PDA

View Full Version : Which gears do I have?


cjsutton
09-03-2009, 12:15 PM
I am trying to figure out which gears I have in my 86 xtra cab. I checked the codes on the firewall and it says the truck came with 4.11's. The truck currently has 31" tires on it. I found a calculation chart online that listed speeds correlating to rpm's. That chart says I should have 4.56's. The speedo is spot on with the 31's.

I believed all of this to be correct, but it still seemed to be too gutless to have been regeared. I jacked up one side of the rear today and put some marking paint on the driveshaft, third member and the tire. I thought I should be getting four and a half turns of the tire for each full turn of the driveshaft. With one full turn of the driveshaft the tire only turns like 2.1 times. I am really confused.

The only other thing I can think of is that maybe a previous owner changed a speedometer gear to match the 31's and that is why the speedo is correct.

Does anyone have any ideas? Am I checking the gear ratio correctly?

Thanks.

corsair23
09-03-2009, 01:13 PM
I tried to find the thread that discussed this awhile back...IIRC there was something about doubling the result or something...I'm sure someone in the know will chime in :D

But, 2.1 * 2 = 4.2 which is pretty darn close to 4.11s

daisydog34
09-03-2009, 01:21 PM
The best way is to pull the third and count the teeth...then use a calc you can find online to calculate the ratio

MDH33
09-03-2009, 02:31 PM
I am trying to figure out which gears I have in my 86 xtra cab. I checked the codes on the firewall and it says the truck came with 4.11's.

How can you decipher the codes to determine the stock gearing? not sure what to look for. I have been wondering what my '82 minitruck has.

cjsutton
09-03-2009, 02:50 PM
This is where I got the info on the axle coding:

http://www.off-road.com/trucks4x4/article/articleDetail.jsp?id=274535

cjsutton
09-03-2009, 09:55 PM
I found my answer elsewhere on the internet. I guess due to the spider gears in the open differential you divide the number of turns on the driveshaft in half which means I need to double my number. So you were right, I actually have 4.11's in my truck. No wonder it seems so gutless. My 4Runner with 35's and 5.29's feels much more powerful.

Thanks.