Frank, Dana, Rich, or any of you other tranny guru's:
I cranked my 86 Dodge 4x4 truck {727 tranny / np208 transfer}, this morning and attempted to back out of my carport. A couple of seconds after it started pulling in reverse there was a metallic type pop sound like maybe I broke a hard part. After I winched it out of the carport I drove it and it shifted and pulled normally through all 3 foward gears.
I can shift to reverse with light throttle and notice a slight pull on the motor but not near enough to move the truck. There is no abnormal noise.
I replaced clutches, steels, seals, bearings, bushings and pump about a year ago and installed a new higher stall converter. It has preformed flawlessly with cherry red fluid until now.
Any suggestions on what part {s} I'll be needing so I can pull it and fix it all at once.
Thanks for any help.

 

Sounds like either the rear band, or servo piston that applies it has broke. It'll be easy to see once you drop the pan.

Frank
CPT

 

I'll drop the pan tommorrow. I suspect it will be the band according to the pop sound it made and according to my fine luck lately. Thanks Frank. I'll post what I find.

 

I have the pan off now. There are 2 pieces of a broken flat part which looks to be the reverse band actuator strut. I don't have a diagram of a 727 but this 518 diagram is similar enough to show what I'm refering to although my piece {1 1/4" long x 1" wide x 1/16" thick} does not have those notches. It broke dead in the center. I have it circled in red in that diagram.
I backed off the adjusting stud all the way and have a good bit of play but I don't know if I can I get another strut up above that pivot piece without having to pull the pin out of the lever?
The housing between the transmission and transfer case has a small corner covering the hole that the lever pin pin will need to come out of. I'm trying not to have to pull the transfer case. I can break that corner {about 1/4"} off the extension housing if needed in order to pull the pin and weld {heli-arc} it back on after I'm through, but If the new strut will fit in with the lever and pivot piece in place, it should be no problem.
Will I be able to get a new strut in there without dissassembling the lever or do you have a better way?

BTW: The actuator piston was pushed out so far, it had the tab on the lever in a bind at about a 45 degree angle. I pryed it out of the bind and it retracted right back to the bottom of the bore, and seems unhurt. Am I lucky or what.
That's a ton for your help Frank, once again.

 

It'll go in as long as the band adjustment is lossened. You may have to get it close, and tap it in with a large screwdriver.

You might want to pull the srvo out and check the rubber seal on it.


Frank

 

I just got back from the machine shop where I had a stud made. The soonest I can get one is 3 days so I'm going to use this one and if it fails, I'll have a replacement. I'm getting back to work on it now. I'll let you know how it turns out. It sure is tight in there!!!

 

I didn't get a servo piston and seals but I'll order them in the morning. The strut was pretty easy to get in after I took the valve body off. The homeade strut works fine but I wasn't as lucky as I thought about binding that servo piston without damage. I suspect the servo isn't applying enough pressure to spin the Swamper tires when I backed up against a tree and started digging, it started to slip and I let off of it immediatley. I imagine the piston got scored when it was in that bind and of course the seals will be trashed as you suggested. I'll need to install the correct strut when it gets here anyway so I'll swap the piston and seals then. It looks like a pressure test port on that servo chamber so I'll check the pressure to be sure, but it makes sense for the servo to be bypassing fluid after as hard as it was binded.
Anyway, at least I can back up now.
Thanks again for the help Frank

 

well isn't this special.
I hooked to a friends truck that was stuck in a ditch with a loaded trailer and attempted to pull him out. My tranny acted like it jumped in neutral. It would not pull in either position of the shifter {1-2-D}.
I climbed under it and tightened the front band all the way in and it pulled out in 2nd gear {no truck / trailer attached, we pulled those out later with my tractor}. Now it starts off from 0 MPH in 2nd gear and if I attempt to shift to D {3rd gear} it binds. If I relax the tension on the band it will not pull period. There is also an consistant whining sound while moving. I have little knowledge about diagnosing a 727.
I guess I already owe you a Thanksgiving turkey and now, what would you like for Christmas.
And thanks Frank for the 9 hundreth time.