Rear End Roar

[CarmMontana]

Hey Guys

I just took my fj55 out for it's virgin mountain trip and had to drive it a couple more miles than I have so far. I have noticed that my rear end roars when I let out the gas and after this trip I think something may be wrong. It whines and roars pretty bad when i let out the gas in all 3 gears. i had to replace a wheel seal about a month or so ago but I hadn't drove it that much. Any idea if I did something wrong when I pulled the diff? I was told by a mechanic friend of mine that I just have a loud differential, but my buddy's fj40 doesn't make even close to the noise mine does. Mine even causes a decent vibration at high speeds. Thanks Guys

Carmon

 

[rustedframe]

Low fluid, bad bearings, backlash not correct. Try some Lucas in there, I use it on everything, keeps everything lubed and quiet, but only if something else is not out of whack.

 

['74 UA FJ]

Sounds like a bearing.

 

[fj hunter]

sounds like ...

when i knocked off the plug and lost all my gear lube in the rear of my fj72.

i agree that the bearings and set up are in question now that the problem has surfaced.

how many miles did you drive it?

 

[John Smith]

Time to pull the rear diff and inspect. Your mechanic friend is wrong, it is not normal for a diff to be roaring, or really making any noise unless you have a auto locker in there.

 

[Poser]

i had to replace a wheel seal about a month or so ago but I hadn't drove it that much. Any idea if I did something wrong when I pulled the diff?

Did you remember to put gear oil back in?

 

[Moneypitfj40]

I have the same noisy problem. I just had my wifes uncle listen to it he works in a trans/diff shop he thought it was a bearing problem in the rear diff. I am actually taking it to him today. There in no way this noob is even going to touch that thing.

 

[CarmMontana]

I did put fluid back in and have checked it a couple of times. So bearing huh? I guess I have a little more homework to do on this. Thanks for the input guys, i appreciate it.

 

[Poser]

I did put fluid back in and have checked it a couple of times.

Good to know there is oil in the rear diff...

So bearing huh? I guess I have a little more homework to do on this. Thanks for the input guys, i appreciate it.

Chock the wheels and leave the truck in neutral. Make sure it will not roll over you when you are under it. Once you have determined that the vehicle is not going to roll over you, crawl under the truck and grab hold of the rear drive shaft where it meets the rear differential. Try and shake it up and down. Is there ANY movement?

Now move to the transfer case side of the rear drive shaft and repeat this procedure. Is there ANY movement?

 

[inkpot]

Howdy! Are you sure that the noise is coming from the rear axle, and not the transfer case? They are a bit noisy at best if you have the original one for the 3 speed transmission. They get real noisy if they have been run dry due to leaks or the proverbial "pumping the gear oil back into the transmission" problem. John

 

[thetaxmonkey]

things to check....

Hey fellow Montanan. I wish you the best on this. I have rebuilt 4 or 5 rear-ends in a 40, 60's, and an 80. It can be a PITA the first time, but once you do it once, it's a pretty simple process and the knowledge you gain will be invaluable if you plan to drink the cruiser coolaid like the rest of us.

I agree with poser, you need to get this up in the air and shake things around, especially the drive shaft closest to the 3rd member. It sounds like a bearing to me. If this rear-end was ever rebuilt, it may have too much or too little backlash, or the bearings were tightened too much. After rebuilding a 60 rear-end I had a nice growl going on and it turned out that I did not have enough backlash.

Most likely, its a bearing. Also, check all of your U-joints. I once had a slight growl and a vibration in my 80 and so I rebuilt the rearend and still had the same problem, I took it apart 2 more times and still had the same issue. What I did not realize was that my U-joint at the transfer case was binding up and almost all of the needle bearings had come out on one side.

Keep us updated.

 

[CarmMontana]

Hey Guys, I love this site. I will get under it tomorrow and do what you suggested Poser. I will double check all the fluids in my tranny and transfer case also, I replaced all the fluids about a month ago but better be safe than sorry I guess.

I also had one more question and this maybe a completely different subject but I guess hi-jacking my own post is kosher, wh knows it maybe related. I have had some real trouble getting this thing to track well on the road. My buddy told me that when I am driving down the road it looks like my axles are not aligned with one another, it kinda looks like my butt end is trying to pull to the right. I have taken measurements from the front to the rear axle and if there is any difference it is somewhere in the 1/8" variety. When I am on the road it gets kinda out of whack and I have to make a big correction in the steering. The front axle is toed in something like 1/4 at the most extreme of the tires. Any input on that one guys?

