Help with Chevy K20 tranny/clutch issue

Joe Dirt

Well-Known Member
Joined
Jan 10, 2007
Location
East TN
First off, my truck is a 1985 Chevy K20 with a 350, 10b front, 14sf rear, SM465 Trans, and NP205 T-case on a Skyjacker 4" Softride.

I was just on my way to drop the truck off at a shop to get new 4.10 gears installed in the front 10-bolt and while cruising along at ~45 mph the rear end locked up tight and I skidded to a stop in the road. I left 2 long black marks in the road and could smell the stench of burnt rubber from my tires.
To be quite honest, I can't figure out what exactly happened. I got under the truck and there is a big place busted out of the bottom of the bell housing so I figure either the tranny blew up or the clutch grenaded.

My clutch pedal became non-existent, and you can push on it but it's hard to push and I can't get the truck into any gear. Luckily I was following my cousin who was going to give me a ride home from the shop, so he pulled my truck back to his farm. Everything else under the truck appears to be intact.
I had to put the T-case in neutral to tow the truck to his house. With the T-case in neutral, I could start the motor but there was an awful grinding sound coming from the clutch/tranny area.

Even though the tranny appeared to be in neutral, I could not start the truck because A) I had no clutch pedal and B) it acted like it was in gear so I had to put the T-case in neutral to get the truck started.

The truck was running fine before this happened, no funny noises or anything peculiar. The guy I bought the truck from had just put a brand new clutch in it (he had the receipts) and then I put a new clutch master and slave cylinder on it a year ago. The clutch has always performed flawlessly, it has never slipped. I've owned the truck for 3 years and ~3K miles.

Any ideas on what happened? Any input will be greatly appreciated. Thanks.
 
Granted Im not going out on a big limb here, but its either the clutch or the tranny.

Not really gonna know until you break it apart
 
Again, without puling it apart, hard to say. I have seen Flywheel, PP and clutch parts cause this, and I have also seen a tranny lock up and do the same thing.
 
Cool,k thanks guys for the responses. My cousin just came by to get the keys from me. He is going to pull it up to another guy's shop that is less than a mile from where my truck is broke down and see what's wrong with it. I talked to my next door neighbor who is an elderly mechanic and he seems to think the pressure plate grenaded. I'll let you know what it was when I find out. Thanks again.
 
off hand, from the bellhousing damage, i would say the pp came apart. it's also possible the flywheel was cracked and let a chunk loose.

it's possible the transmission itself locked, but usually with a cast case there's no visible damage/holes. even if there is, it most likely wouldn't be at the bellhousing. usually a transmission will give some audible signs before it locks up.
 
Me and my friend just got the truck back together. The problem was that the clutch disk grenaded. We installed a new LuK clutch, installed new Yukon 4.10 gears I got from butchcj-8 (in the 10b), and swapped in the 14ff I got from clarkjw24. It worked out pretty sweet because my friend needed the 14sf for his '87 K20.
Only problem now is that the previous owner swapped in a NP205 so the factory front driveline is way too long. I don't need a NP205 so I am going to try and find a NP208 so that I can use the factory front driveshaft and also have shift-on-the-fly.
In researching this T-Case swap, I found that the NP208 behind a TH400 or SM465 were 32 spline and the NP208 behind a TH350 or 700R4 were 27 spline. My cousin is getting ready to junk his '86 K20 and I want to snag his NP208 before it goes to the crusher, but I believe his truck has a TH350 since it has a 14sf rear (I'm not about the TH350 though, I will find out this week)
Questions about my truck:
1) Did the previous owner have to use an adapter kit to mate the NP205 to the SM465? It didn't appear to have one
2) The NP205 in my truck has a slip yoke output, was this a factory job or did someone change this from fixed yoke?
3) Do I also need the crossmember if I get a NP208?
Thanks,
Kent
 
I checked the build codes on my cousin's '86 K20 last night and it has the MX0 RPO which is the 700R4 so his NP208 won't work with my SM465.

I'll keep an eye out for a 32 spline NP208. Does anyone know if I'll need the crossmember as well?

Thanks,
Kent
 
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