97 Suburban troubleshooting

[ccarlson]

I've got a 97 suburban with 112k miles. Driving down the road at a steady speed in 2 wheel drive at highway speeds. Vehicle makes a fairly solid clunking sound and a jarring motion. Started out doing it about every 30 miles and then went to about every 20 miles.

The engine RPMs do not appear to change on the tach. Sometimes it jars harder than others. At first it was doing it on the icy/snowy roads and I assumed my rear wheels had just hit a slick spot, briefly spun and then hit dry pavement. Then I realized it was not that. In between the occurrences, it runs very smoothly and shifts well through the gears as well as into and out of 4 wheel drive with the push button control. The truck does not have auto 4 wheel drive.

Any diagnosis? I can't wait! $$

ccarlson

[DinkADunk]

Have you checked the fluids in the transmission, transfer case, and differentials? Is everything up to snuff in your drive line?

[Jeremy airjer W]

You got me on this one. Good advice to check the drive line fluids.

[Shack]

How often and how many times has this happen now?

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The engine RPMs do not appear to change on the tach.

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This would rule out a trans issue, but not a transfer case or rear diff.

If you check fluids, look for metal flackage in fluid (I.E. rear diff and transfer case). Could be a viscous coupler in transfer case or clutches in rear diff. If I was in Vegas betting, I would bet rear diff.

Besides that, all I can say is have a cell phone in truck and sign up for AAA.

Good luck!

[ScoutII]

Kinda sounds like the pin holding the spider gears is walking out. Retainer bolt breaks off which allows the pin to slide. Not hard to check just pull back cover from rear end.

[Jeremy airjer W]

Quote:

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Kinda sounds like the pin holding the spider gears is walking out. Retainer bolt breaks off which allows the pin to slide. Not hard to check just pull back cover from rear end.

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Wouldn't have thought of that!

[Melon]

Sounds exactly like what my 99 was doing. Ending up putting a new rear diff in. 2 spline left on the thing, ended up rolling into my driveway on the way home from work one day.

[BIG DS]

Good call Scout. Those rear ends are notorious for those spider pinions working out. 4 years ago I had one bust a chunk off of the spider pinion and go through the ring and pinion. You can imagine the banging and clunking and subsequent swearing when that happened. C-clips fell off the ends of the axels when that happened and by the time I got the suburban stopped, the inside of both rear tires were even with the outside of the fender. I managed to twist both axel shafts, crack the carrier, and destroy the ring and pinion. Good thing I am a mechanic or that could have gotten spendy. Now I am into the habit of changing the diff fluid every 6 months. That way I can also keep an eye on the diff parts. Since the catastrophic failure 4 years ago, I have replaced the spider pinion and lock bolt twice and spider and side gear kit once.

[ccarlson]

Thanks for all the tips guys. I'll have a chance to look at it this weekend and will check all the suggestions.

When it happened last weekend, it was on a longer trip. Now we've driven it to work a couple of short trips this week with no problem or clunking. I don't know if that is just luck or if the temp of the differential just doesn't get high enough for it to happen. Either way, I don't plan to let it go so will be checking it out or taking it in if I don't find it.

Thanks again,

ccarlson