Speedo Driver

[Randalla]

Since I'm swapping my 5-speed for another one, I thought it was time to change the speedo gear so the speedometer reads more accurately. I'm currently using a white 19 tooth version and it seems like my speed is reading about 5 mph too fast. I'll be running a close ratio 5-speed and a 3.90 rear end. It seems like changing to a 20 tooth red speedo driver might get me closer. Anyone have the same combination that can advise? Thanks

[Ryanotown22]

My speedo reads about 5mph too fast based on my gps speed app. I am not sure why either.

[Randalla]

Ryan, what rear end are you running, what transmission and what color speedo drive gear.

[Ryanotown22]

I have the black gear drive with the 78 5 speed r200 that I think is
3.54 but I haven’t checked to see if that ratio is true.
I also have 205/55/15 tires. I will check it using this I found
If both wheels are off the ground use this method:

Jack up the rear end of the car supporting it on jack stands and make sure that the tranny is in neutral. Next, wrap a cable tie around the driveshaft and cut the excess to a reasonable length to act as a pointer. You could also just use chalk but I don't keep chalk around the house so....... Point the pointer or mark straight up or straight down at either the 12:00 or 6:00 o'clock position. Place a mark on a tire at either the 12:00 or 6:00 o'clock position. Now, turn the wheel exactly 1 revolution and count how many times the driveshaft turns noting the position of the cable tie pointer. If the cable tie made 3 revolutions and is at roughly the 3 o'clock position the ratio is 3.364 as in:

3 revs and ~3 o'clock - 3.364

3 revs and ~6 o'clock = 3.545

3 rev and ~9 o'clock = 3.70

3 revs and ~11 o'clock = 3.90

4 revs and ~1 o'clock = 4.11

It's not 100% accurate but it should get you close if done carefully.

[Randalla]

Tire size is another variable I forgot to mention. You and I are about the same (reads 5 mph faster than actual). To change that you need to go with a gear with more teeth. In your case, I'd try a blue gear (one more tooth than you have currently). For me I probably need to go from a white to a red. Anyone want to trade my white for your red?

[Duffman]

Randy, I have the same close ratio 5 speed with 3.90 rear end, and the white gear speedo, and have been about 10% high in my speedometer reading (as you know). I think there is definitely a speedo gear option better than the white one for us, it is a challenge, however, to find the red speedo gear available. Let me know what you find!

[Randalla]

I also found a black 17 tooth speedo driver I would be willing to trade for a red one.The white one I have is a 19 tooth driver. I'm looking for a 20 tooth driver.

[Randalla]

Just finished cleaning up the new close ratio 5-speed for my orange Z. Birdman had an excellent recommendation for cleaning up greasy parts (trans, diff, etc.) quick and cheap. The 99 cent store has oven cleaner for 99 cents a can, which is about 1/4 the price of brake cleaner. I sprayed in on the transmission and set it in the sun to work. I then rinsed everything off using a wire bristle brush to further loosen up the sludge. Of course you need to block off all the openings where you don't want water. I used a dental pick to get into the tight areas. Once done I sprayed the case down with WD-40 and wiped it dry. Very happy with the results.

[L320-Dale]

Wow, looks great Randy. Looks like that oven cleaner did the job!
Dale

[Randalla]

Thanks Dale. Just ordered up new input and output shaft seals, clutch release bearing and slave cylinder and hose. Want to be ready to install it when the weather cooperates.