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i've looked pretty hard to try and find this out for myself but i can't seem to find much for my truck (because of its age i guess) its a 1980 with a 351w with a 6 inch lift on 35's i'm trying to see if anyone can help me figure it what the gear ratio is without having to open the diff (it looks like i have to disconnect the drive shaft to open, the friend who helps me with this stuff is out of town) my door code says H2 from reading El Kabongs sticky at the top of the page i assume its a limited slip. i'm worried that my tires may be too big for my gearing. any help would be grear even if you just need to slap me around because i missed the obvious anwser somewhere on the forum.
thanks
 

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I wouldnt worry about the gear ratio as much as I would be interested in the RPM at 70. If it's about 2000 or 2200, it's about right. If it's sluggish and wont spin the tires from a dead stop ....then it's a Bronco.

If you really want to know, easiest way is to "count" the number driveshaft vs tire revolutions. First you need to dtermine if it's a posi.

Find a level spot and jack up the rear end so both wheels are off the ground, and use jack stands for safety.
Take off the emergency brake and put it in neutral.
Crawl under and turn the driveshaft.
Observe the tires/wheels
If both wheels turn the same direction it has posi.
If the wheels turn in opposite direction it is a standard "open" rearend.

Make a chalk mark on the driveshaft
make a chalk mark on the inside of the tire so you can see it turn (one revolution)

If it's a posi, turn the driveshaft, counting each time the chalk mark passes a fixed position. Count the number of driveshaft revolutions until the tire makes 1 revolution.

If it's an open, block a rear wheel so 1 doesnt turn.
repeat the same proceedure.
should be half of the actual gear ratio if I remember correctly.
 

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if your worried about breakage i dont thiink it will be an issue with 35 stock front and rear can handle up to about 37/ 38 you may be a little doggish
 

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Must do this with a helper..Jack one rear tire off the ground then put a jack stand under the axle so the tire is still off the ground ,put a mark on the tire , white works best chalk or white out (kinda ironic).Remember where this mark starts Like a clock at 12.. Do the same on the yoke and using a reference point on the Pumpkin now spin the tire one full time to youre back at the 12 o clock point ....While you or youre helper is counting the times it takes the yoke to turn past its reference point .. and there you go you can get a close idea of what gear you have ..good luck cause if you didnt pay attention in math then i cant describe it ..
 

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all of those will work to get you close, but the only way to know is to count the teeth.

Unless you have owned the truck since it was new then don't count on it being stock, it could have been changed 20 times before you got it.

and if you have to remove the driveshaft to get to the rear end that's not too hard. I've never heard of one of those, but then again I learn something new every single day...
 

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Must do this with a helper..Jack one rear tire off the ground then put a jack stand under the axle so the tire is still off the ground ,put a mark on the tire , white works best chalk or white out (kinda ironic).Remember where this mark starts Like a clock at 12.. Do the same on the yoke and using a reference point on the Pumpkin now spin the tire one full time to youre back at the 12 o clock point ....While you or youre helper is counting the times it takes the yoke to turn past its reference point .. and there you go you can get a close idea of what gear you have ..good luck cause if you didnt pay attention in math then i cant describe it ..
WHY does one need a helper to do this??? Is it because the mark you suggest he make on the tire is on the outboard side? ...guess my previous post #2 wont work......:doh0715:

You also need to read my post as an open rear doesn't return a true count.
 

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Discussion Starter #7
all of those will work to get you close, but the only way to know is to count the teeth.

Unless you have owned the truck since it was new then don't count on it being stock, it could have been changed 20 times before you got it.

and if you have to remove the driveshaft to get to the rear end that's not too hard. I've never heard of one of those, but then again I learn something new every single day...
i think i was wrong i looked at it again and it looks like i just have to disconnect the u-joint to get to it. thanks for the help everyone i'm going to try and work on it this weekend and see.
 

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WHY does one need a helper to do this??? Is it because the mark you suggest he make on the tire is on the outboard side? ...guess my previous post #2 wont work......:doh0715:

You also need to read my post as an open rear doesn't return a true count.
hmm never thought of that m gonna try that ..not that i dont believe you (now i need to know ) and knowing is half the battle ...i do know a helper is eaiser ..
 

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You didnt mention if it was a 8.8" or 9". I'm not sure what came stock in an 1980.

If you positively feel the need to count the teeth:
(it's not just dropping the driveshaft)

If it's an 8.8. you can pull the rear diff cover and access the r&p to count.
If it's a 9" (no diff cover) you cant access the gears without pulling the axles.
 

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-90 xlt, 351w, e4od, man 1356, 3.55, sag, warn hubs, 35s. -73, 400, np435, d20j twin, 35s
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1980 should still have the 9" rear end. Those older ones have some different codes. From this thread:
D7-DANA70 LIMITED SLIP -4.10
23-DANA61 -3.31
24-DANA60-4.10
H2-LIMITED SLIP-3.50
H4-LIMITED SLIP-3.25
H7-NOT LISTED ON MY CHART
H9-LIMITED SLIP-4.11

From the Bronco Graveyard catalog in the back of the book.
 

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Discussion Starter #11
You didnt mention if it was a 8.8" or 9". I'm not sure what came stock in an 1980.

If you positively feel the need to count the teeth:
(it's not just dropping the driveshaft)

If it's an 8.8. you can pull the rear diff cover and access the r&p to count.
If it's a 9" (no diff cover) you cant access the gears without pulling the axles.
i knew there was something important i forgot when i was writing this. it is a 9". thanks again for the help. thanks El Kbong for the ratio
 

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if your have to remove the drive shaft to get to the gears it is a 9inch rear becaus this is a removable style third member rear end if it has the diff cover on the rear it is an 8.8 im assuming that this is a 9inch and assuming that the standard gear raitos for an 80 bronco with a 9in rear were 3.00 or 3.55 neither of which are good for running tires bigger than 31's. so i know this is a flame free zone but who ever said stock gears are good for up to 37's go sit in the corner and raise you hand next time before you speak:twak

look at this chart http://www.4lo.com/calc/geartable.htm
 

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i bet there 3.00 gears i have them also on my 78 which is odd cause i thought they all had at least 3.55 s but on my rear and front tags they say 3.00 s im changing them to 4.10 s though or my baby wont go no where but i couldnt belive it either just imagine the diffrence!
 

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dude read the post again i said he would be doggin with 37 of course higher ratios are better but not every one can afford to run out to yukon gears and replace them i was just saying he could get by with them for now so maybe you need to learn to read before you tell others to sit in the corner jerk
 
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