unsolved vibration mystery (still)

[griswald]

For about 5 months, I have chased down a strange vibration mystery in my 1971 IIA swb...

Symptom vibration between 1700 rpm and 2900 rpm in second and third gear.

Thinking one of 3 things:
1. Something wrong with Carb (weber 34ich) carb idles fine and motor will rev to any amount without a miss, no popping or other concerns. (Entire ignition replaced did not seem to matter)

2. Something wrong with 2nd and 3rd gear bearings? Under load there is a vibration but with clutch in it goes away...

3. SOmething wrong with propshaft. Will vibrate a bit around 65 mph but have changed UJoints and there seems to be no free play in splines.

Truly am at a loss. The vibration goes away around 3k rpm in second and third gear. First and fourth have no issues...

Can not decide if it is the motor shaking under load, or??? Motor mounts and tranny mounts seem "good"

Thanks for your help.

Griswald

[graniterover]

Try 2nd and 3rd in low range at the same rpm's.


For about 5 months, I have chased down a strange vibration mystery in my 1971 IIA swb...

Symptom vibration between 1700 rpm and 2900 rpm in second and third gear.

Thinking one of 3 things:
1. Something wrong with Carb (weber 34ich) carb idles fine and motor will rev to any amount without a miss, no popping or other concerns. (Entire ignition replaced did not seem to matter)

2. Something wrong with 2nd and 3rd gear bearings? Under load there is a vibration but with clutch in it goes away...

3. SOmething wrong with propshaft. Will vibrate a bit around 65 mph but have changed UJoints and there seems to be no free play in splines.

Truly am at a loss. The vibration goes away around 3k rpm in second and third gear. First and fourth have no issues...

Can not decide if it is the motor shaking under load, or??? Motor mounts and tranny mounts seem "good"

Thanks for your help.

Griswald

[griswald]

vibration still there in 3rd 4th in low range with same rpms

[KevinNY]

Take the bonnet off and go for a ride, that way you can see the motor t those RPM's. Just a thought. Remove center seatbox too, so you can see and hear back prop shaft and T case.

[junkyddog11]

Congrats on a couple of things anyhow.....65mph and 3k rpm.......a little vibration at that speed is mother mechanical telling you it's time to back off!

Do you have locking /freewheeling hubs? If not and your turning the front axle it may be the axle u joints, swivel bearing etc.

Try driving without driveshaft (one at a time silly) to narrow down where the vibes are.

[griswald]

Thanks (I guess) Mr. Browne...

Um, this is my third series land rover in 15 years. I know all about little vibrations at speed, and in spite of the fact that my land rover is capable of 75 mph with the RMO engaged, I do not drive it at that speed as the truck is unsafe (in my opinion any series truck at that speed is)

I have driven the vehicle with opposing drives removed...vibration remains regardless.
Please don't offer half cocked advice with a condescending attitude if you really have not read the original post.

If you can manage that, I welcome your advice. Otherwise please post on Jeepin.com

Regards,
Griswald

[junkyddog11]

Sorry, didn't think I was being condescending, or half cocked. A little humor perhaps and in my opinion as someone who solves these issues and more on a daily basis (I get minutes to diagnose....not months), some things to check that you didn't mention in the above post #1 (that I did in fact read).

[kevkon]

Determining the cause of a vibration comes down to determining whether it is related to the power train or the drive train and this will be evidenced by whether the vibration is related to the vehicle speed or not. If the vibration is not increasing or evident at higher vehicle speed, then it's not due to imbalance of the rotating drive train such as the wheels or drive shaft.
That pretty much leaves the power train (engine) as the likely culprit. Since it's unlikely that the rotating components of your engine are that far out of balance, your vibration source is more likely due to the performance of the engine under certain throttle, rpm, and load conditions. It's the combination of all three of these that is important to consider. An engine that runs smoothly at 3000rpm and open throttle might not when the throttle is closed due to the different air/fuel ratio to cylinder volume ( that's where ignition advance comes into play). That in turn would cause roughness to be transmitted to the drive train ( as well as body and chassis components).

