Gearing question...no, not "what gears do I need"

[dommo2007]

I am looking at trading my stock Bronco for an already lifted, modified Bronco. Although I am sure that the previous owner didnt re gear it, and its at a dealership, so they dont know...is it possible for a mechanic(I have no idea what I am doing with gears and all) to pull off the diff covers, and tell me what gear ratio it is running? I suppose that it would be more complex than just looking at the gears, so would that involve removing them? If so, it would probably be a better idea to just replace with new gears, so if this is gonna cost me an arm and a leg, I'll just roll with what ever are on there till I can afford the labor to re-gear it.

Thanks

 

[BroncoJoe19]

You could look at the tag on the rear. IF they swapped out the whole rear, then the tag should be accurate. IF they just replaced the gears, then if you pull the cover the ring gear will have numbers stamped into them. See posts 8 and 10 of this thread.

Here you go... courtesy of Blade262US

http://broncozone.com/forums/index.php?s=&...ost&p=74281

joe

 

[shift1313]

even simpler, just jack the rear end up and count the number of times your wheel rotates in relation to your drive shaft. if you have 3.55 gears your drive shaft will turn 3.55 times for every 1 revolution of your wheel. I suggest jacking both rear wheels off the ground just incase it has a limited slip rear or some sort of spool.

 

[BLADE262US]

Gear back lash will probably make it kinda hard to tell 3:55 from 3:73 useing that method though or 4:10 from 4:56 /emoticons/[email protected] 2x" width="20" height="20" />

 

[shift1313]

Gear back lash will probably make it kinda hard to tell 3:55 from 3:73 useing that method though or 4:10 from 4:56 /emoticons/[email protected] 2x" width="20" height="20" />

i dont believe 3.73s came stock so he would know if it changed from 3.5 to 4.something.

You think backlash would make that much difference? sure there will be some play but if you start your counting once the gear engages there shouldnt be any error

 

[BLADE262US]

Might not be an issue was just thinking a 1/4 of a turn might be a bit hard to determine , Maybe not /emoticons/[email protected] 2x" width="20" height="20" />

 

[shift1313]

/emoticons/[email protected] 2x" width="20" height="20" />

 

[dommo2007]

I figure that even my un-mechanically-inclined-ass can mark the drive shat and spin the tires. Plus, about being able to tell a rather small diference, i.e 3.55-3.73...honestly it doesnt make a huge difference to me, just trying to get an idea IF it was regeared. I figure that if indeed it was, it would be at either 4.10 or 4.56. If not, then it just boils down to stock or not, not WHAT ratio so much. But thank you very much, since it would have nt occured to me that it would be that easy to atleast get an idea of the gearing.

So this will show my ignorance, but thats all right...what is gear backlash? And also, Shift, when you say "when the gears engage" what do you mean? I guess I should say, how do you tell...would it be something I can hear, or is it something I would feel as I started turning the wheel? Also, yes, it has the factory Limited Slip...dunno if tha would make any difference or not, but thanks for everyones help. If all else fails, I will have the shop I am taking it to for an inspection yank the cover off and read the ring gear.

Thanks

 

[BroncoJoe19]

I figure that even my un-mechanically-inclined-ass can mark the drive shat and spin the tires. Plus, about being able to tell a rather small diference, i.e 3.55-3.73...honestly it doesnt make a huge difference to me, just trying to get an idea IF it was regeared. I figure that if indeed it was, it would be at either 4.10 or 4.56. If not, then it just boils down to stock or not, not WHAT ratio so much. But thank you very much, since it would have nt occured to me that it would be that easy to atleast get an idea of the gearing.
So this will show my ignorance, but thats all right...what is gear backlash? And also, Shift, when you say "when the gears engage" what do you mean? I guess I should say, how do you tell...would it be something I can hear, or is it something I would feel as I started turning the wheel? Also, yes, it has the factory Limited Slip...dunno if tha would make any difference or not, but thanks for everyones help. If all else fails, I will have the shop I am taking it to for an inspection yank the cover off and read the ring gear.

