I typically see recommendations for a 34-element intermediate sprag upgrade for TH400 transmissions. What happens when the stock piece fails?

My TH400 is a stock 1966 w/shift kit & high stall convertor. It started slipping in 3rd a couple of months after the shift kit was installed but before the convertor. The slipping is worst at part throttle, which leads me to think it has something to do with slipping clutches, but maybe it's just this sprag. The tranny works well in all other ways.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

Not sure and the 400 but I blew one up in a TH350 early in the race season. I totally destroyed it. My symtoms were no manual 2. When I shifted from 1-2 it wouldn't shift. When I left it in drive I would feel 3 shifts coming down the return road and only 2 shifts going down the track.

Best way to check is to drop the pan. If there are a bunch of pieces in the bottom then the sprag is toast.

If you didn't install an aftermarket oil cooler with the high stall converter, it's possible the oil is cooked and the clutches are slipping on glazed disks.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block buildup now in progress for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car
91 454SS daily driver
95 Homebuilt Harley

 

The fluid is definately not cooked. It only slips when getting on it from cruise, and is a little slower shifting into 3rd under WOT (the last time I ran or drove it, back in 1999). I dropped the pan to drain the fluid when I put in the torque convertor, and there wasn't anything in the pan.

I was under the impression that the sprags did different things in TH400's vs. TH350's, but I may be wrong.

Anyone have any info about this TH400 sprag? I hope to pull the tranny this winter, and would like to have an idea what needs attention.

 

It sounds like the clutch packs are toasted. If the sprag was gone, you would have lost a gear. The stock 16 element sprag is junk. When you rebuild the tranny, put in the 34 element sprag (you will have to buy it separately). I used the TCI master rebuild kit. Also, since your tranny is a pre 69 1/2, you will want to machine down the intermediate drum and add in a spacer. This will prevent the case from eventually cracking during the 1-2 shifts.

There is a really good book on T400's written by a guy named Ron ...... (I think). I have it at home. I bought it at Borders a few years ago. If you want the exact name and title, send me an email so I remember when I get home (tomorrow night).

Miles


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88 427 Camaro
12.18 @ 113mph 1.75 60ft
http://www.geocities.com/mek88427

 

If 3rd gear is slipping and 2nd gear is not, then the intermediate sprag (2nd gear) is holding. When the sprag lets go you will not have 2nd gear. Since you have a pre 1971 you have the correct 3rd gear drum that will accept the 34-element sprag, (assuming the trans has not been rebuilt and the builder replaced the the drum with a 1971 & later drum). When building this unit there are a lot of updates that you can perform that will help the lengthen the life & improve the shift feel of this transmission. I would be glad too help with your questions, you can e-mail me at probuilt1@earthlink.net or call me at 800 7763288 Mon-Sat 10-6 PST. The TH400 is an excellent transmission when setup properly. This transmission can easily handle 800-950 HP.

 

Here is the link to the book on T400's. If the link didn't work, go to my page and it is in the Camaro section.

http://www.geocities.com/mek88427/t400_book.html

Miles

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88 427 Camaro
12.18 @ 113mph 1.75 60ft
http://www.geocities.com/mek88427

 

To revive an old one, w/update:

I pulled the tranny and gave it to a fellow racer who does this stuff for a living. When taking it apart, he said he found a check ball where it is usually removed for a shift kit, and none where he expected one. The missing one is for the 2/3: Both clutches and bands were burnt up because of it.

Appears the TCI Trans-Scat instructions are in error. He's putting in the 34 element sprag while he's at it, but I may have a "talk" with TCI...

Thanks for your insights. More after my "chat".

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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, WP 305 heads ported & polished, Hooker headers & y-pipe, hi-flow 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 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.