151a1 Drivetrain issues

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151a1 Drivetrain issues

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151a1 Drivetrain issues

Postby JeepMagician » November 13th, 2017, 7:07 pm

Owner wanted to et rid of the howl at the 40-55 mph range, so we found him a NOS never been unpack Diff.

I installed it along with four new u-joints in the propeller shafts (they had alot of play) and now there is a low howl, high vibration, and the diff is running in the 190 degree range vs the fronts 92 degrees. I did find however the rear drive shaft is bent apparently I've just never noticed it before. I had the rear jacked up and engine in gear to check for noises and did not hear anything bad. I am hoping the driveshaft is creating a harmonic vibration. But the temp of the Diff is what concerns me. After the initial run I drained the fluid and replaced it (80-90) and found minor metal flakes on the bottom drain. I want to say with a band new diff, slightly high temps and some metal flakes would be normal for a period of time aka break in. But I still feel uneasy.


Any advice guys? The Jeep did not have a heavy vibration before but the Original Diff did have alot of play as well as those prop shaft u joints. Drive Shaft u joints have mim play and have been greased.


Thanks in Advance.
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Re: 151a1 Drivetrain issues

Postby rickf » November 13th, 2017, 7:20 pm

I can't picture how that shaft could get bent, unless it happened outside of the vehicle. I think I would definitely put a dial indicator on it and find out for sure. Was it the drive shafts that you put the u-joints in or the axle shafts? If it was the axle shafts did you use NOS u-joints or the aftermarket ones people on here have been talking about? The temp on the rear is not out of line, remember the front diff has no load on it. There should not be a lot of visible metal in the oil, rebuilt or not. There is nothing in there that should be shedding metal so if you are getting metallic oil there is a problem.
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Re: 151a1 Drivetrain issues

Postby JeepMagician » November 13th, 2017, 7:34 pm

Oh, its bent for sure. There is a rub mark on one side. I never paid attention to it before to ever notice it. I knew about the mark but figured it was where the exhaust rubbed like the past 5 I've worked on. When I disconnected the rear drive shaft I zip tied it to the side. It bolted back up easy. I don't see how the minimal play in the diff blts could cause it.


Far as metal on the diff plug they were tiny little shavings. Which one other Rear ends I have helped with they always told me some was normal and thats why you ran them for 30 or so mins than changed fluid. But that was with Old Guys and Chevy rear ends though.

Thanks rick for the input!
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Re: 151a1 Drivetrain issues

Postby Horst » November 13th, 2017, 10:18 pm

when I got my Barstow M151 with 72 miles on the clock, I was shocked to see that there was quite some metal in the oil of both differentials. I panicked and sourced 2 NOS differentials still in the foam box. Of course I never needed them and probably never will. Looks to me that these differentials are build quite cheap...
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Re: 151a1 Drivetrain issues

Postby paracord » November 14th, 2017, 2:41 am

My rear driveshaft was bent also on my A2. Body has fork lifts dents to show it was moved around by one. If you look closely the very back of the shaft is exposed where a fork can slide underneath it. It was very slightly bent , for it is right before it joins the diff. so there is a lot of support there.You have to have it jacked up, eyeball the shaft. and rotate the tire and you'll see it. My project A2 came with an extra rear shaft and it also was BENT, like 1/4" and wondered how in the h-ll did it get that way , bouncing over a log? (driver error) All the mules I rebuilt back when ,most had bent driveshafts for the same reason. I not talking 1 or 2 but about 20 but again a NOS shaft was $5.00 They loaded these 151's on flat cars or around the yard with forklifts a lot of times. Not all operators then were sober and gentle doing it.It was ram and cram and get them loaded ,I'm ready for another beer. Food for thought RedRiver has or had NOS shafts for $80.00 with u-joints. Was listed on eBay. Others want $170.00 That was about a month ago. One more thing, I'm an old pipe welder ,fitter and checked my rear shaft .I had it off the Jeep against a piece of pipe and eye balled it and didn't catch the bend until I was greasing the u-joints and rotating it, then I saw it . It was ever so sightly bent. If I had ran a framing or tri- square up and down it while it was off I would caught it.
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Re: 151a1 Drivetrain issues

Postby JeepMagician » November 18th, 2017, 12:11 pm

Well, Replaced the driveshaft and the major vibrations are gone. I still get some harmonical vibes in the 20-30 and 40-50 range that phase out when you press clutch in. I understand this could be engine vibrations or transmission vibes being transmitted as well. There is some whine but not alot.

I told the owner that I've done what I can but its just going to be loud and can hope that with miles it will wear in nicely and quiet down.

Thanks for the input guys!
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Re: 151a1 Drivetrain issues

Postby Mark » November 18th, 2017, 1:07 pm

I had my driveshaft balanced---no more finding nuts in driveay--no vibration.I would say the driveline also checked the plum on it too
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