I've had my 97 LX450 for a little over a year now, and like many with lifted 80's, there's been an issue with driveline vibrations at highway speeds. It's not really a case of vibes on deceleration. The vibes start at 2800 RPM's and get worse as RPM's increase. The vibes get particularly bad above 3000 RPM's and I will feel the entire driveline surging or pulsing. This happens most often when I turn off Overdrive and/or shift down into 2nd gear to climb a hill at highways speeds. If I let the surging/pulsing go on too long, it actually triggers a CEL for random multiple cylinder misfires. I never get that code any other time. It only happens when I let the vibes get out of control while climbing a hill - which, unfortunately, I have to do fairly often.
The truck had 247K miles on it when I bought it, and it was lifted pretty high with OME J-springs F&R, Doetsch-Tech 12.5" long travel shocks, and coil spacers (at least 40mm, maybe even 50mm). The PO had installed Man-a-Fre 4" radius arm drop brackets, adjustable upper rear control arms, extended bumpstops, sway bar drop brackets, adjustable panhard rods, etc.
I did not want that much lift, so the first thing I did was remove the coil spacers, but it still had vibes.
Not long after that, I broke one of the Doetsch-Tech shocks on a trail run, so I took that as an opportunity to replace the entire suspension with a 2.5" Dobinsons VT/MRA kit. The stock rear lower control arms were also both bent, so I replaced those with Dobinsons lower control arms, and replaced the "yellow eBay" adjustable panhard rods with Dobinsons adjustable panhard rods (F&R). All new suspension bushings were installed at that time as well.
Here's the current setup with about 256K miles on the truck as it sits today.
Shocks and Springs: Dobinsons C97 146/147 2.5" Tapered Springs with MRA long-travel shocks.
Coil Spacers: 1" DVS coil spacer on the front to level the truck.
Caster Correction: Man-a-Fre Drop brackets for a 4" lift. Dobinson's caster-correction bushings are installed in stock radius arms.
Rear Control Arms: Adjustable upper control arms and Dobinsons adjustible rear lower control arms.
Panhard Rods/Bracket: Dobinsons Panhard rods (F&R). DVS 3" Rear Panhard Lift Bracket. (note: Panhard rod is still not flat)
Driveshafts: Double-Cardan Front and Rear with Spicer-style joints. Front DS is installed "in-phase" with slip yoke on the differential/axle end. Rear DS is installed "in-phase" with slip yoke on the differential/axle end.
Differential/TC Gearing: 4.88's in diffs. Rear was rebuilt approx 5K miles ago. Front probably has 30K+ miles. Stock transfer case gearing.
Axles: Longfield Chromoly shafts in the front. Still Full-Time AWD. (note: wear on front shafts looked OK when front knuckles were rebuilt 5K ago). Stock shafts in the rear.
Bushings: I have replaced all suspension bushings - front and rear.
Wheels/Tires: SCS F5 17 X 8.5 -10mm offset, Kenda Klever RT 35 X 12.5 X 17 - mounted and balanced 8K ago.
Other:
Here's a rundown of the steps I've taken so far to resolve the vibrations:
Caster Measurement (by digital angle finder) is estimated to be about 4 degrees. I realize that this is not an accurate way to get a caster reading. I need to find a reputable place in SoCal to get a real alignment done. But it's pretty clear just from looking at pinion angles that I have a fair amount of caster correction going on. That's to be expected given that I have both 4" radius arm drop brackets and caster-correction bushings. The truck drives as straight as an arrow, and the steering is not heavy at all, so I'm hesitant to undo any of the caster correction if I don't have to.
To isolate the source of the vibrations, the Front Driveshaft was removed - Driveline vibrations still present. When the Rear driveshaft removed - Driveline vibrations went away.
Rear pinion bearing was found to be damaged, and was replaced about 3,000 miles ago. Still had same level of driveline vibrations after replacing the pinion bearing.
Recently, both driveshafts were sent out to a local driveline specialist for inspection, and it was discovered that one joint in the rear driveshaft was badly damaged.
