Speedo Cable and speedo gear box

[thedudeabides86]

Hi everybody.

I know there's been several posts on speedo cables not working and some are from years ago, but I wanted to get a fresh perspective on this. The speedometer on my '72 C20 had bounced sporadically in the past and I bought some Cable-ease to grease it and see if that solved the issue. I opened the end at the back of the speedometer and pulled the cable all the way out, lubed it, and slid it back in. Upon doing that, the needle doesn't bounce or even move now. I noticed the end of the cable at the trans is sorta squared. Does that need to be seated properly in the speedo gear box? How about at the back of the speedometer in the cluster? Is there propery "seating" that should be done?

Since the speedometer stopped moving altogether, I went down to the trans and pulled out the nylon gear at the gear box thinking maybe it was all work, but it looks fine. Do I need to get the to line up properly in the trans? if so, how do I do that correctly? It's set a ways into the trans housing that I'm not sure the right way to line it up. So, that's where I'm at. If anyone has any suggestions, I'd really appreciate it. Thank you.

[72SB]

Yes the square end of cable needs to mate (go into) with the female square base of speedo and plastic speedo gear in trans

[thedudeabides86]

Originally Posted by 72SB

Yes the square end of cable needs to mate (go into) with the female square base of speedo and plastic speedo gear in trans

Got it. Thank you. I'll take a closer look at it and make sure it's all seated properly and test it out.

[thedudeabides86]

So, the cable is mated with the gearbox, but how in the world would I know for certain if I got the plastic speedo gear lined up with the trans? I can put the plastic gear in and spin it with my fingers until I feel in jive with the trans but the moment I attempt to place the speedo box back or any movement for that matter, I misalign them. The plastic speedo gear isn't all chewed up, but would the gear in the trans be? I'm not sure how to check it, I guess.

Originally Posted by 72SB

Yes the square end of cable needs to mate (go into) with the female square base of speedo and plastic speedo gear in trans

[HO455]

It's been my experience that you can turn the cable end at the speedometer end back and forth until it drops into the gear in the transmission.

The cable is supposed to be perfect sized so the cable fitting at the speedometer won't thread on completely if the cable hasn't slid into the end of the gear.

I am assuming your transmission is a T400?

[72SB]

You would need to use a flashlight or probe camera to see the drive gear inside the trans.

If you just put the driven gear in the bullet and slide that in, the teeth should just mesh or you may slightly just need to twist the bullet some until they do. Then put the speedo cable in end of bullet, after you secure bullet with the one hold down bolt & metal tab

If the driven gear has been changed to one with less teeth do to a rear gear swap or tire size change...it "may" be just 1 tooth to small and no longer engaging the drive gear

given, if I understand correctly everything worked before you pulled cable, I suspect you just don't have the speedo cable engaged in either speedo or trans.

For me they have always basically fallen in place when I have worked on cable or gears

if cable is good and engaged and driven gear is good the only other reason for no work is either the drive gear is messed up or the gear inside speedo is. Usually you would see chipped teeth on driven gear if drive gear was bad

[thedudeabides86]

Originally Posted by 72SB

You would need to use a flashlight or probe camera to see the drive gear inside the trans.

If you just put the driven gear in the bullet and slide that in, the teeth should just mesh or you may slightly just need to twist the bullet some until they do. Then put the speedo cable in end of bullet, after you secure bullet with the one hold down bolt & metal tab

If the driven gear has been changed to one with less teeth do to a rear gear swap or tire size change...it "may" be just 1 tooth to small and no longer engaging the drive gear

given, if I understand correctly everything worked before you pulled cable, I suspect you just don't have the speedo cable engaged in either speedo or trans.

For me they have always basically fallen in place when I have worked on cable or gears

if cable is good and engaged and driven gear is good the only other reason for no work is either the drive gear is messed up or the gear inside speedo is. Usually you would see chipped teeth on driven gear if drive gear was bad

So, fitting in with the way my day has gone so far, the nylon gear slipped into the trans housing and I can’t seem to fish it out of there. Can I drive home with the gear in there? I’m at work and can’t drop the driveshaft here. Gotta pick the kids up. Is it bad to drive with the nylon gear loose inside the housing? 🙄🙄
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[thedudeabides86]

Originally Posted by HO455

It's been my experience that you can turn the cable end at the speedometer end back and forth until it drops into the gear in the transmission.

