rebuilt 727 trans problems

[jsrod21]

I rebuilt a 727 transmission for my 66 coronet, not my first rebuild, but my first time of having issues after a rebuild. Everything went smoothly but after installing it in the car the car has slipping forward low gear but goes into reverse fine. I have double checked linkage adjustments and band adjustments and double checked the balls in the valve body. I changed pumps I used a 1974 pump and installed it in a 68 housing. Also I noticed after checking this site that it has a shift lever from a 904 which I think was original in the car. Any information on this would be greatly appreciated.

 

[WileE]

Have you checked the line pressure ?

 

[RT K_line]

Is it slipping in drive 1st or manual 1st?
I think the new pumps are different from the old ones too. What parts of the pump did you use?

 

[jsrod21]

I haven't checked the line pressure I don't have a gauge I will pick one up. I used the whole pump from the 74 transmission. It was from a trans I had previously rebuilt and worked in a previous project. I have seen some comments online that this won't work but I haven't seen definitive awnser why. The other thing is this valve body doesn't have an 11/32 ball in the valve body but I checked a trans from the same year and it didn't have one either,

 

[jsrod21]

Slips in manual first. If you wind it up it goes in and out of gear

 

[silversedan]

there is a difference in the inner diam of the pump where the input shaft sealing rings ride, if you using your original input shaft with the new pump it might be the problem. you have to measure it and compare to your old pump. ran into this before swapping parts around.

 

[threewood]

Did you pressure test the servos for operation? You still can but you have to drop the vb. Did you pressure test the clutch packs?

 

[oldbee]

I'm going with "silver" , low line press. You have to really screw up on a rebuild on a TF. Heck I've done 4 with no problems!

 

[jsrod21]

I pressure tested the serves and clutch packs when I put it together. This is what is making this frustrating, I double check everything before I put it together so I don't have these issues. Ive rebuilt about 10 transmissions dodge and Chevy combined this was has been the first failure. Ive ordered a pressure tester but suspect ill be changing pumps.

 

[oldbee]

jsrod21 sadly I think ur right. Hope the low press didn't hurt anything.

 

[miller]

I pressure tested the serves and clutch packs when I put it together.

I don't have any experience with a later 727, though I know there's differences on the pumps (and maybe ports). Air pressure testing the servos, and clutches, won't tell you anything, if the pump doesn't give the right pressure.
I'd sure look into getting a 'right' pump in there.

 

[dvw]

I air check by stacking the input shaft and both drums on my bench. Drill a hole in the bench to allow the input and reaction support to slide in. This way you test the seal at the rings and the clutch seals. 67 and up input shafts are the same until the lock up converter era. 68 and 74 use the same pump housing and rotors. However the drum bushing and ring location in the reaction shaft support are on different locations and must be swapped together. If these parts were wrong it would affect 3rd and reverse. No forward gears would indicate the rear clutch is not holding. Torn piston seal, broken input shaft seal rings, valve body issue.
Doug

 

[jsrod21]

I finally pulled the trans out found a crack in the valve body and smoked the front clutches. So I went to a different trans pulled the valve body out of it and found it was cracked also. So I went to a third trans and finally found one that wasn't cracked. I didn't realize this was such an issue with the 727.

 

[moper]

I don't believe the pump alone can be changed from pre-'68 to post-'68. Check online sources but I think either the pump and input shaft, or pump and kickdown drum have to be changes together because of the passages and seal placement.

 

[oldbee]

Although I've only done my own, I'd bet a cracked vb is from incorrect tightening.

 

[jsrod21]

Not In the places they were cracked. Ill try to post some picks later in the week. They crack along one of the channels. I believe its a flaw. The one I ended up using was from a 69 and the casting had been changed a bit. The newer casting is reinforced in that spot.

 

[oldbee]

Looking forward to pics, all I ever heard of was 'case porosity' in GM's in the 80's, that could've meant almost anything.

 

[oldbee]

Looking forward to pics, all I ever heard of was 'case porosity' in GM's in the 80's, that could've meant almost anything.

 

[dvw]

I remember Paul Forte from Turbo Action telling me there is one casting prone to cracks. Though in all my years I've never seen one personally. The input shaft/reaction support change is 66-67 .
Doug