Thanks

Dommo2007,

ALthough you posted the question about backlash to Matt (Shift1313) I just checked and he is not currently online. I don't know when you wanted to act on this, but incase it is first thing in the morning, I wanted to give you an answer. Gears are not necessarily totally in contact with each other at all times. There may be a little space between them. So one may need to turn one gear an inch or more before it comes in contact with the other gear, One may need to turn it an inch or more in the other direction before it will come in contact with the other gear and turn it in the other direction. One may call it "play" others may, perhaps more correctly call it "backlash."

Engaged may be defined as: The moment when one gear contacts the other gear, so that it may cause the other to turn.

I hope this helps. IF I am wrong in any aspect, guys please jump in.

joe

 

[shift1313]

nope thats right on the money joe except for the inch part.

i think this is a pretty good picture of a general rear diff

acceptable backlash on an 8.8 rear end is about 0.008 to 0.015", very small amount.

The large gear is your ring gear and behind that is a small gear called the pinion gear driven by your drive shaft. The "slop" between the large ring gear and the pinion gear is your backlash. When you are working on a rear end there are shims that located the ring gear left and right in the housing and this is how you take up for that slop. You can also see 4 other small gears in the middle. well the two on the side are connected to your axle and the top and bottom spin around with the ring gear(actually that whole center section does). This planetary gear set is what allows one wheel to spin faster than the other around turns. In the center of those gears is a spring clip on your ford 8.8" rear end. You remove this clip, undo a bolt holding that center pin that holds the top and bottom gears in(planetary) and this allows you to slide your axles in and out slightly and gain access to the clip holding your axle in place. once the clip is off you can slide your axle out of the rear end and gain access to the LS clutches.

here is a good pic of that spring clip

I couldnt really find any better pictures for you but im sure that is more than you wanted to know.

So to answer your real question on how you can tell. If you climb under your truck with it still on the ground so your wheels cant rotate(in N and parking brake, wheel chocks wouldnt be bad either). Grab your drive shaft and turn it back and forth. The amount you can turn it is your back lash. But ofcourse this isnt going to be .008", it will be a more noticeable amount. Ford 8.8" typically is the diameter of the ring gear. Your pinion is much smaller. Lets say your pinion gear has 14 teeth on it and you had a 3.55 rear gear set, your ring gear would have 50 teeth on it making it much larger. The play typically shouldnt be that much but it will show the wear of the rear end a good bit. If someone is looking to buy an old truck they usually will check that kind of thing to see how much slop is in the rear and how much longer it will last.

If the backlash is excessive it can produce bad wear on the ring/pinion gear set. Ive seen extreme cases where the backlash is so bad that the ring gear is basically smoothed out and the truck wouldnt go anywhere. This is on a vehicle that towed all its life and was never maintained.

hope that answers it for you.

 

[shift1313]

there are some good animations i found if your interested.

http://auto.howstuffworks.com/differential2.htm

i know visualizing how the whole assembly works can be tricky when you throw planetary gears in the mix.

seeing the animation might help see how the clutches work. The clutches include friction plates and steel plates. They are sandwiched behind the small planetary gear that connects to each axle in that center housing. Some of the clutches are splines to the axle, some to the housing. This lets the housing rotate without the axle rotating with it. So basically if one wheel starts turning a lot faster than the other wheel the friction in the clutches grabs the housing and rotates the housing. So the clutches on the driven wheel grab since they are free spinning and turn the housing which makes the clutches on the other "free" axle grab and spin that axle to help out with traction. Its a very simple idea and it used in a lot of different ways. AWD cars use clutches in the front/rear and center to limit slip between all 4 wheels. Could be friction plates like in my quadradrive jeep, could be a viscous clutch like a torque convertor, could be electro mechanical like in a wrx.





you can see the metal plates have teeth on the inside and the friction plates dont, they have the big "ears"

 

[BroncoJoe19]

If the backlash is excessive it can produce bad wear on the ring/pinion gear set. Ive seen extreme cases where the backlash is so bad that the ring gear is basically smoothed out and the truck wouldnt go anywhere. This is on a vehicle that towed all its life and was never maintained.

