Engine and Transmission Tech

I'm beginning to wonder if I have the gear in my tranny. I've traced the wiring & am getting power to the sender, have a good ground... have continuity from sender to sender spot on speedo, good gauge power (speedo sweeps w/ignition on), but no detectable voltage on the sender lead. Hadn't messed with it much, but my tach died recently. I knew about how fast I was going based on RPM's but it's time to fix both now.

Net.. three questions...
1. Should I be able to see voltage on the sender lead while in gear & running? I know it pulses, but expected to see it on my volt meter.

2. Assuming I'd see voltage, can I remove the sender from the tranny tail piece w/o spilling fluid everywhere (put the other way, do i need to drain some fluid first)?

3. If I am missing the gear, are there different colors or some other way to know what I'm after? Tranny is from a 94/95 5.0L Mustang. It's different than normal mustang trannys in that the input shaft is 1" longer; bell housing is longer to account for that, and clutch fork opening is rotated down further. Not sure if there's anything different about the speedo gear/sender. Sender I'm using is an Autometer unit.

Ron,

At least part of the answer is here: [www.ffcars.com]

You may also want to do a site search at the same location as this is a fairly common set-up in the FF cars.

David

Can't answer all your questions, Rob, but the sender can be removed from the xsmn without any fluid leaks other than a few drips. With the sender removed, the drive gear should be visible through the opening.

Hey Rob,
If it's the autometer hall effect sender, You should see a square wave output from it alternating between 0 and five volts.
If it's older you will probably only have alternating infinity and ground.
An ohm meter is probably your best bet for checking.
If you have a programmable speedo then the gear ratio won't matter. Just go for the one that will give you the best resolution,(most pulse counts) that will make your speedo much more responsive.
Cheers
Fred

Cool. I'm pretty sure I need the part of the gear that goes on the sender. I looked up my tranny tag # last night & it should have an 8 tooth drive gear. But, I have an electric programmable speedo so sounds like that doesn't matter. I'd just need a red, black or other high count gear. They're about $15 on ebay so I just need to verify there's not one on the car now & get it ordered.

Thanks again.

Turned out there's a Mustang parts/salvage place about 15 mins from my house called Steve's Mustangs. Picked up a speedo gear & retaining clip for $11. They recommended 18 teeth or less saying the higher tooth counts have thin teeth prone to breaking off. Google search seemed to agree so I picked up an 18 tooth one. Will put it in this weekend. Oh, & the guys there were way into the MG engine swap. The place is a 2-man business connected to one of their houses. One of the two guys did a V6 swap on his MG some time back - small world

Also called Autometer to ask about my tach -- they say the MSD 6A/6AL is hard on the tach when wired to the coil. I may have fried my tach by having it there. There's a tach port on the MSD box. I'm going to test that again this weekend but if worse comes to worse, I'll have to send the tach off for repair.

Quote:

They recommended 18 teeth or less saying the higher tooth counts have thin teeth prone to breaking off.

Ultimately, Rob, you'll have to use the correct combination of drive and driven gears to get a correct speedo reading. My conversion happens to use a green 8-tooth drive gear and a pink 19-tooth driven gear - no problems yet!

With the programmable AutoMeter gauge I don't think the tooth count matters as much (if at all). The speedo will work with any signal (w/in voltage range) of 500-400,000 pulses per mile. It is calibrated while driving a measured 2 mile distance.