The cable is supposed to be perfect sized so the cable fitting at the speedometer won't thread on completely if the cable hasn't slid into the end of the gear.

I am assuming your transmission is a T400?

I have a T350 trans and bad luck. The speedo gear dropped into the trans case and I'm not sure how to get it out.

[LNP]

Were you trying to put the gear in the trans without the gear housing? The housing itself automatically lines the gear up in place. I dont understand how you dropped the gear inside the trans? Get a piece of wire form a hook and fish it out. The tail shaft housing isnt that deep

[thedudeabides86]

Originally Posted by LNP

Were you trying to put the gear in the trans without the gear housing? The housing itself automatically lines the gear up in place. I dont understand how you dropped the gear inside the trans? Get a piece of wire form a hook and fish it out. The tail shaft housing isnt that deep

I had the speedo gear in the box and as I pulled it away, I bumped the housing and *bloop*, right in the hole. I felt around for it and couldn't feel it. I've never disassembled a tranny and I'm parked at work.

[Indyuke]

LNP is correct, the tailshaft housing isn't that deep. Unless the gear slid quite a ways forward, you should be able to pull it out with a piece of wire.

I believe there should be a clip that holds the little gear in place. You may have to pull the tailshaft off eventually to replace that clip.

Driving the truck with the gear inside would be your call. There's not really anything inside the housing that would chew up that little gear if it's just laying on the bottom. Here's a thread showing the area with the tailhousing removed.

[thedudeabides86]

Originally Posted by Indyuke

LNP is correct, the tailshaft housing isn't that deep. Unless the gear slid quite a ways forward, you should be able to pull it out with a piece of wire.

I believe there should be a clip that holds the little gear in place. You may have to pull the tailshaft off eventually to replace that clip.

Driving the truck with the gear inside would be your call. There's not really anything inside the housing that would chew up that little gear if it's just laying on the bottom. Here's a thread showing the area with the tailhousing removed.

That's an awesome post for reference. I'll try and do some fishing, but for now I'll leave the truck parked overnight at work. I'd rather not risk messing the transmission. Thanks for all the help. I'll keep you posted.

[72SB]

If you are going to drive with the driven gear just laying inside the tail shaft, put the bullet back in and the speedo cable in so you don't puke tranny fluid driving

You can try and fish it out...but I suspect you will need to drop tailshaft which will drain all your fluid also

shiat happens, not a big deal, just work to get the tail shaft off. Get new gasket. You could just RTV it...but that is not what I would do

when you put the driven gear in, put it in the bullet first then slide the bullet/gear in

[LNP]

Actually if you think about it driving it even with the gear housing and cable in place it will push fluid out and up the cable housing into the speedometer. The driven gear seals the housing by a seal in it that the gear shaft goes thru. The seal should have held the gear in place but as said sh#t happens. If he cant get it out where it is I would have it towed. But I would put the housing and cable in place to minimize fluid loss.

[thedudeabides86]

Whelp, I think the best way to go about it will be to pull the driveshaft and the extentsion cover and fishing it out that way. I'm glad Indyuke posted the link to the other thread showing what it looks like.

What parts should I replace whilst I'm in there? Bearings, gaskets, etc?

[LNP]

Originally Posted by thedudeabides86

Whelp, I think the best way to go about it will be to pull the driveshaft and the extentsion cover and fishing it out that way. I'm glad Indyuke posted the link to the other thread showing what it looks like.

What parts should I replace whilst I'm in there? Bearings, gaskets, etc?

If everything is working fine then in my opinion nothing. But I would look for anything obvious and I would count the teeth on the drive gear. The speedometer drive gear is the one on the tail shaft. The driven gear is the one you lost inside the trans. If you have to get a new driven gear for any reason you will need to know how many teeth on the drive gear. You cant always go by the color of the gears as the trans fluid tints them so you cant tell the original color. I would get a new tail shaft housing gasket for sure.

