[paradise445]

I got this noise that crops up only when I'm going about 40 miles an hour and up. It gets louder as the speed increases.

I have one video that shows it at around 40 and another that shows it at 55. My Trooper is loud in the video but you can pick out the sound as the only high pitched noise in the video. It's rather steady.

I'd assume wheel bearing right off the bat but I also have heard some crunchy sounds from my transmission. I noticed it after a 30 minute drive at speeds of 55mph+ and then some slight off roading. I put my ear to the shifter and you can tell the difference in sounds when the clutch is depressed versus not. When the clutch is depressed, there's normal transmission sounds. When the clutch is engaged, you can hear the grindy/crunchy sound start. It's quiet enough but still a worry for me that it could be the input shaft bearing going bad. Definitely not the throwout bearing since there's no other noise with the clutch half engaged. It's basically an on/off switch for the crunchy sound.

I did jack it up and try to spin the wheels, check for freeplay but they all seem pretty solid. No real lateral movement. I unfortunately don't have the strength to spin the wheels up to 55 myself but what little bit I did was met only with the rotors and pads making noise. I need to do a brake job soon...

Anyone got any thoughts on this? Input shaft bearing? Maybe another bearing somewhere in the gearbox? Pilot bushing even? I'm not the best story teller so hopefully my points get across fine lol. Apologies for that.

5th gear, 55mph:

1991 Isuzu Trooper whistling noise, 5th gear

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4th gear, 40ish mph:

1991 Isuzu Trooper whistling noise, 4th gear

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[turnerd]

What fluid is in the transmission and transfer case? And are they both full? Additionally, do you have manual hubs/ know that the automatic ones are disengaged?

 

[paradise445]

5w-30 in the transmission and transfer case. Both full. I pumped in oil until it was coming out. However, when I drained out the old oil, I did see a stream of red coming out. I'm guessing one of the PO's put atf in it at some point. I have auto hubs, didn't think to check if they were locked still. What ways can I check them?

 

[turnerd]

5w-30 in the transmission and transfer case. Both full. I pumped in oil until it was coming out. However, when I drained out the old oil, I did see a stream of red coming out. I'm guessing one of the PO's put atf in it at some point. I have auto hubs, didn't think to check if they were locked still. What ways can I check them?

Hmmm a PO using ATF might have toasted an internal bearing.
To check the hubs, put the t-case in 2H and get someone to drive it back and forth a couple feet so you can watch and see if either CV axle spins.

 

[Enemigo]

I think both CVs will spin no matter what with auto hubs.

 

[turnerd]

I think both CVs will spin no matter what with auto hubs.

The auto hubs work like manual hubs but you don't have to get out. It's my understanding that when in 2H the driveline is like with manual hubs unlocked. The front driveshaft, half-shafts, and CV axles are stationary as the wheels spin freely. Once you put the transfer case in 4H you send power through all these components to the wheels. The auto hubs lock the wheels to the axle when the axle overdrives the wheel (so the back wheels slip). This condition is like setting a manual hub to the lock position. Then to undo them, you have to drive in reverse in 2H with the wheel being significantly under driven (no power to the front driveline). This part of the operation doesn't undo easily once they get old, causing them to stay locked in. Note that Isuzu's auto hubs were found on 84-97 U.S. Troopers in various forms, but in 96 (for some models, 98 for all models) they went to solid flanges and shift on the fly four wheel drive meaning the CV axles are always engaged but the half-shafts have an electronic or vacuum disconnect in the middle of them. I can verify all of this on a 95 tomorrow if someone is especially interested. My reason in saying all this to the OP is that it should be easy to check they are unlocked and eliminate any possibility of the noise in question coming from the front part-time drivetrain.

 

[Enemigo]

Both the Isuzu's I've owned were shift on the fly. It still seems to me that the auto hubs are just always locked, and both CVs would turn at all times. When in 2H, the front drive shaft is divorced from the transfer case, so no power can transfer. Isn't that the main reason that people think you'll gain fuel economy by switching to manual hubs? Because it stops the front drive train components from spinning the entire time since the hubs disconnect right at the outer shaft connection?

