4r70w headscratcher WTF!

[Canuck]

I,ve recently done a 4r70w conversion in my 74 bronco. I followed many posts from various members as to the correct parts to use. I have installed quite a few automatic transmission over the years but I,m left scratching my head on this one. My 4r70w came from a 1994 F150 , I also used the flexplate and backing plate recommended by a CB guru on this site. When I installed the torque converter I rotated it a few times to insure it was seated correctly. Once the trans was in place I rotated the flexplate to tighten the bolts to the torque converter, EVERTHING still rotated easily. Final checks, did one last nip on the bell housing bolts and the engine will not rotate, loosen bolts and the tranny rotates again WTF!!!! The Flex plate will only go on one way , thickness of backing plate????????????????? Any suggestions would be appreciated

jim

 

[englewoodcowboy]

Sounds like you do not have the torque converter fully seated. f it is not, it will cause your problem. Def. do not force it to turn or you can damage the tranny. It is not fun to hear this but the best remedy is to pull the tranny, take some measurements from the bell flange on the motor to the mounting surface on the flex plate.Repeat the measuring with the TC fully seated in the tranny (from the tranny bell flange to the mounting tabs on the TC) and compare your measurements. You should actually end up with a little room to spare (I think less than a 1/4" ). If your measurements are fine, it was just a TC seating issue. If they are not, then you may have a spacer in there that was missed or the flange on your crank could be thicker? (I have never heard of that but these days with so many part mfg's it is/could b possible). Good luck and remember to have patience...

You should fully tighten the bell housing to the motor before connecting the TC to the flex plate. The TC should rotate freely and there should be a very small gap between the 2 that will go away when you tighten the TC bolts.

 

[Canuck]

Thanks for responding Englewood. I did have the bell housing fully tightened tothe engine , just did a final snug in my checks before starting the engine. I think I may have to pull the tranny back and check things out F#@*^ !

thanks again

 

[englewoodcowboy]

Knowing that, I would check to make sure something isn't interfering with the flex plate, a bolt head, too long of a bolt or something like tat. I am sure if you pull it apart, you will find the issue.

 

[Broncobowsher]

Going off memory (which is aging)...
The mating surface of the torque converter should be a hair over 1" set back from the mating surface of the bellhousing.
And the mating surface of the flexplate should be about 1" back from the back of the block.

Then don't forget to check for drain plugs on the converter and make sure they clear the flexplate just fine.

Had a stick? did you remove the pilot bushing? If not you need to. The back of the crank isn't deep enough for both the pilot bushing and the snout of the converter. The bushing needs to come out.

 

[hackyrat]

Also check your starter clearance. I had to shim mine back about 1/16" or it would bind on the flywheel. Try removing starter and then see if engine will turn by hand using a wrench on the flywheel. Make sure battery is disconnected.

 

[Canuck]

Thanks guys for your input. The first thing I pulled was the starter to see if that was the issue , as that was the last piece in . It was still locked up.
i,ll slide the trans back and check things again.
It was a C4 I pulled out before the swap so no pilot bearing

 

[BroncinBrandon]

Sounds like the issue I just had on my AOD.. In my case I had the wrong flexplate. It sat about a 1/8th of a inch too far back. Maybe you can eyeball the depth on yours and go to a parts store and eyeball the original Bronco one. I think the last numbers on the flexplate are 205? Hope this helps

 

[blakerj10]

canuck,

Good luck with figuring out your issues.

Can you point me to the part number or source for a backing plate? I was going to use the c4 version out of my 77, but the bottom dust cover doesn't fit. Tried searching with no luck.

 

[Bronchole]

I know you have installed a few auto trans but I thought I'd point out one obvious thing that hasn't been mentioned. Did you install the tin between the trans housing and the engine block?

The one other thing that someone mentioned but I thought I'd go over in more detail. When I install an auto trans the last thing I tighten is the TC to the flexplate nuts. Prior to tightening I make sure that the TC can rotate in the bolt holes (tink, tink the studs in the bolt hole slop) and then I make sure that the TC will move in and out of the transmission, usually 1/8" to 3/8".