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Front wheels spin... help understanding the 4wd system


Mattmill91
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So couple weeks back was out playing after doing some shooting in the woods of centeral Oregon..

 

 

With the girl friend driving I noticed this. When going from stop to slow drive up hill. The fronts wheels spun but the rear didn’t.

 

 

 

It appears the torque travels like water and takes the path of least resistance..

 

I believe it was in 4low..

 

What’s going on here and is there any way to correct it.. or is it just the nature of the system due to not having any lockers and not really being a hard core 4wd.

 

Thanks just looking some knowledge!

 

 

IMG_4756.jpg

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In 4Lo the power should be split evenly between the front and rear axles, although I supposed it's possible if you have the AUTO mode transfer case the clutch packs inside could be toast.  Are you sure the rear wheel on the other side from where she was standing wasn't spinning?  Because the rear diff isn't locked and that's exactly what should happen when struggling; one wheel up front and one wheel out back turning.

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Judging by the angle of the pic and wheel well gap front vs. rear, that seems normal operation to me.  The hill seems more gradual on the passenger side, so it shifted the truck's weight over to the driver's side, mostly towards the rear.  The passenger rear tire would have the least amount of traction, and a rear open diff would allow that tire to spin freely.  Since both front tires would have traction, they would also spin.

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I agree with the above posters, I think you've just cross-axled it and are getting diagonal wheelspin. I would be very surprised if there were only one wheel spinning, as there is no way of getting power to only 1 front wheel in any of these vehicles, being primarily rear-wheel drive.

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+1 to what the others have said. Sounds like the rear wheel on the other side was spinning.

 

When you're in 4x, the front and rear driveshafts spin at the same rate. There's no differential in the transfer case to bias torque front or rear, so the front and rear diffs turn at the exact same rate. Each diff applies the same torque to both wheels on its axle--but if one wheel doesn't have enough traction, it spins and the other doesn't (the torque it takes to spin the wheel without traction is not enough to spin the wheel that does have traction and is trying to move the truck). If the truck is on uneven ground, it'll have less force on two wheels diagonal from each other (think of a four-legged bar stool on an uneven floor). If the suspension can't keep the wheels in good contact with the ground, those two unloaded wheels spin while the truck goes nowhere. Look where your tires are in your wheel wells, your driver's front is drooped way down (unloaded) and your driver's rear is stuffed into the wheel well. The passenger's front and driver's rear were supporting most of the truck's weight, so the other two had bugger-all traction and the truck wouldn't climb.


If you don't have one already, you might try and track down a limited slip rear end (identified by an orange sticker next to the fill port that says LSD OIL ONLY). I like the limited slip in my '93, though it does have its limitations. IIRC the R50 LSD was toned down a little (probably because LSD makes it easier to make the rear end step out if you drive like a maniac. The LSD can be repacked to tighten it up. It's not as good as a locker but it's much better than an open diff IMO.

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11 hours ago, KiwiTerrano said:

...I think you've just cross-axled it and are getting diagonal wheelspin...

 

9 hours ago, Slartibartfast said:

...think of a four-legged bar stool on an uneven floor...

 

Excellent description and analogy.  I totally agree with Slart about the LSD.  Even a weak LSD is going to be better than an open diff. 

 

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It is a 97 se. And has a LSD in the rear.. with a manual tranny and manual hubs up front. I didn’t check the other side.



LSD has been making some odd engagement sounds when going from stop to hard turns..


I have been stuck on a snow bank before with only the front left and back right spinning..



Thanks everyone y’all rock!!

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After closer inspection of the video it does appear that right rear is spinning... much like every one has described.. evidence being some dirt being tossed back from that tire..

So everything should be ok functionally.

But it seems like a pretty lame system... tightening up the lsd.. appears to be some work. Think I have read somthing about adding shins to the clutch pack.


So the rear end clutch pack is just allowing the tractionless wheel to spin while the weighted one doesn’t? If I am following correctly.


IMG_4765.jpg

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1 hour ago, Mattmill91 said:

LSD has been making some odd engagement sounds when going from stop to hard turns..

 

1 hour ago, Mattmill91 said:

But it seems like a pretty lame system... tightening up the lsd.. appears to be some work. Think I have read somthing about adding shins to the clutch pack.
So the rear end clutch pack is just allowing the tractionless wheel to spin while the weighted one doesn’t? If I am following correctly.

 

I'm curious about the noise.  The LSD doesn't quite "engage" per se...whether straight-ahead or turning, the clutch pack is always under compression, but there is a change from no-friction to friction when making turns.  Because there are also spider gears in the diff, any engagement sounds are might be attributed to those, and not so much the clutch pack (i.e., the "limited slip" part of LSD).

