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Old 03-26-2010, 09:16 PM
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Direct Drum

Hi everyone, I'm getting ready to overhaul my 4wd th400. Its getting bolted to a 383 stroker motor for my 1988 K5 blazer. I want to upgrade to a 34 element sprag but I have the roller clutch style direct drum. Finding an old style th400 direct drum thats not $350+ is not the easiest thing to do (other than the direct drum and sprag kit from 400raptor.com for $189).

Anyway I've found some 4l80e direct drums on ebay for under $100 and they are all the smooth sprag style drums. My question is will the 4l80e direct drums be a direct swap into a th400? Thanks for any help.

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Old 03-26-2010, 09:26 PM
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Yes, I've done it many times.
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Old 03-26-2010, 09:38 PM
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so the pistion from the th400 direct drum will work with the 4l80e direct drum? Everything is exactly the same?
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Old 03-26-2010, 09:52 PM
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Yes, the piston will work.
You really need to get the sprag and race for the 4L80E though.
The th400 has a slightly thinner race.
The th400 race fits the 4L80E drum, but the 4L80E race doesn't fit the th400 drum.
The difference is only a few thousandths.
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Old 03-26-2010, 09:57 PM
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I have a 34 element sprag for a th400, your saying I can't use that? Also I read that the 4l80e direct drum uses one more clutch than the th400, is that true?
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Old 03-26-2010, 10:03 PM
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The sprag I bought is the borg warner 34418X, it says it will work in both the th400 and 4l80e
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Old 03-26-2010, 11:35 PM
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How many clutches you can use depends on the piston height. There is less worry using a thin piston and 4L80E drum. If you weren't paying attention and had a th400 shallow drum and thin piston the first steel would get caught under the lugs. This is not a problem since all 4L80E drums are the deep type that can use any piston, I prefer the steel with molded seals.

As far as the race, maybe they use one part now, it makes sense.

Back around 2002 I bought a 34 element sprag and race from bulkpart.com and it would not fit my th400 drum. The guy over there gave me some bs, said he was pulling a drum and race off the shelf as we spoke and it went right on, no problems.
Well then I called Borg Warner, at this point no one knew there was a problem yet.

So with this th400 on my bench and some guy waiting for it I called bulk part back and talked to Mark, by that time he had called BW and they figured out that tens of thousands of these left BW in the wrong box. There were two part numbers, one for the th400 and one for the 4L80E.

I'd find it hard to believe I was the only person who had this problem. I figure by that time everyone was using 4L80E drums, but I scored 50 to 60 sprag type th400 drums from a closed down hardparts supplier.

I don't know the exact size difference but it can't be much because you can force the snap ring on when using a 4L80 race with a th400 drum. You just know it's not right.

Last edited by Jason; 03-26-2010 at 11:43 PM.
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Old 03-27-2010, 05:03 AM
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Alright thanks for your help, I'm gonna go ahead and order the 4l80e drum, I know theres only one oil feed hole as opposed to the two oil feed holes on the th400 drum, but my 383 is pushing somewhere around 400hp so from what I've read I might be ok, I'm thinking about doing that dual feed modification but I'm not sure yet. As for the sprag I'll put the one I have on the drum and see if theres excessive play, if I don't like it I'll go ahead and get the 4l80e sprag.
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Old 03-28-2010, 04:10 AM
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TH400 dog type drums have never been a problem to find for me. So, I don't understand why you can't find them.

There are two basic types of TH400 dog type drums. The common one was factory 4 or 5 frictions depending on the piston. The other was factory 6 frictions. The difference in the drums was that the 6 friction had the snapring groove very close to the edge of the drum. The other drum had the snapring groove noticeably lower. The 6 friction had its own aluminum piston specific to the drum. The other drum used several different pistons, both steel and aluminum, none of which fit the 6 friction drum.
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Old 03-28-2010, 09:30 AM
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The TH400 drums are getting difficult to find. I've cleaned out my local suppliers.

I have a source for new GM drums. The sprag is the same, the difference between a TH400 and 4L80E drum as far as interchangeability is the width of the sprace race. It's .040" wider on a 4L80E because of the 4 clutch intermediate pack.
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Old 03-28-2010, 10:02 AM
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I saw where Art Carr "improves" the 4L60E by replacing the 4L60E drum w/the drum/sprag for a TH400.
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Old 03-28-2010, 10:20 AM
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Quote:
Originally Posted by jakeshoe
The TH400 drums are getting difficult to find. I've cleaned out my local suppliers.

I have a source for new GM drums. The sprag is the same, the difference between a TH400 and 4L80E drum as far as interchangeability is the width of the sprace race. It's .040" wider on a 4L80E because of the 4 clutch intermediate pack.

Yep , we have problem finding the OE t-400 sprag type drum or the supplier wants insane money.

We are developing a replacement sprag type race for the roller clutch drum since we have hundreds of roller design drums around. As most knowledgeable trans folks know the ground down roller clutch race to sprag specs , does not work well.

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Old 03-28-2010, 11:24 AM
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the only place I've seen the th400 direct drums is at 400raptor.com, they sell them with the sprag for $189.

I guess I'm still a little confused about the sprag, every manufacturer that makes the 34 element sprag (that I've seen) only sell one type that says will work with either the th400 or 4l80e.

Last edited by frickenbored; 03-28-2010 at 11:32 AM.
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Old 03-28-2010, 02:29 PM
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Quote:
Originally Posted by jakeshoe
The sprag is the same, the difference between a TH400 and 4L80E drum as far as interchangeability is the width of the sprace race.
I thought I was pretty clear on that.
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Old 03-28-2010, 07:14 PM
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Quote:
Originally Posted by jakeshoe
I thought I was pretty clear on that.

What exactly is a sprace race? I'm just now getting into transmissions, I've taken 3 classes in my college automotive program and so far I've rebuilt a 1999 4l60e and a 1987 700r4. The th400 and 4l80e are fairly new to me.

Anyway what exactly will I have to change when using a 4l80e direct drum in a th400. I don't know what year the th400 is because the vin tag is gone. I was told it came out of a 1970's 2wd 3/4 ton pickup truck.
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