Speedo wrong, but is that all?

Tire size same? Did the transmission or transfer case get changed? There's a plastic gear that is changeable that drives the speed sensor... perhaps that gear is wrong now? You don't have a cable drive speedo, do you? Later speedos are basically a meter movement; the computer puts out volts and the speedo displays mph. __ Steve .

You need to only jack up one wheel to spin and get the ratio.

I chalk mark the tire and the u-joint so I can count it easier. With one wheel in the air only, the wheel needs two rotations to give you the ratio.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

The Hurdy Gurdy Man wrote:

I think you have hit on a very real possibility. If the rear end was swapped aftger a gear change, then the front and rear will now be geared differently, and this could be a big problem for the tcase.

Raise one of the rear tires and spin it a full revolution, the drive shaft will spin twice the number of turns as the ratio. Or, turn the raised tire one-half revolution, and watch the driveshaft. Don't forget to set the trans to N.

I don't think you can use the casting marks because we suspect the gears are not the same anyway. The most common ratios you will find are 3.07, 3.73,

4.10. These are the factory ratios, and the 4.10 is for the 4 banger motor. You should be able to see the obvious difference in 3, 3.75, and 4 turns of the driveshaft.

The gears could have been swapped out, but the speedo was never corrected, and this would explain what you are noticing, and the front and the rear are likely to have the same gear sets.

You need to determine if the same gears are in the front and th erear before you worry about anything else.

I have what is clearly the world's worst news feed being that none of the replies to my original post have shown up yet, but I can see on Google that there have been quite a few. Thanks to all that have replied! Here's what I've done and discovered so far, but it's raised a few more questions as a result (isn't that always the way?).

I put one rear tire up in the air, shifted into neutral, marked a spot on the tire, spun it twice and counted the number of turns of the driveshaft. This gave me about 3.08 ~ 3.10 turns for two tire rotations... accounting for any slop in the process, I'm guessing this means I have 3.07 gears on the rear. It's a 1994 with a 4.0L engine and a five speed manual transmission, which I'm assuming is reasonable. So then I tried this same procedure with the front, but... nothing. With one tire on the ground, one in the air, and the various gear selectors moved into all kinds of different positions (in gear, neutral, 2WD, 4WD, etc.) I couldn't get the driveshaft to move while I turned the wheel. I don't see any sort of locking mechanism on the wheel hubs, and the only tube running into the front differential that seems like it migh control something on the inside seems to only be a vent tube that runs up by the radiator, so I'm not sure what I'm missing here... sometimes you can turn the driveshaft by hand and get a very slight bit of movement in the wheel, but definitely nothing solid and absolutely not the other way around. Is there some different trick I should be trying here? I'm a stranger to the ways of 4WD, and my shop manual is still four days out, so I'm at a loss for what to try next. It seems to me the lgoic behind the procedure is sound, but then I could very well be overlooking something critical.

The speedometer is most decidedly an electronic one and not cable driven, and presumably has been since the day it was born as the gauges have never been changed. The tires are slightly larger than the originals, but that was the case before the accident and the speedo offset due to that was a fairly minor one. Certainly not the 15 or so MPH it's reading off now. I see that quadratec.com sells a recalibration box, plus there's a bevy of potential speedometer gear changes that can be done, so once I figure out exactly why it's incorrect I'll make my next move. It is possible that some portion of the drivetrain was swapped out during the repair, especially considering how much cleaner the transmission is than various other parts of the car... but that information is only suggestive of what happened, and not conclusive.

I'll get under there this weekend and pop out the current speedo gear to see what it is. I don't want to pop open the front differential cover and actually count gear teeth, but if that's the only solution then I will. It's probably overdue for a fluid change anyhow. There's also a temptation to just put the thing up on four stands and put it in gear to see what happens... might be a faster way of figuring out what's up with the front differential!

Thanks again to everyone who has helped on this rather perplexing problem, hopefully I'll be to the bottom of it soon.

Bryan

I think you'll be very displeased when you open it... I think you're going to find lots of broken metal. __ Steve .

Man, you aren't going to be a happy camper when you open that front up.

The 94's have a locked front axle setup, no vacuum or anything else to turn it on. You spin one wheel in the air, the driveshaft must turn....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

The Hurdy Gurdy Man wrote:

You sure there's not a small lump on the passenger side of the axle with some vacuum lines running to it? Start the engine, pull the tc into 4-HI and give it a few seconds. "PART TIME" light should come on. Leave the shift lever there and shut the engine down. NOW jack up one wheel and try it. You have to engage the front axle before you get anything otherwise the little stub axle on the passenger side spins merrily along just as you describe. If the drive shaft still doesn't turn, you probably won't like what you find when you take the cover off the front diff.

3.07 sounds like stock gear>

Up to a 95 has the vacuum disconnect?

Ok, he just needs to put it in 4x4 and drive it a couple feet to click it in then first.

Mike

"L.W.(ßill) Hughes III" wrote:

I think I was mistaken...

Mike

Will H>

Ah, that would explain it... I had been looking at the differential housing itself for a clue instead of outside on the axle tubes... plus I was looking from the front, so I didn't see that vacuum motor-ish thingy hiding away. So I jacked up one wheel, started the car, and put it into 4WD... this seemed to do the trick, I was able to spin the wheel and subsequently rotate the driveshaft. Two turns of the wheel and I got a 3.07 ratio, which is excellent news for me. Thanks again to everyone who helped me sort this out!

I still need to yank the current speedo gear and see what's up with that, but if that's why it's wrong I have to wonder how the wrong gear got put in there. If they swapped in a new transfer case and/or transmission, I hope that isn't a recipe for disaster... like if they put in parts that were originally meant for a smaller engine Jeep if it's the kind of thing where they won't survive behind the 4.0L for very long. Hopefully that's not the case, but I suppose looking at the speedo gear might give a clue. Especially if it's a gear for one of the other factory ratios that were available, maybe the entire transfer case was swapped out including the old speedo sender and replaced with one originally in a smaller engine Jeep. Eventually I'll get to the bottom of this, but for now it's good to know that the 4WD functionality is still there. Thanks again, everyone!

Bryan

Ok, so after some more dabbling, it's a safe bet the speedo gear was WAY wrong... for a 3.07 gear ratio with tires that were somewhere between 28 and

29 inches, the charts I have found say I should have maybe a 29 tooth gear in there. Or maybe a 30, it just sort of depends on whose chart I consult. However, there was a 37 tooth gear in there! I have NO idea why that would be. I do think the transfer case was probably swapped during the repair, since the normal patina of filth covering everything else seems to stop at exactly all the edges of the transfer case. But why this gear was in there... that one just escapes me.

Does anyone know if it'd be possible to do a transfer case swap and actually put on a case meant for a smaller engine, thus creating reliability problems? I hope not, because it would mean all that's left to do now is order the correct gear. Thanks again, everyone!

Bryan

perhaps someone had bigger tyres on before they sold it to you.