[CADisco]

Trying to chase down my vibration problem. Bought this truck about 3 months ago and it's almost undriveable on the highway, and pretty annoying in the city

Symptoms:

• Vibrates when first accelerating (~700-1000rpm) then gets better and comes back on strong around 1900-2000 rpm
  • This happens both while driving and also if I'm just sitting in Park or Neutral and revving the engine up
  • Doesn't seem to matter what gear I'm in
  • Not very much vibration at idle

Things I've done:

• Replaced front drive shaft u-joints with greasable ones, replaced rear rotoflex joint, had both shafts balanced by a driveline shop
• Replaced both motor mounts and both transmission mounts
• Coolant flushed, oil changed, power steering pump and steering dampener replaced
• New spark plugs and leads

Because this is also happening in Neutral it seems unlikely to be a transfer case, prop shaft, or wheel/tire issue, but the truck obviously sat for a couple years before I bought it, so I wouldn't be surprised if there were flat spots in the tires that are not helping the problem.
I don't have any engine codes, I do have the 3 Amigos but doubt that it's related.
Is it possible I have some kind of misfire on acceleration?

Things I can try:

• compression check
• pull spark plug leads one by one to see if there is an effect
• remove the serpentine belt to see if it's an accessory issue
• some threads say to check the injector harness in case there are issues there
• injector balance? does anyone know how to do this? do i need a special computer for it?

Any more thoughts on this or things I should try? I know these engines are not known to be very reliable, is it possible there is a mechanical imbalance in the engine?
I have an independent Land Rover shop around the corner from me so I can also get them to take it for a spin to give me their opinion, just want to make sure I've tried the obvious/easy stuff first.
Thanks!

2002 Land Rover Discovery II SE, 4.0L, 140k miles

 

[masantschi]

I'd pull the front drive shaft. I had one that was out of balance and it acted just like that. Drop the shaft. Lock the transfer and take her for a drive running in rear wheel drive.

If it goes away... rebuild the shaft.

Considering everything else you've done, this will be an easier one.

 

[V50_M66]

02s don't have locking t-cases if I remember correctly. Shouldn't be a driveshaft anyway if it does it just revving in park. I'd carry through with your list of tests. Injectors you can check by unplugging them and listening for rpm drop just like spark plug test (if you can get to them - suckers are buried). Sounds like it might be a bad torque converter or something? I've never really seen anything like this before. Keep us updated.

 

[reverendALC]

I think the early 02 might’ve been equipped with the LT230, but if it’s in neutral and doing it, you can rule out drivelines.

does it hesitate while it’s vibrating? Or does it pull normally?

 

[CADisco]

Yeah sadly no CDL on this one, and agree, not likely to be driveline at this point.

Seems to pull ok when vibrating (doesn't falter or skip) but then again this is my first Land Rover and I've never driven it without this issue, so I don't really know how much power I should have in this range.

 

[V50_M66]

I'm thinking torque converter or some issue with the rotating assembly then. Check the harmonic balancer and all of the accessories on the engine for clear signs of out of balance first. You can use the throttle from the engine bay to get the revs to where it likes to vibrate.

 

[reverendALC]

What he said

 

[CADisco]

Spent some more time on this today. I removed the serpentine belt and ran it, and the vibration was the same, which pretty much rules out all of the accessories and pulleys.
I played around with it a bit more, and it doesn't seem to be misfire related. The engine appears to be running fine, and when I control the throttle from the engine bay, there appears to be less vibration than when I'm sitting in the truck, which makes me think this is less likely to be engine related. The engine itself is not really shaking very much or at all. It's also happening both on acceleration and deceleration, which also points more to it being some kind of unbalanced component.

I'll still pull the plugs to check that off the list, but given that I have no codes, new plugs, and new wires, it doesn't seem likely.

How big a job am I looking at to drop the tranny? I've done it before on a couple different trucks (90s jap pickups) and it's definitely not my favourite hobby. Is there any way I can make sure before I dive in?

 

[V50_M66]

Since you say it isn't bad from the engine bay, it could be the motor mounts that have failed and the engine is transmitting a bunch of vibration through the bad motor mounts to the cabin. That would change with different amounts of throttle while driving (higher loads will make it worse), so try that before ripping the trans out of it. But if it doesn't seem like that, it might be torque converter time.

 

[CADisco]

Already replaced the motor and transmission mounts. I'll start taking a look through the manual to see what I'm in for here

 

[15mpg]

You may consider checking the torque converter bolts to the flex plate.
A missing bolt or flex plate issue is free to diagnose.

 

[Bigmant773]

Had a similar feeling a few months ago. Before you go chasing down mechanical items, try rebalancing your tires. Did it to mine and the vibration went away. Sometimes the simpler solutions are the way to go.

 

[CADisco]

Swapped the transmission fluid, no change in behaviour. I've been looking around trying to figure out how to look at the flex plate without dropping the transmission. Is it worth it to drop the oil pan instead? Can you see everything you need to see through there? I've read that you don't get a good look at the center of the flex plate, which is where it usually fails.

@Bigmant773 I did actually already take it to the shop to get wheels balanced but they were good enough to not charge me and tell me that wheels were not my issue. Now that I've figured out that this is happening in park and neutral as well, it's got to be something upstream of the driveline anyways.

I'm going to get the indy LR shop down the street from me to take it for a drive and give me their 2 cents before I start pulling parts off it.

