Y'all have me scared to do my re-gear

[Steel City 06]

This thread inspired me to go ahead and install the driveshaft balancers. It didn't solve the issue, but seemed to increase the threshold speed where the vibrations started from roughly 75 to about 80. By 90 the vibrations are still quite developed.

I may try relocating the balancer to the other end of the front driveshaft to see if it makes a bigger difference.

 

[Mr. Bills]

. . . By 90 the vibrations are still quite developed.

Shit. Doesn't the owner's manual say that TJ's totally disintegrate at 89?

 

[Steel City 06]

Shit. Doesn't the owner's manual say that TJ's totally disintegrate at 89?

I know they're governed at 92... hit that a couple times passing people when on stock tires.

Though with 35s and stock gearing that "92" is now actually 104... not sure I have the guts to attempt that

 

[mrblaine]

I know they're governed at 92... hit that a couple times passing people when on stock tires.

Though with 35s and stock gearing that "92" is now actually 104... not sure I have the guts to attempt that

You passed the "guts" phase awhile back.

 

[bobthetj03]

In my case, I'm a rainbow Unicorn situation. I've done the work, more than I care to admit. Hubs won't work for my case. It's the rear DS. I've made it better, but a lot of that has to do with removing the hardtop. Still can feel it in the seat kick in about 63 mph. 50-60 there is a slight harmonic. With the soft top, or no top, it's not as noticeable, mostly due to all the other noises going on.

 

[Goatman]

Out of curiosity I'm wondering what the cost of a front hub kit is compared to just buying a new axle in your new gear setup? From my experience with this (far, far less than Blaine's experience) buying a new axle has a very low occurrence of inducing a vibe problem. That may be a better route for some. Although I am a huge proponent of locking hubs, I am also not as financially gifted as many others are.

 

[Liv2Ryd]

I did a 4:10 to 5:38 regear on my 06 4.0L/42RLE thru a reputable shop and have 0 issues so far with the dreaded vibes. Granted, I limit my highway miles and rarely top 75mph as I'm running 35's and 4" lift. Not a great combo for high speed cruising. Nonetheless, I was a bit nervous doing the gear swap but its been nothing but smiles for miles since I did it.

 

[L0jik]

So, heres a dumb question. If someone felt like going through the work, couldn't they remove the inner knuckles from the axle tube and re-weld them at a different angle to keep good caster and good pinon angle?

 

[JMT]

I'm the type of guy that delves into a subject and reads intensely to better understand it. How are you supposed to get better at something if you don't understand it? With that said though, after reading 15 pages of @bobthetj03 thread on driveline vibes, I'm a little wary of regearing for larger tires.

Is this a very common issue when it comes to gearing? After seeing his thread and countless others on this forum and others, it's making me reconsider my choice to go to 5.13 from my 3.73.

So, is this something I should be worried about? Or does the internet just amplify unicorn cases?

The 42rle is the only transmission to have any concerns about, and even then, I don't think it's normally a problem. I think we hear of all the ones that do have a problem, so there is a disproportionate outlook due to disproportionate reporting.

That said, I have a friend on here who regeared his 42rle with 33's, i6, to 456 and added a Rubicrawler. Not sure how it is on the highway, but the offroad is probably pretty good. I think he wanted to avoid the vibes that sometimes come with deeper gears like 513.

 

[Jerry Bransford]

That said, I have a friend on here who regeared his 42rle with 33's, i6, to 456 and added a Rubicrawler. Not sure how it is on the highway...

4.56 with the 42RLE and 33's would be like my previous 4.88 ratio and 35's with that transmission. It absolutely sucked on the highway. Complete with sub-12 mpg that went to nearly 15 after regearing to 5.38.

 

[JMT]

4.56 with the 42RLE and 33's would absolutely suck on the highway.

I assumed as much. The guy said that it was much better than 373's he was driving for a few years. I'm running 456's with my 6-speed, which is optimal, so I know I would dread 456's with a 42rle. I even threw some 35's on my rig for 1 week and wanted 488's.

 

[Steel City 06]

So, heres a dumb question. If someone felt like going through the work, couldn't they remove the inner knuckles from the axle tube and re-weld them at a different angle to keep good caster and good pinon angle?

