have a th-400 trans and im not sure if i have the wide bolt pattern or the small bolt pattern how can i tell what i have?

 

Is the tranny in or out of the vehicle right now?

I'm not where I can go measure right now, but I'll give it a try. If in the vehicle, pull the inspection cover and rotate the engine until a bolt is in view. If it is close to the ring gear, then it's the large pattern: if in a good inch or so, then it's small.

If out of the vehicle, and you have a flex plate available, set it up to the TC and make that comparison. Especially easy if your flex plate has both patterns on it.

If that doesn't help, I'll have to try again when I can do some measuring.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/LB9 block, ZZ3 cam and intake, TBD heads ported & polished, Hooker headers & y-pipe, 3" Catco cat).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

yes the trans is out. forgot to say that this is a bop th400 too.