Clunk when shifting from park to reverse (after sitting overnight)

Howdy folks - I have a 2000 WJ, 2WD, 4.0L, 42RE transmission, just shy of 70,000 miles...

Seemed to notice this after the weather began to cool down... when starting the vehicle after it has been sitting for more than 8 hours, and shifting from park to reverse, there's a brief, one second delay, then a loud clunk / thump, before it feels like it's in gear and starts actually moving in reverse.

If I shift into drive first from park, then reverse, the loud clunk is much less pronounced, but still there.

If I drive the vehicle within a certain window of time (ie: leaving work in the afternoon or going to lunch), the transmission shifts just fine from park into reverse - no loud clunking or delay before it drops into reverse. This happens ONLY when the thing has been sitting in the garage for a while.

Transmission fluid level is OK, and the color seems fine (light reddish color).

Any ideas out there as to the cause?

Thanks in advance.

(please reply to the group - my e-mail address is munged to prevent SPAM)

Reply to
Robert Giles
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Your Factory Service Manual should have a whole transmission section with diagnosis charts.

Here is a link to the charts on a 2002 42re transmission.

Reply to
billy ray

You are describing the noise and feel of a blown u-joint.

If you block the wheels and put it in neutral to unload the drivetrain, you can go under and check the driveshaft u-joints. You twist and push at them as well as do a visual looking for rust stains around the caps. One arm on one will likely be just flopping around.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

Let me take a stab at this:

Your 42re doesn't circulate fluid through the torque converter when it is in park -- the logic from the factory was to minimize parasitic losses when the vehicle wasn't "in use". When the front pump bushing has worn a bit, you get converter "drainback" (whether or not you have a check valve in the cooler line). The transmission pump circulates through the converter and cooler when in any position but park -- so there's the one-second delay from extended shut-down. You're not gassing it during the delay, are you?

On top of it all, that transmission uses unregulated, full-pump pressure when in reverse. Hotter fluid -- therefore thinner and easier for the torque converter to move through -- would make for a softer engagement. I'm supposing that all these factors lead to the harsh reverse engagement -- and therefore the louder clunk than from another gear or a quick restart. So I'm with the others on bad u-joint/worn spiders/bad motor or transmission mount potentially making the audible clunk after a rougher than usual shift from park.

Take a walk over to alt.autos.dodge.trucks, there's a handful of guys (i.e. Tom Lawrence) who are very knowledgeable about this transmission.

Jon

billy ray wrote:

Reply to
Jon

Have you ever serviced the transmission? Has anyone else serviced it? When?

Definitely check the U-joints first, as others suggested. Other misc. transmission problems often come back to an incorrect fluid level, fluid contamination causing internal valve spools to stick causing line pressure problems, foaming of the fluid (usu. due to an internal leak or cracked case) or the wrong type of fluid in the transmission to begin with, most often put there by Jiffy Lube outfits.

Reply to
Outatime

Many years ago I had a Studebaker Hawk that made a noise just like that. I didn't think about it too much until one day I was driving along, gave it some gas to climb a hill, and suddenly it was like someone was beating on the bottom of the car with a sledge hammer.

Pulled over to the side of the road and everything seemed fine, engine was idling quietly, gages all normal. Shut it off and walked around the back of the car where I noticed the yoke from the back of the transmission laying in the sand behind the car, and then the drive shaft a few yards back.

I put the drive shaft in the trunk and started walking (about 20 miles from home, in the middle of Fort Bragg back when it was a shortcut from Fayetteville to Southern Pines NC). I'd never hitchhiked before (or sense) but the first car to come along I stuck out my thumb, they picked me up and dropped me off in front of my house!

Moral of the story, watch your U Joints!

Jeff DeWitt

Mike Roma> You are describing the noise and feel of a blown u-joint.

Reply to
Jeffrey DeWitt

Nope, never been serviced. Have to pull the factory manual out again to find out what "servicing" entails beyond just changing the fluid...

