[LouisianaGuy]

Ok since I lost the sprag in my TH 350 Im pulling it tomorrow to take it to a friend to have it rebuilt.
He said he had a hardened sprag laying in the shop that was new and we are going to get a quality brand rebuild kit for the tranny.
What other items should I consider adding while the tranny is torn down in order to make it hold up better to my 455.
I dont wana have to do this again anytime soon.
And im going to be working on the turbo project really soon so need to make this tranny as good as I can.
Mike

[LouisianaGuy]

Ok since I lost the sprag in my TH 350 Im pulling it tomorrow to take it to a friend to have it rebuilt.
He said he had a hardened sprag laying in the shop that was new and we are going to get a quality brand rebuild kit for the tranny.
What other items should I consider adding while the tranny is torn down in order to make it hold up better to my 455.
I dont wana have to do this again anytime soon.
And im going to be working on the turbo project really soon so need to make this tranny as good as I can.
Mike

[screamingchief]

There are some bushing mods in the th-350 handbook by ron sessions that help.The hardened intermediate race is a good start,only thing better is the high dollar th-400 style sprag and drum assy.And using a modified th700r4 low/reverse clutch assy(sprag)helps,make sure you have good clutches with clearances optimized.Highly recommend new thrust washers and bushings throughout,use the thick drive shell,and the case saver,a good hi-flow filter(mesh style,NO paper).I'm sure there is more,others will have some tips.

[buwalda]

When I switched from a Holley SD intake to the Performer intake on my 455, it blew the inter clutch sprag in my T350, even though it was a new surface hardened heavy duty sprag. All the parts were new, including bushes & cluthes modified as per the Ron Sessions book. The trans only had about 200 miles on it. Luckily, it did not damage anything else. I bought the expensive one-piece direct drum/sprag assembly. That's three years ago & 10,000 miles since. Fingers crossed!

[Cliff R]

The 700R-4/4L60 center support/sprag is a good upgrade, but you will need to use one from a mid year 1987-up unit, the early ones are the same as the TH350's. The intermediate roller type sprag is a sore spot. The good race will not prevent the rollers from breaking when the holding capacity is exceeded. It helps to leave the waved apply spacer in place and the spring in the accumulator. Extremely hard 1-2 shifts are hell on the sprag. The drum Geoff mentions is highly recomended for high torque engines.

There are other sore spots in the TH350 to address during rebuilding. Replace ALL the bushings and loc-tite them in place. If used, replace the front two peice planetary carrier with a one piece unit. Discard any waved apply plates in the direct drum and use high quality steels/frictions. Some units will require apply piston replacment for full friction capacity. We have TH350's running well into the 10's behind 600plus HP 455's without any issues. Overall a good transmission, but you will find building a killer unit more expensive than a TH400......Cliff

[onetru462]

"Overall a good transmission, but you will find building a killer unit more expensive than a TH400......"
Just my 2 cents, but I agree there Cliff. Especially being so many people will let you just drag away a BOP TH400 (at least around most areas I have lived).Brutal strong, easier build. Someting to consider is all.