 

I assembled this chart from FSM data when I repacked some LSDs a while ago:

 

LSDConfigs.jpg

 

Pretty clear the R50 never got what other trucks got, and then Nissan dumbed everything down 03-04.

 

Re-packing does require some work...and homework.  Not so much adding shims but just increasing the friction for the clutch packs.  This can be done by thickening the stack (replacing thinner pieces with thicker ones, or shims), by replacing pieces of one type with another, particularly in the case where similar parts are next to each other.  For example, on 01-02 R50, a 2:9 ratio means that, those 2 friction discs are only in contact with 3 friction plates, at max, and the rest are just used for spacing (FP-FD-FP-FD-FP-FP-FP-FP-FP-FP-FP); all of the breakaway torque comes from the friction on those 10 pieces (5 per side).  The 5:6 models had more than double the friction area, and consequently higher breakaway torques.  However, you'd expect the 6:6 to have higher numbers, too, but the breakaway torque is also controlled by the nominal thickness of the pieces, plus any compression added by spring plates.  That is to say the R50 LSDs used more thinner pieces, which would reduce stack compression and ultimately friction.

 

In your real-world scenario, if you have an LSD and the tire is still spinning, that means the ground resistance on the tire that has traction is higher than the breakaway torque of the LSD.  In that case, it behaves like an open diff because it's defeating the clutch pack and the spider gears (the "differential" of LSD) are allowing the excess torque to rotate the wheel with less traction.

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7 hours ago, Mattmill91 said:


So the rear end clutch pack is just allowing the tractionless wheel to spin while the weighted one doesn’t? If I am following correctly.
 

 

You've got it. The clutch pack can only hold so much before it slips. The breakaway numbers in Hawairish's table above are how much torque the diff is supposed to hold when bench-tested (one axle held, torque wrench on the other). That number may improve a little under load as the spider gears push out against the clutches, but if you've got a wheel off the ground, you probably won't have enough load to make a difference. Apparently you can use the parking brake to add load and make the clutches grab a little better if you're struggling.
 

I knew the later models were de-tuned, but I didn't realize it was that bad! '03-'04 got screwed! I'm guessing the limited slip didn't play nice with stability control.


I've heard of the LSD making chattering noises if it was refilled with the wrong fluid. It's supposed to run oil with a friction modifier to keep the clutches happy (that's why it says LSD oil only on the sticker). Without that, the clutches bind up, make noise, and have a bad time in general. The only noise I've noted from my rear end was a faint hiss that I thought might be the sound of the clutches slipping, but I'm not certain it wasn't just the wheels slipping in the snow that I was stuck in at the time.

If you're looking for an easy swap to a better LSD, the early Xterra rear third member is supposed to bolt right in. CJ Franger on the NPORA facebook page (probably on here as well, not sure what his screen name is) put one in his R50 a while ago. Because it's a 3rd member style rear end, it's completely bolt-on without having to mess with gear lash or clutches, and it looks like it gives you more than double the breakaway torque of what you've got.

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16 hours ago, Slartibartfast said:

You've got it. The clutch pack can only hold so much before it slips. The breakaway numbers in Hawairish's table above are how much torque the diff is supposed to hold when bench-tested (one axle held, torque wrench on the other). That number may improve a little under load as the spider gears push out against the clutches, but if you've got a wheel off the ground, you probably won't have enough load to make a difference. Apparently you can use the parking brake to add load and make the clutches grab a little better if you're struggling.
 

I knew the later models were de-tuned, but I didn't realize it was that bad! '03-'04 got screwed! I'm guessing the limited slip didn't play nice with stability control.


I've heard of the LSD making chattering noises if it was refilled with the wrong fluid. It's supposed to run oil with a friction modifier to keep the clutches happy (that's why it says LSD oil only on the sticker). Without that, the clutches bind up, make noise, and have a bad time in general. The only noise I've noted from my rear end was a faint hiss that I thought might be the sound of the clutches slipping, but I'm not certain it wasn't just the wheels slipping in the snow that I was stuck in at the time.

If you're looking for an easy swap to a better LSD, the early Xterra rear third member is supposed to bolt right in. CJ Franger on the NPORA facebook page (probably on here as well, not sure what his screen name is) put one in his R50 a while ago. Because it's a 3rd member style rear end, it's completely bolt-on without having to mess with gear lash or clutches, and it looks like it gives you more than double the breakaway torque of what you've got.

 

All great points!  Yes, those numbers are bench-test specs, and the value can increase under load due to the spider gear push-out.

 

Yeah, I don't get why the numbers were so diluted for the 03-04.  Stability controls would be a good guess, but I'm not even sure many of the vehicle had anything beyond ABS.  Of the R50s I've seen with VDC (literally one), it didn't even have the LSD.  I think Nissan just got a good deal on those spacers in the units, which consumed the space of 4 pieces in the clutch pack, and still allowed them to market the option.

