4x4 rearend question....

wolfpack · Post by **wolfpack** » Thu Feb 09, 2006 8:57 am

Hey guys have a question, my brother in law was moving down here yesterday and his rearend went out but he made it here at 30 miles an hour and 28 miles to boot. My question is don't i need to get the numbers off the rearend because isn't the gear ratio suppose to be the same as the front gear ratio?. Oh btw it's a 84 ford f150 sorry you know how i ramble...Terry

Doug Comer · Post by **Doug Comer** » Thu Feb 09, 2006 8:49 pm

Yes. The front and rear are supposed to match.

heep70 · Post by **heep70** » Thu Feb 09, 2006 8:59 pm

Depends on what year and if it is an f100, F250 or F350. F250s are usually a 4.09 front and 4.10 rear. Some older years have 4.56s. I believe the difference in front and rear needs to stay with in 8% of each other in order to keep from popping R&Ps.

68half/step4x4 · Post by **68half/step4x4** » Thu Feb 09, 2006 11:04 pm

If the tags are missing, the ring and pinion should have the number of teeth stamped on them. If you divide the ring gear by the pinion gear, that will give you the gear ratio. [35 divided by 10= 3.50, ect...] You should stay with the same in the front and rear or you will be binding up. Not good!

mrung0wa · Post by **mrung0wa** » Sat Mar 04, 2006 6:23 am

OH Yeah it really does matter!

Especially if you have a DANA in the front and a FORD in the back!

If you get the wrong Ratio Ring & Pinnion your sure to F' it up Big time (when your/he's in 4wd of course).

Lawrence

Leadfoot · Post by **Leadfoot** » Sat Mar 04, 2006 7:05 am

Your best bet is to get down and dirty and check the pinion, & ring ratio
you should be kind of interested in seeing the damage, and its safety if there was a gear swap prior.

If you can't read the numbers on the ring gear hopefully you can count the teeth on the ring & pinion. divide big # by the little# and thats your ratio. & use the same ratio.

OR check the front diff tag call an autowrecker and give them that ratio and they will tell you the proper rear end gear to use, and more than likely try selling it to you.

Rockcrusher · Post by **Rockcrusher** » Sat Mar 04, 2006 3:21 pm

heep70 wrote:Depends on what year and if it is an f100, F250 or F350. F250s are usually a 4.09 front and 4.10 rear. Some older years have 4.56s. I believe the difference in front and rear needs to stay with in 8% of each other in order to keep from popping R&Ps.

A 2% front to rear ratio difference is a more realistic figure.

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