Front Grinding on Deceleration - Potential Differential Issue? (1 Viewer)

Joined
Aug 10, 2021
Messages
15
Location
NWI
I realize there are multiple threads on this topic, most of them understandably don't provide a whole lot of guidance because the list of potential causes/solutions are long. The problem I am facing is that on deceleration I get a grinding/rumble from the front of the 80, generally happens between 50->40mph, then again from 30->20mph. Has progressively been getting worse across the MPH, randomly will get an audible grind while turning on occasion (may not be related). Also not sure if it is related, but I get some bad rattling under the vehicle when going over rough terrain at low speeds, sounds also like it is coming from the front axle, but very well could be another issue I need to track down.
  • Car info - 1997, OEM front and rear lockers, 149K on the odometer, no lift (stock height Dobinsons front and rear), 33" tires
  • Purchased the car a year ago, was said to have a full rebuild/service on the knuckles including axle shafts, birfs, seals, and bearings.
  • After first road trip notice grinding noise on deceleration and inspect front housings - seals were already busted and apparently axle shafts were not properly installed (and were cheap parts geek $95 units). Lots of metallic shavings in passenger side dues to birf rubbing the housing. I thought this was the main source of my grinding, luckily I caught it before full blowout.
  • Replaced axle shafts with OEM, Fuji Birfs, new oem seals, and Koyo bearings just to be safe. Inspected spindles, they were worn past my comfort level so I ordered and installed replacements.
  • Take out for a drive, still hearing a grinding noise, but slightly different than the metal-on-metal I was hearing previously.
  • Do some research here, find that it could be new spindle bearings if they are not greased properly on installation. Pull them apart, regrease, test again - still present
  • I think I may have ruined them by not greasing properly on initial installation. Pull them and install old brass bushings from originals (which were in surprisingly good shape), also just to further isolate the problem - still present
  • Somewhere in the middle of this as also installed had new u-joints installed thinking it could be from warn out needle bearings - still present
  • Greased everything I could possibly grease under the car and still present
  • Bought a chassis ear to see if I can further diagnose - hooked up to each end of the front axle, the end of the front differential, and the front and rear of the transfer case. No noises at the transfer case, audible on the front axle and differential. I can upload a video of the noise if needed, it isn't the easiest to hear but I have it.
  • Have changed the Diff oil 3 times this year, no noticeable shavings or discoloration of the fluid
  • I plan to take it out again and put the leads on the left, right and rear of the diff to further isolate.
So after a long 3+ months of messing with it I am convinced at this point it is the diff that is the issue, more particularly the carrier or pinion bearings that are about to give out or aren't properly torqued. The good news is I can take my knuckles apart and get them back together in 30mins or less...
  • Is there anything else I need to look at or should be considering?
  • If it is the diff, is there anything that can be DIY that I can check before I end up bringing it in to the dealership?
  • I looked at Zuks site and saw that I can/should tighten down the carrier bearing preload. Looked at the pinion bearing diy and not sure it is within my DIY skill level. I would be happy to send it off to him, but see that he is not accepting mail-ins for the foreseeable future.
  • Is the dealership the best place to bring this as an alternative? Not sure I trust any of the local transmission/4x4 shops around here to not butcher it, also not sure I trust the dealer... I am located in Northwest Indiana, so have access to Chicago area, Michigan, and Wisconsin.
Sorry for the long story, attempting to put it all out there so you have all the details. so they aren't scattered across multiple posts/questions. Thanks in advance for any help/assistance.

Mike
 
Joined
Jan 5, 2017
Messages
4,056
Location
Charlotte, NC & Alexandria, VA
Good news/bad news:

The good news is that there is nothing special about the differential, if that's the problem. Anyone can check and rebuild them. The cost will be significantly lower if you remove the differential carrier and take just that to a shop, if you decide you don't want to do the work yourself. Better news is that this work is fairly simple and doesn't require special tools, other than a good workbench. If you haven't already, download a copy of the FSM and research the build procedure.