Ok - would fluid contamination be detectable just by looking at the dipstick?

Thanks for the tips, greatly appreciated.

Robert Giles

Reply to
Robert Giles

I'll get under it tonight and have a look... I'm kinda surprised it would only do this when the thing has been sitting for a while, though.

Wouldn't a damaged u-joint pretty consistently give you the same "clunk", when shifting from park to reverse *or* drive? (this only happens going into reverse from park, and only after it's been sitting for a while).

The transmission always seems to shift a bit harsher when it's cooler outside (than our standard 98 degree summer weather)... maybe this is also temperature related, too...

Thanks for the tips -

Robert Giles

Reply to
Robert Giles

Nope - foot on the brake, waiting for the "clunk" to happen. This is definitely a new thing - up until about two months ago, never got the loud clunk or the delay when shifting.

The transmission has always acted strange during the fall/winter months - since I've owned it (2001)... very harsh shifting and abnormal shift points until warm, but I assumed this was the ECU revving the engine higher (3K-4K RPM) to warm driveline components up (but y'all are the experts - I'm just guessing here and have absolutely zero experience with transmission problems).

Ok - would a bad transmission mount be detectable just by looking at it? (I haven't looked, but I'm guessing there's some kind of heavy duty rubber grommets that may crack / degrade over time?)

Ok - thanks again for the help on this!

Robert Giles

Reply to
Robert Giles

Thanks for the URL - I'd skimmed through the 45RFE section in my book (not realizing up until a few days ago that I had a 42RE) and missed the condition / resolution part about "harsh engagement"...

Duh...

Reply to
Robert Giles

Robert,

So I think we have two separate issues, one has pointed out the other.

Transmission servicing will include dropping the pan for inspection, adjustment to the bands, replacement of the filter, and in doing so replacing roughly 1/2 the fluid in the transmission. If you think a previous owner might have had it serviced with the wrong fluid in there (every container of type 3/4 I've come across has NOT smelled distinctly sweet like Dexron -- T 3/4 is rather foul, even mistaken as burnt by those who haven't run across it) you might have to pop for a "fluid exchange" service -- making sure the proper fluid is used. I dunno, that might be overkill, but every source I've found talks at length of the sensitivity of this transmission to the proper fluid type. Since bands that are out of adjustment can give rise to your symptoms, it's worth at least trying to establish a baseline -- you're due for service either way.

U-Joints fail from wear, loss of lubrication, and component breakage....or a combination. In the early stages, a dry joint, or one that has just one set of bearings failing, might not make noise or get shifted out of position by a smooth transition -- sometimes only by a rough shift or higher load do they display a problem. As previuos posters pointed out, a good physical and visual inspection usually does the trick.

Your dipstick won't tell you much about contamination from wear -- the pan accumulates a fair amount of material, and an educated eye can make a judgement call based on amount and size of debris as to whether it's normal for the use/mileage or if something is out of whack.

Yup -- an engine or transmission mount has the rubber isolation pieces break down over time, leading to excessive movement (often exhaust parts contact something they're not supposed to) or metal to metal contact at the mount itself. At 6 years/70k, I don't think that's the #1 source of a clunk, but try this:

Get someone to duplicate the noise for you, while you're down there watching and listening -- out of the path of travel, please. That will let you know what end of the vehicle is making the noise, and I bet dollars to doughnuts you can I.D. the source from there.

Please post as you progress!

Jon

Robert Giles wrote:

Reply to
Jon

Doubtful. I once watched a guy pour a quart of 10w30 motor oil into his transmission fill tube at a filling station once. I've also seen people pour motor oil into their brake master cylinder before too.

Reply to
Outatime

I would have liked to see what a friend saw in England. Someone pouring water into the oil fill with the engine running.

Hydraulic brake system seals swell up on contact with oil. If you need an emergency fluid then water, alcohol, antifreeze or even urine will get you to the next gas station.

Earle

Reply to
Earle Horton

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