Speedo Driver

240Z through 300ZX Z31
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Randalla
Posts: 930
Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Speedo Driver

Post by 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
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
Ryanotown22
Posts: 93
Joined: Sat May 25, 2019 8:26 pm

Re: Speedo Driver

Post by Ryanotown22 »

My speedo reads about 5mph too fast based on my gps speed app. I am not sure why either.
Ryan
‘78 280z sold
‘75 280z
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Randalla
Posts: 930
Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: Speedo Driver

Post by Randalla »

Ryan, what rear end are you running, what transmission and what color speedo drive gear.
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
Ryanotown22
Posts: 93
Joined: Sat May 25, 2019 8:26 pm

Re: Speedo Driver

Post by 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.
Last edited by Ryanotown22 on Sat Aug 31, 2019 5:33 pm, edited 1 time in total.
Ryan
‘78 280z sold
‘75 280z
User avatar
Randalla
Posts: 930
Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: Speedo Driver

Post by 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?
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
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Duffman
Posts: 169
Joined: Sat May 25, 2019 10:52 am
Location: Scottsdale, AZ

Re: Speedo Driver

Post by 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!
Duffman
1970 240Z, #1399
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Randalla
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Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: Speedo Driver

Post by 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.
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
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Randalla
Posts: 930
Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: Speedo Driver

Post by 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.
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1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
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L320-Dale
Posts: 340
Joined: Thu May 23, 2019 6:25 pm
Location: North Gilbert

Re: Speedo Driver

Post by L320-Dale »

Wow, looks great Randy. Looks like that oven cleaner did the job!
Dale
Dale - Gilbert, Az
1965 L320 - Bamboo Tan / 1972 1200 - Sun-light Blue / 1970 240Z - Silver
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Randalla
Posts: 930
Joined: Fri May 24, 2019 8:58 am
Location: North Scottsdale

Re: Speedo Driver

Post by 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.
1967 1/2 Roadster- 1600 4 cyl.
1972 240Z- 280 I-6
1976 710 Wagon- L20B 4 cyl.
1977 620 King Cab - L18 4 cyl.
2003 350Z Track- VQ V-6
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