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Transfer Case and Speedometer

jyreene

jyreene

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Location
Oceanside
Wow, today was not a great day. Dropped off the Jimmy to get some work done that I just don't have time for and something I just can't do. Found out that the transfer case is leaking and needs to be rebuilt, if possible, or just replaced. A replacement, as you all know, just isn't easy to find. Yeah me.

Plus I was trying to get the Speedometer fixed so I could know how fast I was actually going...only to get a call that they couldn't do it and that the nearest shop is 3 hours north....

After calling 4Wheel Parts I might be saved...if I can find the time to get off work early enough and drop it off at a local transmission shop. Anyone in the Oceanside area have any leads about getting the Speedometer to read correctly if the transmission shop can only fix the transfer case?

Of course I'll jump on here and track down a transfer case if it comes down to it.
 
Is the spedo not registering any speed or is it just off? If off then the tcase has a gear you a can change out... say you go to a bigger tire size. With the spedo if it is bad just hit the junk yards.. they seam to be a common part to find. Also check the cable maybe it has snapped.
 
OK, why is the speedometer wrong?
Is it not working, or reading wrong due to the tires?
If its wrong due to the tires, you can change the gear in the transfer case if its an older one, or reprogram the VSS if its newer.
 
The speedo is working. It exponentially is more incorrect. at 15 MPH it's about right. When it reads 85 I'm actually doing about 68, or so. As to the gear, I do know that someone, I would say I but I have never done that before and don't know where to begin or what tools I would need, could replace the gear with the right one. Is it a matter of just doing some math with regards to the tire size I have, the gearing I have, and the kind of transmission?

VSS...variable speed sensor? How do I check if that's what I have. The guy at the shop I take it to said I would have to take it to a speedo shop, the one a few hundred miles away, and they would have to hook it up to their machine to calibrate it correctly. I would think that implies VSS but the last vehicle I worked on religiously was my 73 Camaro and 68 Jeep J2000 and neither of those had anything remotely like a VSS.

I think you are pointing me in the right direction but now I need to know how to go about getting it right and quite possibly getting the transfer case fix. I'll re-post once I find out more this week.
 
Regarding the mechanical speedos: They're set up as a gear ratio, so you'll be off by a percent. As such, it would naturally be closer to accurate at a lower speed and farther off the faster you go. Odd that it would read faster than your actual speed though, unless someone swapped in a different speedo gear in the past to correct for larger tires and then you put on smaller tires. I had a truck that was off by 10%, so I could very quickly calculate my actual speed. Yours seems to be off by about 25% which is pretty big.

The gear is a little plastic thing at the end of the speedo cable - he's not talking about removing drive gears from your t-case. Your truck being an '86 should have the gear, not the VSS.
 
I bought the Jimmy with 33s on it but put 32s on it for a little better gas (which has given me 2MPGs better) but it was reading high when I bought it, just not quite as high. He did change the stock gears to 3.83, I think I have to find that paperwork that states the exact ratio.
 
The change in gears along with the change in tire size from the stock 31" tire likely accounts for why your speedo is reading wrong. You probably have 3.73 gears - I haven't heard of 3.83, but I'm also no expert. You should be able to fix it very easily by experimenting with a variety of speedo gears.
 
3.73 sounds more right. I'm not what you would call an expert mechanic but more of an enthusiast!
 
OK, if you have the mechanical drive, it is probably dead simple to fix.
There are two gears, both plastic.
One, on the end of the speedometer cable, and it can be changed by removing one or two bolts.

Sometimes the other gear that drives that gear has to be changed, and its a little more complicated.

There are a couple of good websites that sell the gears and have charts to show which gears you need.
If no one chimes in with a link, I'll dig it up tomorrow. Try a google on gm speedometer gears.
Or do a search here for the same thing.

A VSS is an electronic box that computes your speed based on the pulses from a pulse generator attached where your speedometer cable is attached now. Your truck does not have one, so don't worry.
 
Fordum said:
OK, if you have the mechanical drive, it is probably dead simple to fix.
There are two gears, both plastic.
One, on the end of the speedometer cable, and it can be changed by removing one or two bolts.

Sometimes the other gear that drives that gear has to be changed, and its a little more complicated.

There are a couple of good websites that sell the gears and have charts to show which gears you need.
If no one chimes in with a link, I'll dig it up tomorrow. Try a google on gm speedometer gears.
Or do a search here for the same thing.

