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Old 08-21-2016, 01:48 PM   #1
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1982 34' Limited
1986 34.5' Airstream 345
Sausalito , California
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New transmission for the Ole Gal

Hey folks,
I'm back in the saddle - which is a long entertaining story that I will relate elsewhere in Vol. 2.

Unfortunately, a big chapter is transmission failure on the way from Portland to CA. SO here I am in Eugene at Oregon Transmission where they removed the original mess of a transmission - bushings shot, fluid yucky - on my 1986 345 classic Moho. I know, It's all happening kinda fast because I'm trying to get this baby to Burning Man in less than a week!

Here's the thing: They tell me that the original tranny was rated for a one-ton truck and that's why it only took me and the PO 79,000 miles.

They haven't started the install yet. They're planning to put in a heavier duty one rated for a 5-ton dump truck. I think it has a turbo of some kind in it. Does this sound right to you-guys? The owner Mark seems nice, has been in business for 30 years and he has one of the few lifts big enough but he also has a boat. So do we, so he has my sympathies.

I did a little search on the forum but frankly, it's hard to do a good search on my phone. If someone could direct me to relevant threads I'd be much obliged.

Very rusty underneath. My friend is concerned about the driveline. Pics to follow when they get her back up on the lift.

Thoughts, threads, and relevant warnings appreciated.

Jenniflow
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Old 08-21-2016, 03:50 PM   #2
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1977 31' Sovereign
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I'm not familiar with the motor homes but am with GM drivetrains. I would assume it has a GM TH400 transmission. A lot of folks call them turbo 400's. If so that is plenty of tranny for your coach. Now if it has a TH350, then yes moving up to a 400 is a good idea but I seriously doubt it came with a 350 behind a big block.
Since you are replacing the transmission I would highly suggest adding an external filter so that can be changed during your normal services. Contaminated fluid wreaks havoc on automatics.
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Old 08-21-2016, 10:19 PM   #3
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Hey Cliffcharb,
Thanks so much for your help here.
I will check on this of course, but I think they mentioned a 460. Do you think that's a bad idea? If so, what's the hazard?

And I will talk with them about an external filter.

Thanks again.
Jenniflow
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Old 08-22-2016, 01:02 AM   #4
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They probably want to upgrade to a 4L60 transmission which has overdrive and is a far better transmission. But that would require a new driveline and a controller. It sounds like the shop knows what there doing, trust them. If you have questions, ask them have them put what the doing on paper. Don't rely on "expert advise" off the internet.
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Old 08-22-2016, 01:21 AM   #5
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Hi, your trans should be a Turbo 475 which is a heavy duty truck version of a Turbo 400. I'm sure by now the 475 can be slightly upgraded. As for how long they will last is unknown. I had one that died at 25,000 miles. If they remove your Turbo 475 and install a Turbo 400, that is a down grade. For the 475, maybe better clutches, shift kit, and up graded torque convertor would be about all they can do for it.
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Old 08-22-2016, 06:18 AM   #6
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1977 31' Sovereign
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Having to trust an unknown shop out of town..... I feel your pain. My family is in the trucking business and I know about shops that just get you out of their door with shoddy work knowing they will not be hearing or seeing you again.
The 400 is a HD transmission, period. the 475 is a 400 with different internals. Those are 3 speeds without overdrive. The 4l60 (700r4) is an overdrive tranny, but was not used in HD applications. The 4l60e is just an electronic version.
If you are happy with the MPH and RPM at your cruising speed, I would leave alone and replace with the same. If you really want OD, just know more than likely you'll have modifications such as relocated cross member and driveshaft change.
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Old 08-22-2016, 11:36 AM   #7
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475 + heavier torque converter

Your comments have been very helpful thanks!

I'm getting a 475 with a heavier torque converter and possibly some other minor upgrades. He's going to itemize it so I can report later.

Also, they've checked the driveline and it's surface rust so I've decided not to worry about that.

Recently, in Portland, they found - thanks again the the Wisdom of the Airforums Sages - the electrical problem that was causing the rear fuel pump to fail - so I'm also not going to worry about vapor lock. Of course my Banks upgrade of years ago help with that too.

So after some local test-driving I'm heading for Grant's Pass going south. Wheeee!

Thanks again!

Jenniflow
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Old 08-22-2016, 03:44 PM   #8
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Franklin Park , Illinois
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Th475

For what it's worth when I bought my 345 it's th475 had a crack in the transmission housing
I was able to get my hands on another TH475 from another motorhome I didn't want to put it in without rebuilding it so I had a transmission shop Rebuild It then I had a truck / RV shop install it. things have been great as far as my transmission when I did my research I found that the innards of the th475 are a little different I believe the planetary gears were streight cut (like a regular gear would look like) and the th400 the planetary gears were Healy cut (like a two screws turning together.)
I believe they said the straight cut was a little noisier but stronger. Healy cuts or quieter but not as strong
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Old 08-22-2016, 04:54 PM   #9
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Interesting. We didn't get into that level of detail.

I've made it as far as Roseburg from Eugene and everything seems to be good!
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