Best way to correct rear pinion angle-adjustable LCAs or UCA's?

[Razorbackcruiser]

I've got a $100 gift certificate from Metal Tech that needs to be used before the end of the year. Been thinking about correcting my rear pinion angle (4" Iron Man Springs with 1" puck spacer) and was wondering what's the best way to do that? Adjustable uppers or lowers? I like the thought of beefing up my lowers but honestly I'm just an overlander and don't see much rock crawling. I could get the uppers cheaper so there's that. Just wonder if there is a consensus about which way is better? Just for kicks here's my rig.

 

[nukegoat]

I'd still go with the lowers even if you don't venture into the rocks.

 

[lcwizard]

Lowers take all the hits. I wouldn't want the lowers to be adjustable. That just adds a weak point . Also the lowers are the link that centers the axle in the wheel well . Toyota's lowers are exactly right. Throw on a set of 37's and you'll see the lower link are just right. The wheel stuffs up into the well
perfectly. Shortening or lengthening them might compromise that. If you replace the lowers do it for the right reason...stronger tubes. Use the uppers for
pinion adjustment. I doubt you'll ever drag those on rocks

 

[Wrench]

Uppers adjust pinion angle. Lowers locate the axle in the wheel wells.

 

[nukegoat]

Also the lowers are the link that centers the axle in the wheel well . Toyota's lowers are exactly right.

Uppers adjust pinion angle. Lowers locate the axle in the wheel wells.

Really? No offense, but both of you guys are wrong here...

The uppers and lowers collectively locate the axle in the wheel well and the only way that link length would have no bearing on the pinion angle would be if it were located at the centerline of the axle housing.

To the original poster - you can extend the lowers to rotate the pinion down and adjustable links aren't going to be weaker than the factory hollow twigs you currently have. If you want to just get a set of adjustable uppers, that's fine too, but I'd be concerned about bending a LCA down the road.

 

[Razorbackcruiser]

Please correct me if I'm wrong but I thought by lengthening your LCA's and leaving the uppers stock then it would rotate the axle back to it's original orientation. Granted the axle will sit farther back in the wheel wells but the pinion angle should be back to stock. Or am I wrong?

 

[nukegoat]

Please correct me if I'm wrong but I thought by lengthening your LCA's and leaving the uppers stock then it would rotate the axle back to it's original orientation. Granted the axle will sit farther back in the wheel wells but the pinion angle should be back to stock. Or am I wrong?

You are right

 

[Razorbackcruiser]

Really? No offense, but both of you guys are wrong here...

The uppers and lowers collectively locate the axle in the wheel well and the only way that link length would have no bearing on the pinion angle would be if it were located at the centerline of the axle housing.

To the original poster - you can extend the lowers to rotate the pinion down and adjustable links aren't going to be weaker than the factory hollow twigs you currently have. If you want to just get a set of adjustable uppers, that's fine too, but I'd be concerned about bending a LCA down the road.

Understood. Good point.

 

[nukegoat]

For what it's worth, I was cheap and just sleeved mine with a much thicker tube. It's a very inexpensive route if you can weld.

 

[landtank]

It's a smaller move to align the pinion angle by lengthening the lowers if you want to retain the stock shaft.

If you are going for a DC shaft then lengthen the uppers.

 

[Wrench]

Really? No offense, but both of you guys are wrong here...

Oh really? This is what Slee says:
"The rear upper control arms forms part of the rear 4 link suspension. When the rear suspension is lifted, the axle will rotate backwards thus forcing the differential pinion to point upwards. The result is that the pinion angle of the rear differential and the flange on the transfer case are not parallel anymore. This can introduce vibrations in the drive shaft. By making the upper rear control arms adjustable, one can rotate the pinion angle down and correct the angles, thus eliminate vibrations."
You doubt me but what about Slee?

 

[nukegoat]

Oh really? This is what Slee says:
"The rear upper control arms forms part of the rear 4 link suspension. When the rear suspension is lifted, the axle will rotate backwards thus forcing the differential pinion to point upwards. The result is that the pinion angle of the rear differential and the flange on the transfer case are not parallel anymore. This can introduce vibrations in the drive shaft. By making the upper rear control arms adjustable, one can rotate the pinion angle down and correct the angles, thus eliminate vibrations."
You doubt me but what about Slee?

He's not saying that the LCAs don't affect pinion angle.

 

[Wrench]

Please correct me if I'm wrong but I thought by lengthening your LCA's and leaving the uppers stock then it would rotate the axle back to it's original orientation. Granted the axle will sit farther back in the wheel wells but the pinion angle should be back to stock. Or am I wrong?

But one thing you have to remember is when the axle compresses it swings backwards. So now you are into the rear fender well.

 

[Wrench]

He's not saying that the LCAs don't affect pinion angle.

Yeah but he is selling adjustable uppers. If adjustable lowers were so great wouldn't he be selling them?

 

[Wrench]

There has to be many drawbacks to adjustable lowers vs adjustable uppers.

 

[Razorbackcruiser]

It's a smaller move to align the pinion angle by lengthening the lowers if you want to retain the stock shaft.

If you are going for a DC shaft then lengthen the uppers.

Man! Now I'm really confused! I thought you would shorten the uppers to rotate the axle down and correct the angle?!? And I've never heard of needing a rear DC shaft for this?!? Maybe I'll just leave it alone.....

 

[landtank]

the rear pinion angle is in between the two shafts. So some will raise the pinion to run a dc shaft while others will lower the pinion to run a stock shaft.

I'm of the opinion that which ever shaft you choose adjust the pinion by means which displaces the axle in the wheel well by the least.

i prefer to lengthen and strenthen the lower to kill two birds with one stone so to speak and save some cash at the same time.

 

[nukegoat]

But one thing you have to remember is when the axle compresses it swings backwards. So now you are into the rear fender well.

For 99% of people, the additional 1/4" - 3/8" length on the lower isn't going to make the tires rub. If it does, shortening the upper even more significantly is going to have the same problem in the front fender well... I don't think the thread starter is on the ragged edge of packaging. If he is, lengthening the lowers around 3/16" and getting adjustable uppers should keep everything centered.

I run 345 KM2s and I lengthened my lowers without running into issues.

Yeah but he is selling adjustable uppers. If adjustable lowers were so great wouldn't he be selling them?

That's a poor line of reasoning and I doubt Christo would argue that adjustable lowers don't affect pinion angle.

There has to be many drawbacks to adjustable lowers vs adjustable uppers.

The burden of proof is on you. Tons of racers, suspension companies, garage fabbers, and mall crawlers have adjustable lowers.

 

[nukegoat]

Man! Now I'm really confused! I thought you would shorten the uppers to rotate the axle down and correct the angle?!? And I've never heard of needing a rear DC shaft for this?!? Maybe I'll just leave it alone.....

Take the time to correct the pinion angle. You can get away with a single cardan OE shaft if you are precise.

Rick was just saying that if you were adjusting your links to support a DC shaft (some prefer them for a variety of other reasons) then you'd probably be better off tweaking the uppers.

 

[Corbet]

For what it's worth I'm very happy with Rick's extended lowers. (Not adjustable) I trashed a few OEM lowers and for me it solved two issues at once. My stock driveshaft is happy. But I'm only at 3" of lift for the record.