2002 montero limited rear end rumble/vibration over 50mph

[spacecowboy7777]

Been getting this new to me montero up to date on maintenance and the truck is butter smooth under 50mph, but about 50mph and higher I get a slight rumble/vibration from what sounds like the rear end. It is definitely speed related, as it comes on at the higher speeds, and as I increase speed, the rumble increases it's pitch. Also, this only happens under acceleration. When I let off the accelerator and coast at any speed the rumble disappears. This is a very minor rumble, no big shaking or anything. RPM does not appear to be correlated at all.

I have already replaced the transmission crossmember mount bushings, which completely solved the 2100-2400 rpm vibration. Also removed both hanging dampers from the transmission and the rear axle. Brand new highway tires, stock size. The front is stock height, the rear is lifted between 1-2" with a spacer. Just got a front and rear alignment.

I'm suspecting the remaining high speed rumble has to do with the CV axles. Either the rear lift is tilting the CVs too far, or one of them is just damaged and needs replacement. Do you all think I'm looking in the right direction?

 

[Inyo_man]

Have you inspected the engine mounts?
Both of the front engine mounts were completly broken in half when I replaced them after over 200K miles of use/abuse.

Cheers

 

[spacecowboy7777]

Have not checked the engine mounts. It sounds like it's coming from the rear of the truck, so I didn't even suspect engine mounts. Is there an easy way to check the mounts?

 

[plh]

Have not checked the engine mounts. It sounds like it's coming from the rear of the truck, so I didn't even suspect engine mounts. Is there an easy way to check the mounts?

monocoque chassis - sounds echo everywhere.

 

[spacecowboy7777]

I'll take a peak at my engine mounts

 

[Inyo_man]

When inspecting the front two mounts, it appears to have a line (crack) all the way around the bushing.

You might also inspect your rear differential mounts.

Cheers

 

[spacecowboy7777]

Great, thanks for the info. Might be next week when I can fully inspect. With these short days I have no light to work in after work. I'll keep ya'll posted

 

[Inyo_man]

Just curious...when was the last time you flushed the transmission fluid? Did you use M.M. fluid?

Cheers

 

[Michael Brown]

I was about to suggest checking the fluid or flushing the transmission. They get a similar feeling to driving down a rumble strip. My 01 did it going uphill around 40-45mph.

The increase in pitch with speed makes me think diff gears, though. Hopefully you find something out.

 

[spacecowboy7777]

Just curious...when was the last time you flushed the transmission fluid? Did you use M.M. fluid?

Cheers

I was about to suggest checking the fluid or flushing the transmission. They get a similar feeling to driving down a rumble strip. My 01 did it going uphill around 40-45mph.

The increase in pitch with speed makes me think diff gears, though. Hopefully you find something out.

Truck is brand new to me, haven't touched the tranny fluid. It's definitely on my maintenance list.

 

[plh]

I did change by dilution on my '05, every engine oil change I also did a transmission pan drain plug dump which is around 4 quarts for the last 50K miles of ownership. Refilled with Aisin SP3. I say around 4 quarts, because sometimes it was 3.5 quarts and other times 4.5 quarts. Fill back to the line on the stick as directed.

 

[spacecowboy7777]

I did change by dilution on my '05, every engine oil change I also did a transmission pan drain plug dump which is around 4 quarts for the last 50K miles of ownership. Refilled with Aisin SP3. I say around 4 quarts, because sometimes it was 3.5 quarts and other times 4.5 quarts. Fill back to the line on the stick as directed.

Did you notice any difference in performance/feel?

 

[plh]

Did you notice any difference in performance/feel?

It was a PM activity, but shifting felt better. Totally unquantifiable. I started this with around 150K miles on the clock. I bought the vehicle with 7x,xxx miles on it. Owned for 10+ years, sold it with 199,xxx miles on it. Miss it sometimes, but needed something newer and with less miles. Replacement happened 2 years ago and is a '14 Outlander GT and am quite happy with it. I'm also following the same transmission change by dilution procedure. J3 fluid is expensive.

 

[Inyo_man]

I wouldn't recommend the "dilution method" if you have never done a complete flush with OEM fluid. If a previous owner did not use OEM fluid, that could be the reason for the vibrations/shuddering. Complete flush takes about 12 quarts. These transmissions are bullet proof if care for properly.

Cheers

 

[spacecowboy7777]

good info, thanks guys. I'll check my fluid level and color/smell and go from there.