The Stovebolt Site Forums The Shop Area Driveline Odd Popping

I bought this truck in 2015 knowing it had this pop that happened sporadically. It did it while I was test driving it, but I figured having extra parts from other '65 3/4 ton's laying around that I could fix it. I have replaced engine mounts, bell housing mounts, complete front suspension including a front disc conversion. Replaced u-joints, cab mounts, core support parts. Rebuilt the transmission. All of which did not eliminate the pop. We have taken this truck on numerous 1,000+ mile trips and nothing leaks or overheats. Just the pop that can happen in succession, or not at all for many miles/days, and then all of a sudden it happens. It will cause the truck to veer a tiny bit and then it corrects on its own. I was thinking the trailing arms, but those are tight, cannot get them to budge with a big pry bar. The only thing I can think of is the rear axle.

Would the "No-Spin" device do this? I have replaced the gear oil in the axle and there was no shavings, nothing out of the ordinary. I did pour in good heavy duty gear oil and limited slip additive when I sealed it back up.

Could it be jumping a tooth or something. When it pops it is loud and if you're in deep thought it'll startle the crap out of you. I just bought an old gopro and am trying to source a proper mount that I can secure to the frame in hopes of catching it happening and then seeing it on video. But have any of you experienced gentlemen had this happen in one of your trucks with an HO52? I am at a loss. I can't see any loose or missing rivets, no odd coloring at the cross member/frame connection points like things are shifting around. I am baffled on this one.

What kind of "no slip" device are you talking about. Also you didnt mention rear brakes. Any chance on something there? Also when does this normally happen? Cruising speed, or parking lots? Straights or turns? After e brake is released? You get the idea. Can you make it do it by duplicating something? One pop, or multiple popping?

There are three types of limited slip differentials. One design uses cone clutches, another has multi-disc clutch plates like an automatic transmission clutch pack, and the Detroit Locker differential has metal teeth that positively lock when power is applied in a turn and one wheel tries to spin. The Detroit Locker is EXTREMELY noisy. Cone clutch differentials pop and shudder a lot unless exactly the right amount of lube additive is used. Disc clutches don't usually give any problems, but they're probably the least effective of the designs at actually equalizing torque in a wheelspin situation. Chances are you've got cone clutches, and you need to add a bit more Moose Juice!
Jerry

My apologies, I forgot to add the other vital information. 1965 C20, HO52 rear axle, borg warner overdrive. driveshafts are solid, the slip is only for the transmission tail shaft. And the main piece of information forgot to mention, is this happens upon taking off from a stop, sometimes while making a left turn, and once in a great while after shifting into 2nd, but that is a rarity.

I also think I mispronounce the traction device, I believe they called "No-Spin". So whatever unit is in there I am guessing it is the stock type no-spin.

Moose Juice...lol... I added a whole tube, maybe two tubes is better?

When making turns in a parking lot it will really start bucking on tighter turns, no popping, but definitely bucks to the point you have to push in the clutch to relieve the tension. I've heard this is normal to the no-spin?

And it cannot be replicated on demand, it only does it when it is darn good and ready, which is the frustrating part.

Check every inch of your frame and crossmembers for cracks or breaks. Pull, twist and pry on everything and use a very strong light. Look at all the rivets and bolt heads for signs of movement.🛠

All "traction-assist" rear ends work the same way, no matter what buzzword the designers and sales people use. To negotiate a turn, the axles have to turn different speeds due to the radius each tire is turning (Hence, the word "differential") That's fine, until one wheel loses traction and tries to spin. Coasting around a turn, or using a moderate amount of power allows traction assist rear ends to differentiate speed almost as well as an "open" axle. When more power is applied, the clutches try to lock the two axles together. If the clutches aren't slipping properly in a power-off turn or one with moderate poser applied, you'll get a pop, a shudder, or some other indication that things aren't right. It might simply be a case of learning to modify your driving habits. A heavy right foot in a turn will definitely cause a noticeable reaction from a traction-assist rear end!
Jerry

I'll check the frame again. Everything looks solid and no signs of movement, but maybe I missed something.

It's definitely not the driving habits, if you rode with me you'd agree. The only time I turn under power is while on I think I'll change fluids again just for the fun of it, that, and it's been three years and about 8,000 miles.

I'll do a closer inspection of the trailing arms themselves while I am crawling around under there.

Sounds like it may be time to look at the clutch packs in the rear end.
Could be it was run without “moose juice “ and scored the plates.

