Rebuild th400 or 4l80e?

82BBC20 said:

I’ve got a 82 C20 454/TH400, I wanted to keep mine old school no computers, added a gear vendors unit which helped but with 4:10 gears still wasn’t where I wanted to be so I’m changing gears to 3:42 now.

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82BBC20 said:

My understanding has been that if you want it to shift automatically it needs some type of a computer, either a aftermarket setup or a used ecm from a obs truck. I changed my 92 C2500 454 suburban to carburetor with a 4L80 & used the stock ecm with a Holley tps & some wiring to capture speed & rpm’s. I know guys that have done swaps with 4L60 without computer but got tired of manual shifting.

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NickTransmissions said:

I normally dont use shift kits in TH400s and 4L80Es as they arent necessary. Dual feed the direct clutch internally, rollerize the output thrust flange, install the Sonnax TH400 boost valve/sleeve and spring kit, drill the high clutch feed out per your converter stall speed and desired shift firmness. Keep both accumulators active and reinstall all the check balls.

I would also incorporate high energy clutches into the build, though the stock clutches are fine for most mild applications. Install a Chrysler A518 forward clutch snap ring in the intermediate clutch pack in place of the factory TH400 snap ring. I usually end up using the .106 thick version and with three factory steels and clutches end up with .040-.050 clearance in that pack which is ideal, IMO.

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txaggie said:

Nick, can you point me in the direction of replacement sprags for this th400?

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NickTransmissions said:

Contact transpartswarehouse.com on Monday and request the intermediate and low roller one way assemblies for your TH400. Specify the type of intermediate OWC you need (dog bone sprag or roller type assembly).

Also if your application is high RPM, street-strip - increase intermediate clutch clearance to between .050-.080 to avoid drag in first gear and install high rate return springs in both int and direct clutch ret spring assemblies. There's other, addl things that should be done for high HP/RPM applications - let me know if yours is bound for such an application and ill reply w/more details.

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txaggie said:

Thank you! This will be for towing and daily driving so rarely will I flex it above 5500 rpm

Will this one not fit the factory drum?

https://transpartswarehouse.com/34652a-4l80e-th400-gm-chevy-transmission-intermediate-sprag-34-element-heavy-duty.html

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NickTransmissions said:

What year is your TH400?

It will if the direct drum that came in your TH40 has a smooth race (1964-1970 units have it). If it has a cammed race for a roller clutch (1971+) you either have to buy the 8-element roller assembly or swap to a 4L80E direct drum. If you do so and use the 4L80E outer race that would be on that drum you can install either the TH400 or 4L80E Intermediate clutch stack and backing plate...Either would be fine for your application. Im mentioning this as more of an FYI. If you do want the 4L80E four-clutch stack, you will need to swap the intermediate clutch apply piston to a late TH400 aluminum/early 4L80E one or a later 96+ piston with the cushion plate and second design 4L80E backing plate IF you have the stamped steel TH400 piston.

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txaggie said:

The turbo 400 is in a 1985 c20 suburban. The sprags look good but I figured while we are there it’s good to replace them with new.

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NickTransmissions said:

Then you don't have any sprag OWCs, you only have roller clutch OWCs (low and intermediate), unless someone has been in the unit prior and replaced the original direct drum with a 4L80E or 64-70 TH400 direct drum (great, if so).

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txaggie said:

Is it necessary to replace these owc’s while in there?

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NickTransmissions said:

Run it through the radiator then to the ext cooler. You're giving up a lot of heat exchange by not including the internal cooler in the system.

Also, Id swap in a 4L80E if it's in your budget to do so.

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Ricko1966 said:

Your tech was wrong. A fluid to fluid cooler is more efficient than a fluid to air cooler.Burn your finger,then wave it in the air,or dunk it in water which one cools faster?And I don't actually 100 percent agree with Nick. I run through the external cooler to the radiator. The radiator regulates the transmssion fluid temperature so it is not too hot not too cold. Transmission fluid should be in the 175 to 225 range. Engineers discovered a long time ago,engines didn't wear as much if they maintained the proper oil temperature,not just as cold as they could keep them. Transmission fluid is oil.

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bucket said:

I installed a temp gauge in my Suburban, back when it was my tow rig and had a 700r4 in it. I ran a fairly large cooler and it was not plumbed through the radiator cooler. The idea being that I wanted to cool the fluid, not put it through a 190* radiator. I often thought about running it through the radiator, because in cold weather, the trans ran at around 100* during normal driving. Working the trans hard in the summer, if the temp got up around 220*, I'd always back off the throttle for a bit until it got down to 190* or so.

Are y'all suggesting that if I ran it through the radiator cooler, it would have ran warmer in the winter and cooler in the summer?

Also, at some point years ago, I saw some chart about trans temps in relation to the life expectancy of the trans. According to it, the life expectancy dropped WAY off with temps over 200* or so. Is there no factual truth to that?

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Ricko1966 said:

Your tech was wrong. A fluid to fluid cooler is more efficient than a fluid to air cooler.Burn your finger,then wave it in the air,or dunk it in water which one cools faster?And I don't actually 100 percent agree with Nick. I run through the external cooler to the radiator. The radiator regulates the transmssion fluid temperature so it is not too hot not too cold. Transmission fluid should be in the 175 to 225 range. Engineers discovered a long time ago,engines didn't wear as much if they maintained the proper oil temperature,not just as cold as they could keep them. Transmission fluid is oil.

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