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Old 10-18-2018, 04:50 PM   #1
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2004 39' Land Yacht 390 XL 396
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Suggestions for a possible newer tranny for my 1983 310 Isuzu Diesel

Are there any folks out there that has a classic Airstream motorhome with the industrial Isuzu Turbo Diesel that has had a tranny replacement? I have a 1983 Airstream 310 with the Isuzu Turbo Diesel and the Turbo 400 tranny that came with the motorhome since it was new in 1983. I have since added a Gear Vendors Overdrive which has caused me some problems. I am on my second Gear Vendors OD, and suspect it is about to give up again because it is starting to slip out of OD. I am tired of shelling out mucho $$$ every year to fix this thing. I would have hoped to have the OD unit last for at least 10 years, but the second one is only about 1 year old. The first Gear Vendors only lasted about a year and a half.

So, I have been wondering if there are any other better tranny/OD units better nowadays? Has anyone tried a different updated and heavier duty units? If so, how expensive?

Thanks in advance.

Russell Decker, Olympia, WA.
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Old 10-18-2018, 05:12 PM   #2
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Okay, a couple of points.....your transmission is a Turbo 475, not a 400; difference being that the 475 has straight cut secondaries, not the helical cut of the 400. A little louder, but way stronger and the dragsters love them.

As to what transmission to change too......you could put in an Allison as my buddy up north with his 325 turbo diesel has a 4 speed Allison AT 545. The only problem is that I think you would need a different tranmission adapter, flex plate, and new mounting system for the transmission to get it in. You also wouldn't gain anything as the final drive for the Allison is still 1:1, the same as your 475.

As far as the Gear Vendors is concerned, I've heard that you can't shift them going downhill and a few other operator error stuff, like not changing the oil regularly, can shorten their lives. Also there is talk that the resonance of certain diesels play havoc with them. The US Gear reduction drive in mine is stouter and engine oil fed, but unfortunately, not an overdrive.

The transmission I'd be thinking about is the Allison MT643, which has a lock up torque converter in both 3rd and 4th gear. It still only has a final drive of 1:1 though.

http://www.candbsales.com/images/int...20mt%20643.pdf

The Allison MD3060 is the unicorn 6 speed motorhome transmission, BUT it's huge and I don't think it will fit. You could go with an Allison 2000, but again getting her in will cost money in computers, throttle position sensors, etc, etc.

The good thing about the turbo 475, is that it can be bulletproofed on the cheap, and there are many out there for cheap. The other upside is there are no electronics with the turbo 475. No electronics are a good thing.

Cheers
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Old 10-18-2018, 07:14 PM   #3
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1982 28' Airstream 280
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I would be interested in the problems you are having with your GV. I have a 280 with Isuzu and GV. The first GV lasted about 50000 miles but I bought it used so actual mileage is unknown. We did 16000 miles to the east coast and Canadian Maritime and another 9000 to Alaska and back plus many shorter trips so it saw a wide variety of roads and conditions.

Something isn't right if you can't get more than 1 1/2 years out of your GV.
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Old 10-19-2018, 10:14 AM   #4
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1982 31' Airstream 310
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Quote:
Originally Posted by Isuzusweet View Post
Okay, a couple of points.....your transmission is a Turbo 475, not a 400; difference being that the 475 has straight cut secondaries, not the helical cut of the 400. A little louder, but way stronger and the dragsters love them.

As to what transmission to change too......you could put in an Allison as my buddy up north with his 325 turbo diesel has a 4 speed Allison AT 545. The only problem is that I think you would need a different tranmission adapter, flex plate, and new mounting system for the transmission to get it in. You also wouldn't gain anything as the final drive for the Allison is still 1:1, the same as your 475.

As far as the Gear Vendors is concerned, I've heard that you can't shift them going downhill and a few other operator error stuff, like not changing the oil regularly, can shorten their lives. Also there is talk that the resonance of certain diesels play havoc with them. The US Gear reduction drive in mine is stouter and engine oil fed, but unfortunately, not an overdrive.

