small block 340 driveline in a big block 727

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Penstarpurist

Penstarpurist

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Trying to get our driveline installed on our 73 duster, but for some reason it won't go in. So my question is this: the driveline is from a 1970 plymouth duster 340 and the transmission is out of a 1970 plymouth sport fury 383 car. Are the splines the same from one to the other? Could the transmission rear seal be different? Or am I just not getting it lined up right?
 
The motor is a big block, the trans is off a big block. The driveline is out of a small block car.
 
Okay, thanks. I'm pretty sure that up until like 1990 that all 727 torqueflite transmissions are the same big block or small. I must be doing something wrong. Any one else out there have any thoughts or suggestions?
 
Splines are the same, seals are the same as long as we are talking about 727 sb vs bb trans. The only difference is the bell housing, the drive shaft should fit.
 
Yes, we are talking about 727 SB and bb. I must just be not getting the splines lined up. I'll have to try again tomorrow morning when I'm not dragging my tail tired.
We have been working nonstop on it. Thanks for verifying what I was thinking was the problem. I'm glad you guys at Fabo are here to bounce problems and ideas off of to help get this done!
 
The guts of the transmissions are the same. The output shafts and drive shaft yokes are the same size and spline. You may have a nick on a spline. Try fitting, clock it a few degrees, try again, etc.
 
That's what I'll do, I had to walk away from it and take a break. I'll be back out there trying again today.
 
Yep at what Brian said. The spline inside the yoke has a flat spot in the splines,just keep rotating it until it slides in.
 
Okay, so I tried and tried to get the driveline into the transmission to no good. It'll start to go in then stop. It can be forced in, but that's not good. So, my son tried to see if it's just me. No luck either. So knowing it supposedly came out of a small block 727 I took the driveline to a small block 727 torqueflite transmission that I have sitting in the garage that goes with a 360 ouy of a duster. Same thing, no go. At this point I'm thinking something has to be wrong with the driveline yoke, that looks to be in perfect shape and has the same spline profile. So, I'm giving up on struggling and going to load up the transmission and driveline and going to have six states driveline shop figure it out. Plus the u joint in the driveline is too wide to fit in the rearend yoke. So, it needs to be swapped out also.
 
Later models (dakotas etc.) With the newer variants of 4 speed autos use a yoke that has the same diameter and number of splines. It looks the same, but the splines ars cut with a different angle on their face. If you try to use one of these yokes on a 727 it will be exactly like you are describing. It could be forced in but will definitely not slide and work as a slip yoke is supposed to. They are easy to mix up....... I have done it, I bought one because of its 7290 u joint size, thinking it was the same. I would guess this is what you have.
 
some a body 4spd's have a small output spline like 904 auto . this 71 duster has the small out put spline . its just a mild 340 driver .

DSC00374.JPG
 
The guy I bought it from here locally is a mopar A-body guru (at least I think so), he has and drives a 71 demon. The demon was a factory 4 spd car but he had put in a 727 torqueflite transmission as a driver until he found all the 4 spd parts. When he went to the 4 spd he pulled the trans and driveline. I bought the driveline from him. I also bought the sure grip rearend from him, 340 torsion bars, leaf springs, throttle pedal, etc. Everything with the exception of the driveline was out of a 340 duster parts car he had. I spoke with him last night and he promised me the driveline was out of a 727 car. I've seen the car, as he still drives it (340, 4 spd). Flawless perfect car. All this guy deals in is mopar, and more specifically A-body cars. Six states built the driveline for him, I spoke with them today and they said the driveline should be correct. But I agree with you d55dave, I think the shaft is wrong. It has to be, otherwise it would fit in at least one of the two 727 transmissions I've got and really should fit both. I think even as informed as my guy is, the possibility exists that maybe his 727 trans was changed or built differently. Only way to know is to take it to the guys who build them.
 
Penstarpurist said:
Okay, so I tried and tried to get the driveline into the transmission to no good. It'll start to go in then stop. It can be forced in, but that's not good. So, my son tried to see if it's just me. No luck either. So knowing it supposedly came out of a small block 727 I took the driveline to a small block 727 torqueflite transmission that I have sitting in the garage that goes with a 360 ouy of a duster. Same thing, no go. At this point I'm thinking something has to be wrong with the driveline yoke, that looks to be in perfect shape and has the same spline profile. So, I'm giving up on struggling and going to load up the transmission and driveline and going to have six states driveline shop figure it out. Plus the u joint in the driveline is too wide to fit in the rearend yoke. So, it needs to be swapped out also.
Click to expand...
Do you have any crud or something down inside the slip yoke
 
I've looked down both with a flashlight and they are clean. I'm thinking either the wrong shaft, or a very slight damage to the driveline yoke that I can't see.
 
Just an update on the problem with the driveline not fitting into 727 trans. Took a 727 and the driveline to six states the local experts, they checked everything over and said the yoke has to be damaged just enough to jam up. So they ordered a couple, said come back tomorrow and they will fund the perfect fit to the trans, swap joints and double check length. Afraid of what the yoke, joints and labor will cost. But at this point, if it all works, it's worth it.
 
Well for those of you who were following the progress on the driveline issue it has been resolved. It turned out that the toke on the driveline was just slightly boogered up. The shop ordered a new one up and it slipped right on. With the new yoke, new joints it cost me $155. Lol, so between the $200 to buy what was supposed to be a recently rebuilt driveline the $155 to make it right I'm into the thing $355. Lol. They charge $350 to custom build a new one. Dang, at least it's in and right. Haha.
 
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