It’s quite common when people build or modify axles. You would need to know in advance what pinion and caster angles you would want.

 

[freedom_in_4low]

Make no assumptions.
1-verify driveshafts are good, balanced perfectly, and in viable condition since they are now spinning faster.
2- verify that rear pinion angle can be dialed in by pulling the front driveshaft and doing the work and test drives.
3- Only after the rear is done should you install front and see what happens. Do the work with a mindful eye on steering and drivability. It does little good to dial out the vibes with a low caster angle and put up with shit steering.

Diagnose, hypothesize, test, use the results to create a forward path to resolution.

Can you expand on #2? Do you have a specific technique or order of operations you go through here? A commonly-successful starting point, specific range of pinion angles and increments of adjustment you go through to find the sweet spot?

-I've tried ~1° above (due to measurement error on my part thinking I was dead-even), and 0.2, 0.9, and 1.4 degrees below shaft angle with the front shaft out. It's still there, and it still pulses/oscillates.
-0.9 was the best at 71mph, but still not completely gone, and at 75mph the peak intensity doesn't seem to change with pinion angle.
-Both shafts are X splines from Tom Wood's and should be balanced as well as they can get them because I specifically asked due to running 4k+ RPM at 75mph (and because the rear was already buzzing). Rear was sent back and re-balanced again and has new straps.
-4.88 with 32's puts my driveshaft vs vehicle speed in the same neighborhood (a hair slower even) as 35/5.13, which is common in the 42RLE crowd so even though it's a weird (and temporary) combination for a NSG370, it's not outside the realm of common configurations for modified rigs.
-LJ with a JB SS SYE and stock belly skid, so my shaft is 29" long and only requires ~11° of pinion angle to be dead straight with the shaft - nowhere near the CV operating angle as the guys running full tucks on a TJ wheelbase.
-vibration is completely independent of load - on the gas, off the gas, clutch in, doesn't change.

These are the same axles (open CAD-eliminated HP 30, E-locker 44, stock shafts), transfer case, and mostly the same suspension (shortarm Savvy UCAs and JJ-retrofitted RC LCAs, Currie front and JKS rear track bars - I now have 4" currie in the front and 3" Zone plus 3/4" spacers in the rear, the TJ had unidentified 3" springs with spacers but about the same ride height), and wheels/tires that were on my '99 AX15 4.56 TJ with zero vibes. I regeared to 4.88 shortly before swapping everything over to the LJ (after my gears ate themselves and I decided to gear for 35s) but I honestly can't even remember if I got it past 60mph before tearing it down so I don't know if it started with the regear, rig swap, or driveshaft.

I know it should get better (or at least move up in vehicle speed) once I get 35's but it's still starting at low enough speeds that the 35's won't move it completely out of range.

 

[mrblaine]

Can you expand on #2? Do you have a specific technique or order of operations you go through here? A specific range of pinion angles and increments of adjustment you go through to find the sweet spot?

-I've tried ~1° above (due to measurement error on my part thinking I was dead-even), and 0.2, 0.9, and 1.4 degrees below shaft angle with the front shaft out. It's still there, and it still pulses/oscillates.
-0.9 was the best at 71mph, but still not completely gone, and at 75mph the peak intensity doesn't seem to change with pinion angle.
-Both shafts are X splines from Tom Wood's and should be balanced as well as they can get them because I specifically asked due to running 4k+ RPM at 75mph (and because the rear was already buzzing). Rear was sent back and re-balanced again and has new straps.
-4.88 with 32's puts my driveshaft vs vehicle speed in the same neighborhood (a hair slower even) as 35/5.13, which is common in the 42RLE crowd so even though it's a weird (and temporary) combination for a NSG370, it's not outside the realm of common configurations for modified rigs.
-LJ with a JB SS SYE and stock belly skid, so my shaft is 29" long and only requires ~11° of pinion angle to be dead straight with the shaft - nowhere near the CV operating angle as the guys running full tucks on a TJ wheelbase.

