TH400 Sprag Clutch, new and ready to install. Fits the TH400. Ships fast from the USA.
This is a BorgWarner heavy duty intermediate sprag for the GM Turbo Hydra-Matic 400, BorgWarner part 06763AM, with 34 sprag elements. It is the part to order when a 400 in a truck, motorhome or muscle car slips or flares into what feels like neutral right after the 1-2 shift, when a rebuild turns up a sprag with chipped or rolled elements, or when you are building a 400 for more power or towing and want the stronger element count. The same sprag is used in the 4L80E and 4L85E, so it also serves those units.
Second gear in a 400 is made by holding the sun gear still. The sprag sits on the hub of the direct clutch housing, which drives the sun gear, and its outer race is splined to the intermediate clutch plates in the center support. When the intermediate clutch applies on the 1-2 shift, the outer race is locked to the case and the sprag wedges its elements between the race and the housing hub, so the sun gear cannot turn backward. When the direct clutch applies for third, the housing turns forward and the sprag simply overruns. That one-way action is why the 2-3 shift needs no timing between two friction elements. In manual Second the front band clamps the direct housing as well, which is what gives engine braking in that range.
An intermediate clutch with burned plates or a leaking center support produces the same flare, so the pack and the sprag are judged together.
Start with fluid level and line pressure, since low pressure makes every clutch slip. Then compare Drive and manual Second on a road test. Manual Second adds the front band, which holds the direct housing directly. If second is solid in manual Second and slips in Drive, either the sprag is rolling over or the intermediate clutch is not holding. On the bench, hold the outer race and turn the direct housing: it should turn freely one way and lock the other way with no slip under hand pressure. Our TH400 common problems guide walks through the pressure checks, and the valve body testing guide covers the 1-2 accumulator and shift valve faults that mimic a slipping second.
This sprag is listed for the TH400 (Turbo 400, THM400, 3L80) and the 4L80E and 4L85E, but only for direct clutch housings with a smooth sprag hub. Many 400s, including the 1975 units in GM's service manual, use an intermediate roller clutch running on a cam hub instead, and this sprag will not fit that housing. Pull your direct drum and look at the hub before you order. If you are unsure, send us the year, vehicle and VIN or a photo of the drum and we will check it. You can see every Turbo 400 part we carry on the TH400 parts page, and our listing for early 1964-up units is the same sprag design.
Orientation is the whole job. GM's manual for the roller version tells you the outer race goes on with a clockwise turn and must not turn counterclockwise once installed, and its trouble chart lists a backwards one-way clutch as a known assembly fault. Check the same way with this sprag before the drum goes in the case. Inspect the hub and the outer race for pitting, ridges or blueing; a damaged race lets new elements roll over again. When you install the drum you will need to twist it so the outer race indexes with the intermediate clutch plates. Replace the intermediate frictions at the same time, which the TH400 clutch module covers, or do the whole unit with a TH400 master rebuild kit. Fill with Dexron type ATF.
| Fits | TH400 |
| Part type | Sprag Clutch |
| Condition | New |
| Brand | Borg Warner |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It fits TH400s whose direct clutch housing has a smooth sprag hub. Units with an intermediate roller clutch on a lobed cam hub need a sprag-type housing to use it. Check your drum or send us your year and VIN.
The engine flares or the transmission feels like neutral after the 1-2 shift in Drive, then grabs again when third applies. Second often holds fine in manual Second because the front band takes over.
More elements share the load, so each one sees less stress and is less likely to roll over under torque. The listing describes it as replacing a weaker 16-element version, which matters on towing rigs and modified engines.
Replace the intermediate clutch frictions and inspect the outer race and drum hub. If the race is pitted or ridged, replace it too, or the new sprag will slip again.
Yes. The listing covers 4L80E and 4L85E transmissions, which use the same intermediate sprag design as the TH400.
