LUVTruck.com

Here's a weird one:

My 81 Luv 4x4 diesel pickup is making two weird noises that I'm having a heck of a time tracking down. They both appeared at about the same time and may or may not be related.

First, whenever I start rolling in 1st gear, as I let the clutch out about 1/2 way, I get a loud "clank" that sounds like it's coming from right under me. This happens if I'm coming out of reverse or if I'm pulling away from a stoplight. It happens whether I'm accellerating gently or hard.

Secondly, in 3rd or 4th gear under load I hear a loud tapping noise that sounds like (but isn't) the exhaust pipe rattling against the frame. It only happens occasionally in 3rd, and frequently in 4th, but only around 45-55 MPH. If I decelerate, the noise stops. If I push in the clutch and rev up the motor, the noise doesn't appear. The rattle doesn't change pitch, but the rattling intensity does increase with RPM. I can't pinpoint this noise, but it appears to be coming from the passenger's side rear of the truck. It is getting louder, and I can now hear it even with all the windows rolled up.

I've checked and/or replaced all the U-joints and CV axles, and they aren't the culprit. I've padded all the moving parts on the tailgate. I've replaced fluids in the transmission and both differentials. I've marked the exhaust in any areas where it might be rattling, and I don't see any rub marks. I've checked for slop in the rear-end. I've checked for loose body parts. I've checked my linkages and return springs.

I'm at my wit's end. Has anyone tracked this down on their own rig?

I have a similar problem, that I have been unable to track down. But it's in a gas truck with an auto trans. If you find something let me know and I will do the same...

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Resident lurker

I have notice the exact noise in my '82 when I accelerate in 2nd or 3rd. It sounds like it is right under the drivers seat, like the tranny is being torqued and bangs agains the underbody. Never been able to run it down. I have just lived with it.

Just a couple of thoughts - how about the transmission mount?

No?

Or possibly the cab mounts?

These points often take more torque to move them (like engine torque) than you can make by shaking things with your hand. Just cause you can't move it with your hand(s) doesn't mean it's not loose.

Again, just my 2¢ worth.

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Bona Fide diesel fanatic.
1994 Chev S10 Ext Cab Isuzu Diesel 5spd
Kubota B6100 HST diesel

Hmm.....I am thinking cab mount as my right front quarter panel came loose a few years ago. Maybe there is some slop in the mounting bolts. I will check that.

I started pulling things apart last night trying to isolate the noise. I thought it might be the driveshaft support bearing. When I got the driveshaft out, I noticed lateral slop in the differential input.

I had checked for torsional slop (Twisting the driveshaft back and forth), but didn't really see any. With the tires off the ground and the driveshaft removed, the input shaft had side-to-side and up-and-down play in it.

My theory is that the torque applied to the differential when I start rolling is sufficient to bump the driveshaft laterally and cause the "clang". At speed, a slight imbalance in the driveshaft and/or the slight angle of the U-joints causes the driveshaft to wobble when turning at high speeds causing the loud , intermittent ticking I complained about. When I decelerate, the differential applies torque to the driveshaft instead of the other way around, thus the shaft is held in place.

I'll pull the differential assembly tonight and see whether my theory holds water. If the pinion bearings are bad, I may just try to swap an assembly from another truck rather than tracking down crush sleeves and 4-foot cheaters to rebuild it.

Assuming the gear ratios are the same, will a differential out of a gas 4x4 bolt up to a diesel? Are the housings and axle splines the same? How about out of a different year pickup or trooper?

Thanks everyone for your suggestions. Is there anything harder than tracking down a noise based on a description given over the internet?

When I started reading I was thinking U-Joints right off, but it sounds like you have your culprit. You can swap the third member from any luv, and most Isuzus up to about 86. Finding the right gear ratio to match what you have might be an issue though. There is a thread from a few months back about how to figure out the ratio by spinning a tire and counting pinion revs. That would tell you what you have, then you just need to find one that is the same.

LUVs typically have 4.10 but depending on year, 2wd vs 4wd, and probably diesel vs gas you may find several ratios. Isuzu Troopers 84-86 will have the same diff and I believe they all have 4.56 gears.

Same here, i've got a tiny bit of slop in my rear U in my shortbed 2wd luv, it clangs alot in reverse and you can feel the slop in it if you accelerate hard in 2nd on mine.

I've got a noise in my trans too, in fith gear though, sounds like something small whining to get out.