 

Good point about the fluid.  Yes, an additive or LSD-safe gear oil is required.

 

Just realizing I omitted specs from the 99-00.5 Frontier for some reason.  MY99-00.0 trucks were 144-178 ft-lbs, then 00.5 went to 138-180 ft-lbs.  But yes, both 00.5-02 Frontier and 00-02 Xterra LSD diffs make great swap options because they had the better numbers and because they used the same gear ratios, specifically 4.363 (48:11) and 4.636 (51:11) options, not the 4.375 (35:8) and 4.625 (67:8) options found on older Nissans.  You can swap the entire 3rd member; completely bolt on.

 

I've actually been sitting on my re-packed LSD for a while now, and re-acquired the other re-packed unit just the other week.  Both eventually replaced by lockers, but I really enjoyed having it.  Lokka + LSD made for a great combo.  I suppose it's time to find those units new homes...

Edited by hawairish
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9 hours ago, hawairish said:

Yeah, I don't get why the numbers were so diluted for the 03-04.  Stability controls would be a good guess, but I'm not even sure many of the vehicle had anything beyond ABS.  Of the R50s I've seen with VDC (literally one), it didn't even have the LSD.

 

You're obviously referring to my JDM beauty. I guess now we really have to drop in the lsd. 

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1 hour ago, Astrorami said:

 

You're obviously referring to my JDM beauty. I guess now we really have to drop in the lsd. 

 

Haha, you know it. Yours is also the only one with TPMS. I’m just jelly. 

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On 1/10/2019 at 6:21 AM, Mattmill91 said:

It is a 97 se. And has a LSD in the rear.. with a manual tranny and manual hubs up front. I didn’t check the other side.



LSD has been making some odd engagement sounds when going from stop to hard turns..


I have been stuck on a snow bank before with only the front left and back right spinning..



Thanks everyone y’all rock!!

Yeah, the R50 LSD is good, but if there's no weight on one rear wheel or it's on an exceptionally slippery surface then it won't work as the breakaway torque is lower than that needed to push the vehicle forward.

The LSD in my R50 makes some pretty bad clunks & other noises sometimes. I've given up worrying as it hasn't got any worse in the 25,000 km I've owned it. I figure it's the differential as I've replaced every single bush in the rear end, the shocks, and have no sway bar.

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On 1/10/2019 at 6:28 AM, Mattmill91 said:

After closer inspection of the video it does appear that right rear is spinning... much like every one has described.. evidence being some dirt being tossed back from that tire..

So everything should be ok functionally.

But it seems like a pretty lame system... tightening up the lsd.. appears to be some work. Think I have read somthing about adding shins to the clutch pack.


So the rear end clutch pack is just allowing the tractionless wheel to spin while the weighted one doesn’t? If I am following correctly.


IMG_4765.jpg

Don't feel too disheartened - the LSD is way better than no LSD. One of my mates has a Terrano exactly like mine with no LSD and I can outwheel his with ease. It makes a lot of difference so long as your rear wheels can both touch the ground - it prevents all the power going to one wheel if it momentarily goes onto looser ground. I'd recommend fitting some longer shocks eg Bilstein or Procomp ES326500, and removing the rear sway bar. Cheaper, easier,much nicer to drive onroad and arguably more effective most of the time than just shimming the LSD up.

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Don't feel too disheartened - the LSD is way better than no LSD. One of my mates has a Terrano exactly like mine with no LSD and I can outwheel his with ease. It makes a lot of difference so long as your rear wheels can both touch the ground - it prevents all the power going to one wheel if it momentarily goes onto looser ground. I'd recommend fitting some longer shocks eg Bilstein or Procomp ES326500, and removing the rear sway bar. Cheaper, easier,much nicer to drive onroad and arguably more effective most of the time than just shimming the LSD up.



Have Considered the sway bar removal? But wasn’t sure how negatively it could affect on road performance..



I don’t have OME springs all around so longer should could take advantage of the height. Think the stock ones I got are basically always topped out..
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Part number for a over length bilstine?


Are the billstine worth it over the pro comp?

Are there a longer kyb options?

Haven’t had any trouble with KYB.


Have replaced damn near everything on the truck



4 springs
4 wheel bearings
Shocks / struts
Rear trailing links
Front control arms
Sway bar links
Sway bAr mount bushin

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Onroad manners are fine without the swaybar. Marginally more prone to understeer but nothing drastic. Removing the front sway bar is what causes dangerous changes in handling. Many vehicles do not have a factory rear sway bar but very few have no front sway bar. 

I'm also running polyurethane bushes front and rear which really helped roadholding too. Not cheap though. 

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