The Stovebolt Site Forums The Shop Area Driveline Big Noises when Slowing Down

Hi,
I had the SM420 rebuilt by a real shop and put it back in along with a new clutch and throwout bearing a few months ago.

Recently I have noticed loud and getting louder, noises only when off the gas decelerating.

It's not the clutch or throwout bearing, and the transmission has just been rebuilt, so I'm thinking U-joints?
Or, I hope it's not the transmission.
Everything is fine while accelerating, or even just keeping a little forward pressure on the driveline.

Any suggestions where to start checking?

Thanks,

Do you have an open or closed drive shaft? Does your rear end have oil in it?

Check for slack or noise coming from the rear end pinion gear bearings. Jack up the rear end and support it securely on jack stands, or put the truck on a rack, and have someone "drive" it at a constant speed, then slow down while you use a stethoscope or a long screwdriver to touch the rear end housing just behind the driveshaft yoke. If there's a bearing failing, you'll hear a loud grinding noise that changes from pull to coast, and might go away or reduce in volume significantly at a "float" neither pulling nor coasting. Be careful to stay away from moving parts like the driveshaft while you're probing for the source of the noise.
Jerry

A whining/grinding noise when you're decelerating could be caused by worn pinion bearings in your rear end. The wear in the bearings allows the pinion to move in towards the the Ring. You wouldn't get the same noise on drive as the pinion is pushed back towards the front of your truck while accelerating or on power.

If you have an open drive, check for backwards and forwards movement on the rear end yoke; there shouldn't be any at all. If your truck has an enclosed driveline it isn't easy to check for movement without taking the driveline apart.

Got it apart today. I thought I'd check the U-joints first. I disconnected the front one, and it looked fine. While I had the drive shaft in my hands, I turned it and noticed excessive slack at the rear. So I removed the rear U-joint, and it too, was fine. The nut on the yoke on the rear end was loose, so the yoke was moving too much. It was a lock nut with splits, not nylon. I checked with several auto parts stores but could not find a replacement, so I put it in the vise and hammered the edges so it would lock. Then I cranked it on and tightened it up.

At the beginning of the test drive I thought I was a real smart guy mechanic. But then a few blocks later the noise was back just like before.

The nut had backed off the yoke again, so it was loose, and the noise again.

I took it apart and inspected, but this time the spring around the inside was all scrunched up and torn. Was I in error to tighten the nut down tightly?

This rear end has leaked oil from the front seal ever since I got it. So I think it needs to come apart anyway.

There is approx 1/8" rotational play and about the same 1/8" or so front to back play in the gears right now. Maybe slightly more.

If this all needs to come apart and out, will I need to take the entire assembly out, axles brakes etc, all of it? Or do I take apart just the pumpkin?

Would pics help?

Should I have a real transmission shop set-up the gears? or is this a DIY job?

thanks for advice,

The nut is loosening because the bearings behind the yoke are deteriorating. There are two pinion bearings, one right behind the gear teeth, and the other just inboard of the seal that's torn up. It's time to take it all apart and at least replace the bearings. It's also possible there might be damage to the gears if the noise has been going on for some time.
Jerry

thanks for the advice. So now we have identified the big noise! Can I take it apart to change the bearings? Or do I need to take it to the transmission shop? I don't want to make a bigger, more expensive mess. Should I just start taking it apart and see what's in there? I have the brown service manual book, but I think that shows an earlier model. This one seems to be an open variety, since I can easily get to all the parts.

I'd suggest that you find someone familiar with rear axle overhaul to walk you through your first attempt at rebuilding one. There are several tricky techniques involved in getting the gears positioned properly and the preload on the bearings right. Make sure your transmission shop guys also have plenty of experience setting up ring and pinion gears.
Jerry

Modern day rears just don't need repair any more and you will have difficulty finding some one with experience in setting up a rear. Speed shops do it occasionally, but they are expensive. If you can find someone who worked on heavy trucks more than 20 years ago, they will know how. Before synthetic lube, we used to have to rebuild rears every 100,00 miles or once a year. Now rears go over a million miles without being touched. Maintenance manuals walk you through the process, but they assume you have some mechanical experience.

Crenwelge,I'll bet you've set the gear timing on a twin-countershaft Roadranger a time or three, right?

Jerry

The axle shafts will need to be removed before you can remove the Pumpkin from the rear end.

You could do a DIY rebuild on your rear end. I've done quite a few different US and European rear end rebuilds now, and they've all worked so far -there's no rocket science involved in a rebuild, but the ring, pinion and differential do need to be assembled with exactly the right settings to run reliably and quietly. If you've never done a rear end rebuild before, you'd do best to read a good manual before you think about taking anything apart. This .pdf document isn't specific to any particular rear end rebuild but will give you good idea of what's involved to do the job properly. Yukon tech manual.

Stuart.

