Another Pinion Angle Thread

[Window&DoorWhore]

Hi all, I had my Jeep regeared a couple years ago and I’ve maybe put 2-2500 miles on it since. Chased vibration for a while and ended up doing Yukon spin free hubs and didn’t really drive it much after. That cured it maybe 60%. Found it too late today to do anything about it and still planning on putting 100 highway miles on it tomorrow with a couple hours of trails in between. Been like it is for a long time. I doubt it’ll hurt anything but it will sure be annoying knowing what it is.

Still has a lumpy type vibe off the line and cyclical droning vibration beginning at 55-60 mph and the faster you go the more intense it gets. I have a digital cube angle finder And I have found the rear pinion is higher than being in line with the driveshaft by 3.6 degrees. The gauge is accurate, I set my saw tables and blades with it. I was underneath for something unrelated and could visibly see it was way off, not sure why I never noticed it before. I guess I had a hard time believing someone could go through the trouble of lifting the Jeep, buying adjustable upper and lower control arms all around and not align it or check angles. In fact the place I had regear it said my control arms were on backwards and that the articulating ends need to mount to the axle instead of the frame. I paid them to put them on in the proper orientation.

At any rate I have been reading a lot about adjusting control arms and have read about having the axle in the optimal location. What’s the optimal location? It’s nowhere near the gas tank and my upper control arms appear to be adjustable without removing an end but they’re at the bottom of their adjustment.

How do I know where to place the axle?

Is this performed on the ground with tires bearing weight?

Could the previous owner have been compensating for a driveshaft that is too short?

Is having tires chocked and a bottle jack under the yoke the only thing keeping the jeep from smashing me while performing this fix?

I usually pay to have work done to it since I work too much but I am finding out the hard way that isn’t always the way. It’s out of sight out of mind in the garage. I haven’t driven it much at all in the five years I’ve had it so it’s easy to overlook things. My son is becoming obsessed with off-roading so it will start seeing daylight more frequently.

03 with 4.0 42RLE Dana 44 rear/lp30 front with 5.13 gears

 

[Jerry Bransford]

I dunno without better photos but it looks like your pinion angle could be a tad high which can cause vibrations, especially when starting hard in 1st gear or when accelerating. I'd lengthen both upper control arms a full turn on both sides (or shorten the lower arms) to lower the pinion angle a tad and see if anything changes or gets better. It's hard to know if the driveshaft length is too short or not without knowing how much is engaged at its slip joint. It doesn't really look too short but...

 

[Rickyd]

Set the pinion angle like it shows below for your type of driveshaft.make sure the upper arms have the same amount of tension on them so the relatively weak brackets don't break. Since your uppers are double adjustable I'd loosen them up with the jeep on the ground and evenly adjust to get the pinion pointed at the transfercase output. If hey don'thave enough adjustment then you have to unbolt one end of the lowers and evenly adjust.but the jeeps frame and axle need fully supported for that.

 

[Window&DoorWhore]

Well the more I look the more I find. Pinion angle is small in the realm of things. My shocks appear too long have 3” before being fully compressed while on the ground at rest. Also the bump stops don’t look like they would ever come into play. Will have to start over from scratch.

 

[Andy-WhiteTJ]

Why are there disconnects on the rear sway bar?

 

[mrblaine]

Well the more I look the more I find. Pinion angle is small in the realm of things. My shocks appear too long have 3” before being fully compressed while on the ground at rest. Also the bump stops don’t look like they would ever come into play. Will have to start over from scratch.

In the meantime, you can adjust the pinion angle easily just with the uppers to dial out the vibes or try to. Your rear pinion angle is too high. With those arms, a quarter of a turn is about 1/2 degree of change.

If you want to use the angle finder, start with both at the same angle and then move down in 1/2 degree increments until it gets better or worse and go from there. The vibe at take-off generally tells you that the angle is too high. The cyclical harmonic is going to be the issue to dial out.

After you get the vibes handled, THEN you can pull the springs and center the tires at full stuff and under articulation. Don't worry about the shocks now, they aren't contributing to the vibes much. (Unless the axle is pushed far enough back that it is messing up the shock bodies)

 

[Window&DoorWhore]

Why are there disconnects on the rear sway bar?

Not sure why. Installed by PO probably bought on the same day the shocks were.

In the meantime, you can adjust the pinion angle easily just with the uppers to dial out the vibes or try to. Your rear pinion angle is too high. With those arms, a quarter of a turn is about 1/2 degree of change.

If you want to use the angle finder, start with both at the same angle and then move down in 1/2 degree increments until it gets better or worse and go from there. The vibe at take-off generally tells you that the angle is too high. The cyclical harmonic is going to be the issue to dial out.

After you get the vibes handled, THEN you can pull the springs and center the tires at full stuff and under articulation. Don't worry about the shocks now, they aren't contributing to the vibes much. (Unless the axle is pushed far enough back that it is messing up the shock bodies)

Good point. Pinion is 3.6* high in relation to the driveshaft. Upper control arms are bottomed out on adjustment, will have to lengthen the lowers. Since only one end is adjustable then a half turn=half a degree or close? 6.5 turns to zero.

Hesitant to use it next Friday with the shocks the way they are. This past Friday when climbing down any small ledge with one wheel first it gets like the bumper was hitting an invisible rock, surprised I didn’t break a shock mount. I’ll have to keep it in mind until sorted with new shocks.

It would be nice to have a little better ride since I don’t trailer it, is there any way to identify who the springs are made by and are there many differences among different manufacturers of springs?

If you have any input on a spring and shock combination that works well as an all around on and off road setup I’d like to hear about it.

Thanks,
Patrick

 

[mrblaine]

Not sure why. Installed by PO probably bought on the same day the shocks were.


Good point. Pinion is 3.6* high in relation to the driveshaft. Upper control arms are bottomed out on adjustment, will have to lengthen the lowers. Since only one end is adjustable then a half turn=half a degree or close? 6.5 turns to zero.

Not sure on the lowers since they are closer to the axle centerline and should be 1"-14. If so, 1 full turn is about 1/16" change and I'm not sure what the angle change will be due to them being closer to centerline. I'd run them out at least 3/8" longer and then start messing with the uppers. Again, just to get the vibes dealt with and then once you know you can do it, then mess with getting the rest squared away.

Hesitant to use it next Friday with the shocks the way they are. This past Friday when climbing down any small ledge with one wheel first it gets like the bumper was hitting an invisible rock, surprised I didn’t break a shock mount. I’ll have to keep it in mind until sorted with new shocks.

It would be nice to have a little better ride since I don’t trailer it, is there any way to identify who the springs are made by and are there many differences among different manufacturers of springs?

If you have any input on a spring and shock combination that works well as an all around on and off road setup I’d like to hear about it.

Thanks,
Patrick

 

[Rickyd]

H&r uses blue springs. But it doesn't matter who made them. so long as they are the same length side to side and you're happy with the height you just need to get proper length shocks and bumpstops for the most balanced up and down travel from ride height possible. Start by measuring the springs,12" and 8" is stock

 

[Window&DoorWhore]

Not sure on the lowers since they are closer to the axle centerline and should be 1"-14. If so, 1 full turn is about 1/16" change and I'm not sure what the angle change will be due to them being closer to centerline. I'd run them out at least 3/8" longer and then start messing with the uppers. Again, just to get the vibes dealt with and then once you know you can do it, then mess with getting the rest squared away.

I did as instructed. Rear pinion is 1* low in relation to the shaft. Vibes off the line are gone but we’re still present at highway speeds. I knew it wasn’t tires because same tires only a few miles different from when I had it regeared.

Pulled rear shaft and went for a cruise on the freeway, vibes 90% gone! I can definitely hear more hardware turning up front since I’m usually driving with hubs unlocked and I wouldn’t say it’s vibe free with the front shaft in play but I could run it up to 70-75 without the console vibrating my elbow.

Called wood’s shop to pick their brain on measurements and got some decent info except he wasn’t going to tell me if there were a sweet spot for axle placement. It doesn’t hit the gas tank and I don’t think I’ll have an issue adding bump stops and making them make contact. He said there’s a half inch forgiveness either way.

Does anyone recommend a certain distance or being within a certain control arm adjustment parameter for placement of the rear axle? I might be overthinking but it’s not often I’m ordering a driveshaft.

I’m inclined to run the old front shaft as is since it’s seldom used and almost always under single digit mph, anyone know how to measure how much spline engagement I have on the front shaft by looking at or peeling back the rubber boot?

Thanks,
Patrick