 

[inkpot]

Howdy! The "dog tracking" problem could be any combination of things. May have bad rubber bushings in the leaf springs, bad/bent/loose ubolts holding springs onto axles, bent frame, broken center pin in the leaf springs. When you dog track going straight, your wheels form a trapazoid instead of a rectangle. The distance from the fronts to rears will stay pretty close to equal. John

 

[maximum destruction]

if the rear only makes noise when off the gas, it's gears. it's got alot of lash on the coast side of the gear. if it was a bearing, it would make noise most, if not all the time. as far as the tracking, it can only be a few things, & being the head frame tech. for a local gm dealership, i've seen about all of them. first thing to do is tram the frame. if u can't borrow a tram gauge from a local collision shop, u can make something easy enough. all it is, is an adjustable rod with locating dowels on the end. all vehicles are designed on 3 boxes. the torque box will be considered the area under the passenger area, say from the front posts to the rear posts. then u have the rear box which includes everything else from the torque box to the rear bumper. next is the front box but we won't talk about it because there is nothing in the front to cause tracking. get under the truck with the gauge & find exact spots to measure from on each rail. the longer the measurement, the more accurate it will be. u want to x across the frame at these locations. my genesis at work doesn't have data for trucks this old, but on newer toy's they give u up to 5 millimeters of tolerance & still be considered square. it should be square unless the truck has had a substantial front or rear impact which could result in the frame being in a diamond. if it's square, check the rear box. if it's square, it's in the rear end (bushings, bent spring in front of the axle, broke center pin, etc...) fwiw, if she's walking to the right, the rear is back on the pass. side or forward on the drive. side. i hope this short explanation can shed some light for ya". LOL

 

[CarmMontana]

Hey Maximum I really appreciate your input. Really quick question though if the frame is square and the issue isn't in the shackles/shocks or u bolts how would I get my axles aligned properly? Alignment shop? I figure that is the answer but wanted to make sure. Thanks again guys, I am going to tear into this stuff tomorrow. I did just replace the shackle/spring bushings an everything looks ok there. I have noticed that the front axle u bolts have been hit. I also noticed there is a added leaf in the spring on the rear drivers side, i just figured for the drivers side sag I hear so much about. I will keep you all posted and hopefully I can figure this out so I can play with my piggie more.

Carm

 

[maximum destruction]

unfortunately there is no alignment to be done on a leaf rear vehicle. u have no adjustment. if u measure the frame & it's square & checked for worn or broken parts in the rear, pull a wheelbase measurement. center the front wheels & measure from the center of the front hub to center of the rear axle on both sides. it should be dead nuts equal from side to side. if it is, u can then try this old alignment trick from back in the day. center the wheels again. then go get some nylon twine. have a friend hold the twine to the front edge of the left front tire. then u take the other end & walk around the truck until u meet him again. make sure the twine hits the sidewalls of the tires close to the same on each. now tie the ends together. if the front is square to the rear, the twine will contact the tire in 2 places(each side of the rim). if the twine is only hitting 1 side, something is out somewhere.

 

[cronic]

Just wondering if you made iany progress on the rear end noise while letting off the gas. I am having the same issue with my 73 fj40 right now. I had the rear end rebuilt less than 10k miles ago because of noise. Now its back on the coast when letting off the gas. I tightened the pinion nut this weekend and the noise lessened by about 75%. It came back little by little over the next 50 miles and the noise is a loud as before, as long lasting as before, and maybe a slightly lower pitch. The u joints are in great shape and I don't have vertical or horizontal play on the drive shaft. I am scratching my head as what to do next?

 

[Poser]

Just wondering if you made any progress on the rear end noise while letting off the gas. I am having the same issue with my 73 fj40 right now. I had the rear end rebuilt less than 10k miles ago because of noise. Now its back on the coast when letting off the gas. I tightened the pinion nut this weekend and the noise lessened by about 75%. It came back little by little over the next 50 miles and the noise is a loud as before, as long lasting as before, and maybe a slightly lower pitch.

You had the rear differential rebuilt less than 10 thousand miles ago and the pinion nut/stake nut was loose?

You were able to tighten this nut on the companion flange of the differential?

I am scratching my head as what to do next?

Drain the oil from the differential and see what kind of pile you have on the magnet.

 

[cronic]

You had the rear differential rebuilt less than 10 thousand miles ago and the pinion nut/stake nut was loose?

You were able to tighten this nut on the companion flange of the differential?


Unfortunately, yes. I was able to turn it a full rotation, and probably could go tighter without a tremendous amount of effort.







Drain the oil from the differential and see what kind of pile you have on the magnet.

I will check it this weekend when I get back home. School is getting in the way of cruiser fixing, lol.

 

[CarmMontana]

Yeah, i got it up on jacks and grabbed anything that could be loose and no go so far. I am curious though. I can take my wheel, a 33 inch mud tread, and spin it roughly 4-5 inches before it engages the drive shaft. This is the case on both sides. Is this normal? I am going to get a better look as soon as I get a little more time. I just started a welding class that is taking up most of the time. Anyway let me know if you guys come up with anything. Thanks