# Axle Ratio Question

Discussion in 'The Garage' started by Old_Miner, Feb 13, 2006.

1. ### Old_MinerRegistered Member

Joined:
Feb 13, 2006
Posts:
9
0
Location:
Idaho
I have read in the forum in the past that if you rotate the tire one full revolution and count the times the driveshaft turns that is your axle ratio.

I have an 1987 GMC Full Sized Jimmy (K5). I turn the tire one turn and the axle only turns 1.75 times. Surely that don't mean I have a 1.75:1 axle ration.

There are no RP codes in the glove box and I wanted to find out the axle ratio so I can gear it for 35" tires.

Any help will be appreciated.

Thanks, Tom

2. ### Jagged1 ton status

Joined:
Apr 25, 2005
Posts:
11,460
1
Location:
SWVA
You sure you didn't move it just a 1/2 turn (180 degrees). If you did, then you'de have ~3.5:1 gear ratio (brain fart on the exact number there)

3. ### Old_MinerRegistered Member

Joined:
Feb 13, 2006
Posts:
9
0
Location:
Idaho
Nope, I turned it one whole turn. I double checked it several times.

4. ### Jagged1 ton status

Joined:
Apr 25, 2005
Posts:
11,460
1
Location:
SWVA
Could try doing it the opposite way. Rotate the driveshaft until the tires turn one revolution.

5. ### sandawgk53/4 ton status

Joined:
Oct 28, 2003
Posts:
6,881
1
Location:
Kitsap County PACNORWEST
If you are only turning 1 tire you need to multiply the Dshaft rotation by 2. With an open dif if only 1 tire spins it has to spin twice as fast. Have I confused you?

Lets say you have 4.10s The driveshaft spins 4.1 times for each axle revolution. If you hold 1 tire so it cannot spin the spider gears will spin in such a manner that if the driveshaft spins 4.1 times the wheel that is spinning will spin 2 times.

The ratio should be 3.08 or 3.73 if they are factory. I do not know if they offered 3.73 in 87 or not mine was 3.08.

Ira

6. ### crazyhole8121/2 ton status

Joined:
Jul 6, 2005
Posts:
228
0
Location:
missouri
get the numbers off the top of the axle tube near the center and call a dealership

7. ### Old_MinerRegistered Member

Joined:
Feb 13, 2006
Posts:
9
0
Location:
Idaho
Yes, Totally confused

Yes, It kind of makes sense.

I spun the tire with both rear wheels off the ground and I noticed the other one turned the opposite direction, so I put that wheel on the ground so it could not spin.

I spun one wheel and the drive shaft rotated 1.75 turns. So if I multiply that times two, I would guess that I have a 3.42.

GM10-308 1258709
3.08
40-13
\$207.33
GM10-342 1258710
3.42
42-13
\$207.33
GM10-373 1259441
3.73
41-11
\$207.33

Does this sound right? Also, who would you recommend me order gears from?

I am thinking about going to 4:11 to turn 35" tires. Does that sound right?

Joined:
Jun 13, 2003
Posts:
29,623
1,379
Location:
Jersey Shore
what tranny?

Joined:
Feb 13, 2006
Posts:
9
0
Location:
Idaho
700r4 NP208

10. ### ryokenPuppy FabricatorPremium MemberGMOTM Winner

Joined:
Jun 13, 2003
Posts:
29,623
1,379
Location:
Jersey Shore
i'd run 4.56's...

11. ### sandawgk53/4 ton status

Joined:
Oct 28, 2003
Posts:
6,881
1
Location:
Kitsap County PACNORWEST
Anything with overdrive and 35 or higher I would run 5.13s. . Unless it is a 10 bolt then scrap it and put in a 14FF .

Ira

12. ### ryokenPuppy FabricatorPremium MemberGMOTM Winner

Joined:
Jun 13, 2003
Posts:
29,623
1,379
Location:
Jersey Shore
yeah, i know, i'm headed that route myself... shoulda put "minimum" after that..

for the average every day DD joe asking, i figure 4.56 will keep the revs and fuel ecomomy reasonable and he'll still use OD.. plus i'm assuming he's talking about a 10b regear...

i'm gonna run 36's with the 700 so i'm figuring 5:13's for myself, but i'm waiting on getting 1 tons..

13. ### Old_MinerRegistered Member

Joined:
Feb 13, 2006
Posts:
9
0
Location:
Idaho
Yeah, I wish I could afford 1 tons, but I have the standard 10 bolt. If I do the gear change myself, I figure it will cost me around \$500.

If I get a shop to do it, they quoted me \$1500.

If I get 1 ton axles it would cost \$3500.

It sucks to be on a budget.

14. ### sandawgk53/4 ton status

Joined:
Oct 28, 2003
Posts:
6,881
1
Location:
Kitsap County PACNORWEST
If you do it yourself it would cost about \$200 for gears and \$100 for install kit it that per axle. The shop that told you \$1500 could lick my nuts. Shop around. I have heard of guys getting it done for about \$400 per at a shop. I did my 14FF and knowing what I know now I think I would have the patients to do my 60Front. There is nothing "hard" about it just takes a little time.

Ira

15. ### Old_MinerRegistered Member

Joined:
Feb 13, 2006
Posts:
9
0
Location:
Idaho
Only thing I have heard is that aligning and setting backlash can be hard. I guess I will find out.

16. ### u2slow1/2 ton status

Joined:
May 9, 2001
Posts:
2,217
0
Location:
Nice part about axles like a Ford 9" or 14bFF is you don't need to press-on/off the pinion bearing each time to change the shims, and carrier bearing use screw adjusters.

Good axles to learn on. All the more reason to get the 14bff now rather than later.

As for budget... last time I did rear brakes, I changed a whole axle instead... it was cheaper.

17. ### sandawgk53/4 ton status

Joined:
Oct 28, 2003
Posts:
6,881
1
Location:
Kitsap County PACNORWEST
It is not hard it is quite easy it just takes some patience and a little time to mess around with changing out shims and what not. Some guys get frustrated cause when you change pinion depth it effects backlash so you have to keep removing and installing shims. For those axles make sure you remove the bearings in 1 piece, then clearance the inside race so they slide on and off by hand. Now you have set of setup bearings. It allows you to change shims easier on the carrier and the pinion. The first step is to get your pinion depth set properly, then adjust your backlash.

Ira

Joined:
Feb 13, 2006
Posts:
9