[SafeAirOne]

I might agree with Matt here--REMOVE the front prop shaft, test it, then reinstall and REMOVE the rear prop shaft and test it. Even though everything might seem tight, a shaft may be out of balance or JUST loose enough to vibrate at those RPMs.

Don't forget that you yourself listed the propshafts as a suspected cause. Removing them will either confirm or eliminate the props as the culprit.

I had a front diff issue a while back and removed my front propshaft--The improvement in vibrations and noise up front at highway speeds was remarkable. Of course, the old vibes and noise came back upon replacement of the front prop shaft.

[I Leak Oil]

Yup, remove one shaft at a time and run the truck, 2wd and 4wd, front hubs locked and unlocked (if you have them). As KB suggested, do it with the middle seat panel removed and maybe even the floors so you can atleast try to narrow it down.
Motor and tranny mount are easy to check. Big prybar and some effort. If they seperate then they're toast.

[griswald]

Thanks for all of the suggestions.
Kevkon I think that you may be correct. The vibration is in the drive line and body under load and acceleration, but goes away when driveline disengaged and is only present under certain conditions, i.e. from 1800 to about 2900 rpms in 2nd and 3rd gear. It does not seem to happen over 3000rpms and it is not an out of sync driveline as far as I can tell.

The car idles fine. COmpression check this morning reveled 130, 127,127,128.

Spark plugs were very sooty (dry) and black.

The weber 34ich may need a rebuild or just be blown out...it will idle very well at 650 rpm and rev through the range to 4k rpm if you give it gas, no miss or dead spot.

One interesting note, I have a vaccuum gauge hooked into the intake manifold, at idle, it registers 21mg/hg...sometimes after a long run, it will fall to about 15-17 mm/hg and then "recover" back to 21...I wonder if a sticking carb float may cause that?

I am not familiar with a Weber 34ich, so I do not know if this is a concern.

Best,
Griswald

[kevkon]

If you see any indication of a vacuum variation it could mean a leak is present. Check the line to the distributor and the advance module. If that's not operating correctly it could cause a poor burn of the fuel/air mixture under certain engine conditions. Check all connections on the intake side including the carb and gasket. On the other hand, you say the engine idles smoothly which is not usually the case when a vacuum leak is present. I would look closely at the distributor advance, both mechanical and vacuum for any issues. Also check the plug wires and coil leads. If there's any doubt in your mind that it could be a bad universal joint an easy test is to go from reverse to first while applying the brakes. If they are bad you should hear a clanking noise.

[griswald]

Kevkon,
Well drove about 7 miles on back roads home today for lunch with the middle seat, cover out, listening to the xfer box, and Rocky Mt. Overdrive.

There is a definate click-click when I push the clutch pedal down under power (i.e. engage/disengage engine power from driveline) there is also a bit of growl but nothing out of the ordinary in the box...

One question I have would be if there was a bearing going bad or something in the xfer or gearbox, or if the RMO was not installed all the way (which can't be cause it works like butter!) would/could this cause a vibration within the RPM and gear ranges and then go away at higher RPMs and speed? (In my mind I would think no, if the vibe is there, it is there constant...)

Thoughts?

Thanks!

[kevkon]

One question I have would be if there was a bearing going bad or something in the xfer or gearbox, or if the RMO was not installed all the way (which can't be cause it works like butter!) would/could this cause a vibration within the RPM and gear ranges and then go away at higher RPMs and speed? (In my mind I would think no, if the vibe is there, it is there constant...)

There are many things that can cause a vibration, sometimes it can be induced harmonically. Sometimes it's something as simple as one part touching another. When vibrations are due to imbalance found somwhere in the drivetrain ( wheels, driveshaft, etc) they tend to become more pronounced as the rotational speed increases. Since you don't seem to be experiencing that, I would concentrate elsewhere. Run up through the rpm range slowly and go thru the gears. See if you can determine specifically when it occurs. Do a thorough examination of the engine, linkages, and check your motor mounts. See if there is any evidence of a metal to metal contact going on.