Speedo correction for 6 speed conversion
Thread Starter
Heel & Toe
Joined: Apr 2007
Posts: 20
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Speedo correction for 6 speed conversion
I recently converted my 1986 Doug Nash 4 speed to a ZF 6 speed. The speedometer is now registering approximately 16% too slow. How do I remedy this?
Thanks,
Tom Urani
Thanks,
Tom Urani
Burning Brakes
Joined: Feb 2008
Posts: 988
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From: Sarasota Fl
Jonathan
Team Owner
Joined: Sep 2003
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Let's do it this way since it seems there are many mods!
1. What axle ratio presently
2. Present tire size/brand/model?
We're going to assume you've done nothing to the ZF so if you know the year and axle ratio of the donor we can guess at it's present internals. It doesn't really matter much because you'll likely need to do maybe a speed sensor swap and the driven gear along with it. The combination might be a very popular one or it could be one thats going to be a struggle. For the time being don't be concerned with the 16%
just the existing known values that "won't change" Those are the 2 questions!
How's that?
1. What axle ratio presently
2. Present tire size/brand/model?
We're going to assume you've done nothing to the ZF so if you know the year and axle ratio of the donor we can guess at it's present internals. It doesn't really matter much because you'll likely need to do maybe a speed sensor swap and the driven gear along with it. The combination might be a very popular one or it could be one thats going to be a struggle. For the time being don't be concerned with the 16%
just the existing known values that "won't change" Those are the 2 questions!
How's that?
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Team Owner
Joined: Sep 2003
Posts: 25,389
Likes: 2,741
Yes but "isn't it" more practical to deal with the knowns and do the math. The calculator would be a good general check of your math after the fact. Either way use the calculator and "confirm" the calculator or do the "knowns" and check your math maybe against the calculator. At this point the only "known" is the ZF "drive gear" and actually that is to be "assumed" but likely or most probable!
Last edited by WVZR-1; Jul 3, 2008 at 06:57 PM.
Thread Starter
Heel & Toe
Joined: Apr 2007
Posts: 20
Likes: 1
No one has mentioned an electronic solution to my problem, so I'm assuming my digital speedometer is ultimately controlled by the drive gear. If this is indeed the situation then it would seem that the simple solution is to install a gear that is 16% larger than the current one.
Team Owner
Joined: Sep 2003
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The ratio of the "drive and driven" need to be what you believe to be 16%. You seem quite confident of the figure so I'm guessing you've used a GPS? That can't always be done with a simple change of "one" gear. The "drive and driven" mesh similar to a "ring gear and pinion" in a differential and if that's not a "good mesh/fit" one or the other, even both will wear very quickly if they work "at all"! The fitting/sensor that the driven gear attaches to is also built to compensate for the gear fit. People post that they've rotated the original 180* to compensate for the other but I've never tried it personally!
If you can answer the questions asked, the math isn't that far away or play with the calculator and see how you do. The formula and calculators are posted "all over the Internet"! Doing "the math" has generally always been considered the most accurate. Look around!
There's electrical solutions but the ERA (electrical ratio adapter) or DRA (digital ratio adapter) is generally more expensive and quite "finicky" in many installs. They don't all perform well in every application! It requires cut/splice for install and is another piece of electronics that requires attention. I would think this to be the "least advantageous" solution. Look around!
If you can answer the questions asked, the math isn't that far away or play with the calculator and see how you do. The formula and calculators are posted "all over the Internet"! Doing "the math" has generally always been considered the most accurate. Look around!
There's electrical solutions but the ERA (electrical ratio adapter) or DRA (digital ratio adapter) is generally more expensive and quite "finicky" in many installs. They don't all perform well in every application! It requires cut/splice for install and is another piece of electronics that requires attention. I would think this to be the "least advantageous" solution. Look around!
Last edited by WVZR-1; Jul 6, 2008 at 02:05 PM.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
The ratio of the "drive and driven" need to be what you believe to be 16%. You seem quite confident of the figure so I'm guessing you've used a GPS? That can't always be done with a simple change of "one" gear. The "drive and driven" mesh similar to a "ring gear and pinion" in a differential and if that's not a "good mesh/fit" one or the other, even both will wear very quickly if they work "at all"! The fitting/sensor that the driven gear attaches to is also built to compensate for the gear fit. People post that they've rotated the original 180* to compensate for the other but I've never tried it personally!
If you can answer the questions asked, the math isn't that far away or play with the calculator and see how you do. The formula and calculators are posted "all over the Internet"! Doing "the math" has generally always been considered the most accurate. Look around!
There's electrical solutions but the ERA (electrical ratio adapter) or DRA (digital ratio adapter) is generally more expensive and quite "finicky" in many installs. They don't all perform well in every application! It requires cut/splice for install and is another piece of electronics that requires attention. I would think this to be the "least advantageous" solution. Look around!
If you can answer the questions asked, the math isn't that far away or play with the calculator and see how you do. The formula and calculators are posted "all over the Internet"! Doing "the math" has generally always been considered the most accurate. Look around!
There's electrical solutions but the ERA (electrical ratio adapter) or DRA (digital ratio adapter) is generally more expensive and quite "finicky" in many installs. They don't all perform well in every application! It requires cut/splice for install and is another piece of electronics that requires attention. I would think this to be the "least advantageous" solution. Look around!
Here is a link to one of the less expensive electronic solutions:
http://www.dakotadigital.com/index.c...rod/prd126.htm
They can be a pain to install and tune to your application, the directions for installation are included in the link, see what you think. If you use the calculator or math solution and at least get the drive gear correct it is easy to swap the driven gear to fine tune later if you miss the first time (1 bolt) and the gears are cheap even at a dealer.
I have rotated the original speed sensor and used it with driven gears over 40 teeth, it seems to work fine, but the correct replacement sensor is not expensive either, your call.
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Brett Foote
Team Owner
Joined: Sep 2003
Posts: 25,389
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Here is a link to one of the less expensive electronic solutions:
http://www.dakotadigital.com/index.c...rod/prd126.htm
They can be a pain to install and tune to your application, the directions for installation are included in the link, see what you think. If you use the calculator or math solution and at least get the drive gear correct it is easy to swap the driven gear to fine tune later if you miss the first time (1 bolt) and the gears are cheap even at a dealer.
I have rotated the original speed sensor and used it with driven gears over 40 teeth, it seems to work fine, but the correct replacement sensor is not expensive either, your call.
Now if you're "very familiar" with DRA/ERA's etc share with us. I've spoken to a couple different manufacturers regarding DRA's to accomplish a tach error "correction" and their products will do that and more. I really was going to try and generate some interest for this "patch" for the '90 cars which seem to have the worst tach problems and fixes don't seem to last. I was going to try and accomplish my fix this summer but it looks more like fall. Their products aren't as inexpensive but similar in operation and install. They seem less "finicky" and one is used by the Ford guys for the Dakota install failures.
