Speedometer calibration....

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Oct 20, 2005 | 11:53 PM

65coop

Thread Starter

Burning Brakes

Joined: Apr 2004

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From: Spring Texas

St. Jude Donor '05

Speedometer calibration....

The car is a '90 L98 w/ 700R4 - I recently installed a D44 w/ 3:91 gears from a D36 w/ 2:73 gears -- The car has an automatic now and will be swapped out for a ZF 6 speed in a few weeks..

I was wondering, what do I need to change - to correct the speedometer for the Auto vs. the ZF? is it the same part for both?

Or....should I just leave it alone until I do the swap?

Oct 21, 2005 | 12:25 AM

sami85L98

Le Mans Master

Joined: Apr 2005

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From: Scarborough ONTARIO

Let the cFI-EFI chime in but assuming u have 275/40/17 wheel tire combo with 3.91 gears according to bowtieoverdrives.com

15tooth -drive gear grey
45tooth- driven gear.

but as i said let the CFI-EFI chime in and correct it.

Oct 21, 2005 | 12:32 AM

65coop

Thread Starter

Burning Brakes

Joined: Apr 2004

Posts: 859

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From: Spring Texas

St. Jude Donor '05

Quote:

Originally Posted by sami85L98

assuming u have 275/40/17 wheel tire combo

Nope.. They are 315/35/17

Where are you CFI-EFI??

Oct 21, 2005 | 12:37 AM

65coop

Thread Starter

Burning Brakes

Joined: Apr 2004

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From: Spring Texas

St. Jude Donor '05

After reading your post again... I think your telling me that I have to remove the tail shaft housing to do this?

I hope not... If so, the speedo will be off till the ZF goes in.

Oct 21, 2005 | 01:15 AM

WVZR-1

Team Owner

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Speedo

Sam,

I'll check that for you in the AM 1st thing

Oct 21, 2005 | 03:43 AM

sami85L98

Le Mans Master

Joined: Apr 2005

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From: Scarborough ONTARIO

Quote:

Originally Posted by 65coop

After reading your post again... I think your telling me that I have to remove the tail shaft housing to do this?

I hope not... If so, the speedo will be off till the ZF goes in.

Yes u have to take out tail housing but thats not a pain, the pain job is to remove drive shaft to get acces to tail housing to replace this but considering installing blk box (abott or dakota) more expensive and involved wiring and drilling too.

Mine is a 85 vette i installed blk box but at that time i dont have info to replace just drive and driven gears, this will be preferable than installing blk box in my view and others too.

But be careful replacing those drive and driven gears, installing wrong kind again u have to do all over again replacing exhaust (partial) and drive shaft to get access to tail housing.

I used this link to calculate speedo gears and even with 315/40/17 iam getting same 15 tooth and 45 tooth.
http://www.700r4.com/speedoCalc/speedocalc.shtml

Oct 21, 2005 | 07:30 PM

CFI-EFI

Race Director

Joined: Sep 2000

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From: The Top of Utah

Quote:

Originally Posted by sami85L98

I used this link to calculate speedo gears and even with 315/40/17 iam getting same 15 tooth and 45 tooth.
http://www.700r4.com/speedoCalc/speedocalc.shtml

Interestingly, when *I* used that link, it read to use a 15/43 tooth combination with those tires and 3.91 gears. Those are the same speedo gears Chevy uses with 3.54 gears with 315/35/17 tires. With these larger tires I think I'd go with the dark grey 44 tooth driven gear, part number 25513051, along with the grey 15 tooth drive gear. The part number of the drive gear will depend in what year transmission you use. For 1990 and earlier, it's a 8642620; 1991 and later, 1250670. The problem will be getting a hold of the 1990 and earlier, 40 tooth + VSS, part number 25007308.

RACE ON!!!

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