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Old 04-30-2017, 03:41 PM   #1
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1991 35' Airstream 350
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Transmission type, 400 series

Can anyone direct me to a feature or maker's plate which will tell me which TH 400 series Trans is in my 91 350 LE? I'd like to determine what I've got before I go out and look for a shop that knows how to rebuild.

And, if anyone knows of a good independent shop in the Lumberton or Fayetteville area of North Carolina, I'd really like to know, and soon.

Best to all.
Rob
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Old 04-30-2017, 04:13 PM   #2
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Is it a stock gearbox?


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Old 04-30-2017, 11:21 PM   #3
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I found a transmission, with overdrive th 200-4R, is it a good transmission that supports our motorhome?
So far I saw no motorhome with that tranmision, almost all change the 400 th for a 4 L80e
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Old 05-01-2017, 06:03 AM   #4
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Quote:
Originally Posted by german6563 View Post
I found a transmission, with overdrive th 200-4R, is it a good transmission that supports our motorhome?
So far I saw no motorhome with that tranmision, almost all change the 400 th for a 4 L80e
To get an overdrive.
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Old 05-01-2017, 06:04 AM   #5
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2 thoughts, if i had 1991 350LE, I would consider installing a 4L80 transmission, or keeping the TH475 and adding a gear vendors overdrive. Either way is going to cost about the same...Don't play around there is only one way to go and that is with Jasper, you will get the best possible product built exactly to your needs. Even if you don't do the work yourself, pay somebody to put a Jasper unit in for you...they also have a nationwide warranty that pays the shop doing the work their current labor rate so it is not hard to find someone if you have a problem on the road to do the work. They just built me a Detroit Diesel engine for my 28 year old Snap-On truck and I would use no one else. Regards, Bob
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Old 05-01-2017, 07:37 AM   #6
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Originally Posted by ralley View Post
Can anyone direct me to a feature or maker's plate which will tell me which TH 400 series Trans is in my 91 350 LE? I'd like to determine what I've got before I go out and look for a shop that knows how to rebuild.

And, if anyone knows of a good independent shop in the Lumberton or Fayetteville area of North Carolina, I'd really like to know, and soon.

Best to all.
Rob
Rob, I'm no expert at GM transmissions but your 91 LE should either have a TH400, TH475 or the 4L80e transmission. Is you rig fuel injected? If it is there is a chance that you might have the 4L80e.

Here's a picture of GM oil pans which should help you at least verify if it's a TH400 series. It would only be a TH400 if a PO removed the original TH475. The difference is the straight cut vs helical cut gears. Straight cut would be the stronger gears in the TH475.

Click image for larger version

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Brad
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Old 05-01-2017, 07:41 AM   #7
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Hi all

That's why I asked the question whether it was stock.

In 91, like my 250, I thought they all came with the tbi and 4L80e.

You can use Brad's diagrams or run your VIN through compnine, which is useful and will tell you the stock setup, incl. tranny.

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Old 05-01-2017, 07:42 AM   #8
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Originally Posted by german6563 View Post
I found a transmission, with overdrive th 200-4R, is it a good transmission that supports our motorhome?
So far I saw no motorhome with that tranmision, almost all change the 400 th for a 4 L80e
Herman, I don't think the 200-4R is really designed to handle the loads of a motorhome. You're much better off looking for a 4L80e or adding a gear vendors on the back as Bob suggested.

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Old 05-01-2017, 08:07 AM   #9
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Its stock so far as I know. 3 speed auto, stick on the steering column. When i bought it about 2004, it came with what I presume were almost all of the maintenance records, and I see no mention of any trans modifications. I put a gearvendors on it about 2008 or so.
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Old 05-01-2017, 08:11 AM   #10
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Thanks very much. I put a gearvendors on it about 2009. I will consider putting an different trans in it, but my immediate problem is finding a shop to do it, four hours drive from home.
Best,
Rob
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Old 05-04-2017, 08:11 PM   #11
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Quick update

Since the weather is not cooperating with my update tonight, I will leave it for another day.

My problem is not tranny, but rear brakes, now completely replaced but not yet working--because we cannot find the master cylinder, or its reservoir. We know where it should be, but there seems to be an awful lot of stuff in the way.

