General 4WD Questions ('92 mainly)

I believe the pre-95 Explorers had a "traditional" 4WD setup where the transfer case locked the front and rear driveshafts when engaged and automatic (sometimes replaced with manual) hubs on the front wheels allowed power to be engaged. There may also have been some sort of front axle disconnect tied in with the transfer case. In no case when in 4WD do the rear wheels travel faster than the front unless something is wrong and you do not have the front wheels engaged (that is to say, your 4WD is not working). The hubs were known to wear out, so they may need replacing, and if there is a front axle disconnect that may need to be checked as well. Some checks you could make: do you hear the transfer case engage when selecting 4WD? On a dry surface and at slow speeds, does the vehicle "bind up" in 4WD during a turn (it should, which is why you shouldn't drive with

4WD engaged on dry surfaces)? On slippery surfaces do the front wheels spin under acceleration the same as the rear wheels?

From your description of the clunking and driveshaft, sounds like the hubs are bad in that vehicle. The front differential does allow slippage so if one side is spinning the other will not turn.

=Vic= Bear Gap, PA

Thanks. I guess I misunderstood something that I read a long time ago. I thought that the gear ratio was different on the front as opposed to the rear resulting in the wheels turning at different speeds.

I'm hoping it's just the autohubs that have gone bad finally. I put Warn manuals on my '91 and have one possibly good autohub left over that I can try and see if it clears up the "clunk" on the '92.

Just a reminder that you should NOT engage the 4WD on any surface that does not allow some tire slip. You suggest that the rears drive at a different speed. Not entirely accurate, BUT when you do turn, the fronts need to turn faster that the rears, since they follow a larger arc than the rears. With the transfer case locked in 4WD, turning will cause the driveline to bind up as the front tries to turn faster than the rear but can't. This shows up as clunking and feels like you have less power. On a loose or slippery surface, no problem as the tires will slip some to allow the difference in speed/distance travelled. But on hard stuff, you really strain things, including the plastic splines in he auto-hubs, when you use 4WD.

The failure mode on the early 4WD hubs is a grinding sound as they try to engage but can't.

Hope this helps!

dr bob

Ulysses wrote:

Well, I guess some dirt is slipperier than other dirt, but I'm getting the clunk on fairly loose dirt where I'm not feeling any binding.

Thanks for the explanation about the tire-turning speeds. I'm not sure where it came from but someone or something said the gear ratio was different on the front. Maybe someone who wasn't real knowledgeable told me that and it got stuck in my brain. So much for my theory about all tires turning at the same rate keeping the car from going sideways. Now I know why so many SUVs have those little propellers on the back. Sounds like a rudder might be useful too for the driving I do (mud over 2 feet deep sometimes). Is there a better tire I should be using for mud? I have Michelins LTXs and they seem to be good overall in various conditions. AAMOF There were people at the top of what we now call "Stuck Car Hill" that were cheering when I actually made it without getting stuck, so maybe the Michelins are pretty good after all. I tried BFG All Terrain/TAs on my wife's '92 and we both thought they were not as good as the ol' recalled Firestone Wilderness tires. They (BFGs) seemed to slide more on ice and mud and were a real bitch to try to put chains on. They seemed to be good on loose dirt though.

So, if the drivetrain is binding due to lack of slip does that mean the front differential on the early Explorers does not slip? I thought (here I go probably being wrong again) that if one side had traction and the other didn't the one without traction would spin and the other would slip.

The binding in 4wd with a locked transfer case is due to the different speeds between the front wheels and rear wheels in a turn, not a locked differential (unless yours has been modified). The rear wheels make a smaller circle when you turn, so they must go slower and if you are in 4wd either a wheel has to slip somewhere or something has to break. You would get the same effect even in a 2wd vehicle with a locked differential. I do understand that some mud racers (off road only, of course) use different gearing in the front and rear to keep the rear spinning for floatation or something, but that is a specialty application. Newer Explorers use Control Trac which, in auto mode, release the transfer case frequently so the bind up doesn't occur, or use AWD which does not lock the front and rear axles together but in effect uses a differential between front and rear (which also means it doesn't supply as much traction in poor traction situations).

I personally don't think you can do better than the Michelin LTX series on an Explorer. The M/S version is the one I prefer overall, having had both, but the A/T version has a more aggressive tread pattern if you spend a significant amount of time off road. In snow and typical muddy farm and logging road use to repair radio repeaters I see no difference in traction and the M/S versions are more pleasant on the highway.

=Vic= Bear Gap, PA

Just a general comment - I thought it was standard practice to cut the front differential ring gear with one less tooth than the rear. This causes the front tires to want to pull more (turn faster) than the rear tires. The reason you want this to be the case is that it adds greatly to the vehicle controlability on soft (dirt, mud, snow) surfaces. You want the front end to pull you into a turn rather than allow the back enbd to puch the front end into a plow.

My experience is limited to the Chrisler products and all I have heard about the others. Local 4WD shops understand that the gear ratios are slightly different front to back on all 4WD vehicles. Their repair experience is high but their design experience is neglegable.

I'll emphasize as others have. If you engage 4WD on dry paved surface, you will most assuredly burn something up very quickly. Bank on it.

Regarding AutoHubs - if you are not very technical, manual hubs are dirt simple and will never mislead you. They are either engaged or not. Either condition is very easy to verify.

I, on the other hand prefer AutoHubs. I think they are mechanically quite sophisticated and very clever in design. Besides they are cute... sometime troublesome but cute.

I probably confused things more than I helped. Sorry

G

Professor,

Time to go back to school. The ring and pinion ratios are identical front and rear. If you modify one, you must modify the other to match them. If not, there would be big driveline problems.

-Fred W

This was my understanding before I posted my question here. But it also seems to me that by having the rear wheels turn a bit faster than the front might be part of the problem I have going sideways in slippery mud. Of course there are so many factors involved here that it might be hard to determine if identical gear ratios would help.

It seems that on the early Explorers it was the autohubs that burned first.

I mistakenly thought that the reason why there is binding on turns in 4WD on non-slip surfaces was because the differential was not slipping on the wheel inside the turn. I now (think) I understand that it is between the front and rear wheels that causes the binding to occur. Right now I'm trying to understand how I could have one autohub working effectively giving me 3 wheel drive and why is the wheel with the traction not slipping but the one with the bad hub just sits there. It seems like with a bad hub neither front wheel would turn.

It's a yes and no issue. There were a few cases of vehicles having different front and rear ratios but it was usually due to the choice of differentials. My memory may be a little off but I think for a while Chevy had a rear diff with a 3.08 ratio and the front with 3.07 or something like that. Not really by "design" but because of the "brand" of axle they choose for each end - that's what was available in each brand. That minor difference isn't a problem off road.