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Old 02-15-2012, 12:19 PM
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turbo 400 moves forwards when in nuetral

I have a 1990 Chevy 1/2 ton truck 4.3 V6 factory 3L80 (Turbo 400 ) automatic transmission. When the transmission is in nuetral the truck moves forward, when I put it in reverse it feels like the brakes are on , you have to step on the gas to make it move. I just had a rear out put shaft seal and O-Ring put on at the shop but I don't think that has anything to do with it . Sometimes at 30 MPH the transmission will shift in and out 2nd and 3rd gears. Any suggestions ?

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Old 02-15-2012, 01:16 PM
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Forward Clutch may be fried, Plates welded together. Did it run low on fluid??
Shift Linkage bent/misadjusted.
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Old 02-15-2012, 04:42 PM
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SSedan64 hit the nail on the head.....forward clutches welded together,caused from quick excessive heat,[rocking in the snow,etc] will give you the exact results you are describing.sorry for the bad news.
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Old 02-16-2012, 08:37 AM
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Quote:
Originally Posted by SSedan64
Forward Clutch may be fried, Plates welded together. Did it run low on fluid??
Shift Linkage bent/misadjusted.
Sounds like you've overhauled plenty of transmissions, I just bought the truck it had been sitting in a garage for 5 years, the fluid was very low but when I serviced it there were very little clutch materials or metal particles, the fluid was'nt burn't. What about shifting in and out of 2nd and 3rd at 30 MPH, Is there any chance that when I took it to the transmission shop and they removed the tailshaft housing and put the seal and O-RING on the shaft they damaged something ?
Thanks , Doesn't hurt to ask.
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Old 02-16-2012, 08:39 AM
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Quote:
Originally Posted by rick 427
SSedan64 hit the nail on the head.....forward clutches welded together,caused from quick excessive heat,[rocking in the snow,etc] will give you the exact results you are describing.sorry for the bad news.
Sounds like you've ALSO overhauled plenty of transmissions, I just bought the truck it had been sitting in a garage for 5 years, the fluid was very low but when I serviced it there were very little clutch materials or metal particles, the fluid was'nt burn't. What about shifting in and out of 2nd and 3rd at 30 MPH, Is there any chance that when I took it to the transmission shop and they removed the tailshaft housing and put the seal and O-RING on the shaft they damaged something ?
Thanks , Doesn't hurt to ask.
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Old 02-16-2012, 10:37 AM
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no...they wouldn't have did anything to describe the problem you are having...falling out of 3rd gear is a problem in the clutch drum...torn lip seal, worn out clutches,bad sealing rings,usually,....and even tho the fluid was not burnt...I can take a brand new 400,as an example,rock it hard- in a stuck in the snow situation -it'll get so hot so fast that it will burn and weld the clutches together,yet not discolor the fluid,because the fluid wasn't hot long enough to change colors...it'll still be red,but have a slight burnt smell to it,but in your case, if you added new fluid to it to bring it up to level,the burnt smell might not have existed...anyways, I used to see that a lot during hard winters with rear wheel drive vehicles welding the clutches together, resulting in your ''goes forward in neutral'' situation.....

Last edited by rick 427; 02-16-2012 at 10:49 AM.
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Old 02-28-2012, 09:30 AM
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Thanks for all the help , you mentioned that falling out of 3rd gear could be a bad seal or worn out clutches in the drum. Which drum do you think there will be a bad seal or worn clutches causing the falling out of 3rd gear.
Thanks Again
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Old 02-28-2012, 10:07 AM
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it's called the ''direct'' clutch drum.
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Old 03-17-2012, 03:07 PM
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tranny creeps forwars in nuetral ,

Quote:
Originally Posted by rick 427
it's called the ''direct'' clutch drum.
Hello again, I took the TH 400 into the shop and they told me probably welded forward clutches. Just like you said, They weren't welded or worn , only one broken steel clutch , he overhauled the tranny , I put it in , it ran fine. Then I took it on the freeway now it's worse than before, In drive it woks great. In nuetral at acts like it's in 1st gear, ( won't upshift ) In reverse it won't move. Any advice or suggestions ??? Thanks
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Old 03-17-2012, 04:36 PM
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Take it back. Did you take it to a reputable tranny shop or a one stop shop?
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Old 03-17-2012, 04:59 PM
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Quote:
Originally Posted by 6426yy
Take it back. Did you take it to a reputable tranny shop or a one stop shop?
They have been in business many years , I'm going to take it back Monday, the guy dissasembled it in about 15 minutes and showed me all the parts, he seemed to know what he was doing. I was hoping that someone had a suggestion on what might be wrong. Thanks
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Old 03-21-2012, 08:29 AM
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Quote:
Originally Posted by rick 427
no...they wouldn't have did anything to describe the problem you are having...falling out of 3rd gear is a problem in the clutch drum...torn lip seal, worn out clutches,bad sealing rings,usually,....and even tho the fluid was not burnt...I can take a brand new 400,as an example,rock it hard- in a stuck in the snow situation -it'll get so hot so fast that it will burn and weld the clutches together,yet not discolor the fluid,because the fluid wasn't hot long enough to change colors...it'll still be red,but have a slight burnt smell to it,but in your case, if you added new fluid to it to bring it up to level,the burnt smell might not have existed...anyways, I used to see that a lot during hard winters with rear wheel drive vehicles welding the clutches together, resulting in your ''goes forward in neutral'' situation.....
Thanks for all your help , just wanted to let you know that the mechanic dissasembled the tranny for me and showed me that the only problem was one broken steel clutch plate (I believe in the forward drum.) After the overhaul and the mechanic hooking up correctly the manual valve in the valve body the transmission works great.
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Old 03-21-2012, 08:34 AM
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Quote:
Originally Posted by 6426yy
Take it back. Did you take it to a reputable tranny shop or a one stop shop?
I took it back , During the overhaul The mechanic didn't hook up the manual valve correctly, he fixed it and it works great. I researched this on the internet, and it seems that he not the first person to make this mistake.
Just passing on information for mechanics.
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Old 03-21-2012, 08:38 AM
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Quote:
Originally Posted by SSedan64
Forward Clutch may be fried, Plates welded together. Did it run low on fluid??
Shift Linkage bent/misadjusted.
The tranny shop found one broken steel clutch plate . After overhaul works great.
Just passing on information to mechanics.
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