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Old 05-25-2015, 09:06 PM   #1
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Year: 1991
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Chassis: G3500 Vandura
Engine: General Motors 5.7L 350 V8
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'91 GMC G3500 Vandura 5.7L V8 350

I changed the plugs, wires, rotor and distributer cap along with the air filter. Oil change and filter change is next. Seems to run really well since the tuneup and the muffler replacement. Not sure if any other engine replacement items would be worthwhile.

The odometer is apparently broken and the trip odometer will not reset. Feels like it is stuck or something when you push the button. I need to see if I can get the gauges working or get something aftermarket. The speedometer may be the only gauge that is working properly. The fuel pump was changed before we purchased it along with the fuel filter.

We seem to have lost reverse. I have posted elsewhere, but thought I would try here as well. It has been too wet to crawl underneath to look for markings on the transmission to see which one it is. Does anyone have direct experience with this? We were told by the people we bought it from that it needed a transmission screen and fluid change. I got advice from a couple of people not to drop the pan. This was before we lost reverse. I have had others say to go ahead and do the screen and fluid change substituting Trans-X or Lucas Stop Slip for one of the quarts. I have great appreciation for the advice I have received on here as well as face to face. I am only duplicating in this section to get more input for anyone with direct GM experience. We are hoping to make what we have last and not have to have a rebuild done on the tranny. We have been looking around for salvage yards. Thoughts on that? Thank you for any feedback.
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Old 06-05-2015, 09:51 PM   #2
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We officially have a transmission fluid leak, so I am going to have to change the pan gasket at some point unless the Lucas Stop Slip I put in it today along with transmission fluid. It said that it can help with leaks. I am going to monitor it and see. It says that two bottle may be needed for larger transmissions. The stuff sure is thick. As of right now, we still do not have reverse. Maybe it is too far gone. Any insight on this would be appreciated.
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Old 12-10-2015, 10:14 PM   #3
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Join Date: Dec 2015
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Year: 1986
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Hello, I was just curious how you're making out with your trans ...I just bought a 1986 gmc vandura and it was low in trans fluid so when I got it home I had to add almost 2 bottles in and when I put it in reverse it seems to take a second or two to go into gear....I dont have any input for you but just a shared experience....I don't drive my bus much yet but will be doing a long trip in the spring...

thanks!!
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Old 12-10-2015, 10:36 PM   #4
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Quote:
Originally Posted by axis View Post
Hello, I was just curious how you're making out with your trans ...I just bought a 1986 gmc vandura and it was low in trans fluid so when I got it home I had to add almost 2 bottles in and when I put it in reverse it seems to take a second or two to go into gear....I dont have any input for you but just a shared experience....I don't drive my bus much yet but will be doing a long trip in the spring...

thanks!!
No progress on the transmission. It leaks a pretty good bit. We want to get it rebuilt, but not a priority at this time. Someone suggested dropping the pan, replacing the screen, replacing the gasket and fill the transmission as needed. They claim it may be fine after that. Does not make sense to me that we would somehow get reverse back by doing that. We do not want to lose the transmission altogether by doing that. Seems a bit of a risk. Hopefully, we will be able to get it back to 100% before the summer. Well, back to better working order.

We have been having trouble with the battery though it is pretty new. It tests out fine and the alternator seems to be doing its job. We have to regularly jump start it which does not make sense to me. Frustrating really.
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Old 12-11-2015, 06:05 AM   #5
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I takes more line pressure to engage reverse that the other gears-so if a plugged filter is restricting things, then yes-it could be a solution to getting things working.
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Old 12-11-2015, 08:53 AM   #6
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sounds like you might have something draining the battery and with all of the original electronics that a bus uses maybe something is hooked up that wouldn't have to be and its draining it? just a guess on my part..I'm still new to the bus or rv owning thing..I had the same thing with mine..I have two batteries and the back heater was draining my battery number 2 so I unhooked it..my battery number 2 runs a stereo,fridge,heater etc...
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Old 12-11-2015, 11:08 AM   #7
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Sorry that I didn't see this earlier. First, you gotta figure out what trans you got, either a 700r4 or a turbo 400. Take a look at the pan and compare it here. http://www.crankshaftcoalition.com/w...Identification
You can try changing the fluid and filter, but I doubt that will solve anything. If your fluid is really nasty, the shuttle valves in the valve body could be stuck, preventing reverse from being engaged. That is about the only thing that might be fixed with a fluid change. I'd have to know the transmission in order to give any other advice(both transmissions are pretty different internally).
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Old 02-05-2016, 06:54 PM   #8
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transmission

I just wanted to check back in and report that my transmission is working better since I put enough fluid in it although sometimes it still takes a little while to catch in reverse..

I think mine is the 700 but I am going to look under it this weekend to confirm.

I just rented a garage to keep my bus in with a cement floor so I can now work on the bus on weekends indoors..

How much does a trans rebuild cost ?

In the spring I am driving the bus from Colorado to the east coast and then back to Colorado again almost 4000 miles..

I want to make sure that she will make it... lol
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Old 02-05-2016, 09:29 PM   #9
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No reverse from low fluid is one thing. Slow engagement on a 700 means the pumps likely shot (could also be clogged or binding valves). If the fluids contaminated you are shedding clutch material. Dropping the pan will only hurt the pocketbook. You also might gain some insight on the contents of the pan. Check for shiny particles (bushing material) and any pieces of larger metal in the pan.

I can't imagine it being a 700 though because that's such a terrible transmission for a bus application. More than likely a th400.