A VSS is an electronic box that computes your speed based on the pulses from a pulse generator attached where your speedometer cable is attached now. Your truck does not have one, so don't worry.
Click to expand...

Thanks Fordum. I've found one site but I'll need to have my Jimmy back to do the math. Hopefully I get off of work early enough to pick it up but I will still have to take it to the tranny shop just to get that damned transfer case fixed.
 
It's essentially been lined out as to what you need to fix the speedo, should be just a gear change.

jyreene said:
A replacement, as you all know, just isn't easy to find. Yeah me.
Click to expand...

It's quite possible that there isn't a cheaper and more available junkyard transfer case than the one one you need, if a shop told you they're rare and wanted $$$ I'd reconsider taking my truck there.
 
It's quite possible that there isn't a cheaper and more available junkyard transfer case than the one one you need, if a shop told you they're rare and wanted $$$ I'd reconsider taking my truck there.[/QUOTE]

Good advice to go somewhere else. I had a shop offer to get rid of my junky 205 and put in a freshly rebuilt 203 they had which is much better. Even though the only thing they were doing was rebuilding the tranny. And they would make me a good deal on it too all I would have to pay on the T-case was the cost of the rebuild.
 
38377k5 said:
It's essentially been lined out as to what you need to fix the speedo, should be just a gear change.

It's quite possible that there isn't a cheaper and more available junkyard transfer case than the one one you need, if a shop told you they're rare and wanted $$$ I'd reconsider taking my truck there.
Click to expand...

Yes I should be able to track down the speedo problem. I do hope it's the one at the end of the speedo cable though. I did some more research after your guys' posts and did find ( http://www.transmissioncenter.org/GM_Speedometer_Gears.htm ). If it's the one that's not easy to get to then no big deal. I think I tracked down a good tranny shop like I said but now I have the knowledge to know if they are bull****ting me.

It's not that they said they are rare just that you can't get them new. The shop has always been honest with me before but this did worry me. Thinking back I see no reason why the transfer case doesn't just need a simple rebuild. The main reason I brought it in was because when I tracked a leak I thought it was coming from the tranny. Apparently it's coming from the where the transfer case halves join. Something I wouldn't mind learning how to fix but just really don't have the time. The four wheel drive works fine but with the leak I'm sure that could change once it was too low on fluid. That said with the way my memory works I could be missing a few details. Thanks for the help. I'll keep you apprised of any new info to make sure I'm not being bilked out of some money.
 
If you need a rebuilt 208, a good friend of mine that has a 4WD shop may have one at a good price. NP208 are not rare they where used in all 1/2 ton chevy's from '81 till teethe late '80's when they changed to a NP241. Your speedometer is off so far probably from the gear change to the tire size. Just need to get the right speedo gear.
 
Teck said:
If you need a rebuilt 208, a good friend of mine that has a 4WD shop may have one at a good price. NP208 are not rare they where used in all 1/2 ton chevy's from '81 till teethe late '80's when they changed to a NP241. Your speedometer is off so far probably from the gear change to the tire size. Just need to get the right speedo gear.
Click to expand...

I'll let you know after I hear from the tranny shop.
 
why does it need a new t-case? Isn't it just leaking? I would think a reseal job would be much cheaper than a reman case.
 
POORBOYK5 said:
why does it need a new t-case? Isn't it just leaking? I would think a reseal job would be much cheaper than a reman case.
Click to expand...

I think he's already established it doesn't need to be replaced, just rebuilt, or resealed at the very least.

Just to add some more thought to this, if they are going to charge X amount of dollars to reseal the unit, it's probably not much more to rebuild it at that point. Take into consideration age and mileage and it may be time for a rebuild anyway.

To the OP. You should verify the axle gears first. That way you can have the trans shop doing the rebuild swap out the speedo gears while they are in there. Do it right and do it once the first time.

These things should be brought up to your trans guy, see what they think or can do.
 
I got the Jimmy back today. The shop manager had no clue what he was talking about. I spoke to the mechanic and it was not the seal joining the two halves together but the seal where the transmission and transfer case that was junked. So that was a relief.

I did manage to find a speedo shop in SD that will be able to put in the correct gear while my wife waits. I'd try myself but I literally have no time so I have to resort to paying someone. Thanks for all the clues as to what I should look out for.

If the speedo shop is a no go I'll revive this one for some more advice but it will have to be at the end of Feb.

Thanks guys!
 
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