mustangGT90210

My tax return will be buying me a 3.55 or 4.10 rear end, truck currently has a 3.08 and sits on 31x10.50s. I know there's something about a little gear I'd have to change to make my gauge read properly with the new gear ratio... So all you big tire lovers and re-gearing people, where do I find that little gear thing to buy, where is located on the truck, and is there more I don't know about in regards to making the speedo read right after this?

Thanks guys!

infantry351

R u doing the gears yourself? If not the shop should do the adjustment cheep while there there anyway

ma94xlt

For the gear swap you are good, the ring tone on ring carrier in differential will compensate for the gear change. But for tire size difference check out this link https://www.f150forum.com/f10/adjust...re-size-18295/

mustangGT90210

What I'll be doing is getting a complete rear end that already has 3.55LS diff in it. I have a 3.08LS rear right now, but the brakes are completely shot. It's cheaper to get a used rear with decent brakes and the gears I want over re-gearing and re-doing the brakes on mine.

Also, my truck is a 1991, so it has a mechanical speedometer. If it was electronic it'd be easy!

Just call me Sean

iTrader: (1)

You'll have to pull the tailshaft housing to change the drive gear, which is held on with a little clip and ball bearing to hold it in place. The driven gear is on that part the cable attaches to, take out the bolt and pull it out.



Make sure you remove that first before pulling the housing or you can damage the gears. I have only purchased the gears from the dealer, you will need to know which color gears you need. I have had 3.55s and 3.08s in my truck and the difference in the speedometer was not much, not enough for me to change the gears. It reads 2 MPH fast at 65 with my 3.08s, don't remember what it read with the 3.55s but I think the gears I have were for the 3.55. They are yellow.

Just call me Sean

iTrader: (1)

Oh, and are you selling that rear? I wouldnt mind a LS and you're not too too far from me.

mustangGT90210

Thanks Sean, I was just waiting for you to see this thread

It will go for sale after I swap in the new. Has a leaking wheel cylinder, but aside from that the brakes still have life. I've been told they are too used to be rebuilt so it'll need new drums and linings and whatever. Basically just all new components

And after hearing that, I think I'll leave the speedo alone. I just did a little gear calculating and with 33's and 3.55 it'll be right about the same ratio on the ground as stock, so no need to recalibrate, it'll be close enough!