Clutch pedal clunk. Only when in 4HI

[gotamotor74]

Hi all, so I've noticed something on this truck I am new too. Here are some details of whats happening. Any thoughts?

So basically were were driving in 4hi-lock since we got it... Guestimating about 150miles. We discovered that we have an NP-203 transfer case and it's a full time transfer case..and that we should be driving in 4hi for normal conditions. Since driving in 4HI, ive noticed and clunk when I let off the clutch pedal when shifting gears. You can feel it and hear it. Sometimes.... If I shift real lightly and on flat ground and hit the clutch just right there is no clunk. But for the most part, a slight clunk. I just noticed today that there is no clunk at all when in 4hi-lock or 4low or 4low-lock... all gears shift smooth as butter in thoes. Just clunk in normal 4 hi..... any thoughts?
I'm gonna go through and grease all the u-joint grease zerks I can find, not even sure if that could be something to cause clunking... drive shaft?... clutch? Idk because it only happens in 4hi, not all the time. But by guess is blind because im not sure what to look at, I'm pretty new to trucks and old gmc/chevys . I need a damn service manual before i should he askin questions probably but... well any recommendations on a service manual?

 

[squaredeal91]

Try jacking up the front and start turning the driveshaft by hand and spin the tires using neutral but changing transfer-case settings to see if you can feel or hear differences and go from there.

 

[gotamotor74]

Try jacking up the front and start turning the driveshaft by hand and spin the tires using neutral but changing transfer-case settings to see if you can feel or hear differences and go from there.

Okay will give a try

 

[gotamotor74]

Just got under the truck, shook the driveshaft around near the u joints. Definantly have some play.. a lot on the rear one near the transfercase.
Going to replace all 4 and will report back

 

[gotamotor74]

So I took my rear drive shaft off this morning, I'm not sure what this part is called.. but is there supposed to be play here?

 

[gotamotor74]

A video would be better not sure how to post one. But the part that holds the ujoint thats attached to the driveshaft.. is wobbly

 

[squaredeal91]

For videos you use youtube account to post and share videos on here

 

[Grit dog]

You probably figured it out. Rear driveline slop somewhere.
When locked in 4lock, the front half is taking up the slack (literally). Doesn’t sound like a clutch issue. (Per your title)

 

[gotamotor74]

You probably figured it out. Rear driveline slop somewhere.
When locked in 4lock, the front half is taking up the slack (literally). Doesn’t sound like a clutch issue. (Per your title)

Hoping so. there is a little up and down play in what I discoverd to be called the slip yoke. I discovered that the slip yoke is... supposed to slip, when I found out the mine was well... not slipping... it was pretty tough on there, my first time messing with a drifeshaft and I thought I was all just one piece at first. I'm hoping the up and down play is normal... or that perhaps maybe I need a longer driveshaft because I hear that you need to do if you lift a vehicle? This one is lifted 6".

Current plan is I got new u-joints, going to put them in, completely cleaned everything up. Got all the old 40 year old gooey glue grease out of the slip yoke, cleaned the 40 years of dirt and grease out of the splines on the driveshaft... I am in current search of the little cork gasket that goes as a seal on the slip yoke. But once I find that, going to put it back in and we will see if any of that makes a difference...

 

[gotamotor74]

Okay, reporting back. Things get done kind of slowly around here sometimes.

Replaced both u joints on the rear driveshaft and cleaned up the slip yoke. The yoke was pretty crusty and nearly un-slipable.

Clunk is still there

Going to move to the front driveshaft components next.

Also going to service transfer case with new oil.

And renew differential fluids as well.

 

[bucket]

An SM465 with a NP203 on it is a rare bird.

Do you have locking front hubs or the original drive flanges? If you have locking hubs, can the truck drive in Hi or Low (non-loc positions) with the front hubs unlocked?

I ask because depending on if the 203 has been part-time converted or not will possibly have something to do with when and why it clunks.

 

[Snoots]

If the slip-yoke had up and down movement, I'd replace it. Unless the output bearing on the x-fer case is shot.