BTW, the 4wd gas luvs and automatic diesels are the onlyones I know of that had the 4.10, the 2wd diesels and gas has a 3.73 and a auto gas has something like a 3.5*

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-Old ride-82 Luv diesel 5spd with some upgrades
-Past rides-82 Sierra, 78 Coupe De'Ville, 91 2dr Blazer, 86 RX7, 86 Porsche 944T (rear-ended and totaled)
-Curr. rides- 1970 Ford LTD 4dr, 390 4Bbl, 2nd owner! With a few Extras 00' Civic beater...

I got everything torn apart and inspected last night. It's almost together again except for the axles..

It looks like the rattling was in the pinion gear preload. I could have fixed that without removing the third member, but at least now I have piece of mind in the knowlege that my bearings and differential internals are in good shape, and that the preload was properly adjusted (IAW the shop manual) instead of just tightened up. Also, I had a bad outer seal on one of my axles which I wouldn't have seen until oil was running from my brake drum. I can fix that now.

U-joints were the obvious suspects, but I ruled them out long ago as being the culprits.

I'll get everything reassembled tonight (assuming I can find the axle seals locally) and see if the problem has been fixed.

The hardest part of the whole repair so far was getting the neighbor's kids to quit tracking oily footprints all over my freshly painted shop floor.

Don't ya love it when kids watch you work, makes ya feel smart seeing as how you can answer there questions, if they have any.

My dad was going to do that to the truck we just bought (change the seals) but the guy we bought it from did it right before he sold it to us.

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-Old ride-82 Luv diesel 5spd with some upgrades
-Past rides-82 Sierra, 78 Coupe De'Ville, 91 2dr Blazer, 86 RX7, 86 Porsche 944T (rear-ended and totaled)
-Curr. rides- 1970 Ford LTD 4dr, 390 4Bbl, 2nd owner! With a few Extras 00' Civic beater...

After all that, the rattle is still there.

I finally convinced my wife to drive (She hates driving a stick.), while I sat in the bed and tried to find the source. At 30 MPH, leaning over either side of the bed with my head inches from the tire, I <i>think</i> I located the noise well forward of the differential.

The noise seems to be coming from the driveshaft center support bearing. I checked that when the driveline was removed, and it seemed OK. Maybe it takes the right combination of torque, RPM, and OSHA nightmare-inducing methodology to bring out the sound of marbles in a tin can?

My fingers are crossed that this is actually the problem. I'm getting tired of working on it, and the transmission would be the next logical step. (Actually I'm replacing shackle bushings next, but just because they're worn out; not because I suspect them for the noise.

The bearing or the U-joint at the start of the driveshaft could be the problem, or a loose bracket. But before you tear into that bearing go ahead and replace the shackel bushings like you said.

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-Old ride-82 Luv diesel 5spd with some upgrades
-Past rides-82 Sierra, 78 Coupe De'Ville, 91 2dr Blazer, 86 RX7, 86 Porsche 944T (rear-ended and totaled)
-Curr. rides- 1970 Ford LTD 4dr, 390 4Bbl, 2nd owner! With a few Extras 00' Civic beater...

As a recap:

Replaced 3 U-joints.

Replaced the driveline center support bearing. Re-check U-joints.

Pulled, inspected, and replaced the 3rd member. Re-re-checked U-joints.

Replaced both axle seals.

Adjusted pre-load on pinion bearings.

Re-packed rear wheel bearings.

Changed tranmission oil twice with different viscosities. re-re-...-checked U-joints.

Changed differential oil. Re-...-re-checked U-joints.

Ordered shackle bushings.

Padded between leafs in springs.

Tightened every clamp and hanger in exhaust system. Several times.

Checked bed mounts, motor mounts, cab mounts, bumper mounts. Did I mention mounts?

The culprit? A rock stuck between the fuel tank and its skid plate.

Well Scott, now you know. LOL

I think my culprit is a worn carrier bearing.

/Puts on death-proof suit/ Well, you likely would have found the rock sooner, if you didn't spend so much time checking the u-joints and mounts! /Runs away quickly in death-proof suit, laughing hysterically/

J/K!!! Glad you found the annoying probem. Things like that drive me crazy. Me, I wouldn't know whether to be glad I finally found the problem, or POed I did all that for something as simple as a rock jammed where it shouldn't have been.

At least that problem is gone.

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Bona Fide diesel fanatic.
1994 Chev S10 Ext Cab Isuzu Diesel 5spd
Kubota B6100 HST diesel