The transmission I'd be thinking about is the Allison MT643, which has a lock up torque converter in both 3rd and 4th gear. It still only has a final drive of 1:1 though.

http://www.candbsales.com/images/int...20mt%20643.pdf

The Allison MD3060 is the unicorn 6 speed motorhome transmission, BUT it's huge and I don't think it will fit. You could go with an Allison 2000, but again getting her in will cost money in computers, throttle position sensors, etc, etc.

The good thing about the turbo 475, is that it can be bulletproofed on the cheap, and there are many out there for cheap. The other upside is there are no electronics with the turbo 475. No electronics are a good thing.

Cheers
Sidekick Tony
One more thing about the AT545 Allison. This really struck me on our most recent trip out west and in the Rockie Mountains where we were climbing and decending grades one right after another. It's very nice to have that extra gear when having to downshift going up or coming down. I can downshift into 3rd at 45mph +- and maintain comfortable torque and RPMs up to about 50mph. Comes in very handy on those rolling highways pulling long steep grades. Ive never driven one of our rigs with the GM475 so I don't know how that compares but it felt good to be able to maintain a "reasonable" speed. (still holding up traffic behind though . Decending you get the same benefit of the extra gear so you're not riding the brakes and using the tranny......always with a close eye on RPMs. As Tony says, still a 1:1 final in fourth gear but the benefits seem to be in 2nd and 3rd. Like I said, this really struck me when climbing to over 12,000 feet and then decending the same roads. Same applies in some areas we have been in western KS, PA, and upstate NY.

From what Ive read here on the forums, I would explore every option available before swapping to electronic controls. I think a few have been successful, maybe, but the headaches involved in the swap sound monstrous and get expensive real quick.....especially for all the little parts that pop up being needed. It also seems that the folks that have tried it have mad mechanical skills and have tackled the swap on their own.....(I don't fall into that category, not even close)
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Old 10-19-2018, 12:38 PM   #5
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1982 28' Airstream 280
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When you have limited power adding gears helps to make better use of the power available. That is why trucks have so many gears, 13 speeds is pretty common. As Mike said the 4 speed Allison does help.

The GV makes the TH400/475 a six speed maybe. I say maybe because the ratios aren't necessarily spread as evenly as a six speed transmission. In other words 2nd gear overdrive isn't half way between 2nd and 3rd. It helps but is not perfect. Where it really shines is in top gear overdrive. It brings the RPMs down enough to give a very comfortable cruising speed. The draw back is the GV doesn't like down grades which puts you back to the original 3 speeds.

Another option is to change the rear axle gear ratio. It's not overly expensive however once you gear for that comfortable RPM/cruising speed, your jackrabbit starts get really sluggish. The Isuzu isn't exactly "lively" from the stop light so making your starts less lively is something to think about.

A 4 speed Allison would give you that extra gear and you could gear up the rear axle for a better cruise speed and maybe not lose quite as much from the stop light start. You have to play with the available gears and pick a happy medium. Everything is a compromise.

The bottom line is we are dealing with 35 year old rigs and the new technology isn't developed for the small quantity of rigs like this to be cost effective. We have to pick and choose from what is available for other applications. Also consider the amount of time spent on those mountain grades to the time spent cruising at highway speeds. Sometimes you just have to stay right and sit back and enjoy the scenery and let the world and traffic pass you by.
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Old 10-19-2018, 03:16 PM   #6
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1982 31' Airstream 310
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"The bottom line is we are dealing with 35 year old rigs and the new technology isn't developed for the small quantity of rigs like this to be cost effective. We have to pick and choose from what is available for other applications. Also consider the amount of time spent on those mountain grades to the time spent cruising at highway speeds. Sometimes you just have to stay right and sit back and enjoy the scenery and let the world and traffic pass you by."

X 2
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Old 10-19-2018, 03:49 PM   #7
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I guess that's the point....we don't drive the 55mph that these rigs were engineered for; and it can be down right scary having a semi bearing down at you from behind with a minimum 25 mph closure rate, but probably a lot more.
I can't blame people for wanting to get more speed out of these old queens, but as you stated, it doesn't come easy; or cheap.

Cheers
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