TH-400 in MH service?

[Gary - K7GLD]

Since we look to be getting a 27 foot Winnebago MH next week - if all works out - I'm sorta curious as to the track record of the older GM ('88) versions of the TH-400 auto trannies. These are supposed to be a slightly heavier version than the units commonly used in lighter GM vehicles - and those themselves had a pretty decent reputation for durability as far as I know.



The MH we will get has just under 60K miles, and everything else seems to have been extremely well maintained and serviced - but MH service can be tougher on the drivetrain than regular service - so what might I expect out of the ordinary?

 

[fox]

The turbo 400 GM trans is a stout trans for that application.

 

[HBarlow]

The TH-400 is considered very strong and reliable. It was used in 3/4 ton Suburbans and 3/4 and one ton GM pickups behind 454 V8s before GM shifted over to overdrive transmissions. I think the same basic transmission was modified to provide OD.

The TH-400 is the transmission of choice for hot street set-ups or drag strip use behind strong running Chevy gas V8 engines. The TH-350, the lighter duty version, is not nearly as strong or durable. It will be a gas guzzler though. A MH will probably have 4. 10 gears so your final drive ratio will be 4. 10:1 and it will be buzzing 3500 rpm at highway cruise.

You and big oil, the companies you love to hate, are going to have an intimate relationship. It shouldn't be too difficult to swap in the later overdrive version.

My '56 Chevy uses a new GM 350 crate motor and a TH-700R4 (overdrive automatic). It's a simple bolt in.

 

[ata]

Gary, I know they are BULLET PROOF. Because a friend of mine shot his with his 243 when he was putting his gun back in the cab of his truck and it still worked fine until it ran out of oil. The TH 400 is probably the best 3 speed auto out there. Change the oil in it about every 50000.

 

[Gary - K7GLD]

The TH-400 is considered very strong and reliable. It was used in 3/4 ton Suburbans and 3/4 and one ton GM pickups behind 454 V8s before GM shifted over to overdrive transmissions. I think the same basic transmission was modified to provide OD.



The TH-400 is the transmission of choice for hot street set-ups or drag strip use behind strong running Chevy gas V8 engines. The TH-350, the lighter duty version, is not nearly as strong or durable. It will be a gas guzzler though. A MH will probably have 4. 10 gears so your final drive ratio will be 4. 10:1 and it will be buzzing 3500 rpm at highway cruise.



You and big oil, the companies you love to hate, are going to have an intimate relationship. It shouldn't be too difficult to swap in the later overdrive version.



My '56 Chevy uses a new GM 350 crate motor and a TH-700R4 (overdrive automatic). It's a simple bolt in.

As an old hotrodder, I'm well aware of the use of the TH-400 in that application - and used one behind the B&M Supercharged engine I built up and installed in my earlier '76 Chevy 3/4 ton pickup, Yup, the MH will likely - as all MH's are - be a gas hog, but we plan to use it primarily on relatively short fishing/camping outings, rather than long distance hauls - and to this point, have had to tow the 5th wheel with the truck, and the boat with my wife's car - so that combined MPG wasn't very spectacular either, and was the motivation for the MH...



I seriously doubt the conversion to a later O/D transmission in the MH would even begin to be cost effective...

 

[AClayton]

The TH400 will be just fine... . only problems I've seen is the e-brake and park brake get a little troublesome. You can still get chassis parts through Workhorse Custom Chassis for that though. A 27' footer should have 16" wheels but my source says that an optional chassis with 19. 5 wheels was available. 16" wheels get the 4. 10 and 19. 5 get a lower ratio but the final drive will be the same. I had the 22'Chieftan and easily got 10mpg... . as long as you don't drive over 65. The TH400 does not have a lock-up converter and will have the rpm's up around 3K while cruising at 65. These rigs get the best mileage... . and handling! at 55 or even 60. I was serious when I suggested you upgrade to Bilsteins in another thread... . take the advice and do it!!



