Speedometer not working. Gauge good, cable not turning. Common problem?

[buckroseau]

Picked up my new to me 1985 M998 last Wed. Had to pick up some new batteries for it, got those in this weekend. Did a quick check of some basic things and wanted to take it for a spin. Everything seemed to work except the speedo?

I pulled the gauge cluster and popped the speedo out. Hooked a cordless drill up to it and it spun up, so that's working. I then took it for a quick spin down the driveway while holding the cable end in the dash, it is NOT turning.

I followed the cable back, looks like it goes into the top of the T case. I didn't pull the cable off that end yet. Just wondering if anyone else has seen this problem and is there something common I should be looking for. Cable or in the T case itself.

Thanks in advance, Matt

 

[hummer4x4guy]

Matt, I've had issues with my speedo cable until I installed the longer cable and routed it with a larger wider bend towards the back. I don't have the man off hand but that did help and some guys have filled the cable with speedo cable grease.

 

[Retiredwarhorses]

You won't know till you take it off the speedo adapter at the case, I would also remove the speedo adapter, I see a lot the keys break, as they are supposed too...what I do is test from the taste forward...so take your drill and do the same test, that will check the cable...cables are cheap and easy to run.

 

[papakb]

This is actually a fairly common problem. There is a small right angle adapter on the transfer case that's part of the speedo drive system that sometimes loosens up during use and there's a short (~2") piece of speedometer cable that connects it to the trans. When this happens that cable rounds out and won't drive the main speedometer cable any more. Sometimes all you have to do is tighten it back up. If that doesn't fix it remove the gearbox from the trans and drive that with your drill and see if you get a reading. If you do then the gear in the trans could be broken but that isn't very common.

Kurt​

 

[buckroseau]

This is actually a fairly common problem. There is a small right angle adapter on the transfer case that's part of the speedo drive system that sometimes loosens up during use and there's a short (~2") piece of speedometer cable that connects it to the trans. When this happens that cable rounds out and won't drive the main speedometer cable any more. Sometimes all you have to do is tighten it back up. If that doesn't fix it remove the gearbox from the trans and drive that with your drill and see if you get a reading. If you do then the gear in the trans could be broken but that isn't very common.

Kurt​

When you say, "gearbox" you are referring to the 90 degree part that adapts the cable into the t case, correct?

I crawled underneath there tonight. I see the large nut from the speedo cable that goes into the, "gearbox". And then what looks to be a large nut that threads onto the top of the T case on the gear box. I'm assuming if I back that large gearbox nut off the T case it pulls straight out? Nothing to screw up?

 

[papakb]

Yes, that is the part I'm referring to. Part #24 is the segment that wears out.

Kurt

 

[buckroseau]

Yes, that is the part I'm referring to. Part #24 is the segment that wears out.

Kurt

I haven't had a chance to take that apart yet, probably won't until this weekend. Assuming the key is sheared, where do I obtain one?

 

[papakb]

the Hummer Parts Guy would be one source. http://www.hummerpartsguy.com/

 

[Pablo66]

I recently had the same problem.. That key snapped in half. Hummer parts guy didn't have it, but Kascar did.

 

[buckroseau]

Ok, I think I found the problem! The red gear inside the T case is obviously toast as you can see. Before I took the cast piece off the top of the T case I could see with the mirror that one side was jacked up a good 1/8" so it was installed incorrectly or not straight. Now I have a couple more questions?

1. Are there different versions of this red gear? I counted 35 or 36 teeth but I could be wrong, this thing is ground down pretty bad. Found this one, will it work? https://www.real4wd.com/zedSuite/catalog/partdetail.aspx?PartNo=12342602

2. I was looking in the T case with a mirror underneath, I can see part of a green worm gear I'm assuming the red gear drives off of, looks fine. But I can't see what's underneath the fluid. Is there a pin or hole that the red gear sits on. I'm assuming there has to be, and can you kinda feel it when you install the gear into the T case?

FYI My Humvee is a 1985.


Thanks Matt

 

[buckroseau]

I was able to peel back some of the melted plastic and get an accurate count, it is a 36 tooth. Now is that correct for an 85?