All new joints were installed in the rear driveshaft, and both shafts were rebalanced.
Though it appears the problem is likely with the rear driveshaft, I'll just mention that the front driveline angles are clearly off. There's about a 5-6 degree difference in the angle of the front pinion flange and the transfer case output. At one point, I did try reinstalling the stock (non-double cardan) driveshaft up front, but it had no improvement, so the DC driveshaft has been reinstalled up front. (Note: I'm aware that from the factory, the front driveshaft is supposed to be installed "out of phase", and mine is "in-phase". For what it's worth, I've been told that for my lift, it's better to run the front driveshaft in-phase. Let me know if you agree with that.)
As far as the rear driveshaft goes, pinion angles in the vertical plane look perfect, but there appears to be a pretty noticeable lateral angle to the rear driveshaft. I understand that some lateral angle of the driveshaft is normal, but in my case, it looks like it could be more extreme with the rear axle centered at ride height. Adjustments were made to shift the axle over a bit to the passenger side, which reduced the lateral misalignment of the rear driveshaft. We had to shift the axle over quite a bit (3/4"+) to the passenger side in order to get the lateral angle straighter. This did the result in a reduction of vibrations, but now the axle is noticeably off-center. The tires on the driver side were tucked under the fender, and sticking out noticeably on the passenger side. So the axle was shifted back to the left a little.
Note: I'm also aware that my rear driveshaft is currently installed backwards from the factory orientation. Mine has the slip yoke pointing towards the transfer case, not the rear differential. All I can say is that's the way the rear driveshaft was when I purchased the truck, and I've had three good shops work on it since then, and nobody has recommended swapping it back around. Swapping the rear driveshaft back around will probably be the next thing I try, but I'd be interested to know if anyone else has ever found this to be a source of vibes.
Vibrations are currently still present and very noticeable above 2800 RPM's, but were reduced a little below that with the axle shift to the passenger side. Above 3K RPM's, it's still obnoxious as hell. It still starts to pulse/surge, and it will still trigger a CEL if I let it go too long.
So with all that info, I am hoping to get some direction on next steps. Thanks!
The truck had 247K miles on it when I bought it, and it was lifted pretty high with OME J-springs F&R, Doetsch-Tech 12.5" long travel shocks, and coil spacers (at least 40mm, maybe even 50mm). The PO had installed Man-a-Fre 4" radius arm drop brackets, adjustable upper rear control arms, extended bumpstops, sway bar drop brackets, adjustable panhard rods, etc.
I did not want that much lift, so the first thing I did was remove the coil spacers, but it still had vibes.
Not long after that, I broke one of the Doetsch-Tech shocks on a trail run, so I took that as an opportunity to replace the entire suspension with a 2.5" Dobinsons VT/MRA kit. The stock rear lower control arms were also both bent, so I replaced those with Dobinsons lower control arms, and replaced the "yellow eBay" adjustable panhard rods with Dobinsons adjustable panhard rods (F&R). All new suspension bushings were installed at that time as well.
Here's the current setup with about 256K miles on the truck as it sits today.
Shocks and Springs: Dobinsons C97 146/147 2.5" Tapered Springs with MRA long-travel shocks.
Coil Spacers: 1" DVS coil spacer on the front to level the truck.
Caster Correction: Man-a-Fre Drop brackets for a 4" lift. Dobinson's caster-correction bushings are installed in stock radius arms.
Rear Control Arms: Adjustable upper control arms and Dobinsons adjustible rear lower control arms.
Panhard Rods/Bracket: Dobinsons Panhard rods (F&R). DVS 3" Rear Panhard Lift Bracket. (note: Panhard rod is still not flat)
Driveshafts: Double-Cardan Front and Rear with Spicer-style joints. Front DS is installed "in-phase" with slip yoke on the differential/axle end. Rear DS is installed "in-phase" with slip yoke on the differential/axle end.
Differential/TC Gearing: 4.88's in diffs. Rear was rebuilt approx 5K miles ago. Front probably has 30K+ miles. Stock transfer case gearing.
