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[lizardland]

I've developed a whining/grinding in the front end of my Grand Cherokee. The whine builds with acceleration but if you lift your foot and let the revs drop (but road speed stays the same) then the whine stops then starts again. I'm assuming this means it isn't the wheel bearings.

My guess is that the U-joints on the driveshaft need changing. Is there any easy way to test/check the UJ's just to confirm? Could it be the CV at the axle end of the driveshaft?

I don't know if it's related but I'm getting poor gear changing with the auto box at <50mph. It's especially bad at around 30mph, the revs go very high (3000-4500) before it changes gear. When it does change it's harsh with a real jerk.

Cheers,

Stuart

[Mike Pavelin]

You don't say what sort of Grand Cherokee you have, but it sounds like you need to get the auto transmission checked out. Get the vehicle scanned for fault codes as they suffer from various sensor failures that can cause poor shift quality.

[Tank]

I know its not related as such,but im interested to know how you get on Stuart as i have a td lwb Mitsubishi Shogun that has exactly the same symptoms,although older so may not have fault codes.

[lizardland]

You don't say what sort of Grand Cherokee you have, but it sounds like you need to get the auto transmission checked out. Get the vehicle scanned for fault codes as they suffer from various sensor failures that can cause poor shift quality.

It's 98 4.0L Petrol with LPG conversion. Haynes manual mentions something about jerky gear shifts being related to worn UJ's which is what made me think the noise is coming from the drive shaft.

[Mike Pavelin]

I reckon the noise is the torque converter wailing as the Jeep hangs onto low gear. The 4.0 has the 42 RE transmission. Common causes of delayed upshift are output speed sensor and governor pressure sensor. These will show up if the Jeep is scanned for trouble codes.

[lizardland]

Would the noise still be there as the speed builds and the tranny settles into the right gear? Cruising at 75 it's a constant whine, quite loud, auto box sitting quite happy in 4th, just over 2k rpm.

Cheers,

Stuart

[Mike Pavelin]

Could you have a noisy front diff plus a transmission problem as well. It's pretty difficult to diagnose noises on the internet!
Check the oil in the front axle and check if it's full of glitter, and try removing the front propshaft and taking a short drive to see if the whine goes away.

[Dave69]

I've developed a whining/grinding in the front end of my Grand Cherokee. The whine builds with acceleration but if you lift your foot and let the revs drop (but road speed stays the same) then the whine stops then starts again. I'm assuming this means it isn't the wheel bearings.

My guess is that the U-joints on the driveshaft need changing. Is there any easy way to test/check the UJ's just to confirm? Could it be the CV at the axle end of the driveshaft?

I don't know if it's related but I'm getting poor gear changing with the auto box at <50mph. It's especially bad at around 30mph, the revs go very high (3000-4500) before it changes gear. When it does change it's harsh with a real jerk.

Cheers,

Stuart

If the note changes when load is taken off and not speed then it would be safe to say it's not axle/wheelbearings as these are road speed related.
 I'd offer a good guess that it isn't the prop shafts as they behave in the same manner as the axles and are road speed related as well but at a different speed due to the gear ratios.
 with the GC being an automatic you can play around with the throttle, by adding more or less gas and not realy affecting the speed as the torque convertor will soak most of the increase in the engines speed before it gets transmitted through the gearbox and to the driveline. If by doing this you can alter the whine repeatedly without significantly changing the jeeps speed then you can guess at the problem being in the gear/transfer box area which will need and examination either by computer first then a visual

[lizardland]

Did as you suggested, Dave, played around with the throttle on the way home. The noise is definitely speed related rather than varying with the gearing. I also rolled it down the ramp up to the garage, engine off, everything in neutral, there is still a noticeable grind.

It was a lot worse today so I jacked it up and wobbled the wheels. There is no play so I guess the bearings are OK. Got underneath and noticed straightaway that the left wheel CV joint boot is torn in two. Could this be the source of the grinding?

A bit of experimenting in the supermarket car park showed up that the dodgy gear changing is only when steering -- going in a straight line, the gears shift as normal.

Anyone reckon this is it or is the CV joint a red herring?

[Dave69]

if you can get at the cv joint with the wheel in the air and have a look at it. with the boot split prise it apart and have a look at the joint. if the boot has just recently split then the joint will be relatively clean and greasy. if it has failed quite some time ago then it stands the chance of being covered with road grime and grit which might have been ground into the joint and created some wear.

the messy bit try and hold onto the joint and rotate the wheel, sometimes you can feel the joint grinding on itself, which might not be good for your pocket

[Mike Pavelin]

Fix the CV joint first, but it still looks like front diff noise to me.