Greetings all. I need some help identifying and fixing a peculiar noise with my 1977 FJ40. I'll try to provide as many details as possible.
1. When driving in 2wd with the front hubs locked or unlocked there is no discernable unusual noise coming from the front drivetrain. This is consistent at all speeds.
2. When driving in 4wd with the front hubs locked, I get a rumble/growling sound front the front axle/t-case area when I either let off the gas or give it more gas. This growling sound is fairly violent and reverberated throughout the entire truck and is very noticeable over the already loud engine. (2F). If I hold the gas pedal just right I can make this growling sound happen continuously. This sound gets louder and more violent as speed increases, but doesn't appear to be linked to engine RPM since it only begins to be noticeable at 30mph or greater and grows from there. It is predominantly noticeable when letting off the gas to coast down a hill for instance. Instant growling noise, and if I let off the gas quickly the noise happens and then disappears just as quickly.
3. When driving in 4wd with the front hubs unlocked I get the same rumble/growling sound almost continuously, and it begins to be noticeable at much lower speeds. Maybe 5mph or so I can begin to hear it, and its completely undrivable (for fear of exploding something) by around 25-30mpg.
4. When driving in 4wd with the front hubs either locked or unlocked the noise disappears instantly when the t-case lever is thrown into 2wd only. I've only done this at low speeds. (5-20mpg) But the horrible growling noise instantly disappears.
5. What I've done so far to troubleshoot:
A. I've greased the front driveshaft.
B. I've ensured that the front driveshaft is in phase according to the FSM, and have the grease zerks all lined up correctly.
C. I've tried the trick of adding a hose clamp to the front axle to see if it was out of balance. All this did was cause a vibration in the truck that appears unrelated to the growling noise. I'm guessing my front driveshaft is correctly balanced as is.
D. I've tightened up the front differential pinion bearings while installing a new pinion seal. This did not have any affect on the growling noise.
E. I've removed the front drive shaft and checked the front output flange of the t-case. All appears to be tight, with only a small amount of movement when in 4wd. When in 2wd I can spin the output shaft about 45 degrees before it catches the front dif splines.
6. My best guess based on my troubleshooting so far is that the problem is a loose bearing or mating surface in the T-case front output, but I've never opened one of these up and don't really know what is going on inside or what could be broken/worn/damaged. When I go the tranny/t-case combo it had been sitting in the back of the FJ40 for what could have been decades, with no known maintenance.
Looking for any constructive help with the noise I've got and what needs to be fixed in order to deal with it.
P.S. 4wd works, and seems to work well outside of the noise and vibration.
1. When driving in 2wd with the front hubs locked or unlocked there is no discernable unusual noise coming from the front drivetrain. This is consistent at all speeds.
2. When driving in 4wd with the front hubs locked, I get a rumble/growling sound front the front axle/t-case area when I either let off the gas or give it more gas. This growling sound is fairly violent and reverberated throughout the entire truck and is very noticeable over the already loud engine. (2F). If I hold the gas pedal just right I can make this growling sound happen continuously. This sound gets louder and more violent as speed increases, but doesn't appear to be linked to engine RPM since it only begins to be noticeable at 30mph or greater and grows from there. It is predominantly noticeable when letting off the gas to coast down a hill for instance. Instant growling noise, and if I let off the gas quickly the noise happens and then disappears just as quickly.
3. When driving in 4wd with the front hubs unlocked I get the same rumble/growling sound almost continuously, and it begins to be noticeable at much lower speeds. Maybe 5mph or so I can begin to hear it, and its completely undrivable (for fear of exploding something) by around 25-30mpg.
4. When driving in 4wd with the front hubs either locked or unlocked the noise disappears instantly when the t-case lever is thrown into 2wd only. I've only done this at low speeds. (5-20mpg) But the horrible growling noise instantly disappears.
5. What I've done so far to troubleshoot:
A. I've greased the front driveshaft.
B. I've ensured that the front driveshaft is in phase according to the FSM, and have the grease zerks all lined up correctly.
C. I've tried the trick of adding a hose clamp to the front axle to see if it was out of balance. All this did was cause a vibration in the truck that appears unrelated to the growling noise. I'm guessing my front driveshaft is correctly balanced as is.
D. I've tightened up the front differential pinion bearings while installing a new pinion seal. This did not have any affect on the growling noise.
E. I've removed the front drive shaft and checked the front output flange of the t-case. All appears to be tight, with only a small amount of movement when in 4wd. When in 2wd I can spin the output shaft about 45 degrees before it catches the front dif splines.
6. My best guess based on my troubleshooting so far is that the problem is a loose bearing or mating surface in the T-case front output, but I've never opened one of these up and don't really know what is going on inside or what could be broken/worn/damaged. When I go the tranny/t-case combo it had been sitting in the back of the FJ40 for what could have been decades, with no known maintenance.
Looking for any constructive help with the noise I've got and what needs to be fixed in order to deal with it.
P.S. 4wd works, and seems to work well outside of the noise and vibration.
