1969 mustang trasmission problems

[jeff69becky]

I currently finished putting a roller cam 5.0 engine out of a 91 mustang gt into my 1969 mustang. when I drive it a get this really horrible vibration and have a couple ideas why but ive never had the problem so I was hoping somone knew. theory 1: I need to use the harmonic ballencer from the 91 engine instead of the factory one that came of the 69 motor. theory 2 I have the stock 3 speed auto in it and put the old flex plate in due to the bell housing was too small for the newer flex plate out of the 91 which could inturn though off the engine because I know that the flex plates are weighted diffrently. hopefully somone knows what I can do to fix this remedy, thanks Jeff

:SNSign:

 

[69Rcode_Mach1]

That is your problem, your flexplate and harmonic balancer are not the correct imbalance. The 5.0's use a 50oz imbalance where the older ones used the 28oz imbalance.

 

[D.Hearne]

Ditto. Swap the balancer and flexplate. You can buy a 50 oz/in flex that fits your transmission new thru Summit Racing B&M part # you need is BMM-50239. If your balancer doesn't work with the front accessory drive for the 69, you'll either need to use the 5.0 stuff or buy a 50 oz/in balancer that's got the 3 bolt pattern for the older pulleys. Some of the classic Stang suppliers sell these.

 

[xoxbxfx]

Ditto. Swap the balancer and flexplate. You can buy a 50 oz/in flex that fits your transmission new thru Summit Racing B&M part # you need is BMM-50239. If your balancer doesn't work with the front accessory drive for the 69, you'll either need to use the 5.0 stuff or buy a 50 oz/in balancer that's got the 3 bolt pattern for the older pulleys. Some of the classic Stang suppliers sell these.

what he said