Th400 experts?

SquareRoot

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Got a newly rebuilt 400. Runs great, no issues. However, I got this odd noise that I'd like to diagnose. It only occurs on deceleration when I first let off the gas. And I think it only happens in 3rd but I could be wrong.
It sounds like something is spinning (whirring) really fast like it's engine braking and when the truck slows enough it suddenly releases and the whirring stops.

Could this be the governor? Truck has 4:56 gears so it's wound up pretty good but like I said, it's just a noise, everything that can be felt is normal.
 

Craig 85

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I had my TH-400 rebuild and ran it for a couple months in warmer weather. This past winter, when it got under 50 degrees outside, it would start whining at cold starts. It would go away as soon as the fluid got warm. It turned out it was the pump. Thankfully it was under warranty.
 

86Peter454

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any chance you can post a video with the sound?

if i was to guess its something to band around the direct drum? hard to say without hearing it or knowing anything about transmissions lol.
 

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I am going to say it's the pump, but mainly because of the filter. I have been tracking down pump whine in my TH400 for a couple months along with some other issues and finally got a brass transmission filter, not the dacron type. ATP has the dacron type, and it restricts flow, or it does in my truck anyhow. Put in the brass filter on Sunday and all of my problems have gone away. If you choose to drop the pan yourself or have them do it, make sure they use the brass filter.
 

SquareRoot

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I find it hard to believe that it's the pump because the trans got rebuilt about 500 miles ago with a new convertor. It's not the typical whine like a power steering pump makes, it's a high speed whir like something is being "overdriven or not releasing- then instantly, it stops. That's why I was thinking the governor, those weights look like they could make that noise and suddenly release. I'll try to get a video of it and post it.
 

akchevrolet

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Did u figure this it because mines doing the same thing. I whirring noise on decel.
 

AuroraGirl

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Did u figure this it because mines doing the same thing. I whirring noise on decel.
that sounds like a converter. I forget the exact source list but basically a defective seal or perhaps one that had a bad situation where crankshaft or flywheel runout or other mounting problems wore the bushing and the assembly isnt balanced properly, or wore a bushing thats allowing the wrong fluid circuit to try and spin or something. Im a mess rn but that brain spit may have something someone else can shed light to. but I would look at if you have any leaks, inspect the area with cover off, and double check fluids and make sure your trans is properly detenting the shifter on the trans into each gear, make sure your fluid cooler is properly flowing and any check balls or the like to prevent the fluid to leak back or not stay in the proper parts of trans are working. I know a lot of cooler lines have a converter ball for drainback stopping. not sure of this vintage.
is your th400 have a lock up
 

akchevrolet

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That idk its on a 1987 305 2wd
 

AuroraGirl

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That idk its on a 1987 305 2wd
I find it highly unlikely but not impossible but Still questioning if your truck has a TH400 because a 305 and 2wd is the kind of thing you use a 700r4 for in 1987, at least sensibly.
 

SquareRoot

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Did u figure this it because mines doing the same thing. I whirring noise on decel.
No, not really. I ended up having it rebuilt at the trans shop. It was pretty worn out. I know the friction discs were worn down to basically nothing, they appeared to be original though. Then I swapped it out for a NV4500.
 

akchevrolet

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I would love to put a manual transmission in the truck. its a 400 has the vaccuum modulator on the side. like this
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AuroraGirl

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I would love to put a manual transmission in the truck. its a 400 has the vaccuum modulator on the side. like this
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i mean its strange but if you want to switch to something else you have a good bargaining chip as it is
 

akchevrolet

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maybe when I don't have a car seat in the way of the shifter. haha. It has had a couple things happen leak at the dipstick where lost almost all fluid. the driveshaft support bearing went out then the rear diff end yolk came off when I stopped at a red light so had to replace that. the sound was there before all that happened. I think the rear seal for the transmission where the driveshaft goes in.
 

AuroraGirl

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maybe when I don't have a car seat in the way of the shifter. haha. It has had a couple things happen leak at the dipstick where lost almost all fluid. the driveshaft support bearing went out then the rear diff end yolk came off when I stopped at a red light so had to replace that. the sound was there before all that happened. I think the rear seal for the transmission where the driveshaft goes in.
yeah if the support bearing went out and the trans especially wasnt mounted solid or also the rear diff had play from bad bushings on the leaf springs or the leafs were broke would all contribute. as well as a sticking slip joint(they need grease)

Wait. did you say you have a slip yoke and a center support? that doesnt seem right, especially since you also prob had a 700r4 originally. Fixed output would make sense for that slip shaft. thats a lot of weird side loads and pivot point shifting that maybe accelerated wear, esp if the shaft was not long enough and it was barely in the case
 

akchevrolet

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Sry this guy.
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