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Old 08-17-2015, 01:01 AM   #15
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Help with my transmission

I was pretty sure that all THM 400s used the same output shaft, but I guess I could be wrong about that.

What I would do in your position is to get a transmission yoke that fits your new transmission and your driveshaft and use the transmission that you already have.

This should be a simple solution that will get you on the road with minimal expense and time.

The reason MOST transmissions break at the bell housing is because the transmission to engine bolts get loose.
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Old 08-17-2015, 01:39 AM   #16
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Help with my transmission

Ok, so while most THM 400 transmissions used a 31 spline yoke, some used a 27 spline yoke.

This yoke was also used on the THM 350 and is interchangeable with those used in THM 400 transmissions.

You can 99.9% order a slip yoke that will;

A; fit your transmission

And;

B; fit your driveline.

You need to know...

A; The length of your old yoke

And;

B; The series of the front universal joint,


http://www.driveshaftspecialist.com/...D%20Guide.html


http://m.summitracing.com/search/dep...0spline&page=2

Edit; upon further review, if your RV uses 1410 series universal joints you may be out of luck, if it uses 1350 series, you have an easy and cheap fix.
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Old 08-17-2015, 05:15 AM   #17
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Help with my transmission

These guys know a lot more about the GM transmission than I do and have provided some good guidance. I've done a few transmission upgrades into classic vehicles. All electronically shifted Ford 4R70W. We've used controllers from these guys.

http://www.usshift.com/?gclid=CjwKEA...1kNxoCO5bw_wcB

They are plug and play for the most part. Lots of advantages to going with a modern 4 speed with OD and lockup.

https://en.m.wikipedia.org/wiki/GM_4L80-E_transmission
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Old 08-17-2015, 12:16 PM   #18
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Unless a person drives a whole lot, installing an electronically controlled OD transmission has a very long break even point.

The THM 400 was among the strongest and most reliable transmissions ever put behind a gasoline engine. Simple elegance, well mannered, and reliable.

If you have all of the pieces, another option is to have the break in the bell housing welded.
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Old 08-17-2015, 03:33 PM   #19
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Unless a person drives a whole lot, installing an electronically controlled OD transmission has a very long break even point.

The THM 400 was among the strongest and most reliable transmissions ever put behind a gasoline engine. Simple elegance, well mannered, and reliable.

If you have all of the pieces, another option is to have the break in the bell housing welded.

Probable not as long as the break even point of owning a MoHo! There is a certain satisfaction, at least for me, of updating something to make it better. I've wondered why some guys install overdrive units when one could swap one of these OD with lockup transmissions. The fuel savings aren't going to justify it but there are other benefits. Less engine roar at cruise. Less heat generated. Longer engine life... After all we spend a lot of effort and money to update and make every other aspect of these coaches better.
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Old 08-17-2015, 03:54 PM   #20
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Agreed!
Putting a OD transmission in is not cost effective even doing it yourself...
Nor is putting a diesel in...

But we are not logical about what we love!
Which is why I have a 4L80E under my bench...
It looks good, but I am planning to rebuild it... at $175 it was a steal!

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Old 08-17-2015, 05:25 PM   #21
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Agreed!
Putting a OD transmission in is not cost effective even doing it yourself...
Nor is putting a diesel in...

But we are not logical about what we love!
Which is why I have a 4L80E under my bench...
It looks good, but I am planning to rebuild it... at $175 it was a steal!

Steve, I've got a 4L80E out of a Chevy box truck sitting on my shop floor as well! Once the Argosy is up and running with the original transmission I'll then take the time to swap in the 4L80E. Shouldn't be as difficult for my Argosy as the parking brake(s) are located at the rear axle so I don't have to mess with the transmission mounted brake.

Brad
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Old 08-17-2015, 05:47 PM   #22
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...

The next step would be to replace it with the next generation transmission... The 4L80E, or its HD counterpart, the 4L85E.
....!
Question for Keyair and Brad:
If the TH400 in our Motorhomes is really a TH475 (heavy duty version of the TH 400), why would you want to put the 4L80E in as a replacement instead of the 4L85E?
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Old 08-17-2015, 05:57 PM   #23
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Question for Keyair and Brad:
If the TH400 in our Motorhomes is really a TH475 (heavy duty version of the TH 400), why would you want to put the 4L80E in as a replacement instead of the 4L85E?
Peter, my Argosy only weighs around 8500 lbs so a 4L80E is well within it's capabilities. Personally I think even with a 310 a 4L80E would be probably sufficient.

Per the Wiki site: "The 4L80E was rated to max GVWR of 18,000 (Axle and vehicle dependent)[2] Applications"

I'm thinking the 310 is definitely less than 18,000 lbs. and even towing a car on a trailer with my Argosy I should be well within it's weight rating.

Brad
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Old 08-17-2015, 10:34 PM   #24
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Beat me to it Brad!

Lucky you, that you don't have to deal with the parking brake issue!

Peter, you are correct, and everything I have read about the 4L80E and 4L85E points to them being brothers like the TH400 and 475. I gather that the 85 has straight cut planetaries too.
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Old 08-18-2015, 12:27 AM   #25
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Hello everyone
thank you very much for all the information I received.
My transmission is 31 spline and the other I got is 27.
here in Germany is quite complicated to get a house of HD, so ask if the housing of the TH 400 with 27 spline is equal,
Only I have to take him to a professional to change places with all new elements and ready
of all professionals here wondering, none could tell me if the houses are the same, and do not want that start to experiment with my transmission
Herman
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Old 08-18-2015, 09:30 AM   #26
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The 31 spline shaft is maybe a little stronger, the case and internals are the same except for maybe the removable tail shaft housing.

The difference in strength between the 27 spline and the 31 spline shaft is not enough to worry about in my opinion.

If I were in your situation, I would carefully select a yoke to fit your transmission and driveline and put it in the RV.

If your truck uses 1350 series universal joints this will be easy, if it uses 1410 series universal joints this will be difficult or impossible unless you are willing to modify the driveline, and at this point things start becoming more trouble than swapping for a 31 spline transmission.
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Old 08-18-2015, 11:10 AM   #27
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Smile

thanks for that information, I'll see if I really get an HD so I have no more problems
Herman
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Old 08-19-2015, 03:17 AM   #28
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Hello everyone
I found a digital transmission with 32 spline (my transmission is 32, it was my mistake to see only 31)
The transmission is a 1988 Suburban.
you there is a difference between the transmission of suburban and believe my transmission?
Herman
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