I just got my new-to-me Sammy together (rebuilt engine, new clutch, paint, and exhaust) and it has a drive line whine in 4th and 5th.
It is on pull or coast, and is worst between 35-55mph, after which the noise of the tires is as loud as the whine (either the tire noise is louder, or the whine gets quieter).
Normally, I'd suspect the rear differential, but the guys here who say they are familiar w/ Sammies say it's a common transmission problem, and not the rear dif. It'd louder if you stick your head outside of either side window (don't remember that w/ dif noise).
If it's there at all in 1-2-3 gears, I can't hear it, even at the speed it starts being noticeable in 4th.
All of the other posts mentioning transmission whine address the LOWER gears, not 4th and 5th.
If it IS the transmission, do I need new gears, or is the whine most likely bearings? On pull, it sound kinda' like poorly adjusted differential gears, but on coast, when you let off the throttle, it sounds more like bearing noise (less "whiney").
It was there before the rebuild, BTW. It was just hard to hear over the exhaust system (no cat, and a cherry-bomb terminating halfway under the vehicle). Now with a "legal" exhaust (cat, muffler, and tailpipe past the rear bumper for state inspection), the engine and exhaust is so quiet the whine is very obvious.
I have a couple Samurai's that have had whining problems...but not quite as you describe yours. I would run yours at a given speed - say 45mph and compare the noise in both 4th and 5th gear. If the frequency is the same in either gear, then the source is most likely in the transfer case or perhaps the differential. If the frequency of the noise changes depending on the gear, then it would seem to be in the transmission.
You can also try shifting the TC into 4wd hi and lo to see how that affects the noise. If it is the same for both for a given engine rpm and gear, then I would suspect the input side of the TC. If the TC position doesn't affect it, then it would seem to be in the differential.
I have a couple Samurai's that have had whining problems...but not quite as you describe yours.
I would run yours at a given speed - say 45mph and compare the noise in both 4th and 5th gear.
If the frequency is the same in either gear, then the source is most likely in the transfer case or perhaps the differential. I agree, since these would be turning at the same speed in any gear. If the frequency of the noise changes depending on the gear, then it would seem to be in the transmission. No, it seems to be constant with SPEED, regardless of gear or transfer case range.
You can also try shifting the TC into 4wd hi and lo to see how that affects the noise. If it is the same for both for a given engine rpm and gear, then I would suspect the input side of the TC. If the TC position doesn't affect it, then it would seem to be in the differential. The noise appears to be constant with ROAD speed (not with transfer case or transmission gear, or engine RPM), so that's why I am leaning toward differential, though if the transfer case output is sensitive to load (torque applied), then I suppose it could be that as well.
Of course, I cannot get the road speed up to the upper speeds in LO transfer gear to completely duplicate the noise in the HI range, but at 35mph in 5th LO I can certainly hear the noise start as it does at that speed in HI range.
It seems that above maybe 55mph, the noise gets a bit quieter, though this may be only perception since other noises at the higher speeds may just drown out the gear noise at those higher speeds.
I have noted with other bad differentials I've had in my life that they seem to be speed-range sensitive, and actually start at some speed, peak at some particular speed, then get somewhat quieter above a resonant speed band (which always seems to be right in the band I want to drive in 90% of the time!).
if the noise is not RPM related and only speed related, as you seem to indicate, then it's going to be either on the output end of the T-case between the T-case output and the wheel. That leaves a lot of things that could be causing the noise. A good thing would be to do a fluid change and see if theres any glittery metal powder or particles in your gear case. Check both the Tcase and the diff.
Just before I purchased the vehicle (long distance sight-unseen via an acquaintance in WA State 2200 miles from home in TX a few months before I could go and tow it home), the fluids were all drained, flushed and refilled w/ Asmsoil gear lube, no doubt removing most, or at least some, of the "evidence."
Maybe I should drive it the rest of the summer, then drain and examining the fluids to see what comes out, before making a firm decision on which component to disassemble first.
I'd be more unhappy given the noise, but the chassis is absolutely rust free (not even surface rust anywhere underneath), so that tempers my dissatisfaction somewhat.
Are the T-Cases prone to bad gears or bearings that get noisy? In other words, what would a betting person think was the culprit: T-Case or Differential?
My father bought a 84 sierra new and it started to whine in 5th (at any speed) just after the warranty ran out. That was 25 years ago and it still whines, but nothing has broken or fallen apart.
Maybe you shouldn't do anything for the moment to see if it gets worse.
When shifting gears is it "notchy", even when warmed up?
I tried Pennzoil Synchomesh gear oil in mine and noticed an increase in the whine and a notchy shift feel. The plus for it was easier shifting at room temperature and probably a better MPG. Replaced it with NAPA's Sta-Lube 80/90w GL4 rated hypoid gear oil and it really reduced the whine and gave me back by a smoother shift feel when warmed up. Although both are dino oils, the Pennzoil was much thinner than the Sta-Lube stuff.
Just drain out the Amsoil and save it. Try the Sta-Lube and it it doesn't help, then the Sta-Lube can still be used in your steering box.
Didn't even think about the weight. If the previous owner put in the wrong weight of gear oil then you'll need to change it. Since it's an unknown, you should change it regardless.
80/90 GL4 is what should be used. You can use synthetic or non-synthetic, but it has to be 80/90 GL4. Thicker is better. These aren't high RPM high preformance applications.
Some of the GL5 lubricants and synthetics have sulfer in them that will eat brass. Don't use that in your transmission! It has brass synchros. I don't think it will harm your t-case or diffs, but why bother if you can just use the same gear oil in all your gear boxes it makes it a lot simpler. Make sure if you use synthetic it says non-sulfer on it. Had a lube shop change my case oil once and they put GL5 synthetic in the transmission... didn't know about it at the time and 2 years later I was replacing the tranny. (synchros were destroyed)
There is a lot of debate on whether GL5 eats up the brass sychronizers in transmissions, but unless it states on the label that is is "yellow metal safe", stick with GL4. GL5 is not just an improved version of GL4 as it has different additives.
Take Baratacus's advice as it is not worth the risk using it in your transmission as I haven't seen anyone posting that they have used GL5 in their transmission for 5 years or 50k miles without any problems.
GL5 is what is recommended for the differentials in the FSM, so you should be fine there.
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