Bad news: these problems are almost impossible to diagnose unless you have the axle in front of you. You may get a lot of sympathetic advice, but no one is going to be able to do your problem justice without being there.

If you can remove the carrier, and post photos of the printed ring and pinion pattern, maybe we would know something, but that's a maybe only. It's possible the problem is a coast side pattern problem, but there's no way to know without removing the carrier. The good news here is that removing the carrier, while a PITA, isn't much more involved than removing a tire; it requires no special tools, except maybe a jack, and you won't need any new parts, other than new gasket, gear oil and crush washers for the plugs.

FWIW, I seriously doubt your bearings are improperly preloaded unless someone has recently removed the old ones and installed new ones.

I have a similar problem that's existed on my '94 since I bought it 6 years and many miles ago. Under the right conditions, which I still haven't been able to consistently replicate, the axle under the passenger floorboard sounds like a playing card in bicycle spokes. I used to build heavy duty off-road axles for a living, and I have no idea what is causing this noise. One day, after I retire, I may tear the axle down just for grins.
 
Joined
Nov 9, 2012
Messages
13,239
Location
Olathe, KS, USA
I realize there are multiple threads on this topic, most of them understandably don't provide a whole lot of guidance because the list of potential causes/solutions are long. The problem I am facing is that on deceleration I get a grinding/rumble from the front of the 80, generally happens between 50->40mph, then again from 30->20mph. Has progressively been getting worse across the MPH, randomly will get an audible grind while turning on occasion (may not be related). Also not sure if it is related, but I get some bad rattling under the vehicle when going over rough terrain at low speeds, sounds also like it is coming from the front axle, but very well could be another issue I need to track down.
  • Car info - 1997, OEM front and rear lockers, 149K on the odometer, no lift (stock height Dobinsons front and rear), 33" tires
  • Purchased the car a year ago, was said to have a full rebuild/service on the knuckles including axle shafts, birfs, seals, and bearings.
  • After first road trip notice grinding noise on deceleration and inspect front housings - seals were already busted and apparently axle shafts were not properly installed (and were cheap parts geek $95 units). Lots of metallic shavings in passenger side dues to birf rubbing the housing. I thought this was the main source of my grinding, luckily I caught it before full blowout.
  • Replaced axle shafts with OEM, Fuji Birfs, new oem seals, and Koyo bearings just to be safe. Inspected spindles, they were worn past my comfort level so I ordered and installed replacements.
  • Take out for a drive, still hearing a grinding noise, but slightly different than the metal-on-metal I was hearing previously.
  • Do some research here, find that it could be new spindle bearings if they are not greased properly on installation. Pull them apart, regrease, test again - still present
  • I think I may have ruined them by not greasing properly on initial installation. Pull them and install old brass bushings from originals (which were in surprisingly good shape), also just to further isolate the problem - still present
  • Somewhere in the middle of this as also installed had new u-joints installed thinking it could be from warn out needle bearings - still present
  • Greased everything I could possibly grease under the car and still present
  • Bought a chassis ear to see if I can further diagnose - hooked up to each end of the front axle, the end of the front differential, and the front and rear of the transfer case. No noises at the transfer case, audible on the front axle and differential. I can upload a video of the noise if needed, it isn't the easiest to hear but I have it.
  • Have changed the Diff oil 3 times this year, no noticeable shavings or discoloration of the fluid
  • I plan to take it out again and put the leads on the left, right and rear of the diff to further isolate.
So after a long 3+ months of messing with it I am convinced at this point it is the diff that is the issue, more particularly the carrier or pinion bearings that are about to give out or aren't properly torqued. The good news is I can take my knuckles apart and get them back together in 30mins or less...
  • Is there anything else I need to look at or should be considering?
  • If it is the diff, is there anything that can be DIY that I can check before I end up bringing it in to the dealership?
  • I looked at Zuks site and saw that I can/should tighten down the carrier bearing preload. Looked at the pinion bearing diy and not sure it is within my DIY skill level. I would be happy to send it off to him, but see that he is not accepting mail-ins for the foreseeable future.
  • Is the dealership the best place to bring this as an alternative? Not sure I trust any of the local transmission/4x4 shops around here to not butcher it, also not sure I trust the dealer... I am located in Northwest Indiana, so have access to Chicago area, Michigan, and Wisconsin.
Sorry for the long story, attempting to put it all out there so you have all the details. so they aren't scattered across multiple posts/questions. Thanks in advance for any help/assistance.