Alan

 

[Garlic]

Ballooning torque converters!!! Big issues for Big block Chevys and TH-400's. There are many "anti-ballooning" converters on the market for reasonable prices. Synthetic ATF and a real good cooler are going to be yor best investments. The converter swells during load on a TH-400, so much that it will 'push' or wear out the crankshaft thrust bearing. The tell tale signs are a weeping or leaking rear main seal. The factory transmission cooling system for it was just marginal, any additional cooling will be of great benefit.

I have worked on these coaches for upwards of 30 years and that was the biggest killer.

There are some 454 issues that with a little money and some time can be over come to eliminate any future problems. Spark plug wires, fan clutch, exhuast manifolds, fuel pump/filter, belts, thermostats, timing just to name a few. Over all I feel it was one of the best combinations for a coach under 38' with a gasser.

 

[BDaugherty]

Generally, motorhomes got the TH475. It's pretty much the same as the TH400, but has more pinions in the gear planetaries and straight cut gears instead of helical. TH400s are tough as everyone has already mentioned. A common upgrade is to use the converter from an Allison 1000. Two other things that I consider a must have with any TH400:



1. Temp gauge. Installing it in the pan is fine. Gas engines don't lug and very often hard pulls will be made with the t/c unlocked.

2. Cast aluminum pan. Factory stamped pans all seem to be prone to leaks. An aluminum pan will help reinforce the trans case and it will be much easier to seal. Lower temps with a higher capacity pan is debatable, but to me it's worth the premium just for the strength and resistance to leaks.



Also, for my own personal peace of mind, I would service the trans and look at the condition of the fluid and magnet. Look closely at the coolers and lines. Often people add additional coolers. That's good, but you need to make sure that they are securely installed and that the lines aren't rubbing. Also, if you have any aftermarket trans coolers, make sure that the lines are at least as large as the factory lines. You don't want any restrictions to flow. I like a 15-20K mile or 1 year fluid service interval when operating in "severe" conditions.



Check out some of these links for additional info/opinions:

TH400/TH475 - Off-Road Forums & Discussion Groups

4X4REVIEW. COM: Top 10 Off-Road-Worthy Transmissions of All Time

 

[AClayton]

Generally, motorhomes got the TH475. It's pretty much the same as the TH400, but has more pinions in the gear planetaries and straight cut gears instead of helical. TH400s are tough as everyone has already mentioned. A common upgrade is to use the converter from an Allison 1000. Two other things that I consider a must have with any TH400:



1. Temp gauge. Installing it in the pan is fine. Gas engines don't lug and very often hard pulls will be made with the t/c unlocked.

2. Cast aluminum pan. Factory stamped pans all seem to be prone to leaks. An aluminum pan will help reinforce the trans case and it will be much easier to seal. Lower temps with a higher capacity pan is debatable, but to me it's worth the premium just for the strength and resistance to leaks.



Also, for my own personal peace of mind, I would service the trans and look at the condition of the fluid and magnet. Look closely at the coolers and lines. Often people add additional coolers. That's good, but you need to make sure that they are securely installed and that the lines aren't rubbing. Also, if you have any aftermarket trans coolers, make sure that the lines are at least as large as the factory lines. You don't want any restrictions to flow. I like a 15-20K mile or 1 year fluid service interval when operating in "severe" conditions.



Check out some of these links for additional info/opinions:

TH400/TH475 - Off-Road Forums & Discussion Groups

4X4REVIEW. COM: Top 10 Off-Road-Worthy Transmissions of All Time

I did not know the TH400 had a lock-up converter.









Anyway,yesterday... . when I posted my reply,I was having a brain cramp and could not remember what GM called the park feature. It is called auto-park and a pressure sensor inside the steel box,mounted close to the trans and on the driver side frame rail... . is what fails and will routinely lock up on you and leave an idiot light on the dash labeled Auto-Park. In some instances,I have heard that it would apply the trans brake while moving down the road. I never experienced that myself,but my Grandfather did and had to stop on side of Freeway and disconnect it to get home... . he had an 86' Chieftan 33'. The Auto-Park was designed to lock the transmission output shaft when shifted to Park so that the Park pin inside didn't assume the weight of the coach. The upgrade kit from WCC eliminates all the hassles when and IF you experience this and certainly would not alter my decision to purchase this rig.





Alan