Going off of local PD speed checking radar, my speeds looked pretty good after putting on the 33" tires. I was almost dead-on at 45 mph. However, this method is not the most accurate. We all know that radar doesn't work.. especially if you have ever had a speeding ticket.
On our recent off-roading trip, I checked my speed against the others in the convoy, driving trucks with factory tires, and it was suprisingly off by 10-15 mph. While the difference is hardly noticed at low speeds, highway speeds appear to be well below actual speed. I checked the speedo gear chart, seen below, and figured I needed a 32 tooth gear. It only takes one day for the Parts/Service section of your dealer to order this baby, it is $18.
Gears | Tire Diameter | |||||
---|---|---|---|---|---|---|
33" | 32" | 31" | 30" | 29" | 28" | |
3:07 | SG26 | SG27 | SG27 | SG28 | SG28 | SG29 |
3:55 | SG31 | SG31 | SG32 | SG33 | SG33 | SG34 |
3:73 | SG32 | SG32 | SG33 | SG34 | SG34 | SG35 |
4:10 | SG34 | SG35 | SG36 | SG37 | SG38 | SG39 |
4:56 | SG36 | SG37 | SG37 | SG38 | N/A | N/A |
Example: SG34 = speedo gear with 34 teeth
In order to figure out if your t-case requires the short (2.2") or the long (4.3") shaft gear we need to look at the connection. If you have the newer electronic type of connection at the t-case where the speedo gear is you will have the short shaft (1993-2000). If you have a cable type connection at the t-case where your speedo gear is you will have the long shaft (1987-1993). You may want to remove and measure it just to make sure.
Short shaft part numbers (1993-2000) - 52067629 - 29 tooth - 52067630 - 30 tooth - 52067631 - 31 tooth - 52067632 - 32 tooth - 52067633 - 33 tooth - 52067634 - 34 tooth - 52067635 - 35 tooth - 52067636 - 36 tooth - 52067637 - 37 tooth - 52067639 - 39 tooth - 52067640 - 40 tooth - 52067641 - 41 tooth |
Long shaft part numbers (1991-1993) - 2538929 - 29 tooth - 2538930 - 30 tooth - 2538933 - 33 tooth - 2538934 - 34 tooth - 2538935 - 35 tooth - 2538936 - 36 tooth - 2538939 - 39 tooth - 2538940 - 40 tooth - 2538941 - 41 tooth - 2538942 - 42 tooth |
Long shaft part numbers (1987-1990) - 53001492 - 29 tooth - 53001488 - 41 tooth - J3212729 - 29 tooth - J3212730 - 30 tooth - J3212731 - 31 tooth - J3212733 - 33 tooth - J3212734 - 34 tooth - J3212735 - 35 tooth - J3212739 - 39 tooth - J3212740 - 40 tooth |
Procedure:
I just got a TSB letter in the mail today about the ODB light in my Jeep Wrangler.