Excellent response Matt!

Can anyone give me an idea how many degrees one would be able to rotate the driveshaft in trying to determine what an acceptable backlash vs excessive would be?

This is my problem: I have limited experience, and no experienced coach. Often a manual will state "if excessively worn, replace" I often don't know the difference between what is acceptable wear, or not.

 

[shift1313]

thats a tough one. the only real way to tell is to pull the diff cover(on anything but a 9") and check it with a magnetic base dial indicator. Ive never really turned a driveshaft by hand and then checked the backlash its just the kind of thing where you go" wow thats a lot of play" The rear end in my daily driver has about 215k on it and it moves a good bit. Id say i can move the drive shaft a few degrees. the one in my bronco has under 30k on a new ring/pinion and it moves almost nowhere. You have to remember how the two gears line up and what you are actually talking about with back lash. The gears are helical so they engage like this pic:

only your ring gear is beveled and your pinion is beveled as well but they engage the same as the pic. When the play between them gets larger since they are beveled they also get farther away. So think about the tooth on a sprocket being 1/2" tall, and the chain only riding on 1/4" of the tooth where there is less meat, its going to wear it down a lot faster than if it had full contact. so what im trying to get at with this is once the play gets larger its not a linear thing. Meaning you wont get 1degree rotation for 100k miles and then 2degrees at 200k miles etc. The longer the backlash is excessive the quicker it will wear out because of the taper of the gears and the torque applied to the material. Next time im under my truck i will get you an exact angle that i can rotate it so you know whats too much.

that means i should probably fix that

just as a note before i bought my f150 i had a mechanic look it over for me just for piece of mind and he told me the rear end play was excessive. He said i should fix it because i only had about another 100k before it went. I thought to myself 100k, ive got some time Ive been into my rear diff a few times and there is no wear on the ring/pinion so ive never taken the time to worry about it but i should have fixed it by now, shame on me. but i only put about 5k on the truck a year and the heaviest thing i haul is a 300lb motorcycle or jetski.

 

[BroncoJoe19]

"wow thats a lot of play"

LOL... I can relate to that!

Hmmm calculations, I made... 100K/5K per year, fix that you MUST! Last only 20 years it will.

 

[shift1313]

"wow thats a lot of play"LOL... I can relate to that!

Hmmm calculations, I made... 100K/5K per year, fix that you MUST! Last only 20 years it will.

haha,

 

[dommo2007]

Well, I have said it in a few other posts...dude, you guys rock!!! I know I have said it about you, BroncoJoe, and Shift, you just added yourself to that list as well. Honestly, yeah, that was way more than I thought I wanted to know...but I am very happy you explained it to me. I had planned on doing a probably less-than complete once over on the truck, and then if everything looked decent, take it in to a shop for a more in depth inspection, compression test, stuff like that. But, if nothing else, this gives me one more thing to check my self(atleast in the sense that if I can get a full turn of the driveshaft while its still on the ground, there just might be something wrong...lol) before I go drop more money on an inspection.. Like I said before, I leave the "fixing" part to people WAYYYYY smarter than myself...I keep to the breaking things, I let them fix it, but I still want to know what the **** exactly I am breaking. At any rate, you guys are awesome, and you both just made my Christmas card list...lol.

Y'all take care,

Dom

 

[shift1313]

no problem and good luck with it. really there isnt a hard task when working with a car, just some more time consuming and some require more brute force(in place of the right tools).

im sure there is enough knowledge here to walk you through any task you need to handle if you want to save your money.