[Mana]

What controls the automatic gear shifting in an automatic ZJ?

Is it the speedometer, and speedometer gear in the TC?

I am going to a larger size tire and want to keep my shifting as close to normal as I can. I intend to add a new speedometer gearing so my gauges are close to being accurate, but would also like the shifting fairly normal.

Thanks in advance!

[drrm123]

I never tried to see if the gearing on the speedometer would effect shifting if it's wrong. But the governor pressure,TCM,TPS and road speed all play a part in it. If your asking if your speedometer is not accurate because of larger tires? (The only way to find out is to try it). I dont think that will affect the way it shifts, just the speedometer would be wrong. If you dont like the way it shifts with the larger tires you can play with the throttle valve cable to get to shift harder or softer. I have a non off road jeep. LOL all stock not lifted or larger tires. But the speedometer gear is easy to change only 1 bolt needs to be removed and it slides right out.

[SA59GRAND]

I have a 3" lift and 265/75-16 tires on my ZJ Flickr Photo Download: My 5.9 with Skyjacker 3" coil springs and 265/75-16 Wrangler TD tires and it shifts normal, my speedometer is off thought which I can fix with a 33 tooth speedo gear if I decide to do that. But as far as shifting I have Never had it shift any different with the Lift and Bigger tires.

[Mana]

Originally Posted by SA59GRAND

I have a 3" lift and 265/75-16 tires on my ZJ Flickr Photo Download: My 5.9 with Skyjacker 3" coil springs and 265/75-16 Wrangler TD tires and it shifts normal, my speedometer is off thought which I can fix with a 33 tooth speedo gear if I decide to do that. But as far as shifting I have Never had it shift any different with the Lift and Bigger tires.

Ok, good. I was hoping this would be the case. I was worried about creating shifting headaches living in the mountains.

[comptiger5000]

The shift into / out of OD and TC lockup are controlled by the PCM, so they rely on a correct speedometer. However, the basic shifting between 1st, 2nd and 3rd gear is not computer controlled.

[ZJ5point2GCL]

Originally Posted by comptiger5000

The shift into / out of OD and TC lockup are controlled by the PCM, so they rely on a correct speedometer. However, the basic shifting between 1st, 2nd and 3rd gear is not computer controlled.

how far off do you think the spedo would have to be off to affect the OD shift?
bigger tires would make the spedo read slow, so that would mean the OD shift would just be delayed?

[ratmonkey]

Governor pressure is controlled by the pcm by the following inputs.
Throttle position
Transmission speed sensor
Vehicle speed sensor
Tranny temp sensor(also the pressure sensor)

having the speedometer being off will alter your shifting, mostly causing late shifts according to actual vehicle speed. You probably won't notice tho.

[baxy]

some years are different , some the 3 speed uses the output speed sensor for speed signal and vehicle speed sensor for OD and LU
some years use output speed sensor for the whole show

[NEVADAGARY]

I have 33" tires on mine and the speedo is off about 9MPH at 70.... it reads 61