SM465 Gear Knock/Tick????

[Jimk20]

Hello everyone. I have a 72 chevy k20, sb350-sm465-np205-dana 44 front-14 bolt FF rear. Just picked this truck up a couple weeks ago and it's my "new to me" daily driver (I know, I know, what am I thinking). Anyway I'm in love with this truck but I'm starting to have some transmission concerns.

A couple days ago I started noticing a knocking sound/heavy ticking sound. This only happens when I'm DECELERATING, clutch pedal DEPRESSED (clutch disengaged), and going under 10 or so MPH with the transmission in or out of gear in ANY gear (except for granny low, never tried it in low gear before). It might make the noise all the time for all I know, but the truck is loud and the trans knock is only audible when doing the above things mentioned and the engine more or less idling. Also, you can feel this knocking sound in the shifter. It's a steady, rhythmic knock that's always there when the truck is coasting slowly. As of now, im not worried about it. I've driven trucks before with 465 trannys and I know how rugged and durable they are. It just bugs me because the knocking sound is kind of loud, loud enough that when I coasted next to a fellow motorist on the highway, the old man told me "Beautiful truck, but what the hell is that noise?"

Like I said I'm not worried about this issue, unless I should be hahhah. This truck is an animal and its driven at least 30 miles a day for work, both highway driving up to 65 mph and in town driving combined. On the weekends I'll take it for trail rides in the NJ Pine barrens, and even going in the woods doesn't make the noise worse, or better for that matter. My names Jim and I'm new to this forum. Any help to my issue is really appreciated.

[old Chevy guy]

If it only does it with the clutch in Id be thinking about the throwout bearing. Or possibly something hitting the pressure plate? Check and make sure all your bell bolts are tight also. Try turning the engine off while coasting and see if that makes any difference, being careful if the truck has power steering or brakes of course, do it where nobody is around.

[Jimk20]

Ok thanks!!! I forgot to mention I just put a slightly built small block in it from my dad when I first got the truck. During the process I put a new clutch kit and flywheel in, which included replacing the throw out bearing. Im 99.9 percent sure I didn't screw up the throw out bearing, but I'll check it again.

[Chucks72Longbed]

Did you check the u joints? When they get dry they'll make some weird noises.

[Jimk20]

The only u joints I've done are the front axle joints for the 44. Other than that no, but the driveshafts seem tight. I just checked the throw out bearing and the clutch assembly and everything seems ok. I think it has to be in the trans. I mean it sounds like it's right under my feet let alone feeing the knock in the shifter. Tomorrow I'll put the truck on jack stands spin the drivetrain up and take a listen at a stand still.

[Jimk20]

One more question. If it comes down to me getting another trans, can I get a craigslist figure 8 sm465 10 spline in and out with a hydraulic clutch bell housing and directly swap the hydro bell housing for my mechanical housing or is there a difference?

[Chucks72Longbed]

Putting up on jack stands is a great idea. Just because the drive shaft feels tight doesn't mean you don't have a dry u-joint

[old Chevy guy]

I thought about U joints too but just seems like it would do that with the clutch in or out if it was.

[Chucks72Longbed]

You're right, my apologies, I went back and re-read your original post again. That is weird...to only make the noise with the clutch depressed.

[Jimk20]

I know right? The only thing I can possibly think of is that maybe the countershaft has to much play, and when I am coasting with no load on the trans, the shaft gears are rubbing/knocking on something they shouldn't be. Same possible theory goes for the main shaft. I do know the input shaft has 0 play in it because when I had the motor out and replaced the throw out bearing, I checked to see if it had any, which it did not.

[jeffahart]

pull the U joints and look at them. Knock Knock is usually a U joint. And it feels like it's under your feet; and they can act funny when going out. Process of elimination and U joints are easy to pull out.

Just pull and inspect, as long as you are under the truck.