TH400 Direct Drum/Sprag Question

[NickTransmissions]

Thanks for the tip on quoting your posts. I had edited my last post to include a question about the friction discs if you don't mind taking a look.

Never ever reuse frictions if going back through a transmission, that's flate rate tactics....Flat rate shops fix only what has already failed, leaving everything else in, regardless of wear, so that the other comsumables fail shortly after their 30-90 day warranty expires. This puts the customer back to square one, money down the drain.

 

[tenthirtytwo]

Thanks for the info!

For the bearing conversion of the rear thrust washer, is GM P/N 9436851 what I'm looking for? (for the bearing). What PN are the shims for the new bearing?

I concur with everything that Nick has already stated. Here's another option for rollerizing the output shaft in the TH400, all in one kit. Sonnax offers their 34006-SPB TH400 HD Case Bushing Kit. I use this kit regularly on anything used in HD, 4x4 & definitely on snow plow truck applications. You should be able to find it on Amazon or Summit

 

[Matt69olds]

Make sure you take some detailed notes on how far down in the bore each bushing sets.

Before I had the fancy bushing driver tools, I used a cam bearing installation tool for a lot of bushings. Once again, unless your planning to build a lot of engines and transmission’s, it’s probably best to just pay a transmission shop to drive the bushing in for you.

Know anyone with a lathe? You could probably machine a driver pretty easily.

 

[Kilian]

Make sure you take some detailed notes on how far down in the bore each bushing sets.

Is it just good practice to replace the bushings when in the transmission?

 

[NickTransmissions]

Is it just good practice to replace the bushings when in the transmission?

Yes, always - unless bushing kits are not available for a given unit (ie FMX, last time I checked). You wont have that particular issue with the GM long. 3 speeds like the TH400. They are hard on bushings, always replace the existing ones. Drive the rear case bushing in from the rear so it's flush or slightly below - check with your output shaft, th350 pump bearing and shim installed (put the black side of the bearing face down in the case).

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[Kilian]

Yes, always - unless bushing kits are not available for a given unit

What about the Torrington thrust bearings, should those also be replaced?

Also, I haven't had time to go through all of your videos yet, but do you have a picture of the plug used when doing the dual feed setup? Thanks!

 

[NickTransmissions]

What about the Torrington thrust bearings, should those also be replaced?

Also, I haven't had time to go through all of your videos yet, but do you have a picture of the plug used when doing the dual feed setup? Thanks!

Use a 3/8" cup plug, red loctite around the OD. These should be available online. That portion of the dual feed process where i install the cup plug should be in PT3 of the "4L80E high performance" video series (yellow transmission).

If the bearings are in good shape it's fine to reuse unless the trans either overheated or sufferered a gear train failure - Id replace if so.

 

[Kilian]

If the bearings are in good shape it's fine to reuse unless the trans either overheated or sufferered a gear train failure - Id replace if so.

Good to know, thanks.

As far as the modulator, any recommendations for what to use? I figure that should be replaced as well to make sure that I'm starting with something good.

 

[NickTransmissions]

Good to know, thanks.

As far as the modulator, any recommendations for what to use? I figure that should be replaced as well to make sure that I'm starting with something good.

Order a standard vacuum modulator for a TH400 from any transmission parts supply shop or buy from a local trans parts supplier.

 

[Kilian]

Use a 3/8" cup plug, red loctite around the OD. These should be available online. That portion of the dual feed process where i install the cup plug should be in PT3 of the "4L80E high performance" video series (yellow transmission).

Finally getting back to the TH400 project. Is this the type of 3/8" cup plug needed for doing the dual feed conversion?

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Also, I wasn't able to find a video on your YT channel that described TH400 or 3L80e dual feed conversion, I didn't see it mentioned in PT3...can you point me to the right one? Thanks!

 

[NickTransmissions]

Finally getting back to the TH400 project. Is this the type of 3/8" cup plug needed for doing the dual feed conversion?

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Also, I wasn't able to find a video on your YT channel that described TH400 or 3L80e dual feed conversion, I didn't see it mentioned in PT3...can you point me to the right one? Thanks!

That should work - put a little RTV or red loctite on the outside diameter of the cup plug prior to installation and don't install it until the case is fully assembled so you know that there's no possibility of it having to come apart again.

I actually don't have a dedicated dual feed video but I show the process in my TH400 Rebuild Series...

In short, here are the steps:
1. Leave the interior lip seal off of the direct drum
2. Leave the 2nd from the top sealing ring off of the center support
3. Install the 3/8 inch cup plug in the high-reverse feed port in the case (it is the hole immediately to the right of the center support feed bolt)
4. Drill the 2-3 feed orifice to .115 to start for a stock application (your call if you want to block off the 2-3 accumulator)
5. Install all check balls into the case to start - they can be removed later (the intermediate check ball and reverse check ball must remain regardless of what else is done)

I will likely put together a dedicated TH400/4L80E dual feed video soon but let me know if you have any questions in the meantime.

 

[Kilian]

4. Drill the 2-3 feed orifice to .115 to start for a stock application (your call if you want to block off the 2-3 accumulator)

Thanks for the reply. Do you have a photo of this being done? And what are the pros/cons of blocking the 2-3 accumulator?

 

[NickTransmissions]

Thanks for the reply. Do you have a photo of this being done? And what are the pros/cons of blocking the 2-3 accumulator?

Here's my TH400 rebuild video series, Part 2 where I start discussing the process.

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I'll try to put together a quick video on the dual feeding itself perhaps later this week if time permits and post it here...I'll have all the steps consolidated into one short vid.

 

[Kilian]

Here's my TH400 rebuild video series, Part 2 where I start discussing the process

Thanks...was watching this one earlier and saw mention of not using the seals, I think your next one in the series showed the plug getting installed in the port, but I've not come across the feed orifice procedure.

I found someone else's video online that showed drilling a small hole in the drum for exhausting fluid...if wasn't mentioned in your list, above, so do you not recommend doing this as well?

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[NickTransmissions]

I found someone else's video online that showed drilling a small hole in the drum for exhausting fluid...if wasn't mentioned in your list, above, so do you not recommend doing this as well?

Will you be turning north of 6000 RPMs on a regular basis?

I do show that hole being drilled in my 4L80E High Performance build series but that TH400 shown didn't warrant the additional bleed hole.