Can anyone help by providing a photograph, or better, experience, of where the master cylinder and its reservoir are on the 350LE??

Best to all,

Rob
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Old 05-05-2017, 01:01 AM   #12
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If you are running with a P32 GM chassis, you are best to consult the Chevrolet Motorhome Chassis Manual (there is a 91 version kicking about) or the unit repair manual which will tell you everything you need to know. That is on the sticky.

In simple terms, drivers side wheel well, remove the metal shroud or put your hand through the gap and there it is.
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Old 07-15-2017, 02:11 PM   #13
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Thanks, Update, and a question

Thanks to all for your replies. It's been a while since I could reply--But here is an update:

The problem was not tranny, but TWO locked brake calipers (on the rear duals). Replaced hubs/rotors/pads and fluid, as well as bearing seals. Now the brakes work very well indeed.

But, to get back to the tranny. On my way home (four hours) I had to floor the old girl to get out of the way of an idiot in a Winnebago pulling a full size pickup who was merging onto I-95 and trying to force me to move over a lane--which I could not do because of traffic our hero could not see. To avoid a collision, I put my foot down hard, and the old girl pulled up her skirts and flew.

But about forty miles later, the kick-down switch began to engage itself without reason. The tranny began to drop down a gear, and we would proceed at increased revs for five or six miles until the tranny would pop back into drive for another 20 or so miles and then repeat. My mechanic has tried locally to find a new switch to no avail, being told that the part "has been discontinued." We had decided to replace the switch because there is no other evidence of transmission failure that we could find.

Anybody know where I can get a kick down switch for the TH400 Trans??

Best to All
Rob
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Old 07-16-2017, 04:27 AM   #14
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Rock Auto, Regards, Bob
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Old 07-16-2017, 05:25 AM   #15
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Quote:
Originally Posted by ralley View Post
Thanks to all for your replies. It's been a while since I could reply--But here is an update:

The problem was not tranny, but TWO locked brake calipers (on the rear duals). Replaced hubs/rotors/pads and fluid, as well as bearing seals. Now the brakes work very well indeed.

..
Rob
Have you checked if the brakes are unlocked now, even with the new brake components? Instead of a bad kick down switch you may have a pre load condition of your brake system caused by the master cylinder/hydroboost system.
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Old 07-17-2017, 10:32 AM   #16
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I have not checked the brakes. Can you suggest a way to do this which doesn't involve jacking it up? The ground is really soft where I am parked at the moment. It has rained every night for a week.

Thanks,
R
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Old 07-17-2017, 11:07 AM   #17
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If the concern is the rear brakes, drive around 15 or 20 miles and use an inferred thermometer to compare the front brake temp to the rear. If brakes are not releasing they get hot real quick.
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Old 07-17-2017, 11:23 AM   #18
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Are you sure it was the transmission kicking down? If your Gear Vendor's unit kicks out it would give you the same symptom. My bet is on a loose connection.
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Old 08-17-2017, 03:59 PM   #19
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TH400 w/Gearvendors

Sorry for not replying to your post--the vehicle was in the shop, so I couldn't troubleshoot.
I take your point about the Gearvendors, because when it does kick in, my RPM's go down from 2800-3000 to about 2200. I checked with tech support at GV;they say that as long as it is not low on oil, and the control switches all work as they should, then it should work properly. If it doesn't work properly, then the problem is more likely to be in the tranny controls.

So, I have changed the GV oil (it was overdue, but not much) and am going to replace both the transmission throttle control switch (if I can find it) and the solenoid in the tranny that it operates. They are 26 years old, after all. After that, we will see.

Does anyone know exactly where the kickdown switch is?? (also called a transmission throttle control switch, or a transmission detente circuit switch). The information in the chassis manual on page 8-3 (it's on the internet) is incorrect. It is NOT under the dash above the driver's LEFT foot. And it is not anywhere in the throttle linkage that either I or my camera can see.

Best to all,
Rob
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Old 08-22-2017, 02:30 PM   #20
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Try section 9 (see link below) or expanded parts blow out on the Chevy parts prime site or GM wiki

http://www.73-87chevytrucks.com/tech...ice_Manual.pdf
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