roaring amc 20

roaring amc 20

tn trooper

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dover tn
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1985 cj-7 304 v-8 3 spd. dana 20 t-case.
hey, i have an 85 CJ7 and the rear end roars when giving it any gas. when i go down the road its a loud roar that only does it when i apply throttle when i let off the gas it goes away. any ideas on what it is?
 
could be worn gear teeth and or low diff oil (which could be causing worn gear teeth). Bad u joints generally just vibrate when under load without alot of noise.
 
hey, i have an 85 CJ7 and the rear end roars when giving it any gas. when i go down the road its a loud roar that only does it when i apply throttle when i let off the gas it goes away. any ideas on what it is?

Not sure what roaring means, high pitch or low pitch? can you feel it or just hear it?
 
Could be wheel bearings, too... or loose lug nuts.

If the gear oil is just low, top it off with GL-5 gear oil. Do NOT use GL-4. GL-4 is for your TRANSMISSION, not for your differential.

Also, don't use GL-5 gear oil in the transmission unless it's also rated for GL-4. GL-5 doesn't supercede GL-4. I had to educate the local NAPA people about that this morning... they thought GL-5 could be used anywhere that GL-4 could. If it's not rated for GL-4, though, it'll eat the synchromesh out of the transmission.
 
i think its a low pitch roar but it's loud and maybe partly because it echoes while the hard top is on. but it only does it when i give it gas.
 
IMO it sounds like a bearing than. could be a bearing in the diff.
Your going to have to jack both wheels off the ground and turn the axle and see if you can hear or feel where it's comming from.
 
do you think its a pinion bearing. my jeep came with 272 gears stock and i had them replaced with the 354 gears from another AMC20 rear end but we didn't replace any bearings but the teeth on the gears looked good.
 
Did you put the yellow paste on the gears??:confused:
 
Somebody else posted this before, then deleted their post...

Is the muffler OK? Is this just noisy exhaust?
 
i didnt pu them in but i dont think they put anything on them and i'm positive its not the exhaust.
 
i didnt pu them in but i dont think they put anything on them and i'm positive its not the exhaust.


The yellow paste is what you use to check the alignment on the gear set If the gears were just pulled and put back in with the same shims and the same crush sleeve the gears will howl , or worse. check for play in the pinion shaft and if there is any slop in the gears when it is turned back and forth while on stands. There may even be a noticable "clunk" when you go from forward to backward.
 
Ok - does it make the same sound when it's up on jackstands? If you can get it to do that (it might take using a little brake with your left foot while you give it gas with your right foot), it should't be very hard to track down exactly where the noise is coming from.
 
thats what we did pulled them from one rearend and put back in mine without changing any bearings or shims. I'm pretty sure thats whats wrong cause it does howl. can i still use the gears and just have it shimmed up and replace bearings. or should i just get new gears.
 
thats what we did pulled them from one rearend and put back in mine without changing any bearings or shims. I'm pretty sure thats whats wrong cause it does howl. can i still use the gears and just have it shimmed up and replace bearings. or should i just get new gears.

Can’t say, that’s a tough call, how many miles how hard you drive did you tow anything? yada yada. Take a look and make a call. At minimum you need bearings and shims and some one that knows how to dial in a differential. Dial indicator torque wrench foot pound and inch pound, a good strong air compressor and impact, micrometers. This is a real adventure; you will remember it for the rest of your life. Have fun; let us know how it turns out.
 
Anytime you swap a ring and pinion from one housing to another you run the chance of having noise (never quite get the wear pattern the same). Since the R&P was just swapped without setting backlash or pinion depth, I'd say that is the culprit. I'm hoping the R&P isn't shot as every diff housing is different.
 
I fell out of touch on this one... not that I was ever really in touch with it (evidenced by my earlier posts).

No matter what, you'll need to redo the work to make that differential work right... whether with new R&P or with what you have. First thing to do is check for binding or play on the yoke. That'll tell you a little about it - if you have a little play, that's better than binding. Binding can very well have eaten your R&P. Next, open it up & get a good idea of the mesh between the ring & pinion gears... examine EVERY TOOTH on each of 'em VERY THOROUGHLY for any visible signs of damage. Magnification won't hurt here.

Damage means it's gone. There's no use in trying to touch it up with stones or sandpaper - the fit is really pretty critical if you're going to get any life out of it. So's your choice of gear oil for it.

If you don't find ANY evidence of damage - if it all still looks PERFECT along every surface of every tooth - you can probably do a reinstall (CORRECTLY) and be fine. That reinstall should take some time to get it right.
 
OK, I have been really busy this week at work and not posting much so let me ask a question or two.
Did you say you took the gears from another rear end and did not set them up in the new set?
Were you there (kinda get the hint you were not from your return to the paste question) ?
Like said, any time you put gears into a diff you need to reset them up for alignment, and this goes triple for a set of used gears. The problem with used gears is they are already worn to each other so when setting them up again you need to get them dead nuts to the old setup or you are going get loud noise, extreme wear and possible crack the gears if they are running at more that a degree or two from the old setup. Remember each diff housing is different and do vary from each other in size and angle degree in mating area. In other words they are not made to great tight tolerances and get worse over use. Diff work is not the place for those with out good mechanical ability or those who do not use good mechanical practices.
 
I don't have much to add to the above posts.
There is a reason most shops charge a few hundred $ to set up gears.
If you don't have depth gauges and indicaters you should leave it to someone that does.
 
Thanks for all of the advice guys, looks like i'm prob gon take it to someone who knows what their doing and buy a new ring and pinion. Thank you all again
 
Good luck, putting used gears in a different diff isn't difficult, but it does require very strict setup procedures.
 

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