How I know my diff ratio????????? (1 Viewer)

[saad94]

I want to know my diff. gear ratio?
My car is 82 manual 4spd
How hard is the rear differential, if the car is V8 350ci?

Is the 4spd great with 33'' tire or change it to 5spd for the DD and highway use?
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[shelfboy1]

82 manual 4 speed covers a lot of vehicles being more specific may help .also the search function works pretty good .

 

[75/76FJ40]

You can jack up the rear of your cruiser - remember wheelchocks front and back on both the front wheels. Mark the driveshaft with a chalk line and spin (slowly) the tire (axle) one full revolution. Count the number of times the mark on the driveshaft comes around during the one full revolution of your tire (axle). Just less than 4 and you most likely have a 3.73 rear...Slightly more than 4 and you have a 4.11 and so on...This will be your gear ratio.

I have 33" tires with my 4speed and i think it is fine for my daily driving which is some highway, but not much over 50mph.

 

[pbgbottle]

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you can also only jack up one rear tire and rotate it 2 times and count the driveshaft rotation if you have no locker in the rear.

i run 38.5's and 4.11 gears with my V8

You can jack up the rear of your cruiser - remember wheelchocks front and back on both the front wheels. Mark the driveshaft with a chalk line and spin (slowly) the tire (axle) one full revolution. Count the number of times the mark on the driveshaft comes around during the one full revolution of your tire (axle). Just less than 4 and you most likely have a 3.73 rear...Slightly more than 4 and you have a 4.11 and so on...This will be your gear ratio.

I have 33" tires with my 4speed and i think it is fine for my daily driving which is some highway, but not much over 50mph.

 

[bikersmurf]

I'm running 4.11s with a four speed, 33s, and a 350, I DD it and it's quite happy on the highway @ 65 mph. With 33s the spedo is approximately 14% low.

Swapping diffs is fairly straightforward, just time consuming. I've contemplated 3.70s, as I can easily start off in second gear, but they would not be as good off road.

A five speed is not a cheap swap. You'll likely need new driveshafts, mounts, an adaptor, and a transmission.

Do you go rock crawling? Logging road driving? Or?

 

[saad94]

I'm running 4.11s with a four speed, 33s, and a 350, I DD it and it's quite happy on the highway @ 65 mph. With 33s the spedo is approximately 18% low.

Swapping diffs is fairly straightforward, just time consuming. I've contemplated 3.70s, as I can easily start off in second gear, but they would not be as good off road.

A five speed is not a cheap swap. You'll likely need new driveshafts, mounts, an adaptor, and a transmission.

Do you go rock crawling? Logging road driving? Or?

The car will be daily driver and dunes the car is V8 350

 

[bikersmurf]

I don't think you need to worry about maximizing your crawl ratio if mostly on the street and some dunes.

Your ideal diff ratio IMO would be the 3.73 gears that came stock in US Fj40s after 79. Unless someone has swapped you gears, you'll still have them.

My Stock F motor never seemed very happy above 2500 rpm, but I've run the 350 at 3000 rpm all day long without any problems. With 31" tires 3000 rpm was about 65 mph. With 33" I'd estimate 2700 rpm with 4.10 gears. 3.73 gears would be more like 2500 rpms. I know there are calculators out there... But these are just estimates.

 

[cjhollenshead]

you can always pop the inspection cover off and devide the number of ring gear teeth by the pinion teeth.

 

[pbgbottle]

if your gonna pull the cover off no need to count anything just read the numbers stamped on the ring gear

10x37=3.73
9x37=4.11


to get the ratio you divide the 37 by either the 9 or 10

see pic

you can always pop the inspection cover off and devide the number of ring gear teeth by the pinion teeth.

 

[bikersmurf]

Checking the gears is the most certain way to determine the ratio.










My covers don't come off.