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Old 01-21-2007, 03:49 PM
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T-400 clutch drums

Are all factory TH400 clutch drums the same length? I ask this because I need to build a TH400 for a one-ton truck. According to the FSM, different versions of the TH400 could have had four, five, or six composition plates in the direct clutch (for example - the forward clutch pack is similar). I'm assuming that the one ton big block trans would have used the six plate configuration. If the drums are all the same, I can start with any TH400 truck core but if the drums are different then I probably need to start with a one-ton big block core (ka-ching). Any experience here? Thanks.

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Old 01-21-2007, 04:04 PM
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There is a 5 clutch drum configuration and a 6. There may have been some TH400's with 4 clutches but the piston would be the difference and not the drum.
A 5 clutch drum is adequate for a 1 ton truck and more.
The 6 clutch drums are relatively hard to find and I save them for racing builds.
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Old 06-10-2007, 09:10 PM
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Old thread, I know, but it came in a search and I have relevent info.

The direct clutch drums in the TH400 are the same. The 5 clutch drums have a wave ring that takes up the extra space, the 6 clutch assemblies replace the wave ring with a plate to allow room for the extra clutch. Many people (including myself) take out the wave ring and place two steel plates first followed by a clutch plate , then followed by the first steel plate of the regular 5 clutch assembly to convert a 5 clutch assembly to 6 clutches. Some may feel this is hokey or ineffective, but it's my transmission and I'll do what I want. If you feel inclined to do the same, it's your transmission and your call.

The 5 clutch drums are just fine for just about everything. The 6 clutch drums were primarily used in very early TH400s and in industrial uses usually with DRWs, although the majority of DRW trucks still came with the 5 clutch drums.

The 6 clutch drums are still best for drag racing or 4 wheeling as they shift noticably firmer and generate less heat as a result. I hope this helps with someones future search.
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Old 06-10-2007, 09:50 PM
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Quote:
The direct clutch drums in the TH400 are the same.
that would be incorrect.. the drums were cut to different depths below the snap ring groove over the years.

As mentioned in one post the aluminum piston was taller when a smaller friction count (4) used..

Some of the late applications used a conical style cushion plate against a new design aluminum piston. These conical cushion plates often broke.

I often install 7 or 8 frictions in these drums for serious high HP use.
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Old 06-10-2007, 10:12 PM
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Thank you for the correction. I found a 6 clutch drum in one of my TH400s that was identical to the 5 drum, except that instead of a wave ring it had a plate (not a clutch steel, just a lipped plate with no spurs that took up less space than the wave ring). This is the only 6 clutch direct assembly I've ever seen.
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Old 06-10-2007, 10:27 PM
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Actually the original question was about length (now that I re-read it)

The drums externally were the same size - length to my knowledge.

You do need to watch the placement of the bleed off check ball when mixing parts up. The drum assembly needs at least one in the piston or the drum.
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Old 06-10-2007, 11:03 PM
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On all my TH400 builds, I drill a small bleed hole in the direct drum on the outer circumference to prevent centrifugal apply. However most of the TH400's I do will see 6K+ rpm often.

Crosley is correct, they way the inside of the drum is machined is different on the 6 clutch drums. They have a very short area for the piston to travel.
You can usually squeeze 6 clutches into a 5 clutch drum by using the forward steels and machining the stepped part of the pressure plate (where the snap ring sits) down .050".
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Old 06-17-2007, 06:35 AM
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The 6 pack aluminum apply piston is shorter also, not just the snap ring groove.
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Old 06-17-2007, 12:39 PM
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yes there are a multitude of aluminum piston heights to watch for.

A builder would need to watch how short the piston is too..... you do NOT want the piston too short where the first steel plate against the piston can drop below the grooves in the drum and then turn. This would cause a "no apply" situation since the turned steel would hold the apply piston down.

The steel plate lugs into the grooves of the drum.... the plate must not drop below these grooves.

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Old 06-17-2007, 11:02 PM
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I agree!!!
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