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Discussion Starter · #1 ·
Finally trying to chase the insane driveline lash I’ve got.

Just replaced both rear axle shafts as well as the hubs to the heavy duty terrafirma flanges. Was in the process of replacing the rear prop shaft as I THOUGHT that was where the play was, but now I’m thinking it’s the diff. Video below, am I missing something I should be testing (like try doing this with one wheel in the air or something), or is this just a sign of a ton of play in the rear diff?

 

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Discussion Starter · #3 ·
I get a brutal clunk when i get on and off throttle. Another piece of feedback, when the clunk is bad, there's actual movement and play in the shifter. Could that be a sign that the issue is actually in t-case? Or is the inevitable conclusion that i have too much play in literally every moving thing in the drive line :)
 

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That is what we call excessive backlash.
It is however not an indication that the rear diff is bad.
It is more likely transmission main shaft spline wear coupled by worn final drive gear spines.
You'll need to remove the transfer case to check and replace the worn parts to remedy.
 
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Im less concerned with the rotational play, but looking closely at the rear pinion, it almost appears as though there's vertical/horizontal play like the pinion bearings may have play. Hard to say from the video though, could be an optical illusion.

If you push up/down or side to side on the flange, is there any movement?
 

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Discussion Starter · #6 ·
Im less concerned with the rotational play, but looking closely at the rear pinion, it almost appears as though there's vertical/horizontal play like the pinion bearings may have play. Hard to say from the video though, could be an optical illusion.

If you push up/down or side to side on the flange, is there any movement?

I’ll grab a video of this in a moment.

here’s what the front is doing:

 

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Imma go with everything in the driveline. That said, you could prob go years like that.
You do have excess backlash in diff. I have run Moab with twice as much for what its worth.

Find a local to you forum member with a new Ashcroft or Gen diff. The feel by hand is smooth. Super small amount of play.

Driveshaft slop comes from bad U-joints.
 

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Discussion Starter · #8 ·
Imma go with everything in the driveline. That said, you could prob go years like that.
You do have excess backlash in diff. I have run Moab with twice as much for what its worth.

Find a local to you forum member with a new Ashcroft or Gen diff. The feel by hand is smooth. Super small amount of play.

Driveshaft slop comes from bad U-joints.
Yeah, it all works just fine, I’m just tired of the experience in stop and go (and the experience for passengers!)
 

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Discussion Starter · #9 ·
It is more likely transmission main shaft spline wear coupled by worn final drive gear spines.
You'll need to remove the transfer case to check and replace the worn parts to remedy.
Anyone have a guide for how I can go about doing this? And if I’m pulling the t-case, anything I should do at the same time? Seems like brand new ones from Ashcroft are surprisingly affordable compared to other driveline parts?
 

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First things first.
Your truck is 40 years old, some items may be original.
Check all bushings, esp. A-frame ball joint Any slop there will be noisy/clunky. Plenty of YouTube content on this.
I think we have already established your diffs are out of spec. Either have rebuilt or buy rebuilt. Ashcroft, RN, GBR, TerraFirma etc. all can provide.
The HD drive members should need to be tapped onto axle shafts with a rubber mallet. If they glide right on, splines are worn.
Check CV’s, and for swivel joint play while you are there.

I am trying to stress a methodical approach. A new T-case would be great, but would get hammered every time it takes up differential slop. Isolate issues, and repair in sequence.

Those of us who have had the experience of driving “fresh” drivetrain trucks are amazed at the lack of noise or slop. You’ll get there.
 

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The transfercase is likely not the culprit, but needs to come out to verify the condition of the main shaft splines and final drive gear (the gear that slides over the main shaft and protrudes into the transfercase), see post 4.
The later gears were cross drilled to allow for better oiling to reduce spline wear.
 

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Discussion Starter · #12 ·
First things first.
Your truck is 40 years old, some items may be original.
Check all bushings, esp. A-frame ball joint Any slop there will be noisy/clunky. Plenty of YouTube content on this.
I think we have already established your diffs are out of spec. Either have rebuilt or buy rebuilt. Ashcroft, RN, GBR, TerraFirma etc. all can provide.
The HD drive members should need to be tapped onto axle shafts with a rubber mallet. If they glide right on, splines are worn.
Check CV’s, and for swivel joint play while you are there.

I am trying to stress a methodical approach. A new T-case would be great, but would get hammered every time it takes up differential slop. Isolate issues, and repair in sequence.

Those of us who have had the experience of driving “fresh” drivetrain trucks are amazed at the lack of noise or slop. You’ll get there.
I've slowly gone through most of this over the years. all bushings new, a frame ball joint is new, drive shafts and flanges are new, so really all that's left are diffs, prop shafts, t-case, and transmission.

Sounds like maybe it's going to be all of the above!
 

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Discussion Starter · #13 ·
The transfercase is likely not the culprit, but needs to come out to verify the condition of the main shaft splines and final drive gear (the gear that slides over the main shaft and protrudes into the transfercase), see post 4.
The later gears were cross drilled to allow for better oiling to reduce spline wear.
I'm going to dive down the YouTube rabbit hole today, but if i get the t-case off, can i replace the main shaft and final drive gear in situ? or do I need to pull the tranny?

I'm kicking myself bc i had the entire motor out last summer. I replaced the clutch then, should have gone through the whole thing when i had access. That said, I'm going to be doing major seatbox and interior work this winter that will mean the seatbox is comign out, which would be an opportunity to have better access to transmission and t-case.
 
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The final drive gear can be replaced after the transfer case is out, but with the transmission still in place.
You'll need to disassemble the transmission to change the main shaft after removing the transmission from the vehicle.
 

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Discussion Starter · #15 ·
The final drive gear can be replaced after the transfer case is out, but with the transmission still in place.
You'll need to disassemble the transmission to change the main shaft after removing the transmission from the vehicle.
ugh, devastating
 

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Discussion Starter · #17 ·
Just an opinion but would guess the lash/slop is in your onesy LT95. In my experience these can be quite sloppy in terms of lash. They also typically make gear whine sound like a 1940's 2 ton truck transmission.
I'll take a video of the shifter movement as the lash is taken up or let off this weekend. It's absolutely worse than when I got the truck 7 years ago, and i suspect it wasn't in tip top shape then. At this point coming on and off the gas is almost a violent movement.
 

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Discussion Starter · #18 ·
Well with the British Pound where it is, I think it would be insane not to make moves ASAP. Ashcroft doesn't do the rear diff, only the front. Any ideas where to source a rear?
 

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Ashcroft doesn't do the rear diff, only the front. Any ideas where to source a rear?
Ashcroft sell both front and rear. That said, it is unlikely the Salisbury needs replacing, just an overhaul. Any shop familiar with Dana axles can do it. If you go off road, though, it is a good plan to put in a locker.
 

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Discussion Starter · #20 ·
Dave himself said they're doing front only these days. But duly noted that the rear is serviceable, I'll find a good shop. Now i'm just trying to figure out whether I'm going to have to drop the entire tranny to make this thing improve at all.
 
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