Either one will be easy to R/R for a rebuild. Depending on damage and trans guys you can start at 500 bucks and up.

P.S. Avoid stop leak anything for stuff you want to own/depend on. They are very bad in the long run.
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Old 02-07-2016, 10:06 PM   #10
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After looking at my trans today and matching it with the chart above in this thread I think you are correct in that it's a TH400..


I started the bus and ran it a little in reverse today and it still took a while to start to move in reverse..


maybe before my trip I should just have it rebuilt and also check the engine as well.. I don't want this thing letting me sit along the road..
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Old 02-07-2016, 11:13 PM   #11
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GM Turbo 400 Transmission Stock Up to 450HP | eBay

Not a bad price with converter. Shipping might be a bit depending on where you are. If you can pull the transmission and install yourself it's hard to beat the above price.

I don't know much about th400's but I sure hope they have lockup converters. Save you a ton on fuel and reduce transmission heat tremendously.
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Old 02-08-2016, 02:38 PM   #12
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Quote:
Originally Posted by uhlhazard View Post
GM Turbo 400 Transmission Stock Up to 450HP | eBay

Not a bad price with converter. Shipping might be a bit depending on where you are. If you can pull the transmission and install yourself it's hard to beat the above price.

I don't know much about th400's but I sure hope they have lockup converters. Save you a ton on fuel and reduce transmission heat tremendously.
I thought lock up converters are overdrives and create heat. I'm not a tranny guy but this makes good learning conversation.
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Old 02-08-2016, 04:05 PM   #13
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I thought lock up converters are overdrives and create heat. I'm not a tranny guy but this makes good learning conversation.
From wikipedia:

"Lock-up torque converters

As described above, impelling losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the impeller and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and virtually no power loss."


Overdrive comes from the internal transmission gearing. The best a torque converter could give is a 1:1 drive ratio.
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Old 02-08-2016, 04:12 PM   #14
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The usage of the term "overdrive" for gm transmissions means any ratio below 1:1. On the 4l60e /700r4 4th gear is .7:1 where 3rd gear is 1:1.

On the turbo 400 which only has 3 speeds, 3rd gear is 1:1 there is no overdrive. From what Ive read theres also no lockup option available either.

It is however a very stout transmission but shes showing her age.
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Old 02-09-2016, 11:11 AM   #15
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Chassis: GMC blue bird
Engine: 350 chevy
After looking on Craigslist in Colorado I found a few rebuilt TH400 trans for $350 to $400....Looks like some great deals here....Denver is around a 5 hour drive for me but can't beat these deals...


Is the fact that the trans that I have now doesn't always catch in reverse a sign that I really should change the trans before I take my trip back to Pa from Co? I have no way to know how many miles is on the trans that it has now..
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Old 02-09-2016, 02:16 PM   #16
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Transmissions have a multitude of challenges in a bus. First, age. Seals deteriorate and the th400 is a tank of a transmission.

Its probably been around since the early 90s carrying a bunch of sticky kids on stop and go trips in all weather conditions.

If maintenance at your place was anything like mine, then shes likely rocking vintage 1991 model year fluid. When a transmission sits up the fluid settles low leaving exposed iron parts to atmosphere and condensation. This means rust. A lot or a little doesnt really matter.

When the clutches sit long enough and the rust hits them it can delaminate the clutch material in chunks. Fluid has both a mileage and a time interval to change.

Thermal cycling breaks mechanical parts down. Car parts getting hot and cooling down is like quenching a sword on every use. The problem is, you arent a samurai. The parts shift at a molecular level and temperature changes accelerate this phenomonon. Perfectly flat disks become warped, drum surfaces irregular etc.

You are rocking a by-gone era transmission. Techs today dont know how to use a vacuum gauge to troubleshoot, they need a computer to diagnose the problem for them. Finding someone who can troubleshoot your bus is likely more effort than its worth and since its such a critical part I myself would have it rebuilt or replaced based on the information you have shared.

Now, if you find a reman trans for 500 bucks (which might be an awesome price) make sure to remember you need an application specific torque converter as well. You absolutely do not want to reuse your existing converter. They go from 100-200 bucks a piece for a decent quality daaco brand.

And finally depending on trans failure it might have dumped a ton of contaminants into your transmission cooler system which can include your radiator side tank trans cooler , any rubber lines joining hard lines, and the transmission cooler actual.

My apologies for posting here with such verbosity. I thought I was replying to the original poster.
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Old 02-09-2016, 05:44 PM   #17
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No problem, man. Good information to have. I've never been inside an automatic transmission.
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Old 02-09-2016, 08:15 PM   #18
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Since it is a 1991 model I would lean more towards a 4L60(E) or a 3L80HD rather than a TH400 or TH700R4.

It will cost somewhere in the neighborhood of $3K to R&R the transmission.

Personally, if I had doubts about the transmission, I think I would take it to a local shop that has a good rep and have it taken care of before I went anywhere. I would spend the extra $$$ to get it with a nationwide warranty.
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Old 02-09-2016, 09:51 PM   #19
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There is no such thing as a 4l60e until 1993 in any gm platform.

Best way op can ID the trans is to post up a picture of his rpo sticker. Mine was under the passenger visor stuck to the headliner. They are usually found in the glove box, followed by the body near the door striker on the drivers side.
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Old 02-10-2016, 08:43 AM   #20
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If you get any trans, make sure it's for the bus. Things like converter stall, governor weight, and maybe even the clutches might be different depending on usage. So I doubt any old 400 of craigslist will work for you.
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