New speedometer cable and teeth still no dice

[Caseindaplace]

Hello,

I have an 86 GT with no cruise and no VSS.

My speedometer was bouncing and showing 10mph more than actual traveling speed. Forum searching directed me to a new cable and gear (17 tooth) from LMR which was installed.

Upon lubrication and installation the speedometer was still bouncy and off and then eventually stopped working all together.

A check underneath at the transmission (pulling out cable) showed everything to be hooked up and spinning freely as it should.

A check behind the instrument cluster showed the cable still attached. Upon disconnecting it I could spin the bearing or notch connected to the needle with my fingers and watch the speedometer needle climb slightly. Once I can get another partner I will spin the cable gear under the car and have the partner observe the disconnected cable behind the cluster to ensure the cable is spinning.

my car has 96k - no turn overs. I’m hoping I do not need a new cluster.

Thoughts?

[dynodon64]

How does the drive gear on the trans output shaft look? Could have some broken teeth.

[Caseindaplace]

How does the drive gear on the trans output shaft look? Could have some broken teeth.

is that the gear that connects on the end of the speedocable into the transmission? If so, brand new along with the new transmission fluid

[Broncojunkie]

is that the gear that connects on the end of the speedocable into the transmission? If so, brand new along with the new transmission fluid

Nope. It's the one that engages the gear on the end. There is another plastic gear inside the transmission. It's round and slides onto the main shaft (internally). Sometimes, it's retainer clip will fail and the gear will slide out of place.

[Caseindaplace]

Nope. It's the one that engages the gear on the end. There is another plastic gear inside the transmission. It's round and slides onto the main shaft (internally). Sometimes, it's retainer clip will fail and the gear will slide out of place.

oh well dang how do I check that?

Side note I did check the cable and it does spin on both ends, the Mrs helped me out.

someone also mentioned that the speedometer and cable mating point is magnetized versus a mechanical connection and grease will come between the points and disrupt the connection. True : false?

[Broncojunkie]

To check the drive gear, pull the cable/driven gear out of the tail housing and look in the hole with a flashlight. You should see a plastic gear... probably a dull yellow color. If you can see the steel main shaft, it probably slid out of position. As for the speedometer end being a magnet, I'm not sure on that one but it seems correct. It's been a long time since I've messed with that end I guess.

[Bryan Knebworth]

A friend of mine had the speedometer start 'bouncing' was when he went out for his first spin. During that time, he reset the trip odo as the car was in motion (probably had never been reset since new), and heard this weird -crunch- sound, and the needle jumped all the time, after that. Did you do anything similar?

[Caseindaplace]

To check the drive gear, pull the cable/driven gear out of the tail housing and look in the hole with a flashlight. You should see a plastic gear... probably a dull yellow color. If you can see the steel main shaft, it probably slid out of position. As for the speedometer end being a magnet, I'm not sure on that one but it seems correct. It's been a long time since I've messed with that end I guess.

Im doing exhaust today so I will check that out when it’s on the lift and reply back

[Caseindaplace]

A friend of mine had the speedometer start 'bouncing' was when he went out for his first spin. During that time, he reset the trip odo as the car was in motion (probably had never been reset in 30 years), and heard this weird * crunch * sound, and the needle jumped from that point on. Did you do anything similar?

no I have not. When I bought the car it was already disclosed to me and I saw the speedometer issue. I assumed it was a bad cable or gear after a few searches. I did reset my trip after I filled up a few times but the issue was already present

[Bryan Knebworth]

no I have not. When I bought the car it was already disclosed to me and I saw the speedometer issue. I assumed it was a bad cable or gear after a few searches. I did reset my trip after I filled up a few times but the issue was already present

Previous owner may have done so. My friend bought a replacement speedometer and had a professional sync-up the odometer. Works fine today, it was like nothing happened. Once the speedometer starts bouncing, there's really nothing you can do.

[dynodon64]

The speedometer needle is hooked to a metal bell. The cable hooks to a drive that has a magnet. The magnet runs inside the metal bell. It doesn't touch the bell, it works by a magnetic flux. The inside of the bell tends to rust. This then allows it to start to rub on the magnet that spins, and it can cause the needle to jump.

[Caseindaplace]

The speedometer needle is hooked to a metal bell. The cable hooks to a drive that has a magnet. The magnet runs inside the metal bell. It doesn't touch the bell, it works by a magnetic flux. The inside of the bell tends to rust. This then allows it to start to rub on the magnet that spins, and it can cause the needle to jump.

So I may need to get a new cluster if this is what has happened. Is there anyway to check?

[dynodon64]

You only have to change the speedometer if it is bad, and not the whole cluster. Check the drive gear first.

[Caseindaplace]

You only have to change the speedometer if it is bad, and not the whole cluster. Check the drive gear first.

alright cool I’ll check out the drive gear and report back. I did my exhaust and it completely slipped My mind while it was on the lift so I’ll have to crawl under and iPhone flashlight it / record a video to see

[Caseindaplace]

You only have to change the speedometer if it is bad, and not the whole cluster. Check the drive gear first.

Took a photo for you.

saw yellow gear that’s it.