These are the same axles (open CAD-eliminated HP 30, E-locker 44, stock shafts), transfer case, suspension (4" Currie with shortarm Savvy UCAs and JJ-retrofitted RC LCAs, Currie front and JKS rear track bars), and wheels/tires that were on my '99 AX15 4.56 TJ with zero vibes. I regeared to 4.88 shortly before swapping everything over to the LJ (after my gears ate themselves and I decided to gear for 35s) but I honestly can't even remember if I got it past 60mph before tearing it down so I don't know if it started with the regear, rig swap, or driveshaft.

I know it should get better (or at least move up in vehicle speed) once I get 35's but it's still starting at low enough speeds that the 35's won't move it completely out of range.

We start with the front driveshaft out and then work on the rear until we get it as far as we can take it. One thing we have noticed over time is some have been adjusted to what I would have predicted to be undrivable and are perfectly fine. Pull the front shaft out and start raising the rear pinion a little at a time and testing that for vibes. I had one where the front was 5-6 degrees low and the rear was 5-6 high with zero vibes at 75.

 

[freedom_in_4low]

We start with the front driveshaft out and then work on the rear until we get it as far as we can take it. One thing we have noticed over time is some have been adjusted to what I would have predicted to be undrivable and are perfectly fine. Pull the front shaft out and start raising the rear pinion a little at a time and testing that for vibes. I had one where the front was 5-6 degrees low and the rear was 5-6 high with zero vibes at 75.

thank you! front shaft is already out (per your earlier advice in this thread).

"as far as we can take it" - as in the extents of what the control arm adjustment will allow, or the vibrations minimized as far as you can? Do you have an objective indicator to compare two different angles to know whether the vibration is getting better or worse? A vibration measurement app on my phone is what told me 0.9 low seemed better at 70mph than both 0.2 low and 1.4 low, but I'm not totally sure the difference I feel isn't psychological, and since it's analyzing a sample over a few seconds, I'm not sure the results are consistent if I don't start the sample at exactly the same point in the pulse. Can it get worse before it gets better or if it gets noticeably worse do you stop and go back the other way?

I can't picture you guys spending 1-2 days for each shaft finding the right pinion angles, so you must have an increment that gets you to the sweet spot faster but not so large that you jump right over and miss it? I don't want to overshoot and miss it, but it's going to take me a month if I do this half a degree at a time and end up at something like 5°.

I know I need to "do the work" so I don't want to come across like I'm trying to take shortcuts, but the whole point of forums is leveraging the experience of those more experienced in order to avoid having to rediscover that which is already known, and I'm trying to fit this in between preparing to list a house in 3 weeks and be able to drive this thing 600 miles when the sale closes and panic is taking hold.

 

[mrblaine]

thank you! front shaft is already out (per your earlier advice in this thread).

"as far as we can take it" - as in the extents of what the control arm adjustment will allow, or the vibrations minimized as far as you can? Do you have an objective indicator to compare two different angles to know whether the vibration is getting better or worse? A vibration measurement app on my phone is what told me 0.9 low seemed better at 70mph than both 0.2 low and 1.4 low, but I'm not totally sure the difference I feel isn't psychological, and since it's analyzing a sample over a few seconds, I'm not sure the results are consistent if I don't start the sample at exactly the same point in the pulse. Can it get worse before it gets better or if it gets noticeably worse do you stop and go back the other way?

I can't picture you guys spending 1-2 days for each shaft finding the right pinion angles, so you must have an increment that gets you to the sweet spot faster but not so large that you jump right over and miss it? I don't want to overshoot and miss it, but it's going to take me a month if I do this half a degree at a time and end up at something like 5°.

I know I need to "do the work" so I don't want to come across like I'm trying to take shortcuts, but the whole point of forums is leveraging the experience of those more experienced in order to avoid having to rediscover that which is already known, and I'm trying to fit this in between preparing to list a house in 3 weeks and be able to drive this thing 600 miles when the sale closes and panic is taking hold.

As far as we can take it means we get the vibes as low as possible at a target speed. I shoot for 70 mph and try for no vibes. I have no indicator other than perception. It vibes or it doesn't and I don't need anything other than me in the seat to tell that.

You can drive it that far without a front shaft.

 

[freedom_in_4low]

As far as we can take it means we get the vibes as low as possible at a target speed. I shoot for 70 mph and try for no vibes. I have no indicator other than perception. It vibes or it doesn't and I don't need anything other than me in the seat to tell that.

You can drive it that far without a front shaft.

ok, thanks, that's what I was hoping you meant.

I know I can drive it that far without a front shaft, I just want to at least have the rear tuned out before I make the drive so I don't have spend $1400 on new tires first or stay below 60mph the entire way.

How far do you adjust the angle at a time to get there in a reasonable number of adjustment cycles without skipping over it? Can you go a full degree at a time and find it or is the window smaller than that?

It drives me nuts that my TJ was vibe-free on the first try and this one is giving me so much trouble. It makes me second guess my build plan because now I don't really want to do a tuck and have to find the magic pinion angle again.

 

[Nutro]

ok, thanks, that's what I was hoping you meant.

I know I can drive it that far without a front shaft, I just want to at least have the rear tuned out before I make the drive so I don't have spend $1400 on new tires first or stay below 60mph the entire way.

How far do you adjust the angle at a time to get there in a reasonable number of adjustment cycles without skipping over it? Can you go a full degree at a time and find it or is the window smaller than that?

It drives me nuts that my TJ was vibe-free on the first try and this one is giving me so much trouble. It makes me second guess my build plan because now I don't really want to do a tuck and have to find the magic pinion angle again.

Did you ever figure this out? I'm dealing with it now on a 4" lift on an 04 LJ with 4.88 gear 32.7" tires and new front and rear driveshafts, SYE, double adjustable rear upper arms and aftermarket fixed lower arms and a Barnes bolt on skid. I also installed a new trans mount and it vibrated horribly so I bought an Anchor brand and it is rubber and much better.

I had BAD vibes at 60MPH so I removed the front shaft and it drastically reduced it. I took it for a drive and it still vibes at 60MPH. I am sending that front shaft back to the manufacturer. The best I can get on angles is 13.7 on the shaft and 14.7 on the pinion. I installed 2 washers totaling about 1/4" between the frame and skid plate. When I did that, I had 13.2 on shaft and 14.9 on pinion. I cannot rotate the pinion up any further than this point as the lower rear coil bucket binds on my rear shocks and prevents them from cycling.

 

[freedom_in_4low]

Did you ever figure this out? I'm dealing with it now on a 4" lift on an 04 LJ with 4.88 gear 32.7" tires and new front and rear driveshafts, SYE, double adjustable rear upper arms and aftermarket fixed lower arms and a Barnes bolt on skid. I also installed a new trans mount and it vibrated horribly so I bought an Anchor brand and it is rubber and much better.

I had BAD vibes at 60MPH so I removed the front shaft and it drastically reduced it. I took it for a drive and it still vibes at 60MPH. I am sending that front shaft back to the manufacturer. The best I can get on angles is 13.7 on the shaft and 14.7 on the pinion. I installed 2 washers totaling about 1/4" between the frame and skid plate. When I did that, I had 13.2 on shaft and 14.9 on pinion. I cannot rotate the pinion up any further than this point as the lower rear coil bucket binds on my rear shocks and prevents them from cycling.

Not really. I went to 35s which moved the speed where it started up into a range that's somewhat tolerable. Mine aren't particularly strong or violent, and if I hadn't heard and felt them with the hard top to know what to look for, I'm not even sure I'd have noticed with the soft top and windows out. I would still notice them with the soft top all buttoned up though, and even if I can't hear them, I can feel them in the floor.

What is strange to me is that for a while they didn't seem to come on until a our 74, and now I'm picking them up closer to 70-71.

I need to pull the front shaft again and see what they're like with just the rear since my last round of adjustments.

 

[LONGJP2]

The best I can get on angles is 13.7 on the shaft and 14.7 on the pinion. I installed 2 washers totaling about 1/4" between the frame and skid plate. When I did that, I had 13.2 on shaft and 14.9 on pinion. I cannot rotate the pinion up any further than this point as the lower rear coil bucket binds on my rear shocks and prevents them from cycling.

Before you go any higher with the pinion; did you start with them lined up (equal angles)?
Or better yet; pinion down 1° from driveshaft?
If you're only adjusting the upper, don't forget to check for diff./ gas tank clearance.

Also, cutting the back of the lower bucket off is not uncommon.