Truck info in my sig if needed. 4 speed granny.
Im in 4th by 20mph. But when i let out on the clutch in 4th sometimes i get a clunk. I felt for driveshaft slop when i bought it. In gear the shaft wouldnt twist any by hand. Yeah ujoints go bad when they want to but im not sure its the joints. No vibration while coasting or decelerating other than rotor shake.

Np435 8.8 rear. Do these have some slack built in? Its not causing a problem or anything. Im just curious.

 

You checked for driveshaft movement with the transmission in gear, but what about slack in the differential with the transmission in neutral?

 

No i didnt. I realize now that it wont turn because its connected to the rear gears. I dont know why i thought it would free spin. Duhhh stupid me. Seriously your comment made me realize im a dumba&&. Sheesh. I feel really stupid. Ill check that way too.

On a side note. Is there a hd/upgraded set of u~joints i should put in if i change them?

 

A clunk when you go into 4th at 20 mph? Doesn't your truck have gears like mine does? 3:1 or 3.08:1?

If so, you're really lugging your motor. According to Ring & Pinion, with 31'' tires and 3:1 gears, you're at around 650 RPM in 4th at 20 MPH. I don't go into 4th until I hit 30 or 35, and I always usually shift around 1800 to 2100 RPM (whatever sounds like it's going to blow up at the time, due to the Thrush glasspack dumping under the bed). 2000 RPM for me sounds almost like it should be 4000 for a V8. By the time I let the clutch out in 4th, I'm around 950 to 1100 RPM.

Lugging that low, clunking could be all kinds of stuff. Transmission mounts, motor mounts, the rear end, something in the bed or behind the seat, something in the engine bay, etc. Where does it sound like it's coming from?

 

I paid attention today and heard it in 3rd too. Sounds like the carrier ujoint. Was busy running my daughter to the doc. Then storms popped up when i was 1/2 mile from home. Ill have more time tomorrow.

Nope. Doesnt lug or bog at all at 20. Tiny bit slow pulling to 25~28 but pulls like a freight train after. If im just cruisin around with no one behind me and not pulling a hill i wont touch the gas til 3rd. Doesnt idle high either. Yep its either 3.0 or 3.08. Some day ill put a tach in.

 

About the only time i can hear it is when the back glass is open.