The Stovebolt Site Forums The Shop Area Driveline driveline noises

Yesterday I drove the truck (53 one ton) for the first time on the road, took it up to get safety inspection (it passed) about 15 miles. No problems on the drive up, but on the way back I started getting noise from the drive line. I didn't notice the noise until I was within about four miles of home, and I managed to get home with no problem other than the noise.

The noise is a very heavy, very noticeable while, but only occurs when slowing down or accelerating. No noise at all at steady speed. I'm hoping it's in the rear end, not the transmission (SM420 four speed). Happens in all gears except first, and it might happen then but I haven't driven it in first.

Parked the truck, bought new oil for the differential, and I'm waiting on getting the new gasket. Then I'll pull the cover, check out the inside and refill.

Is there anything I should specifically look for while I have it apart? I'll admit that the rear end and tranny are the only parts of the truck I didn't rebuild during the restoration. I had put about 15 miles on the truck before this excursion, all low speed on my road. Could the high speed run (I got up to 50 MPH at one point) have caused serious damage?

Tim

Congrats for finally hitting the road! Seems like getting up to 50mph in an ol 1 ton means you got a lot of things right.

u joint angles?

Sounds like it's worth it to do more test driving and replicate the noise under more specific conditions.
A hand at the base of the shifter might help to feel if/when/how the driveline is shaking.

PS. I'm not a sm420 expert yet, but mine seems in really good shape despite having gear noise sometimes

One could also jack up both rear wheels and run it in place while you could have a buddy listen near each rear hub.

Ed

Goes without saying that differential fluid level is good, same with tranny.

So no one has any suggestions on checking out the differential? Today it's warmed up enough that I'm going to tear into it, pull the cover, look at things, clean it out and fill with oil. I'd like to know what to look for while I'm in there, like things that should or shouldn't move, stuff like that.

Tim

Once you get the cover off and the gear oil drained you should be able to see anything that is obviously wrong. Metal in the gear oil is a clear sign that you may have wear problems, any side to side movement in the ring gear would point to carrier bearing trouble. Any slack or excess backlash would indicate wear between the pinion and ring gear or the pinion not being shimmed properly. If the ring or pinion gear are knife edged you know you have some serious wear and more than likely need to replace the gear set.

The noise you're describing is almost always associated with a failing pinion bearing. Check the pinion flange behind the rear universal joint for movement, either up and down or in and out. It shouldn't have a noticeable amount of slack in any direction. You can also jack the vehicle and support both rear axle tubes on sturdy jack stands, run the transmission in high gear, and use a stethoscope or a piece of garden hose to check for noises. Be VERY careful to stay clear of moving parts like the wheels and the driveshaft while doing that kind of testing!

If there's a 2-piece driveshaft, also check the center carrier bearing between the shafts for looseness or bearing failure.
Jerry

Thanks for the suggestions. I'm about to go out and check things out. I doubt that it's the center carrier bearing, I replaced that during the rebuild, as well as all of the u-joints. I'll report my findings when I'm done.

If it's the pinion bearing how difficult is that to change out?

Tim

Well, I got the cover off the differential and found that there was no oil in there. Well, a little bit sitting in the bottom below the edge of the cover. So that might account for some of the noise!

I used a two foot pry bay and couldn't detect any movement in anything, including the pinion. I'm going to clean it out as well as I can with mineral spirits, then fill with oil and see if that helps.

Wish me luck!

Tim

The first thing a guy must do when he gets one of these trucks is check or change all the fluids.
George

Yeah, I knew that, just got lost in the adventure of all the other stuff. And it had been running OK when I parked it in 1982!

Who knew that the toughest part of this job was going to be lining up the bolt holes when I put the cover back on.

Ready to fill it up now and see what happens.

Tim

Well, today I got the truck out on the road and all the noises seem to have gone away. I won't feel really confident until I take for a longer drive, like 10 or 15 miles, but for now it looks like adding oil cleared things up. Yeah!!!

Tim

When lining up assemblies, one can make a pilot by removing the head of a proper size bolt and making the end pointed, insert by hand or visegrip partway into some of the holes to guide you in, works for diff. Covers, PTO covers, trans. into bellhousing, oil pans, etc.

Ed