*side note - when I reinstalled the cable, I tightened down on the bolt that secured the cable clamp to the transmission. Think I over tightened the bolt, it slipped passed a point and now doesn’t get tighter, it is snug but will not get tighter as I tighten it just stays neutral snug. What now?

[mudgepondexpress]

Easiest way to fix it other than a helicoil / perma-coil / EZ Loc (which is the best solution):

Get a stud the same size as your bolt and maybe a 1/2 longer (add length of head). Mix up some JB Weld, spread it on the engaging part of the stud and snug the stud into place. Let dry overnight and then use a nut on it to hold the gear in. There is very little stress on the bolt.

Just one of many possible solutions.

Kenny

[4eyedblind]

You can run the speedo cable with a hand drill at the transmission end to rule out the cable and make sure the gauge is reading right. if that works ok, it's the drive gear in the tailshaft.

[Caseindaplace]

You can run the speedo cable with a hand drill at the transmission end to rule out the cable and make sure the gauge is reading right. if that works ok, it's the drive gear in the tailshaft.

Ran the speedo with the drill - worked

so talk to me about drive gears lol

I need to do some research

[Broncojunkie]

I've never seen a drive gear go bad. I guess it's possible. I've only seen the little retainer clip come loose or break and get chewed up inside the gearbox.

Here's a better look at it. I had one apart a few weeks ago.

Edit: Don't pay attention to the black ring sitting against the gear. That's just a ring that seals the opening in the tailshaft to keep the fluid in until it's installed in the car. The retainer clip isn't visible here. It's underneath the drive gear.

[Caseindaplace]

I've never seen a drive gear go bad. I guess it's possible. I've only seen the little retainer clip come loose or break and get chewed up inside the gearbox.

Here's a better look at it. I had one apart a few weeks ago.

Edit: Don't pay attention to the black ring sitting against the gear. That's just a ring that seals the opening in the tailshaft to keep the fluid in until it's installed in the car. The retainer clip isn't visible here. It's underneath the drive gear.

I agree I don’t see many from research that go out, mainly swaps for gears.

Can I manually turn say the shaft from under the car and video it perhaps to verify it moves and works properly?

[dynodon64]

With the transmission in neutral, The output shaft can be turned by grabbing the drive shaft and turn it. You will be looking for damaged teeth. If the teeth look fine, then I would say the speedometer cable is not going in deep enough to engage the two gears together.

[4eyedblind]

It's rare to wear a drive gear, bc it is huge and the driven gear is small but, they are plastic and this is thirty year on or so from manufacture. I have seen them actually spin on the output shaft. LMR sells, I think....

[Caseindaplace]

It's rare to wear a drive gear, bc it is huge and the driven gear is small but, they are plastic and this is thirty year on or so from manufacture. I have seen them actually spin on the output shaft. LMR sells, I think....

Yes I agree the gear looks good

[erratic50]

Wonder if its something to do with the output shaft on the transmission. AFAIK the newer shafts don't have provisions for a speedometer gear to be installed.

The older shafts that have provisions are getting more expensive and harder to find. The transmission guy I had build the T5 in my 86GT said he's been messing with using roll-pins. He started with epoxy and JB-Welded but didn't like that those made it near impossible to remove the gear without heating the output shaft to release the glue and he was worried about ruining it.

Also if the T5 gets particularly hot a some point the epoxy or JB-Weld may let go.

The main reason to switch gears inside the transmission is for better access to speedometer drive gears. You can get a 6T, 7T, or 8T gear for the transmission output shaft.

Depending upon gear ratio and tire size you're using out back, some people have needed to gain access to more accurate speedometers in situations where there's no great answer with the tooth counts available for the gear that's installed currently.

LMR publishes a table.

This is one where I know this stuff because I somehow ended up with an 8T gear in my transmission during the last rebuild where-as I've always had a 7T before.

My builder had an 8T he had already drilled for install on an output shaft that didn't have provisions for a gear which is what he's been using during his T5 to T5Z conversion builds.

So for me with a 2.73 or a 3.08 rear gear and a 26" tire there's no answer that gets me an accurate speedometer. Need to tear it down and swap it back to a 7T then a 15T or 16T drive gear will give me what it needs...... Currently I need around a 13T speedometer gear which nobody makes....

[homer302]

That cable is a true PITA to properly connect to the speedo. Are you SURE it is all the way in? If you can just pull it out of the back of the speedo without depressing that tab on the side, it's not properly connected. The drive gear looks fine and you said if someone spins it at the bottom of the car it spins at the top of the cable so the cable at least "appears" to be good. Bouncing speedos are usually caused by a cable that has run dry of graphite lubricant but this one is new. Of course, new doesn't not necessarily suggest that it is GOOD, it's just new. I have utmost confidence it was assembled by a 12 year old child laborer in a sweat shop in who knows what country. You don't have to properly route it and secure it but I wonder what happens if you put the old cable back in with the new LMR gear. At this point, what do you have to lose? Also please post a picture of the new driven gear you installed on the cable.

EDIT: also need some confirmation on your comment that you "ran the speedo with the drill and it worked" did you just put a drill on the speedo or did you put one on the end of the speedo cable under the car at the transmission and spin it?