adjusting the speedo to fit the new tires. - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 08-09-2001, 12:11 PM
**DONOTDELETE**
Guest
 
Posts: n/a
adjusting the speedo to fit the new tires.

84cj7 - brothers-- i just put some 33"s on the kids jeep and his speedo is 15 mph short of what he is doing. i told him to just remember that he is doing 15 mph more than what he is showing, but being 19, he will forget, not care, or probably thinks im fulla crap..can i adjust the speedo myself? i would like to keep him out of trouble.

304/th400/ford 9"s front/back 7"lift 15x10/35's
it will run someday
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 08-09-2001, 12:21 PM
**DONOTDELETE**
Guest
 
Posts: n/a
Re: adjusting the speedo to fit the new tires.

your speedo is off by a percentage so the fast you go the more it is off superlift make a device that will allow u to set the speedo correctly

'87 jeep wrangler in process of building
post #3 of (permalink) Old 08-09-2001, 01:58 PM
jeepfiend
Guest
 
Posts: n/a
Re: adjusting the speedo to fit the new tires.

What???!!![img]/wwwthreads_images/icons/crazy.gif[/img] Speedo gears are like any other gear right. I don't think that I have ever seen a gear set with non-linear behavior[img]/wwwthreads_images/icons/shocked.gif[/img]. Perhaps if the speedo was driven by a couple of pulleys with variable diameters with a set length belt you could get the, faster you go the farther off you are error[img]/wwwthreads_images/icons/wink.gif[/img], but Jeeps, at least the old ones, have a mechanical speedo. If you are off by a certain percentage at one speed you will be off by the same percentage at every speed. Maybe I am missing something, but how could you have that type of non-linear response? i.e. if you are off by 15mph at 55 you will also be off by 15mph at 90, if a Jeep could go 90. At low speeds the speedo may not be acurate since it is not getting good input.

Cage Up, Wheels Down
Jeepfiend
All my Jeeps are in pieces!
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 08-09-2001, 02:08 PM
Keyboard Implanted
 
Join Date: Aug 2001
Location: Vermont
Posts: 2,348
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: adjusting the speedo to fit the new tires.

You are telling the story two ways. You say ". If you are off by a certain percentage at one speed you will be off by the same percentage at every speed." And you are correct. 15% of 55 is a much smaller # than 15% of 90.
to solve this problem you can simply get a new spedo gear. the gear is located in the T case and you just need one that will correct for 33's. Call the dealer closest to you if they don't have one the will be able to tell you where to find one.

91 YJ swaped in 4.0L 2 inch lift. (work in progress)
Olin18 is offline  
post #5 of (permalink) Old 08-09-2001, 02:08 PM
Can't Get Enough
 
RickB's Avatar
 
Join Date: Dec 2000
Location: Erie, Pa
Posts: 1,125
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: adjusting the speedo to fit the new tires.

The percentage error remains the same. If your off by 10%, the error is 6mph at 60mph, 5mph at 50mph, and so forth.

Rick
80 CJ7
RickB is offline  
post #6 of (permalink) Old 08-09-2001, 02:31 PM
 
Join Date: May 2001
Posts: 1,271
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: adjusting the speedo to fit the new tires.

CJ8'er...

The short answer to your question without all the background is: yes, you can adjust your speedo yourself. Basically you will need to get a new speedo gear for your transfer case (I got mine through Advanced Adapters). If you get somebody who knows what they are doing, they can even tell you what you need. Basically you will need to tell them tire size, axle gearing, transfer case, and what type of speedo you have (manual or electronic, with CJ's being manual).

Personally with an Atlas II, 4.56 gears, 33" tires I run a 36 tooth long cable gear Advance Adapters part number 2538936 (green).

'83 CJ-7 nothing original but the tub and axle tubes
bluseman2a is offline  
post #7 of (permalink) Old 08-09-2001, 02:35 PM
ibscrmbln
Guest
 
Posts: n/a
Re: adjusting the speedo to fit the new tires.

You are off by a percentage and it can be fixed for a few bucks. A replacement gear can be bought at your local Jeep dealer or from many of the parts houses including Parts Mike. Costs about $8 to $11 for the gear and a few minutes to install.

The gear is located in the rear tailshaft housing on the backside of your t/c where the speedo cable attaches.

To determine what gear you need, use the following formula: Drive the vehicle to a highway with mile markers. Record odometer reading at a mile marker, drive ten or more miles, then record odometer reading again. Calculate miles traveled according to the odometer, including tenths of mile.

Use the following formula to find the number of teeth needed on your speedometer driven gear.
B = Miles traveled according to odometer
A = Actual miles traveled (per mile markers)
T = Number of teeth on driven gear used to calculate miles traveled

(B/A) * T = Number of teeth needed on driven gear (round off to nearest whole number)

Example: B = 16.4, A = 17, T = 41 (16.4/17) * 41 = 39.55 rounded to 40

When rounding decimals off: .50 or less round down, .51 or more round up.

If you get your speedo withing 2 or 3 mph of accuracy you are doing pretty good.

Good luck! Ken.


83 CJ8, 4.0 HO/AW4, 2.5 Superlift, 1" Daystar body, 33x12.50 GY MTs, 4.10, Lockers f&r, ob air, Custom bumpers, rockers, and skid plate, etc.
post #8 of (permalink) Old 08-10-2001, 12:49 PM
**DONOTDELETE**
Guest
 
Posts: n/a
Re: adjusting the speedo to fit the new tires.

thanks for all the info.. i think that the kid should know that is is going faster than it shows..i have enough work to do on my jeep, i cant give in and start doing work on his. he'll just have to live with it..

304/th400/ford 9"s front/back 7"lift 15x10/35's
it will run someday
post #9 of (permalink) Old 08-10-2001, 01:39 PM
jeepfiend
Guest
 
Posts: n/a
Re: adjusting the speedo to fit the new tires.

I stand corrected! Man is this crow good, you should try it batter fried.[img]/wwwthreads_images/icons/wink.gif[/img]


Cage Up, Wheels Down
Jeepfiend
All my Jeeps are in pieces!
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome