Pinion slope

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Joined
Sep 22, 2013
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Location
Portland, Oregon
I have a '99 LX470 with 215K miles where I've converted the hydraulic ride system using a Strutmasters conversion kit. Did this conversion in the fall of 2014 (very improved ride). Most all my driving is highway with an occasional pulling my utility trailer or trailered drift boat.

This last year or so, I've been getting a "drone" vibration around 55 mph and up when the truck is under load (accelerating or up-hill). Goes away when I let off on the accelerator. Recently purchased new Michelin tires and the vibration still exists. I'm ruling out a tire imbalance or "out-of-round" because the vibrations are higher frequencies.

I've taken my rig to a couple of different Lexus dealers. Drove with a tech for 30 minutes one day demonstrating the vibration. One dealer wanted to R&R front axles, the other dealer, who's tech rode with me, thought it could be a worn pinion gear.

I've been doing research on this issue and have been reading about the relationship of drive shaft angles and/or transfer case output slope to pinion slope. I was thinking (dangerous, I know) since I've converted the suspension, maybe pinion slope might be my problem. Here's what I've measured - truck on the ground, TC (rear) output flange at 89.3 deg and pinion flange at 89.5. I'm thinking my pinion angle should be tilted down a bit more resulting in the (rear) pinion flange at approximately 87.3 degrees so the rear pinion can rotate up during "cruise throttle".

I've heard about guys removing a shaft, locking the transfer case and checking for vibrations. Can you safely test drive the vehicle (55 to 65 mph) with just one drive shaft?

Any comments or suggestions would be greatly appreciated..
 
The flanges need to be parallel with at least .5 degree variance up to 1.0 degrees.

Start here, scroll down to the pictures of the driveline angles: Pinion & U-Joint Angles

Good discussion here: Rear Pinion Angle
 
What about "wrap up" of approximately 2 deg on acceleration and "Cruise throttle". I remeasured my angle again, TC output 0.1 deg down, prop shaft 2.4 deg down and pinion 0.5 down (according to taking measurements outlined in the posts I've read above).
 
Good question. I talked with Tom Woods about this as I had similar questions. He said little to no wrap up on our 4 link suspension. Certainly not enough to account for.

Maybe if all the bushes in the stock arms are toast there could be some pinion movement but still very little.

Axle Wrap up is primarily attributed to leaf spring suspensions.
 
You can safely drive with one drive shaft. Broke front diff and drove from Moab to Grand Junction at 60mph with just rear driveshaft.
 
Sounds like pinion bearing to me. One way to check is yo crawl under the truck and check how much play the driveshafts have (up, down and side to side), also check for how much play you have turning the shaft clockwise and counter clockwise.
 
You can safely drive with one drive shaft. Broke front diff and drove from Moab to Grand Junction at 60mph with just rear driveshaft.

Hey thanks Skidoo.. I had read where folks are driving with only one shaft. Will remove my rear shaft and see how this affects my vibrations. Am trying to figure out where the vibrations are coming from by the process of elimination (front or rear).
 
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Sounds like pinion bearing to me. One way to check is yo crawl under the truck and check how much play the driveshafts have (up, down and side to side), also check for how much play you have turning the shaft clockwise and counter clockwise.

I definitely have play in the shaft. Doesn't seem to be an U-joint issue, but I do have play rotating the shaft. Am going to pull the rear shaft, drive and see if I can tell some difference. With the shaft removed, will check for play on both the output shaft of the transfer case and rear dif pinion.

Haven't explored what's involved with R&R of parts/bearing in a differential. I'm sure folks have it done. Wonder what the longevity might be once you rebuild one of these..
 
Sounds like pinion bearing to me. One way to check is yo crawl under the truck and check how much play the driveshafts have (up, down and side to side), also check for how much play you have turning the shaft clockwise and counter clockwise.

Crawled under again today in an attempt to remove the rear prop shaft. I noticed a very small bit of play in the prop shaft where the spine enters the prop shaft receiver. Has this ever been an issue for anyone? Is this normal? It's very small, but I don't know if it's a contributor. The vehicle has been in for regular service, so I don't know if anyone has greased it lately. Plus I've heard you have to be careful and not over grease this area, otherwise it won't compress properly producing adverse affects on the drive shaft components.

Here's my other problem. I tried to loosen the nuts on the pinion flange. They are T I G H T and wouldn't budge. I'm soaking them with PB Blaster, but have no idea if this will help. An extender out of pipe? I see you can buy an extra long 14mm x 17mm oil plug wrench that's 16 in long. Maybe a torque wrench adapter and breaker bar (will need to acquire one to retorque nuts)? Any suggestions?
 
