diff ratio on a manual 4JG2 bighorn

[markduyvesteyn]

my diff is making a bit of noise so am wanting to swap it out with one from the wreckers.

the truck is a stock standard 4jg2, manual long wheel base bighorn. is does a touch under 3K revs at 100kph.

What diff ratio do these usually have?

is it a big job to change it out?

thanks for your help.

[pig75]

If it came with 245-70-16 tires it should have a 4.3 diff

[geeves]

I would of said 4.3 but those revs seem high. You need to check the ratio by lifting a back wheel and rotate by hand watching the number of turns of the driveshaft. Divide by 2 for the answer which will be 4.3 or 4.56.
To change drain and support both sides of the axle on solid blocks remove wheels and brake calliper assemblies. Undo the 4 bolts that hold the axle in the housing and pull out 6 inches or so. Climb under and undo the driveshaft and push out of the way. undo the bolts holding the diff head in place and pull out. A couple of be very carefuls. Make sure you blocks are safe and secure. If they fail while your under the car you become very flat. Placing the tyres under the chassis rails gives a little more safety but restricts room to work. When you remove the diff it is fairly heavy at around 20kg. I did mine by useing my chest to support it but it did leave a bruise. Its still not a nice item to manoeuvre under the car.

[markduyvesteyn]

thanks geeves, i did what you said, jacked up one wheel and marked a point on the drive shaft as well as a point on the wheel with chalk.

i spun the wheel and for each rotation i counted the number of marks i saw on the drive shaft go round, some times i saw 2 and some times i saw 3.

after about 30 spins of th wheel, i calculated the diff ratio to be 4.52, which must mean its the 4.55 version.

now i just have to find a diff close to Hamilton!

[scruff123]

im a bit confused, spun my wheel once and shaft went round 4 1/4 times? what ratio is that? im wanting to swap diffs with lower ratio ones if i can find them, to make up for the 33 inch tires.
cheers

[Fly3r]

yes, you need the same ratio front to back when you've engaged 4wd, otherwise you will break something, and it could be expensive. while you are in 2wd its ok and should do any damage... but I wouldn't go 4wding till they are the same

[geeves]

im a bit confused, spun my wheel once and shaft went round 4 1/4 times? what ratio is that? im wanting to swap diffs with lower ratio ones if i can find them, to make up for the 33 inch tires.
cheers

4 1/4 = 4.25 or approximately 4.3 Had it been the other option of 4.56 it would of gone round 4 1/2 times.
To get this result though you must of had both wheels off the ground or pushed the car along the groundwhich would explain the inaccuracy.

[scruff123]

will a rear 4.3 ratio diff head out of a 88 bighorn fit the front diff on my 1995???
cheers

[geeves]

87 will but it will be 4.56

[scruff123]

ok cheers