Mike
Are these factory locking differential or aftermarket?

Never underestimate the "expertise" of the PO.

Assuming the PO was chasing the same sound, he may have "rebuilt" the differential and screwed it up. Also possible that he ran it out of oil and toasted the pinion bearing.

You have done everything the way I would have done it, including replacing the parts.

Make sure the knuckles are filled with moly grease, make sure the cavity between the wheel bearing full of grease.

Check to make sure the front DS is 90' out of phase and the slip yoke is at the differential.

Your wheel bearings need to be tightened to 35 LB-FT on the inner nut and 45 LB-FT on the outer nut.

What u-joints did you have installed? Did they adjust properly with different thickness snap rings? Are they aligned with grease zerks pointing the same direction?
 
Joined
Aug 10, 2021
Messages
15
Location
NWI
Thanks for responding, and I realize it is a needle in a haystack when it comes to front axle noises :) I am on the fence about my skill level with the differential, but may take a crack at it and as you mentioned if it seems too difficult once opened up I will just take it to a shop. I can also take some pictures and add to the thread.
  • Are these factory locking differential or aftermarket? Factory Locking, have tested them and was able to get them locked/unlocked
  • Make sure the knuckles are filled with moly grease, make sure the cavity between the wheel bearing full of grease - Yes, double/triple checked this
  • Check to make sure the front DS is 90' out of phase and the slip yoke is at the differential - Have tried both in and out of phase with no change
  • Your wheel bearings need to be tightened to 35 LB-FT on the inner nut and 45 LB-FT on the outer nut. - Yes - utilized info from the boards and OTRAMM for this
  • What u-joints did you have installed? Did they adjust properly with different thickness snap rings? Are they aligned with grease zerks pointing the same direction? - OEM u-joints, not sure if they adjusted snap ring thickness. Not completely ruling this out, but noise was there before and after new u-joints.

At this point I am going to start pulling together the parts needed for a diff rebuild/refresh. If there are any suggestions on a good place to find a premed kit that is reputable, I am open to suggestions. I have also started digging through Zuk's site for info on the process, tools needed, and parts.

One thing I noticed on his site is that he recommends OEM bearings over the koyo bearings that are all over the net because of the angle of the rollers in OEM v. Koyo, saying with the Koyo's after about 1 year, pinion slop will result and require a rebuild again."

This is not a DD, but also don't want to be back in there for another 150K miles if possible.

Thanks again for the responses.
 
Joined
Jan 5, 2017
Messages
4,056
Location
Charlotte, NC & Alexandria, VA
Thanks for responding, and I realize it is a needle in a haystack when it comes to front axle noises :) I am on the fence about my skill level with the differential, but may take a crack at it and as you mentioned if it seems too difficult once opened up I will just take it to a shop. I can also take some pictures and add to the thread.
  • Are these factory locking differential or aftermarket? Factory Locking, have tested them and was able to get them locked/unlocked
  • Make sure the knuckles are filled with moly grease, make sure the cavity between the wheel bearing full of grease - Yes, double/triple checked this
  • Check to make sure the front DS is 90' out of phase and the slip yoke is at the differential - Have tried both in and out of phase with no change
  • Your wheel bearings need to be tightened to 35 LB-FT on the inner nut and 45 LB-FT on the outer nut. - Yes - utilized info from the boards and OTRAMM for this
  • What u-joints did you have installed? Did they adjust properly with different thickness snap rings? Are they aligned with grease zerks pointing the same direction? - OEM u-joints, not sure if they adjusted snap ring thickness. Not completely ruling this out, but noise was there before and after new u-joints.