Hotrod, I ran RT125-13s in the 70's, RT14609s in the 80's and 90's and now run FR and FRO 16210. Nothing ever happens to the FR and FRO's with the synthetic oil we have these days. I bought a very low mile wreck a couple of years ago with a RTLO16139A in it and one my drivers just had to have the 13 speed. They put a worn out shift lever in it that allowed the straight through gear to go half way into gear and chewed the teeth right out of it. I figured I knew all about twin counter shafts until I got into that thing. Never again. I think I got it timed right on about the 5th attempt.

I think the biggest nightmare I tried to maintain was an Eaton 15-speed in a 68 Freightliner. That's the one with the 5-speed main box and 3-speed rear ends. The rears are actually electric-shift 2-speeds, but the intermediate range is achieved by putting one axle in low range, and the other one in high, and letting the power divider synchronize them. Each main box gear splits 3 times for a total of 15 forward gears. One of the company drivers missed a shift, coasted about 300 feet downhill, and then the thing slammed into gear. It sheared off a 1 3/8" diameter power divider input shaft, and I ended up doing a roadside overhaul on it 100 miles from the home shop.
Jerry

My first Diesel truck was an Emeryville with a 5 and 3. The 5 speed was a single countershaft Fuller behind a 220 Cummins. And the 3 speed was a nightmare. The selector was electric and would carbon over. I got to where I could take the cover off the shift lever while I was driving and spray the contacts. There were solenoids that actually controlled air shifters that were pretty reliable except for the fact that the bushings in my Hencrickson suspension were so worn out that the shifter would hit the frame on a tight turn and break the shifter off. I fixed that by welding a chain to the top of the banjo housing and bolting the chain to the frame on the opposite side to keep the axle in place. The power divider was a nightmare. I carried spare parts and did most of my repairs on the side of the road. There were times I got caught without parts. The spider gears would run so fast in intermediate that they would eat the thrust washers and eat into into the interaxle differential housing. More than once I picked up beer cans on the side of the road and made thrust washers out of the tin with a pocket knife. I drove that truck over a million miles, the last 750 thousand of which were with a 250 with a turbo which made it a 270. The ratios were really nice and I never had to shift the stick between 50 and 65 mph. Only had to shift the 3 speed... that is when it would shift. Looking back, I think I can see why my father thought I was crazy that I wanted to drive a truck.

Mine was in a Freightliner cabover behind a 270 Caterpillar 1674 engine. It needed all 15 gears, and then a few! That was about the most gutless truck I think I've ever driven!
Jerry

This is an interesting post because my newly resurrected truck (55 first series) may have the same issue. I was thinking it was in the transmission until I read this post. I have not removed the driveshaft yet so I cant check for in an out play of the yoke but rocking the truck back and forth with my hand on the yoke, I can feel a rather unsmooth mesh of the pinion and ring gear. Its probably the only part of the truck I haven't replaced yet. I will post pictures once I get the cover off. Jerry - I may need some pointers:-).

Joe

Anytime, Joe- - - -I owe you several favors! Anybody who can keep a vintage Harley running shouldn't have much trouble with a stovebolt rear end, but I'll be glad to help out- - - -just give me a shout when you're ready to dig into it.
Jerry

Thanks Jerry! I had my son drive the truck down the road while I laid in the bed with my ear to the floor. Not as much noise as I would have expected. I did take off the driveshaft and the differential yoke (wow that nut was on there!) there is no "in and out" slop of the pinion but the pinion seal was shot in fact it was hard to keep oil in the rear end. Anyway I am thinking its gear backlash in the transmission but if you are ever in the area, I will have you give it a drive and tell me what you think. There's a free lunch in it for you :-)

Joe

LOL! Us old geezers definitely like our groceries! I'll do my best to get together with you soon. I just got the Gold Wing back together after a long preventive maintenance session, so a trip to your neighborhood would make a good shakedown cruise!
Jerry

Can't help w/the OP but I wouldn't mind meeting up w/Jerry & Joe whenever this E TN get together occurs. Depending upon the location my 49 can carry me there.

Dave

I am in Cleveland TN, all are welcome but it won't be a party without Jerry!

Dave, you're actually a little closer to Joe than I am. I'm about 150 miles away from Cleveland, just above Huntsville Alabama. Maybe we can pick a time and date that's convenient for everyone. I'm getting my farm ready to host 50+ people from the Guns & Ammo magazine forum on Memorial Day weekend, so I'm up to my ears in alligators for a while.
Jerry

I'm just north of Knoxville in Knox county. Cleveland is a good 1.5 hr interstate run from me which unfortunately would be asking too much of my mostly stock 49 to make. Running 411 through Maryviile and all the other little towns inbetween is a possibility, if I leave out a day early

That all said, I would still like to do a meet and greet one of these days. Whenever Jerry can point that Goldwing eastward for a day or so.
I would also like to add that Stovebolters are welcomed around my humble abode too.

Sorry for the hijack
Dave