john71

Ok guys I need some help here. I had a 71 350 with a professionally built TH350 trans bolted to it. I have since sold the 350 and had a 70 455 rebuilt to put in my car. When i bolted the trans to the BB the torque converter was tight against the bellhousing and so tight against the new flexplate I couldn't turn the converter to align the bolt holes. The trans housing is a 78 which some refer to as the metric trans. Again this trans was mated to a 350 with no issues. My fears of course are there is not enough clearance (tolerance) to allow some flex in the flexplate etc. thus tearing apart the trans pump and who knows what else. The torque converter is about 12 inches dia x 6.5 inches deep (stock to my knowledge) Please advise and Thanks in advance

svnt442

It sounds to me like the torque converter is not seated properly. It should sit back about an inch from the face when fully seated in the pump.

john71

Randy, Converter is seated all the way. It is sitting 1/8" away from bellhousing on bottom near pan. Thats what has me puzzled. I know the converter is seated all the way but yet stiil tight against flexplate no room to turn it

OLDSRALLYE350

If you can get your fingers between the torque converter and the front pump in the transmission it is not all the way back. Best way i know to check it.

john71

No way to get my fingers to front pump. Converter is tight to bellhousing. Thanks

svnt442

Well I can tell you the dimentions of the 350 and 455 in that area are identical.

Bluevista

Something's wrong, have to have at least an 1/8th to 3/16th of an inch play between the flexplate and converter or you will mess things up.
Did they use a different size/depth converter for a 455 with a turbo 350?

svnt442

No.
Like I said the 350 and 455 have the same dimensions in that area of the block and crank.
Also the TH 350 and TH 400 use the same torque converter and the bellhousing dimensions are the same so the only answer is the converter is not seated properly.

Oldsguy

Welcome to CO John. I hope you can get the problem worked out.

drec02

Make sure you have a BOP torque converter or it won't seat properly and will cause the binding issue. Learned the hard way!

john71

Thanks guys. Well I do know the converter is seated. I even had a guy over that has been building BOP engines & trans etc for years and he can't understand it other than a converter issue. He has also verfied converter was seated so we're still workinging the issue.

64Rocket

Don't want to sound to silly, but are the bolts still in the bolt lugs? Also make sure you are not hung up on the counter weight on the flex plate.
Gene

john71

Gene, no statement is silly at this point. The bolts were removed and on the ground beside me. Also looked at counterweight issue. No issue there. The issue is strictly a forward and aft clearance. Thanks for your input and guidance.

70 cutlass s

If it was me I would drop the transmission and pull the tq. conv. then seat it. Just to make sure it was right.

john71

Trans has been dropped 3 times and re seated tq each time. Re looked at new flexplate all is good there. The only thing that does come to mind is i bought the motor used. I have heard of guys using the 425 crank in 455's for destroking them. Does anyone know if this could be the case?

joe_padavano

The 425 and 455 crank flanges stick out the same amount from the rear face of the block, so that isn't the issue.

john71

Thanks Joe. Just grasping here trying to figure this issue out.

jpaulwhite

Wow im interested now. Im planning on swapping a 70 455 for a 69 455 this weekend. In a 70 Olds 98. Crossing my fingers that nothing goes wrong.

john71

Ok Guys I got it. I changed the torque converter and it worked. After measuring everything again I found that the problem child was actually almost 13" diameter. A friend told me it may have been an issue of the converter going bad. He said they balloon sometimes. Can't say for sure but I know the new one mounts just fine. Thanks to all for your input and help.