TH350 Reverse doesn't work

GXPWeasel

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Like the title says pretty much..
Got the truck running and verified I got forward (all 3 gears) and reverse while on jack stands. Went ahead and took it for a quick spin around the block. Once I got back, the truck wouldn't back back into the garage. The drive is slightly up hill, and it just wouldn't go. It will move the truck in reverse in the shop (on flat ground) but definteley won't back up a slight incline. I get all 3 gears in forward no problem.

A little back story, I just rebuild everything on this truck, except the transmission. It's a TH350, and I did drain, add the trans go shift kit, replaced the filter, and filled her up. I haven't done anything else to the transmission at all. It has sat for 10 years or so since moving, so I'm sure some seals are dry and need some lube. I know for a fact the shift shaft seal is gone, and I need to replace that. But I'm not touching that until I for sure get a good working transmission.

Any ideas?
 

Turbo4whl

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Missing check ball when you removed the valve body? Wrong plate gaskets?

@Matt69olds will know
 

Matt69olds

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Make sure you assembled the transfer plate, support plate and dual feed plate in the core t order. Those are the parts in front of the valve body, held in position by the 7 (I think) short bolts.

If that’s not it, make sure you have the valve body gaskets correct.
 

GXPWeasel

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Hmm, I'd have to look back at my kit (I think I still have the kit box) and look at the instructions. That or I wonder if I can get the instructions again without purchasing the kit again... Of course that all means I have to drain and remove the transmission pan and open it up again to check. I guess a small price to pay vs a broken part in the transmission.
I appreciate the quick response guys. I'll look for the installation instructions.
 

GXPWeasel

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Quick question @Matt69olds ....
I do remember now that after I got back for my first short drive. I was in the shop (level floor) and when in reverse I gave it a little throttle, and the trans jumped before it did move. Felt like wheel hop or that the trans mount wasn't secured. The wheels did not spin, and the trans is secured as it should be. Would that also be a sign that I maybe installed the TransGo shift kit incorrectly?

Sorry for all the questions. I'm frustrated in myself if that is in fact the case, and ready to get this truck on the road. However if the incorrect installation of the shift kit is a good chance at being the culprit, then it's something easily / cheaply fixed, and better than the alternative of needing a new trans.

Thanks.
 

Matt69olds

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Technically, a 350 trans will work with just one check ball (in the passenger rear corner) so chances are good you got the needed ball in the right spot.

Does the trans have a good solid 3rd gear? Meaning it makes a good firm 2-3 shift? The same clutch pack that locks the forward clutch to the direct clutch is also used to drive the trans in reverse. If 3rd gear is good, chances are the frictions are good enough for reverse.

Get the truck up to 30ish mph, put the shifter into manual 2nd, then shift to 1st gear. Each time you drop a gear, there should be a noticeable increase in engine speed, along with a noticeable sensation of the truck slowing down. If so, that means the low/reverse clutch pack is in decent shape. The low/reverse clutch provides engine braking in manual 1st, it’s also the holding clutch for reverse.

If the trans worked before installing the shift kit, chances are you either mixed up the gaskets, got the transfer plates installed wrong, or you have a valve body issue.

TransGo is usually pretty good about replacement parts. You could probably call them and get replacement gaskets for their shift kit. If you do remove the valve body, it’s easy to air check each clutch pack. If you have compressed air, you could make a blow gun using 3/16 brake tubing. You can bend and cut the brake tubing however needed to reach the passages in the case. You should be able to hear each clutch apply with a thud. It’s potentially messy, so be prepared for a oil shower.
 
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GXPWeasel

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Thanks again for the reply @Matt69olds
The main problem here is that I don't "know" that the trans was good before my install of the shift kit. The fluid looked good, was full, and didn't smell burnt or look like it had any water in it. So I drained it, installed the shift kit following instructions carefully (to the best of my memory) because I had never done more than a fluid/filter change before on a transmission. This work was performed outside of the truck, so the trans was upside down. It's possible I mixed something up during the install though, since the video / instructions mostly reference a transmission in the vehicle (right side up).

I can't guarantee that I made it to 3rd gear on my short drive the other day. I will have to get back in the truck, use my phone for my speedometer (mine isn't hooked up) and confirm I'm going fast enough to get to 3rd gear. I'll try the downshifting you described for me to do as well. I'm very familiar with engine braking, as my '15 silverado has this during the tow/haul mode, and I use it frequently when towing my camper.

I'm really hoping it isn't something like a valve body issue you described. As I stated before, I've never really done any work on a transmission (of course now I have experience installing a shift kit, that was hopefully installed correctly).
 

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