TH350c Slipping

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scenic760

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Jan 12, 2021
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Location
SoCal
First Name
Chris
Truck Year
1981
Truck Model
Suburban K10
Engine Size
350
Hey All,

I have finally gotten back to my project after getting pulled in 50 different directions over the last month...my wife asked me what I wanted for Father's Day and I said how about 6-8 uninterrupted hours of wrenching?!

I got a tranny jack from Harbor Freight and as I got on the ground to pull everything, I said hmmmmm I really don't want to do this if I don't have to....I wonder if shifting the transfer case affects anything? I rebuilt the transfer case at the same time so yet another variable to contend with...

Well...I shifted it into 4w-lo and it acted like a completely different truck..throttle response, no slipping, etc...so I did a quick search and saw where someone installed their np208 shift lever upside down?! I ran out of daylight (yeah...it wasn't exactly 6-8 uninterrupted hours!) to check it but does this sound like a possibility?
 

scenic760

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Location
SoCal
First Name
Chris
Truck Year
1981
Truck Model
Suburban K10
Engine Size
350
Hey All,

So I'm not sure if I should post a new thread or just keep this one going but until I get it 100% solved, I guess I will keep on here!

I took the truck to a transmission shop and he said jump in and let's go for a drive...while driving he asked me on my rebuild if I did this or that and about a minute or so in, he said I don't have 1st or 2nd gear...so what I thought was slipping was starting in 3rd gear..of course he said it's really hard to say what the issue is without having been in there himself. I was going to leave it there but he said they were full and I'd have to bring it back hopefully in a few days...

In the meantime he told me to check the governor to make sure it was working, which should be easy enough. However as I was driving back home I found a notebook the previous owner kept in a seat pouch with EVERYTHING he had ever done to it, including gas fill ups- date and $$. It looks like there was a shift kit installed about 3k miles before it sat for 5 years.

Question would be, if there was a shift kit installed and I did the dual feed mods (plug reverse feed/omit center seal/omit center ring) would I get the behavior I'm experiencing?

Thanks again!
 

IdahoJOAT

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Jul 11, 2022
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Location
Idaho
First Name
Rodger
Truck Year
1984
Truck Model
K20
Engine Size
350
Hey All,

So I'm not sure if I should post a new thread or just keep this one going but until I get it 100% solved, I guess I will keep on here!

I took the truck to a transmission shop and he said jump in and let's go for a drive...while driving he asked me on my rebuild if I did this or that and about a minute or so in, he said I don't have 1st or 2nd gear...so what I thought was slipping was starting in 3rd gear..of course he said it's really hard to say what the issue is without having been in there himself. I was going to leave it there but he said they were full and I'd have to bring it back hopefully in a few days...

In the meantime he told me to check the governor to make sure it was working, which should be easy enough. However as I was driving back home I found a notebook the previous owner kept in a seat pouch with EVERYTHING he had ever done to it, including gas fill ups- date and $$. It looks like there was a shift kit installed about 3k miles before it sat for 5 years.

Question would be, if there was a shift kit installed and I did the dual feed mods (plug reverse feed/omit center seal/omit center ring) would I get the behavior I'm experiencing?

Thanks again!
Looking forward to hearing an update.
 

scenic760

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Joined
Jan 12, 2021
Posts
318
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206
Location
SoCal
First Name
Chris
Truck Year
1981
Truck Model
Suburban K10
Engine Size
350
Looking forward to hearing an update.
I waved the white flag and dropped it off last week. I checked in on it today and he said they pulled the trans out today and will crack it open tomorrow...I'm curious at this point as well. I did realize I never cleaned/rebuilt the valve body when I had it apart...
 

scenic760

Full Access Member
Joined
Jan 12, 2021
Posts
318
Reaction score
206
Location
SoCal
First Name
Chris
Truck Year
1981
Truck Model
Suburban K10
Engine Size
350
Ok...so here is the update..

I just picked it up and drove it home about 6 miles..all seemed to work well but I think I need to adjust the timing now that the tranny is fully engaging it seems to knock a bit when I floor it...

They pulled the tranny apart and he said that indeed the valve body had some issues and whoever installed the aforementioned shift kit didn't do it correctly. He also said that I had burned up the 3rd gear clutches and it was pretty dirty inside not only with clutch material but also a lot of lint. There didn't seem to be any 1 smoking gun but I think just my inexperience at what I was looking at was the main culprit. The shop said "Hey, that's how you learn." I think I received a little street cred with my garage rebuild actually..

He also opened up the transfer case and went through it and said I did everything correct in there.

All in all I'm glad I did it, I was able to get the 5 clutch piston and hardened sprag in there and at the end of the day learned something in the process. I'm really no worse off $$ wise than I would have been if I had taken it to the shop to begin with...except the cost of the new clutches which I think ended up being $25.

I actually bought a used th350 to swap out a few months back that I will probably rebuild in the future..I actually kind of liked putting it together. Now pulling a tranny and a transfer case from a fully assembled truck in the driveway doesn't sound like a lot of fun..
 

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