Axles: Longfield Chromoly shafts in the front. Still Full-Time AWD. (note: wear on front shafts looked OK when front knuckles were rebuilt 5K ago). Stock shafts in the rear.
Bushings: I have replaced all suspension bushings - front and rear.
Wheels/Tires: SCS F5 17 X 8.5 -10mm offset, Kenda Klever RT 35 X 12.5 X 17 - mounted and balanced 8K ago.
Other:
- Extended swaybar brackets, bump stops, brake lines. Whiteline HD rear swaybar. Brand-new HD Tie Rod Ends.
- De-flared, cladding removed, and my fenders have been trimmed/rolled for bigger tire clearance.
- Aftermarket front and rear bumpers, spare tire swingout with jerry cans & HilLft, sliders, basic rear sleeping platform.
- Differential fluid has been changed F&R, and transfer case fluid checked - level and color looks good.
- New Engine Mounts were installed approx 3K miles ago. Trans mounts are old. Not sure of age, or condition.
Here's a rundown of the steps I've taken so far to resolve the vibrations:
Caster Measurement (by digital angle finder) is estimated to be about 4 degrees. I realize that this is not an accurate way to get a caster reading. I need to find a reputable place in SoCal to get a real alignment done. But it's pretty clear just from looking at pinion angles that I have a fair amount of caster correction going on. That's to be expected given that I have both 4" radius arm drop brackets and caster-correction bushings. The truck drives as straight as an arrow, and the steering is not heavy at all, so I'm hesitant to undo any of the caster correction if I don't have to.
To isolate the source of the vibrations, the Front Driveshaft was removed - Driveline vibrations still present. When the Rear driveshaft removed - Driveline vibrations went away.
Rear pinion bearing was found to be damaged, and was replaced about 3,000 miles ago. Still had same level of driveline vibrations after replacing the pinion bearing.
Recently, both driveshafts were sent out to a local driveline specialist for inspection, and it was discovered that one joint in the rear driveshaft was badly damaged.
All new joints were installed in the rear driveshaft, and both shafts were rebalanced.
Though it appears the problem is likely with the rear driveshaft, I'll just mention that the front driveline angles are clearly off. There's about a 5-6 degree difference in the angle of the front pinion flange and the transfer case output. At one point, I did try reinstalling the stock (non-double cardan) driveshaft up front, but it had no improvement, so the DC driveshaft has been reinstalled up front. (Note: I'm aware that from the factory, the front driveshaft is supposed to be installed "out of phase", and mine is "in-phase". For what it's worth, I've been told that for my lift, it's better to run the front driveshaft in-phase. Let me know if you agree with that.)
As far as the rear driveshaft goes, pinion angles in the vertical plane look perfect, but there appears to be a pretty noticeable lateral angle to the rear driveshaft. I understand that some lateral angle of the driveshaft is normal, but in my case, it looks like it could be more extreme with the rear axle centered at ride height. Adjustments were made to shift the axle over a bit to the passenger side, which reduced the lateral misalignment of the rear driveshaft. We had to shift the axle over quite a bit (3/4"+) to the passenger side in order to get the lateral angle straighter. This did the result in a reduction of vibrations, but now the axle is noticeably off-center. The tires on the driver side were tucked under the fender, and sticking out noticeably on the passenger side. So the axle was shifted back to the left a little.
Note: I'm also aware that my rear driveshaft is currently installed backwards from the factory orientation. Mine has the slip yoke pointing towards the transfer case, not the rear differential. All I can say is that's the way the rear driveshaft was when I purchased the truck, and I've had three good shops work on it since then, and nobody has recommended swapping it back around. Swapping the rear driveshaft back around will probably be the next thing I try, but I'd be interested to know if anyone else has ever found this to be a source of vibes.
Vibrations are currently still present and very noticeable above 2800 RPM's, but were reduced a little below that with the axle shift to the passenger side. Above 3K RPM's, it's still obnoxious as hell. It still starts to pulse/surge, and it will still trigger a CEL if I let it go too long.
So with all that info, I am hoping to get some direction on next steps. Thanks!