 

[V50_M66]

Swapped the transmission fluid, no change in behaviour. I've been looking around trying to figure out how to look at the flex plate without dropping the transmission. Is it worth it to drop the oil pan instead? Can you see everything you need to see through there? I've read that you don't get a good look at the center of the flex plate, which is where it usually fails.

@Bigmant773 I did actually already take it to the shop to get wheels balanced but they were good enough to not charge me and tell me that wheels were not my issue. Now that I've figured out that this is happening in park and neutral as well, it's got to be something upstream of the driveline anyways.

I'm going to get the indy LR shop down the street from me to take it for a drive and give me their 2 cents before I start pulling parts off it.

Pulling the oil pan is kind of a PITA too. Tons of bolts, and everything is in the way. Crossmember has to come out if you follow the book instructions, which trust me - it won't want to come out without a fight - I jacked my truck up up all the way and then spun the oil pan around to clear the pickup tube and sent it out towards the rear. Not a fun job. Half of your bellhousing bolts come out too. You might be able to take a look at your flex plate to look for cracks, but if it's the torque converter you won't be able to tell from the engine side. Good luck

 

[Bigmant773]

Swapped the transmission fluid, no change in behaviour. I've been looking around trying to figure out how to look at the flex plate without dropping the transmission. Is it worth it to drop the oil pan instead? Can you see everything you need to see through there? I've read that you don't get a good look at the center of the flex plate, which is where it usually fails.

@Bigmant773 I did actually already take it to the shop to get wheels balanced but they were good enough to not charge me and tell me that wheels were not my issue. Now that I've figured out that this is happening in park and neutral as well, it's got to be something upstream of the driveline anyways.

I'm going to get the indy LR shop down the street from me to take it for a drive and give me their 2 cents before I start pulling parts off it.

Glad you checked the wheels first! Sounds like it was free and you can now rule it out. Does it feel like it’s coming from a particular side? I wonder if it could be a wheel bearing?

 

[discovering]

Can you see everything you need to see through there? I've read that you don't get a good look at the center of the flex plate, which is where it usually fails.

You can easily see the torque converter bolts through the access port but you cannot see much else. You could remove the bolts that secure the torque converter to the flexplate, push it back to keep it from fouling on the flexplate, start the engine and see if the vibration is gone with the converter disconnected. If the vibration is gone, I guess it's time to drop the tranny and investigate further.

 

[V50_M66]

Glad you checked the wheels first! Sounds like it was free and you can now rule it out. Does it feel like it’s coming from a particular side? I wonder if it could be a wheel bearing?

It happens in park and neutral too, which rules out driveline besides engine/trans

 

[CADisco]

Dropped it off at the indy LR shop down the street from me yesterday for inspection and diagnostic, we'll see if they come up with anything.

I've heard some things about a harmonic dampener, but haven't had a chance to look into it yet, anyone know anything about that? The vibrations do come around at roughly double the frequency (900rpm and 1800rpm ish) so seems like it could be a harmonic thing....

 

[CADisco]

Went and chatted with the LR mechanic today, apparently he's been working on these Discos for a long time (in Hermosa Beach, LA). We played around a bit with the throttle and watched the harmonic dampener, could not see any visible wobble from it, and he also doesn't think that it's something wrong in the engine itself. He basically said that it's got to be something on the crankshaft, but not in the engine, which only leaves the pulley/dampener, or the flywheel/flex plate/torque converter on the other end. Since the pulley doesn't look visibly out of whack, seems like the next step is to look at the other side of the engine.

Sounds like I can remove the flex plate to torque converter bolts from the inspection holes in the bell housing and push the torque converter back so that the engine spins without it to isolate that. But also sounds like the only way to properly inspect the flex plate and flywheel is to drop the transmission, so no matter whether the torque converter is good or bad, I'm still dropping the tranny at some point. He did say that the flex plates do fail a lot on these, but they always have noise as a symptom, and we're not hearing anything like that.

Is it worth pulling the harmonic dampener off and swapping to another one to see if that solves it? Seems like a bit of a shot in the dark, especially with swapping weights around. New ones are insane expensive ($790 on AB!?!), used ones are ~$70 but who knows if they're any good.

 

[V50_M66]

Went and chatted with the LR mechanic today, apparently he's been working on these Discos for a long time (in Hermosa Beach, LA). We played around a bit with the throttle and watched the harmonic dampener, could not see any visible wobble from it, and he also doesn't think that it's something wrong in the engine itself. He basically said that it's got to be something on the crankshaft, but not in the engine, which only leaves the pulley/dampener, or the flywheel/flex plate/torque converter on the other end. Since the pulley doesn't look visibly out of whack, seems like the next step is to look at the other side of the engine.

Sounds like I can remove the flex plate to torque converter bolts from the inspection holes in the bell housing and push the torque converter back so that the engine spins without it to isolate that. But also sounds like the only way to properly inspect the flex plate and flywheel is to drop the transmission, so no matter whether the torque converter is good or bad, I'm still dropping the tranny at some point. He did say that the flex plates do fail a lot on these, but they always have noise as a symptom, and we're not hearing anything like that.

Is it worth pulling the harmonic dampener off and swapping to another one to see if that solves it? Seems like a bit of a shot in the dark, especially with swapping weights around. New ones are insane expensive ($790 on AB!?!), used ones are ~$70 but who knows if they're any good.

Probably not a harmonic balancer if it's as bad as you say and can't see any wobble. Most likely flex plate or torque converter. Might have to bite the bullet and drop the trans