power brakes... IOW, mine PULLS (cantilever linkage forward of the firewall) instead of PUSHES like your manual brakes.

Seems I heard from Toad that they are different pedal arms, but seems like AMC would be too cheap to make 2 different parts... wanted to see exactly where the stud for the pushrod sits (maybe I have a hole for one already?), so I could keep the same arm... just modify it to push.

Since we have identical brakes (axle end) I'd LOVE to be able to lock them up and if that means ditching the booster... well, I'll make someone a great deal on it!
 
Waaaaaa,waaaaaa,waaaaaah.
I will charge the battery on the camera and snap a pic or two for you.

Yours is also an auto, so just one wide pedal. Mine may be a different setup. I have one of those funny looking 3rd pedals. Still not sure what it does.:flipoff2:
 
wbcarver said:
Wassa matta ?
3rd leg too short??
:lol:
Click to expand...
First the rod is too long, now the 3rd leg is too short. Make up your mind, Bill. Some people you can't ever please.:D
 
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