Also, this popping happens 97% when taking off from a stop while going straight. It has never done it while taking off from a turn. When it does pop in a turn it's a 90* left turn through an intersection while traveling 10 to 15 mph. Rarely does it happen while going faster than 25 mph, and when it does it's while going straight. Parking lots or very slow turns on pavement is when the no-spin loads up and the drivetrain loads and unloads, but no popping happens in these slow tight turns.

That's why I suspect it may be a torque related thing.

Are your rear tires a matched size and equal air pressure?

Yeah all four match

You mentioned that the truck does a little side step when this happens.
Does the steering wheel always go back to the original position, or does it change?

No correction of the steering is required. It's an oddball thing that's for sure. Last August Pop went with me to Yuma to get that 292, and he had nothing as to what may causing it and he is a retired mechanic that is old school and good at figuring things out.

Just got back with some 85w140 gear oil and an 8 ounce tube of moose juice. Eating lunch and then I'll pop the cover and check inside the diff, and check the frame. Luckily I'll be in the shade under there, it's already over 100*.

The differential looks the same as the photos posted earlier in this thread. No chunks of metal, wear pattern on the gears looks normal. It'll get fresh juice back there so that's a good thing. While I was down there I spoke with Pop, he said he remembers the popping but was baffled by its sporadic nature. He said he doesn't think it's internal, like inside the rear or trans, but said to check over the engine mounts to the frame as he thinks it's torque related. I think I'll just replace those bolts.

And there is no telltale signs of cracks, loose rivets, movement, nothing on the frame.

I'm going to weigh in and say it might be a suspension issue. You stated that you replaced the front suspension. If I'm reading your initial post correctly you just replaced the front suspension with an identical one...no IFS. That stated I don't suppose you are utilizing a stabilizer bar up front. I had one of those crack on me. It made a "bang/pop" when it encountered movement...not always so it was hard to detect. I initially thought is was a broken ball joint...I at least could tell that the issue was in the front of the truck. Finally found it but like you it sure was/is a head scratcher. Let us know what the issue was.

The last sentence above was purposefully stated in the past tense...I'm confident you'll find it!

The suspension is IFS and was replaced with known good A-arms with brand new ball joints and minimally used bushings. The popping happened when I test drove it before purchasing the truck. All replacements and rebuilds came post purchase.

Tie rods were brand new, shocks, and everything else that was rebuilt or replaced. I do have a sway bar to install, so it's on the patio. The only items I haven't replaced are the front cross member bolts, engine mount bracket bolts, and rear trailing arm bushings and bolts.

I respectfully doubt it is IFS related because it only happens under high torque, slow speed conditions. I can drive twisty mountain roads at 50 mph (depending on conditions) and the truck handles great. Steering is tight for a stock manual box, and the stock springs handle great for their age.

I wiil find it.

While talking with Pop today, he told me about a new car that was sold at our little Chevy dealer. Had to be 60s or 70s. There was a rattle that could be heard but not readily replicated. Many mechanics looked and tried to find the cause of the noise to no avail. Someone hit the car and when Pop's boss was removing the rear fender he found a can with a note inside it, "You finally found it".

I know this is not from some assembly line worker on his last day, as this truck has lived, it has not been a garage dweller or a trailer queen, it worked and still does. It's a survivor that needs some attention to an ailment that I am trying to locate.

Some IFS replacement part pics

I know you guys ask the questions and make suggestions and educate, and I truly appreciate it. I am just a wart on a pigs butt compared to the knowledge you guys possess. That said, I am not one of those dummies that runs bias ply on two corners and radials on the other two and wonders why the vehicle won't track straight.

I have done my best to describe this and all the various things I've done to try and correct it.

I'll say it again, I appreciate your suggestions. It's difficult to diagnose something via written words. For some reason I cannot get anyone to ride under the truck while I drive around. I guess they're afraid of getting wrapped up in the driveshaft or something. Not sure why...psshhhh

Cowards!

-Kevin

Here's a trick I've used when diagnosing oddball suspension problems. Connect a cable "come-along" to the rear axle tubes one side at a time, and try to pull the axle housing forward and back by hooking the ratcheting end to a frame crossmember. It can pinpoint sloppy bushings that need more force than a pry bar to cause things like the trailing arms to move back and forth. I've also seen suspension noises come and go with rainfall- - - - -when the undercarriage is wet, there's no noise, but when things dry out the noise returns. Good luck!
Jerry

I do have a comealong, that is something I can try and not spend any money to do so.

