Sheared Speedo Sending Unit??

[skid542]

So last Wed. I'm sitting at the light, on the line (with an older black Vette behind me) and the light goes green. I do what I usually do and string out 1-2 and hit third a little, getting it up 65 (it's a 55 zone) upon which I slow it back down to 60.

Much to my surpise the Vette was staying up with me the whole time. I wasn't surprised he could, just I don't find many people who have a fast car and actually drive it. It was cool. He actually shot up beside me when the road went to two lanes and gave me a thumbs up so I threw a friendly wave.

But that small bit of the story aside, after I started dropping the speed back down to the limit I all of the sudden see my speedometer drop to zero.

Well, I had just replaced the cable with a brand new, OEM, cable the week before. I forgot to put the wire clip on the tranny sending unit to hold the cable in and just figured the cable had popped out.

I get home, let it cool down and go out for a look-see. I shove the cable and it seems to still be seated but it did move about a 1/16". So I pulled it all the way out, and pushed it all the way back in.

Take the car for a drive - nothing. Not wanting to dig into a lot that night I just let it sit until this morning.

I had recalled reading a previous issue where another member had a broken sending unit after a 4eat->5mt swap where the little flat on the sending unit sheared off. Concerned that this might be the case, I pull out the sending unit, and sure enough it had completely sheared off... explains why the speedo wasn't working...

So my question is - is there a distinct difference between the AT and the MT sending unit that would cause this type of failure? I have a brand new cable and it doesn't appear to be bound up, I can spin the inner cable pretty easily by hand so I'm inclined to believe it's not the root cause. Perhaps it was just a matter of running a sending unit that's 135k mi. old?

Any thoughts? I'm calling the dealership this week and having a new one sent in, I just don't want to have to keep doing this.

Perhaps I'm just making tooo much power for it to handle ?

[Legacy777]

When you are talking about the sending unit....what exactly are you calling the sending unit? There really isn't a sending unit on the trans, just the adapter sticking out.....or at least that's how it was on my trans. I've been using the AT cable without any issues, so I'm not sure....

[skid542]

By sending unit I mean the piece that screws into the transmission. It has a little flat spade that fits into a slot in the tranny. The cable then gets shoved into the other end of this screwed in piece. The WRX tranny had an electrical one that I unscrewed and then screwed in the one off the AT.


I replaced the cable on account of upsetting the original one. I had disrupted the little tabs that hold the cable to the back side of the instrument panel and choose to get a new one instead of worrying about it coming loose again. Seperate issue than the one I'm experiencing now.

I'm just unsure what would have caused enough force to break the tab.

[Legacy777]

The MT I used had an extension of a few inches, so it's possible your cable is a little too short.

You can kind of see it in this picture.
http://main.experiencetherave.com/subar ... P_3008.JPG

[skid542]

Hmm.... My cable does not have that extension on the end but I told the parts guy I wanted a cable for a manual car.

The cable seems to be long enough in that it reaches okay, could stand to be a little longer I guess. But the cable didn't shear off, it was the adapter in the tranny that did. Maybe the short cable was binding too much and that's what caused the failure?

[Matt Monson]

Lee,
Do you hear any strange noises when you drive the car? Can you secure a second set of hands so that you can jack up the front end and have someone spin the wheels with it in neutral? Then you can look down into the speedo drive hole and see if the broken shaft is still spinning in there. My concern is that you maybe burned up the gear. Thankfully it's a plastic gear and can't do much damage in there.

However the bottomline is that I doubt you'll be able to get your speedo back without splitting the case on the gearbox.

[beatersubi]

Isn't it just the short extension that always breaks first? I know it did on my 5mt @~ 250k mi.

[skid542]

However the bottomline is that I doubt you'll be able to get your speedo back without splitting the case on the gearbox.

Damn Matt, bout' gave me a heart attack . I was just going to wait until tomorrow to swap in the new sending unit I got (huge thanks to Todd, Wtdash) for getting me a new one today. But after your statement I couldn't wait.

Turns out it was just the sending unit that broke. I swapped in the new one and everything's just fine. I took it all apart, all three pieces that is, and cleaned it real well and lubbed it up with some nice synthetic grease and put it back together. Quick install, 30min, including drive around the block, and all is well again. Speedometer works just fine.


As far as funny noises, I hadn't heard anything. I do hear a distinct rattle now when I engine brake but I'm pretty sure that's something in the cabin rattling due to the new Grp N mounts all around. I had noticed a couple of times the speedo 'stuck' at a particular speed for a couple of brief seconds but then got back up to speed. This occured, maybe twice. No strange noises though. I have noticed my car does out accelerate the speedo but I suspect that's a function of the gauge cluster.

I will be taking it back apart though and filling a small 'break-away' notch in the spade just to be sure it gives first. But for right now all seems to be okay.


Any thoughts?


On a small aside Matt, what year dipstick tube did you put in the tranny? It doesn't seem to match the 02' WRX dipstick I bought. I did fill it with the FSM spec'd 3.7-3.8 qt. of fluid but would like to know for sure. Otherwise though the tranny's been great - first Auto-X is this upcoming weekend where I'll really get to wring it out .

[Matt Monson]

Lee,
Sorry to scare you. I was just being paranoid. It's my work and if anything goes amiss I start working worst case scenarios on my head. Glad it's sorted out.

We never removed the dipstick tube on the transmission. There shouldn't be any issue there.