T5 Transmission speed sender issue - solved

[Blitzboy54]

Hi gang,

So I have been looking into why during my go karting the speedometer doesn't read anything. Just sits at 0. I have the FFR Autometer unit that comes standard. I am running a rebuilt T5 and the RF wiring harness. I have pulled many threads and reviewed and looked at potential grounding and while some say it has to be calibrated to work at all I am not sure that's actually true. So here is what I have seen and the steps I have taken to troubleshoot.

1. During go karting or spinning the drive shaft I do not see any speedo read back (the transmission came rebuilt with an already installed sender)

2. I jacked the back of the car, put the transmission in neutral, then rotated the tires after grounding the grey wire to the chassis. - No read back

3. I found the new sender that came with the kit and plugged it into the harness. When rotating with my fingers the speedometer reads between 10-20 miles per hour depending on speed (yay!)

4. I swapped the sending units in the transmission. I plugged the old unit into my harness and rotated by hand. I got the same 10-20 mph feedback (uh oh)

5. I re tested the new sending unit in the transmission by rotating the driveshaft via rotating the tires and I get nothing.


I can assume then that the gear on the sender is not contacting the drive gear on shaft. Before I pull the trigger on a GPS module and move on is there anything anyone knows that I can try to get these 2 parts to engage that doesn't involve me pulling the transmission back out? They guys that built it said they would take it back and repair it but I would have to ship it to them and that seems like a lot of work and probably close to $100 in shipping cost.

[phileas_fogg]

Certainly no need to pull the transmission to replace a speed sensor. You should be able to remove, inspect (you might need a mirror), & replace it by crawling under the car.

https://live.staticflickr.com/4320/36289757675_396003724b_4k.jpg (https://flic.kr/p/XhNuDa)IMG_2582 (https://flic.kr/p/XhNuDa) by jhsitton (https://www.flickr.com/photos/91016165@N07/), on Flickr

I seem to recall that there are different sensors with different length shafts, but my memory is very hazy on this (https://www.ffcars.com/threads/speed-sensor-mounting.571961/#post-5419625). I'd pull the sensor you've got, use a depth gauge (usually the back side of your micrometer) to measure the fitting on your T5, and compare that to your sensor.


John

[Blitzboy54]

Like every other technical issue I've had. I figure it out within moments of starting a help thread.

I confirmed that the gear in the transmission is turning. I had my daughter turn the rear wheel and felt it with my finger. I also confirmed the sensor is rotation by using a multi meter on both leads and measuring resistance.

What I think happened here is when I did my test drive I did not have the sender circuit properly grounded. Now that it is I confirmed it works by turning the sender with my fingers. What I did not realize is I cannot generate enough rotation by manually spinning the wheel to get the speedometer to engage.

In the end it was not really an issue but I learned a bunch of stuff so a win I guess.

[Norm B]

You said the transmission was rebuilt. Pull the sensor and take a picture down the port. Make sure the drive gear was installed during the rebuild.

Norm

[phileas_fogg]

Ha! I was going to mention the wiring, but your description of showing 10-20 mph on the speedo led me to believe all was well electrically. Did a second test drive show you've got this problem sorted?


John

[Blitzboy54]

Ha! I was going to mention the wiring, but your description of showing 10-20 mph on the speedo led me to believe all was well electrically. Did a second test drive show you've got this problem sorted?


John

Yeah the issue was it wasn’t sorted with my test drive but was during my finger test. So that’s my bad.

I have not taken her back out because my pipes are getting coated. I learned from Papa and Kleiner not to run my sniper without the pipes as it will mess up the O2 sensor and the goober up my plugs. I’m hoping to have them next week so I will definitely take a scoot around the neighborhood then.

[steno]

You should be able to pull the sender and see the gear that it is supposed to engage. Check to see what color it is. Also, the gears are different for manual and automatic transmissions.