727 locking up when in manual low

[ShaneG.]

Like the title says when I place the car in drive it shifts fine other than a quick 1-2 shift no matter where I set the kickdown. If I put the car in manual low/1st and take off the trans will lock up along with the entire drivetrain...not a good thing!
I have noticed that if the kickdown is left very loose the point at which it happens is later.
This trans was rebuilt and put into the car and then sat with very little use until I bought it and got it going again. It was built with heavy duty internals and a 9.5" PTC convertor. Engine is 12.25cr 440 with 3.91 gears in a 8 3/4.

I assume there is a issue with the valve body causing the trans to go into 1st and reverse at the same time? I don't know if it's a valve sticking or somekind of pressure leak causing it. I had the pan off and it was very clean inside, I pulled it because the tab on the tailshaft borke off at somepoint and the low/reverse band shaft fell out. I replaced all this and re- adjusted the band.
Any trans guru's have a thought on this?
Thanks

 

[Darter6]

I had the same happen to me once on a 727 and it was a incorrect band adjustment
Don't know what I did wrong the first time but pulled the pan, adjusted both bands again and it cured my problem.
Hope this helps. It does have me wonderin' about the kick down problem you stated it may not be just bands.

 

[oldbee]

If you got rear band adjusted correctly, I would guess an internal leak in valve body. Maybe DVW will chime in.

 

[ShaneG.]

I adjusted the rear band to 72in lbs and backed it off 2.5 turns if I remember correctly. The first time it done it was right before the shaft fell out...probably with in an hour or so.

 

[493 Mike]

I adjusted the rear band to 72in lbs and backed it off 2.5 turns if I remember correctly. The first time it done it was right before the shaft fell out...probably with in an hour or so.

Usually reverse band is backed off 2 turns. I never saw a band apply shaft back out even to the retaining tab. Usually the pin is all the way in and the hole is packed with mud! Is there a aftermarket shift kit installed? If so try to get the instructions that came with it.
Mike

 

[ShaneG.]

I do believe it does have a shift kit in it. I think they are to hard to not have a kit in it. I know the guys that built the trans but it's probably been close to 10 years ago I think. The car sat a long time there at the shop because the owner never came back and paid for the work and they kept the car and just got the mechanics lien 2 years ago.

 

[Dipstick]

When it locks up on the manual 1-2 upshift, does the car come to a screeching halt or is the lockup momentary?

 

[ShaneG.]

Screeching bash your face off the steering wheel halt. As soon as you knock it into 2nd gear it frees back up. I'm not sure if it is trying to shift into 2nd when it locks up.

 

[turbine68rt]

Other than making sure both bands are properly adjusted as previously mentioned, some other areas to check are; accumulator for broken rings or sticking, remove valve body and inspect for damage/sticking valves, with vb out do an air check for proper engagement of front & rear clutch. If disassembly is inevitable, check or replace overrunning clutch springs and rollers and inspect related parts.

 

[1 Wild R/T]

The fact shifting out of manual low releases the lock up proves the rear band is working, it applies & it releases... That means something else is applied/locked when in 1st gear...

Rear clutch is supposed to be applied in 1st/2nd & Drive... If the front band is applied it wouldn't go into 1st when taking off....

You need two elements applied to create a gear... Three elements applied locks the trans... Think trans brake...

That application can be caused either in the valve body or a part can mechanically fail in the applied condition....

 

[ShaneG.]

Thanks for that chart. I'll pull the pan and remove the valve body. I was thinking thats where the problem lies but wasn't sure. I may just order a reverse manual and put it in.