The only non-SOTF Trooper I owned never ran so I never could test this out. I'll have to defer to your explanation turnerd since I guess I haven't driven one. I've always heard about backing up to get the vehicle out of 4wd, but never experienced that actually working in real life.

 

[mudoilngears]

Both the Isuzu's I've owned were shift on the fly. It still seems to me that the auto hubs are just always locked, and both CVs would turn at all times. When in 2H, the front drive shaft is divorced from the transfer case, so no power can transfer. Isn't that the main reason that people think you'll gain fuel economy by switching to manual hubs? Because it stops the front drive train components from spinning the entire time since the hubs disconnect right at the outer shaft connection?

The only non-SOTF Trooper I owned never ran so I never could test this out. I'll have to defer to your explanation turnerd since I guess I haven't driven one. I've always heard about backing up to get the vehicle out of 4wd, but never experienced that actually working in real life.

SOFT doesn’t use any type of freewheel hubs. They are solid drive flanges.

 

[Enemigo]

I know, but aren't the CV axles the same (except for length) on the pre-sotf models?

If not, it makes more sense to me why people call auto hubs weak. Because on the SOTF stuff, there isn't really anything to be weak, as it's all solid.

Sorry for deriving from the direction of this thread. We can get back on topic.

 

[paradise445]

Okay, sorry yall, had to run to Florida for a job interview. Got the job so the beach life will be here soon.

Just checked the rotation of the CVs, they do spin in 4wd. Good news there. In 2wd, the fronts do NOT spin. One hub was seeming to get a little stuck as it took a few tries to get it unlocked again. However, still having the same noises going on. No change at all really. Wondering if I should just go ahead and take everything off and grease everything up, check for worn down parts, replace anything needing it.
Same for the transmission. I don't think I have time to crack open the entirety of the transmission for a rebuild but I'm wondering how easy it is to replace the input shaft bearing at the very least.

Never any issue to get more knowledge even if it's slightly off topic. There's a lot to learn about Troopers so I'll take what info I can get. I appreciate the conversation from yall.

 

[Enemigo]

Did it still make the noise while it was up on jack stands? Any chance you could narrow down where you think it is coming from?

 

[paradise445]

Well, was finally able to really get under there with all 4 wheels off and jackstands under it. Put it in 4th and let it idle, you can definitely hear noise coming from both the passenger front and somewhere closer to the rear of the transmission. Maybe the transfer case.. Sounds like someone grinding marbles in there. When I changed the fluid, there were no fragments whatsoever, just the usual metallic goop that comes out on the drain plug. But it doesn't sound healthy regardless. I feel like the wheel bearing/hubs won't be too big of an issue but what about something deep within the bowels of the transmission?

Got one video from underneath the car, one letting the clutch out and hearing the noise start up, and one with it already in gear. I'm not too sure if it's very audible from inside the car but on the underside, you can hear it fine. It's loud enough. Also a neighbor came by to tell my wife to woes of his old truck from back in the day so that's present in the videos lol.

PXL 20220701 011026130

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PXL 20220701 011112701

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PXL 20220701 010933651

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[mudoilngears]

Did you replace both the transmission and transfer case oil?

 

[mudoilngears]

Nevermind. I read back and saw you filled both.

 

[paradise445]

Yeah, did get both replaced since I had read it needed regular engine oil. Figured most wouldn't believe that and would put in some other kind of transmission fluid. That assumption was correct. Even I thought it was a little crazy to put engine oil since I've never really heard of it before.

 

[DSUZU]

As long as it is SECURELY on jackstands, you can get under there, use a long screwdriver and place the handle against your ear, and touch the blade to various parts of the drivetrain to isolate noises. If the tranny is making noise, you could try adding some Lucas additive as this stuff sticks to various gears and bearings and MIGHT help (only a real overhaul will cure it. Welcome to Florida. Hope you don't mind humidity (and hurricanes). Dennis