At this point I am going to start pulling together the parts needed for a diff rebuild/refresh. If there are any suggestions on a good place to find a premed kit that is reputable, I am open to suggestions. I have also started digging through Zuk's site for info on the process, tools needed, and parts.

One thing I noticed on his site is that he recommends OEM bearings over the koyo bearings that are all over the net because of the angle of the rollers in OEM v. Koyo, saying with the Koyo's after about 1 year, pinion slop will result and require a rebuild again."

This is not a DD, but also don't want to be back in there for another 150K miles if possible.

Thanks again for the responses.
The FSM is the place to go for technical advice. I wouldn't start buying parts before I pulled the carrier; the problem may be elsewhere.

FWIW, as long as we're talking quality bearings and not chinese crap, bearings are bearings. I have yet to hear the opinion of another engineer who thinks differently. And I'd be surprised if the OEM bearings weren't Koyo. If they're not, they are Timken, and functionally equivalent to FAG, INA, SKF, or anyone else's.
 
Joined
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Messages
15
Location
NWI
The FSM is the place to go for technical advice. I wouldn't start buying parts before I pulled the carrier; the problem may be elsewhere.

FWIW, as long as we're talking quality bearings and not chinese crap, bearings are bearings. I have yet to hear the opinion of another engineer who thinks differently. And I'd be surprised if the OEM bearings weren't Koyo. If they're not, they are Timken, and functionally equivalent to FAG, INA, SKF, or anyone else's.
Thanks, yeah will take a look at the FSM tonight and dig in. Not planning to buy any parts yet, just thinking ahead so I am prepared for the worst :)
 

jynx

Turd Herder
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Generally speaking, if it is on the deceleration side, then it is likely that the coast side of your gear pattern is off. Could be as simple as adjusting backlash on the carrier bearings or checking the pre-load on the pinion bearings. Progressively getting worse makes me think that this is your issue. Especially since you have checked everything related to the actual axles and outer components.

You may not need a full rebuild, I had an issue with a "professionally" set up rearend that started getting progressively noisier. I pulled it and found that there was nearly no preload on the carrier bearings and the no preload on the pinion bearings. I swapped the crush sleeve for a solid spacer and then set the pinion preload to spec. Then I adjusted the backlash and put some preload on the carrier bearings and pretty well fixed my issues.

Gears seem daunting, and I haven't ever set up a set from scratch, but tweaking preload and adjusting backlash is actually not too bad. Just need a beam style torque wrench and a dial indicator and magnetic base.

I also agree, you need to pull the carrier to see what you are working with before you jump into it too much. Good luck
 
Joined
Aug 10, 2021
Messages
15
Location
NWI
Generally speaking, if it is on the deceleration side, then it is likely that the coast side of your gear pattern is off. Could be as simple as adjusting backlash on the carrier bearings or checking the pre-load on the pinion bearings. Progressively getting worse makes me think that this is your issue. Especially since you have checked everything related to the actual axles and outer components.

You may not need a full rebuild, I had an issue with a "professionally" set up rearend that started getting progressively noisier. I pulled it and found that there was nearly no preload on the carrier bearings and the no preload on the pinion bearings. I swapped the crush sleeve for a solid spacer and then set the pinion preload to spec. Then I adjusted the backlash and put some preload on the carrier bearings and pretty well fixed my issues.

Gears seem daunting, and I haven't ever set up a set from scratch, but tweaking preload and adjusting backlash is actually not too bad. Just need a beam style torque wrench and a dial indicator and magnetic base.

I also agree, you need to pull the carrier to see what you are working with before you jump into it too much. Good luck
Thanks, for the encouragement :) Getting it pulled looks like the easy part, scanning the FSM I see that having the factory lockers adds a bit more complexity but not anything I can't handle. Once I get it on the bench it will hopefully make more sense what I am looking at, and I guess worst case scenarioI can always come back here and ask for help!
 

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