Drivetrain Speedo gear ate itself

[keel]

Speedometer stopped working and it looks like the plastic gears inside the trans and on the VSS/speedo cable have worn down. I'm having some difficulty figuring out what combination of speedo gears I need since I have a 2.73 rear ratio and most kits are for more aggressive gears. Anyone know for sure which tooth counts I need?

I think I basically need to maximize the number of teeth on the output shaft and minimize the teeth on the speedo cable.

 

[nicholase]

https://lmr.com/products/Mustang-Speedometer-Gear-Calculator

 

[AeroCoupe]

Would need to know rear gears, trans, year of car, and rear tire size.

 

[keel]

'89 T5 with 2.73 rear gear and 235/45/17 tire.

I used the LMR calculator and the combo it spit out is still pretty far off, says I need a 15-ish tooth driven gear when using a 7-tooth drive gear and they sell a minimum 17-tooth driven gear.

Ideally I would use an 8-tooth drive gear but none of the mainstream websites for fox parts seem to have it. I also am having trouble finding a driven gear that is 15 teeth, although I can find a 16-tooth on some websites.

Looks like the best I can do is a 7-tooth drive, 16-tooth driven unless you guys know where to get some of the more unusual ratios.

 

[AeroCoupe]

So you have a 7 tooth drive gear (the one that is in the transmission and on the output shaft) if it is still stock. With that you will need a 15 tooth driven gear (one that goes on the VSS). I would get a mirror and flashlight to check the drive gear on the output shaft to see if it is still in good shape. You typically do not see a low tooth count driven gear get torn up.

 

[AeroCoupe]

PM me your address and I will send you an 8 tooth drive gear for free. I think I have one or two of them.

Me personally I would just pop some 3.27 gears in the car and use an 18 tooth driven gear...you know the cheaper solution.

 

[keel]

PM me your address and I will send you an 8 tooth drive gear for free. I think I have one or two of them.

Me personally I would just pop some 3.27 gears in the car and use an 18 tooth driven gear...you know the cheaper solution.

Haha yeah I definitely thought about doing a rear gear since I just had to replace my pinion seal too... one of those "while you're in there" type deals. But I love the long gears for road trips. Such a nice car for grand touring.

Just checked the gear inside the trans like you suggested and all the teeth in the middle part are flat. I also took the time to count the teeth when I was in there and looks like I have a 7-tooth drive and a 16-tooth driven so I'll just replace it with the same parts. Guess I should have just done that to begin with instead of starting this thread.

In the mean time I popped out the driven gear so it won't grind itself to shreds any further.

Really appreciate the offer for the 8-tooth drive gear though, where did you get those?

 

[AeroCoupe]

From later T5’s. Pull them to run 6 tooth drive gears for deeper rear gears.