Yesterday I decided to do other things than work out in the blazing heat. Today while driving I was trying my best to replicate this popping, although I wasn't successful replicating it, it did do it while taking off from a stop and navigating through a left turn, about mid-turn through an intersection. If I haven't mentioned it's loud when it happens, IT IS LOUD when it happens. Left turns is when it has been happening the most within the last month, but it still happens on the straights and only while under 15 mph. I have the mount for my gopro now, I want to see this happening on video since nobody will crawl under there and hang from the frame while drive around. I'm going to start with it pointing towards the rear trailing arm-to-frame connections. If that doesn't produce anything, I will point it at the rear of the axle. If that doesn't produce anything, then it will be moved forward of the trailing arm connections. I am doing the more forward video last because of the heat off the exhaust and engine. This always feels like it's from the left side of truck, and of course the exhaust is routed to that side. I don't have a youtube account so I can't upload any video to show you guys the results, but I will report back what I find.

Sounds like you have a plan now at least. Dont overlook the leave springs. 1 cracked one can make all kinds of wierd noise.

Don't trailing arm rear suspensions use coil springs?
Jerry

My trailing arm bushings looked good, great actually, until I pulled them out and discovered that they were full of sand, 50 years old, worn out, and in need of replacement. They may look good, but if they’re original, why not change them out?They need it. Plus, you have a lot of new stuff under there; it bugs me when I have old and new stuff mixed together....


Maybe this is why I’m so good at ripping trucks apart?! 😉

Yes sir, this is a four-coil truck.

I was all set to replace the trailing arms about 4 years ago. I had new u-bolts made and was scheduled to have a shop replace them while I was working. They quoted about $300 for the labor. I bought trailing arms about 20 years ago from LMC for my other '65 C20, Mean Green. That truck got rolled in May 2005 and I now just have parts from that truck. Anyhow, since LMC at the time, and I just looked and it's still the same, they don't show trailing arms specific to C20 trucks. So I had bought them thinking they'd work, NOPE. After I brought the freshly made u-bolts home I checked them to the hole spacing on the trailing arms, and the holes are narrower than what it is for the HO52 axle, so that tells me the C10 trucks got the Dana axles with smaller diameter tubes. Since then I got married and the truck doesn't get worked on as much as it did previously. I mainly drive it and do preventive maintenance. I do have the trailing arm bushings, but they too, are not specified for C20 according to LMC. I may be SOL for new bushings if they don't work. New bolts would be a plus, though. What material are the trailing arm bolts made from? Stainless steel? Zinc coated steel? They have to be grade 8, at least I assume they would need to be that strong or stronger if they make stronger bolts than grade 8.

Is this amount of slop acceptable? If not, how can it be tightened up?

What's the backlash, measured with a dial indicator on the ring gear teeth? The only way to correct that slack, and not create a deafening gear whine, is to install new gears- - - - -which nobody is making any more.
Jerry

Twist in the yoke as you show is mostly play in the spider gears and looks about right.
You would need to pull the back cover to see where it is all from, some could be too much backlash between the ring and pinion, but you would most likely hear some whining from that.

In what orientation do you place the dial indicator? On the side, or against the teeth? I have never checked backlash before so it is a foreign procedure until I perform it. The gears are not loud at all, just sloppy, and I do not want to make them loud. I have another '65 that is not running, I could check that HO52 to see what the slop is on it. If it's not bad I could swap over the third member.

Moose Juice, is that gear oil or the limited-slip additive?

I had the cover off a week or so ago, and it looked the same as the photos I posted in post #4 on the first page of this thread. And the gear oil that came out when I changed it looked fine and there wasn't any flakes.

I don’t think the diff is your problem.

Use a magnetic base dial indicator with the stem set up to measure the movement of the ring gear teeth, as close to 90 degrees from the rotation of the gear as possible as you try to turn the ring gear with the pinion flange held rigid. I like to see a ballpark measurement of .010"-.015", but somewhat more isn't bad if there's no gear whine. The backlash can be reduced by moving the ring gear closer to the pinion with the carrier bearing adjusting nuts, but that also changes the wear pattern on the teeth. Doing that to a set of used gears almost always sets up a whine and results in rapid wear of the gears.

The spider gears and the cross shaft can also induce slack, along with the fit of the axle splines to the side gears. None of that will be adjustable.
Jerry

That slop in the rear diff is just that, slop. Its not what is making this popping sound. Focus on the popping noise. Dont create problems that aint really there. It might be time to find a trustwodthy mechanic and take him for a drive, make it make the noise, and see what he thinks? If its as loud and scary as you described, its only going to get worse and reveal itself... eventually... Probably sooner than later.