Good question. I talked with Tom Woods about this as I had similar questions. He said little to no wrap up on our 4 link suspension. Certainly not enough to account for.

Maybe if all the bushes in the stock arms are toast there could be some pinion movement but still very little.

Axle Wrap up is primarily attributed to leaf spring suspensions.

Lets say, based on my readings (TC 0.1 deg down & pinion 0.5 deg down), if the diff rotates 1 deg upon "cruise throttle" , it will put the planar difference between the transfer case flange and the pinion flange at approx. 1.4 deg. Think that's acceptable? (I've got a feeling I'm over thinking this too much..)
 
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Extender with pipe or impact wrench. Most likely those have Loctite on them so a bit of heat (torch) will break down the Loctite.
 
Haven't explored what's involved with R&R of parts/bearing in a differential. I'm sure folks have it done. Wonder what the longevity might be once you rebuild one of these..

Check out the below link if you want to do anything to a diff. Do not mess with the large nut in middle of pinion flange, unless you are prepared to rebuild the diff.
Gear Install Harrop
 
Lets say, based on my readings (TC 0.1 deg down & pinion 0.5 deg down), if the diff rotates 1 deg upon "cruise throttle" , it will put the planar difference between the transfer case flange and the pinion flange at approx. 1.4 deg. Think that's acceptable? (I've got a feeling I'm over thinking this too much..)

Maybe Im not following your explanation of the rear diff flange direction but if the TC flange is pointing DOWN then the diff flange should be pointing UP. In simple terms if you are 1 degree down the at TC flange then the diff flange should be pointing up 1 degree to be parallel to each other.

/——-/ not /——\
 
Maybe Im not following your explanation of the rear diff flange direction but if the TC flange is pointing DOWN then the diff flange should be pointing UP. In simple terms if you are 1 degree down the at TC flange then the diff flange should be pointing up 1 degree to be parallel to each other.

/——-/ not /——\

To make things a little more clear. My TC flange vs pinion flange is (0.1 deg) /-----/ (0.5 deg)

Yes, I understand the concept, just don't understand the terminology. Here's why.. I read this article (several times).

Pirate4x4.Com - Extreme Four Wheel Drive

I kept getting hung up on the article's definition of "Axle Pinion" slope. (I would have assumed the pinion flange slope was "UP", since it was facing in the upward direction) But based on the statement below, I called it a "DOWN" slope. BTW, your simple illustration was rather ingenious.

Remember that the slope is "down" if it is higher towards the center of the vehicle, and lower at the end of the vehicle.

For now, I've got to tool up a 14mm box end with and extension to get those flange nuts off. Remove the rear prop shaft and see if the vibration goes away running with just front wheel drive. I might have issues in the rear diff that's causing the problem. It could be something in the prop shaft itself. I have a little play in the spline and spline receiver area (very little, but it's there). Will most likely replace u-joints and check balance once I get the shaft removed.

She's an old truck, but a great truck. Hate to give up on her.
 
Check out the below link if you want to do anything to a diff. Do not mess with the large nut in middle of pinion flange, unless you are prepared to rebuild the diff.
Gear Install Harrop

Thanks for the link. Good info.. (The guy is very thorough with all the pictures.) If it come to a problem with my rear diff, I won't be messing with anything other than R&R of the diff assembly.
 
Rear driver shaft is off. Here's a dumb question.. Are the U-joints on my shaft replaceable? If so, do you go with aftermarket U-joints (recommended to me by "Drive Line Service" of Portland) or OEM? Thanks..
 
U-joints are replaceable, the tricky part is the clip rings come in different thicknesses, and the u-joint only comes with one set.
You want to choose the right set of clip rings so u-joint is centered and minimum play so it does not shift around.
A lot of folks overlook the different clip ring thickness and then have vibration after replacing the u-joints.
I don't know if aftermarket vendors have the different thickness clip rings.
 
go with the factory u-joint, it will come with three sets of snap rings of different thicknesses for installing the u-joint. your probably going to need the copper color snap rings, thats the common size
 
go with the factory u-joint, it will come with three sets of snap rings of different thicknesses for installing the u-joint. your probably going to need the copper color snap rings, thats the common size

Got it. Took my shaft in to have it inspected and balanced. Haven't picked it up yet. The U-joints look tight, but the rebuilder and I both agreed that OEM kits with the selection of circlips are the way to go.

Kinda pointing to problem with the diff.
 

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