Bouncing speedometer

[Dutch Rutter]

My speedo was doing great for the longest time. Then it started reading just a little slow, then it started bouncing when coming to a stop and when leaving a stop.

I replaced the cable, and recently replaced the speedometer itself. Still the problem persists. It's even gotten a bit worse. When the speedo reads 65mph I'm actually traveling 75mph (2200-2300 rpm, in OD with the 700r4 and 305x70x16s (32.8" tall)).

I'm thinking the problem is in the gear that feeds the cable off the side of the transfer case (not sure what it's called). Would that be a correct assessment? And if so, how do I go about fixing this thing?

Thanks.

 

[73c20jim]

Bad tooth on either plastic gear in the transmission???. One comes out from the speedometer cable and one is in the tailshaft.

 

[Goldie Driver]

My speedo was doing great for the longest time. Then it started reading just a little slow, then it started bouncing when coming to a stop and when leaving a stop.

I replaced the cable, and recently replaced the speedometer itself. Still the problem persists. It's even gotten a bit worse. When the speedo reads 65mph I'm actually traveling 75mph (2200-2300 rpm, in OD with the 700r4 and 305x70x16s (32.8" tall)).

I'm thinking the problem is in the gear that feeds the cable off the side of the transfer case (not sure what it's called). Would that be a correct assessment? And if so, how do I go about fixing this thing?

Thanks.

Do you have cruise ?

Most of my problems went away when I replaced the cruise module although sub 10 MPH it still bounces some.







Over 85, too.



( The immediate above is 100% . I have never had the speedo above 70. )

 

[Dutch Rutter]

Those drive/driven gears are the exact ones I was thinking is the problem. Guess I'll be pulling into those this weekend. Should I order the gear combos and have them on hand before opening things up, or are those something the local NAPA should have?

@Goldie Driver
I do have cruise however, it's completely disconnected and has never functioned while I've owned the truck. Would that still cause some trouble?

If I didn't want to replace the speedo anyway I'd be kinda kicking myself in the butt for spending the $130 for the new one. New one does have the hundred thousand mile counter though so that's a nice change.

 

[SirRobyn0]

Do you get any noise with that bounce? It's easy enough to check the gear simply by pulling it out of the transmission housing and giving it a visual inspection. If you replace that, or decide that it is still good and you rule out the cruise control, I'd have another look at the speedometer cable. A cable that is to long will bind at lower speeds and cause bounce. As they age they will tend to get longer as the cable stretches, it's also not uncommon to get one all ready to long as it seems they are not manufacturing them to as tight of tolerances as they use to. You can test this issue by sliding a small washer onto the cable between the speedometer head and cable. If you drive it and it's better remove the cable and grind an 1/8" or less off the end of it and reassemble. The added washer should then be removed. Using a washer to check for length issue is a great test but long term could damage the cable.

 

[Bextreme04]

A bouncy speedometer and reading lower than actual speed is almost always from too much resistance in driven side of the cable. So that would mean speedometer, cable, or cruise control module. If you have replaced both cables and the speedometer, then the cruise module is the next most likely culprit. There isn't enough slack in that little gearbox or the drive gears to cause a bounce or a wrong reading. Do you have the speedometer cable unhooked from the cruise module and going straight to the back of the speedometer? Did you make sure there are no tight radius bends?

 

[Goldie Driver]

Those drive/driven gears are the exact ones I was thinking is the problem. Guess I'll be pulling into those this weekend. Should I order the gear combos and have them on hand before opening things up, or are those something the local NAPA should have?

@Goldie Driver
I do have cruise however, it's completely disconnected and has never functioned while I've owned the truck. Would that still cause some trouble?

If I didn't want to replace the speedo anyway I'd be kinda kicking myself in the butt for spending the $130 for the new one. New one does have the hundred thousand mile counter though so that's a nice change.

If by disconnected you mean the speedo cable no longer goes into it or out of it then yes, I'd say that eliminates it.

If the cables still go into it then possibly.

I changed mine for that reason - it pretty much worked. The cruise worked with the old module, too.

 

[Dutch Rutter]

@SirRobyn0

Thats a good idea. When I replaced the cable I did the whole thing outter and inner. I felt it was the correct length maybe a 2-4 inches too long.

@Bextreme04

While installing the new cable I was pretty careful routing it, but I'll slide under there and make sure nothing moved around too much. And yes the cable is ran directly to the back of the speedometer and has been that way since I've owned it so I'm guessing a previous owner removed/bypassed the cruise module.

No real sounds after I replaced the speedo. The old speedo did kind of sound like a feint dry spring sound when coming to a stop but that seems to have disappeared with the new one.

I'll crawl under there tonight after work and see about pulling that gear thing and see what I can see.

 

[Vbb199]

Kinked cable

Oh nvm

Damaged gears in trans?

 

[Dutch Rutter]

Alright all knowing gurus. Cable still looks good and not kinked. This is what I had underneath and second picture is where I have it now. Does that circular part come out of the transfer case? Also should I open that box piece I took off?

Edit: I already did... see third pic

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Looks like a PO used RTV or some **** on that circular piece.. I gave it some light taps and couldn't get it to budge. Really don't wanna bust the teeth bits off it.

 

[Itali83]

What is that gear box for between speedo gear drive and the cable?

ben

 

[Dutch Rutter]

What is that gear box for between speedo gear drive and the cable?

ben

Looks to me to be an adapter for the larger tires. There are all metal gears inside of it that seem to be interchangeable. Teeth in there all look good.

I've never seen one like this before. But thats not saying much, I'm in pretty unfamiliar territory.

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[gmbellew]

shouldn't you be able to swap the gears in the transmission itself (getting the right parts for the current tire size and gear ratio) and skip the adapter if it is broken? or they may still make adapters like that, I don't know...

 

[Dutch Rutter]

Here it is. Got the damn thing out with some ingenuity. And here's all the gears. Don't look half bad I don't think.

So are we thinking it's that box doodad?

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[gmbellew]

https://www.tciauto.com/speedometer-gear-calculator

I'd start here and get the right stuff to ditch the adapter box.