TH350 5 neutrals (delayed shifting/won't go into gear)

[IcePatch]

I've got an '83 GMC S15 with a 350/TH350 swapped into it. It's had delayed engagement since I've bought it and it finally got so bad it doesn't want to go into any gear at all anymore. I suspected a valve-body issue since once it would go into gear it would upshift, downshift, and enginebrake just fine without any noticable slipping.

After letting it sit in a field for 2 years, I've got it up on jackstands and dropped the trans pan. Very minimal amount of gunk in the bottom of the pan, a hardly noticable amount of sparkles. Dad used to be a mechanic at a buick dealership and he didn't think the contents of the pan indicate anything catastrophic.

I dropped the valvebody, took out the plungers one at a time and made sure there was no hangups or broken springs, everything looks good in that department. I carefully peeled the separator plate/gasket off the bottom of the trans (managed it without dropping any check balls on the ground) and found the attached picture on the transmission side of the plate. It looks like moisture got in through the vacuum doohickey, causing the plate to rust and the gasket to blow out across a bunch of fluid channels.

The governor screen, the pump screen, and the pan screen were all pretty clean so I'm optimistic that the gasket was the issue. I'll be ordering a shift kit, gaskets and fluid in about a week and once I get everything back together I'll post an update.

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[Hunter79764]

I've got a TH350 in another vehicle that did/does something similar. Does it go into gear better if the RPM's are higher?

 

[IcePatch]

I've got a TH350 in another vehicle that did/does something similar. Does it go into gear better if the RPM's are higher?

Negative, I tried reverse, drive, 2 and 1, got the RPM's up to about 3000 in each and it just acted like it was in neutral.

I was actually sitting in the truck on my phone with it idling for about 5 minutes and it suddenly went into reverse. No slippage, backed it over to the front yard but it hasn't gone into any gear since.

 

[IcePatch]

It should be noted that I confirmed the shift linkage was not loose. Before dropping the valvebody I also confirmed that each gear on the ratchet shifter matched up with the shifter tang on the valvebody. Everything lined up perfectly there so not a linkage/shifter issue.

 

[Matt69olds]

Before putting the pan on, verify the dipstick is correct. The full mark should be even with the pail rail.

 

[RecklessWOT]

Man, just the sight of a valve body scares me. Automatic transmissions are the one thing I will ditch or replace at the first sign of trouble. Good on you for being able to figure it out lol

 

[vr1967]

There is a WIT Trans parts in SLC if you want to just buy a gasket or two without the shift kit

 

[IcePatch]

Before putting the pan on, verify the dipstick is correct. The full mark should be even with the pail rail.

That's a great idea! It's got an aftermarket floppy dipstick on it, ill make sure its the correct height while the pan's off!

 

[MikeB]

Man, I've never seen a valve body gasket that looked like that. I guess it could be your problem. I'd suggest removing and checking the valves and springs on the side of the valve body to make sure they move freely. Even then, I have to wonder about junk in the valve body and the fluid passages in the case itself.

 

[IcePatch]

Man, I've never seen a valve body gasket that looked like that. I guess it could be your problem. I'd suggest removing and checking the valves and springs on the side of the valve body to make sure they move freely. Even then, I have to wonder about junk in the valve body and the fluid passages in the case itself.

Thanks! I did take the valves and springs out one by one to make sure they operate smoothly. It's quite clean in the valve body, part of the gasket just got stuck to the transmission valve passages. I scraped it clean with a razor being careful not to get gasket gookies up inside the transmission. I'm fairly confident it's clean, but time will tell!

Shift kit with new plate and gaskets arrives next week, once I get it back together I'll definitely post an update.

 

[MikeB]

Shift kit with new plate and gaskets arrives next week, once I get it back together I'll definitely post an update.

Which brand? I highly recommend TransGo's 350-1&2 Reprogramming Kit. I've installed at least three of them over the years, as far back as the late 70s! So, they've been around a while and their tech support is great. The main difference between Stage 1 & 2 is the pressure regulator spring, along with governor springs.

Short story: I bought a used TH350 from a guy who said it had a TransGo kit. When I got it home, I pulled the pan, took some pictures, and e-mailed them to TransGo. I got an immediate response telling me that it had their 1&2 kit, and to check to see which pressure regulator spring I had. Turns out I had the stiff one. So the TransGo guy sends me the softer spring, along with a couple gaskets and a separator plate, because, as I recall, a hole had been added or enlarged. Since it was a couple days before Christmas, he said there was no one in the office to bill me, so he sent me the parts for free.

On the other hand, I once had a B&M "shift improver" kit that I bought for cheap. I got what I paid for! The kit was very crude, with only a handful of parts, and the shifts were very harsh! I left repeated messages for B&M but never did hear back from them. I threw that junk in the trash and got another TransGo kit.

I don't have any experience with other kits.

 

[IcePatch]

I got the transgo kit with gear command! Been watching a lot of videos and reading forum posts for valve body modifications and the transgo kit comes with a little insert to lock the valve in place for gear command. Other people were talking about welding the valve to the valvebody but that gives me the heebeejeebies so this kit seemed like the way to go.

 

[MikeB]

I'm not familiar with gear command. I'll have to look it up. Just don't go overboard on line pressure, or you will have some brutal shifts that can't be good for the drivetrain.

 

[Matt69olds]

That transmission has had some water in it at one time. That’s what valve body gaskets look like after soaking in a ATF/water bath for a while.

The B&M kit severely restricts accumulator function, and is a little more aggressive with spacer plate drill sizes. I actually prefer the B&M kit IF the car in question has a aftermarket torque converter. The looser converter with higher stall speed really tames the shift feel just cruising around. With a stock converter, it’s not a pleasant daily driver.

The TransGo kit is more “civilized”.

 

[Matt69olds]

I got the transgo kit with gear command! Been watching a lot of videos and reading forum posts for valve body modifications and the transgo kit comes with a little insert to lock the valve in place for gear command. Other people were talking about welding the valve to the valvebody but that gives me the heebeejeebies so this kit seemed like the way to go.

Piece of copper tubing in place of the spring is what I use.

Pull the valve, remove the spring, put a piece of tubing in place, reinstall the valve and you’re done. If the roll pin won’t fit, take a punch and LIGHTLY tap the valve to compress the copper tubing until the roll pin just fits. The length of the tubing isn’t critical as long as the valve can’t move.

The only thing to keep in mind is with no spring pressure pushing against the pin, the roll pin can fall out. Once the roll pin is in place, pack the end of the valve bore with Vasoline. That will hold the pin in place long enough to install the valve body. Or you can install the pin part way, and lightly tap the pin with a small hammer to put a slight bend in the roll pin. It will fit snug in the bore.