[thedudeabides86]

Originally Posted by LNP

If everything is working fine then in my opinion nothing. But I would look for anything obvious and I would count the teeth on the drive gear. The speedometer drive gear is the one on the tail shaft. The driven gear is the one you lost inside the trans. If you have to get a new driven gear for any reason you will need to know how many teeth on the drive gear. You cant always go by the color of the gears as the trans fluid tints them so you cant tell the original color. I would get a new tail shaft housing gasket for sure.

I stopped at Oreilly to see about a tail shaft gasket and they couldn’t find anything in their system that would work. Is there a proper name or term I should have them search? I tried LMC but didn’t see anything there either.
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[LNP]

A lot of people call it a extension housing or output shaft housing, instead of tail shaft housing. Its a big o-ring. Heres a link to a seal kit. It has the housing seal drive shaft seal new seal for the inside and outside it the speedo gear housing. Comes with a new bushing as well. It goes at the end where the drive shaft yoke slides in.

https://www.classictransmissionsolut...free-shipping/

[thedudeabides86]

Well, update on the nylon speedo gear. I've retrieved it from the tail housing on the trans and got the drive shaft back in. Drove it home from work, still nothing on the speedo or the odometer. So, a car buddy of mine mentioned I could take the end off the gauge itself, and see if it's spinning as I drive it. I'll see if I can't tape a zip tie to the end of it and watch it spin?

[guyryan100]

Yes this would be an easy test, if you can lift a rear wheel you could do that test without driving, which might be easier to see the cable end.

[Accelo]

You can reuse the gasket on a THM400. If you want to add a little sealant that's fine also.
Just pull the driveline and the 6 bolts on the tail housing and retrieve the speedometer gear. No trick to reinstalling the housing. I typically install the gear after the housing is installed. Easy to inspect the gear when the housing is off. Just grasp the plastic gear and be sure it doesn't turn on the shaft. Only light hand pressure is all that is needed to prove it isn't loose.
Cheers

[HO455]

Originally Posted by guyryan100

Yes this would be an easy test, if you can lift a rear wheel you could do that test without driving, which might be easier to see the cable end.

You wouldn't even have to start the engine doing it this way. Just have a friend or a kid turn the wheel while you check the cable.

[thedudeabides86]

Thanks to everybody for all the valuable input. On Sunday I put a drill on the speedo cable at the trans end and gave her hell. The wife said the needle was needling and the odometer was odometering. So, it's gotta be something in the speedo gear box or on the shaft itself. None of the teeth on the nylon speedo gear were chewed or worn and the driven gear looked all good. The clip holding the driven gear was in place as well. I've found through forum links a replace speedo gear sleeve housing but not the whole gear box itself. Should they be any movement at all on the speedo gear box when it's installed and fastened down? What I mean is, when it's bolted it good and tight, I can wiggle the whole gear box as the cable housing on the speedo cable allows. I imagine that should be all tight and snug. Now that the white devil (snow) has spread across the land, I'm not driving the truck until spring. Ugh. I'll have to keep at it. Thanks again everybody.

[guyryan100]

Yes, nice and snug it should be. Could you share photos?

[mr48chev]

Do you have this style of speedo gear housing?

has anyone done any mixing and matching of speedometer drive parts?

With that style of housing you have to have the correct housing for the tooth count of the driven gear. It also has to be clocked correctly in the hole. Meaning turned so the tabs on the hold down clip are on the notches on the housing. That orients the housing so the gear properly meshes with the drive gear.

I've never had any real trouble getting the end of the cable to go in the driven gear but have had to turn more than one to get it lined up. usually you can do that at the bottom when you are trying to line them up. You just turn it a minute amount and gently go again.

Make sure that the cable is routed smoothly from the trans to the speedometer. Sometimes we try to get it in too tight of a bend and it wants to bind up. I've seen that both in cables that were too long and ones that were too short.