69SSC5

700r4 transmission in a c4
just like title says speedo will work great until i hit a big bump then speedo will stop working. if i get under the car and wiggle and giggle all the vss wires the speedo still doesn't work... if i pull the vss out of the transmission and turn it with a drill my speedo works great. if i remove the vss and immediately reinstall the vss the speedo will work great until a big bump. drive gear teeth are not stripped, driven gear teeth and gear hole are not stripped. like i said, Remove and re install the vss speedo works great.

so im coming to the conclusion that the driven gear is coming off of the vss sensor when it hits a big bump. last owner had the rear changed, they also changed the drive gear and clipped it to the wrong hole (forward most clip point). when you look into the trans hole where the vss goes the drive gear is all the way tword the front of the trans... i understand that the drive gear is clipped to the wrong location but im just having a hard time understanding how/why the vss and gears work great until i hit a big bump.
anyone have any insight?

Cliff Harris

What year is your car and what colors are the drive and driven gears? Do you know what the differential ratio is?

It sounds like the gears are becoming unmeshed somehow. There are two VSS housings. One moves the driven gear farther away from the drive gear to allow for more teeth (larger diameter) on the driven gear. This is for high numerical differential ratios (like the 3.54 in the chart below).

If the drive gear is in the wrong hole it might be possible to move it through the VSS opening. The drive gear should be centered in the opening. As I recall, the holes are about 3/4" apart, so it should be really obvious if it's in the wrong hole. Personally, it was VERY hard to get the drive gear off when I took my 700r4 apart. The clip wouldn't depress enough to release the gear.

This chart from the parts book might be helpful:

69SSC5

from turning the wheels and watching the drive shaft the rear is either a 3.33 or 3.45. I tried many different driven gears, the only driven gear that touched the drive gear was the 44T driven gear. the drive gear is deffinatly clipped to the wrong hole. the drive gear looks to be a cross between blue/grey and green. not to sure what color the gear was before the atf fluid ate the color,, could have even been red.

i know the issue can be fixed with the correct installed drive and driven gears. i just dont understand how a bumb will and does make the two gears stop meshing together. maybe they just barley touch to begin with?

the VSS sensor i have is part ##25007224, 25007338. It was the only VSS i was able to find. i was not aware that you could still buy the 42T + VSS. I tried installing the VSS i have both the correct way and rotated 180*. It made no difference, both ways worked until a big bump

C4KC

I am having the same issue as you. My VSS broke and I replaced it with one from NAPA. Didn't display speed. I tried the drill test and it displays the speed just fine.
While I drive I get "0", but yesterday it worked for a few seconds and then back to "0".
I dont think my gear on the VSS can be pressed in far enough to connect with the ring gear on the Trans.
Have you found a solution? Maybe we can compare notes.