https://landroverforums.com/forum/di...acement-11702/

Rather than bump the thread above, I thought I'd ask this as a different question. It sounds like I've got a "robo chipmunk" under the hood. The sound only occurs under load/acceleration. On gas--sound. Off gas--no sound. Like a light switch--on/off.

I initially thought it might be the vent tubes from the t-case and tranny that I found melted under the truck. But, that wasn't the "fix it" button. But at least I found a different problem that needs to be fixed before it's a crisis.

Regarding the "robo chipmunk" under the hood, I thought it might be the belt needing a tad bit of tensioning. However, I *think* that the belt is auto tensioned by the green colored part in the illustration below.



So, if it's the tensioner and the tensioner functions automatically, then would the "robo chipmunk" sound be a clue that the part needs replacement? Or, can I create more tension in the system to check this?

Or? Any other thoughts on what would create a load-dependent "robo chipmunk" sound?

Thanks so much, fellow LR amigos!

--Gabe

 

Belt can be worn out - look for strands coming off, missing sections of rib, cracking. If a lot of degreaser got sprayed on the pulleys, may be slipping.

Tensioners can also wear out. You can also listen to pulleys by a long screw driver or stick held to fixed mount of pulley and to your ear.

 

1) Put the truck into Neutral. Trans in neutral.
Take engine to 2,500 RPM. Listen. Robo Chipmunk sound?

2) Let gas off. Robo Chipmunk sound?

Trick is to test it whilst stationary.

-----
If you are moving - then this could also involve the transmission or transfer case.

Anything on the serpentine belt circuit will make a "robo chipmunk" sound at whatever speed you are going - fast or slow.
Pulleys, water pumps, alternators don't care if the gas is going on - accelerating or decelerating.
These only know how fast they are going.

If you have SLACK in the belt - and it is rubbing on something - then it may make a difference if you are hitting the gas or letting it off.

My rover makes a horrid whirring sound whether I am in Neutral, driving slow or whatever. The noise is around 500 to 1700 RPM.
Above that, it fades into the wind and tire noise of higher speeds.

Maybe my transmission is resting on the frame due to rubber components rotted.

One thing I did note:

The Discovery I power steering pump is shock mounted via rubber.

The Discovery II power steering pump has no rubber shock mounts and is
mounted right to the accessory plate. That has to transmit a lot more poser steering pump noise to the accessories plate and to the engine assy.

How for that noise to reach the cabin?

Well, there are engine mounts.
Nice sturdy rubber mounts.
If those are OK, then how for the noise to transmit to the cabin?

What other mounts can rot and put the transmission / engine assembly
in contact with the body and or frame?

These may be your next steps.

 

Take a can of spray liquid silicon. With engine running and robo-chipmunk in action, spray onto center area of each pulley. (Basically, where the bearing is). If robo chipmunk is silenced, replace said pulley. Wave goodbye to robo chipmunk.

 

Also if you are moving, it could be the front driveshaft.

Hopefully it is only making the sound while stationary (thus ruling out the drivetrain). The technique I've used to figure out which accessory bearing is making the noise is to spray a lightweight lube (WD40, silicone, whatever) onto one bearing at a time. When the noise goes away, you've found the source.

 

If my kids weren't distracting me, I'd have gotten in before you!

Excellent advice.

 

First don't use any spray on the belt, that can/will glaze up the belt.
If you have never replace the 3 belt idler pullies, I would remove the belt and spin all the pullies, if it is an idler pulley, replace them all cause they always have issues when older.

 

Thank you guys! I'll trouble shoot today and report back with what I find out.

 

Well, one way to describe the robo chipmunk is "intermittent." The truck has sat for several days and what was a fairlt consistent sound the other day was a bit difficult to reproduce today. What I was able to do today...

The belts looked fine, I really don't think they're the issue visually.

The sound does not occur when the rig is in neutral and the engine revved--though I did get some funny looks in the parking lot.

The sound retains it's accelerator-related on/off nature.

The sound is more pronounced when under load--for instance, accerating up a hill--than under light or no load--for instance, light throttle on flat ground.

So, my SWAG is that this is in the drivetrain somewhere. Perhaps the tranny or t-case. Or, perhaps, a driveshaft issue.

 

Check the transmission fluid level with the engine ON in neutral or PARK.
PARK is safer - as you will not get run over by your own truck.

Check fluid level in the transfer case.

Check the fluid level in both differentials.

Grease the drive shafts with a grease gun using the provided grease nipples.

My bet-
is that your transfer case is low.
You MUST NOT drive at all.
Until you get that noise figured out.
Or you will RUIN your transfer case.
It will turn into literally a case of loose and damaged gears.