Sterling 10.25 Backlash Spec - Ford Powerstroke Diesel Forum
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Old 05-02-2013, 05:08 AM
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Sterling 10.25 Backlash Spec

Having lots of confusion adjusting backlash of the ring gear in my rear diff. which is a 10.25 sterling with LSD and recently installed 4.56 gears. Im doing the repair because carrier shims came out and carrier was walking left and right so i could not get a before backlash reading.

Right now as i have it set up i measured backlash at 3 different spots on the ring gear and i have an average of .006-.007

From doing a search i see that the range is .008-.015
Alldata/Service Info says maximum backlash should be .004
Tech support from a drivetrain co. says .012 is what you want
Who is right???????

First off do i need to increase my backlash?
What does to little backlash do to the diff? What does to much do?
If backlash is a little out of spec but pattern is ok should it be left alone?
What can you use to check pattern if you dont have pattern marking compound handy?
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Old 05-02-2013, 12:33 PM
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Quote:
Originally Posted by 7.3 on 40s View Post
Having lots of confusion adjusting backlash of the ring gear in my rear diff. which is a 10.25 sterling with LSD and recently installed 4.56 gears. Im doing the repair because carrier shims came out and carrier was walking left and right so i could not get a before backlash reading.

Right now as i have it set up i measured backlash at 3 different spots on the ring gear and i have an average of .006-.007

From doing a search i see that the range is .008-.015
Alldata/Service Info says maximum backlash should be .004
Tech support from a drivetrain co. says .012 is what you want
Who is right???????

Ford says .008-.015 is acceptable range for backlash. Ford's preferred setting is .012-.015.

First, Backlash is the amount of play between the ring and pinion to the effect of when you turn the pinion this is how much space there is between the pinion not contacting the ring and when it finally does.

First off do i need to increase my backlash? Yes, increase to .012
What does to little backlash do to the diff? Too little backlash and the pinion and ring are essentially grinding against each other. This causes a build up of heat from the friction destroying the gears What does to much do? Too much play and the gears will bang on and off each other until the ring and/or the pinion chip and crack to death. What you are looking for is the balance between grinding and bouncing of the gears that still allows the gear oil to stay between the meshing pair
If backlash is a little out of spec but pattern is ok should it be left alone? There is a spec for a reason...
What can you use to check pattern if you dont have pattern marking compound handy? I go to a office supply store and grab some paint pens but thats me. I haven't done a ring job in 12 years.
See above and send me a PM with your email address.
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Old 05-02-2013, 03:01 PM
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The best is to run used gears at about the same as they were prior, or you can get some gear whine.

But if you don't know, I would run on the tighter side of Ford's recommendation myself.
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Old 05-02-2013, 08:00 PM
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Thanks for the replies. Ill reshim to get .011-.012 I need to tow as soon as im back together so i would rather do everything the best i can. It makes sense that if backlash is to little it can cause excessive heat and that might cause lockup or major gear wear.
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Old 05-02-2013, 08:51 PM
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WIth new gears I always set up to the tightest spec because they will loosen up when it breaks in. If they are still real new go with the tighter side. If they are well broke in do your .011-.012 and when you run the pattern see if it runs close to the exiting pattern marks.
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Old 05-04-2013, 04:36 AM
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Thanks again for all the help. Link that bigfuel sent me seems very clear and accurate in stating the range is .008-.015 and the ideal number you want is .012. I am doing the procedure correctly so thats a good thing.

Gaius - have you had any experience with going with the tighter side having new gears? I honestly could not tell you how new the gears are, is there a way to tell? Is that usually the case when you say it will loosen up after break in? Only reason asking because in my mind im thinking they will tighten up after heating up.
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Old 05-04-2013, 07:35 AM
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Ok so after reshimming another time i think i ended up with perfect carrier bearing preload (took a light tapping with hammer and wooden dowel to seat shims). Pattern looks decent. Doing some more research i found most ring gears will have runout due to the carrier not being perfect. They say runout will be around .002 from highest to lowest point. My lowest backlash number is now.009 and highest is .012

Also from what was said in this post that if the gears are new ending up on the tighter side is ok. I looked at some pics of new and old gears and mine are def on the newer side of things.

Im going to run 75-140 full synthetic motorcraft with 8 oz. of lsd additive. I hope and think ill be much better off with all that being said. Before this i had leaking axle seals, a leaking diff. cover, a carrier walking around from shims coming out, and was running with maybe 1.5 quarts of fluid, and was not experiencing any issues.
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Old 05-04-2013, 04:17 PM
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Run it 500-600 milees at very light load, and then change the oil and you're good to go....

and read that site he sent you Very Carefully, as the Sterlings set a bit different than a regular rearend...I cannot remember what exactly the difference was , as I rebuilt mine about 11 years ago..... I DO remember you need to Get the shim pack as tight as possible, even to the extent of prying the ears of the carrier apart to get the last one in, or the bearings are not pre-loaded enough. The Sterlings also run VERY hot, and I bought a PML diff Cover because of that...it's made of finned cast aluminum, nice and thick, and holds almost another Quart, (0.8 quart), over the stock cover, and cools one HELLova lot better.

in 11 years, no problemmo's.... check them out here :

http://mrtruck.com/mrtruck/wp-conten...old/covers.htm

Last edited by OL' OutLaw; 05-04-2013 at 04:21 PM.
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Old 05-04-2013, 05:22 PM
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Quote:
Originally Posted by 7.3 on 40s View Post

Gaius - have you had any experience with going with the tighter side having new gears? I honestly could not tell you how new the gears are, is there a way to tell? Is that usually the case when you say it will loosen up after break in? Only reason asking because in my mind im thinking they will tighten up after heating up.
I do. I haven't done a lot, maybe 3-4, but friends with a local here that everyone brings their rigs there for regears. Going by his recommendation that's what I have always done. After I've set them to the tight sode of the range, after they are heat cycled and the faces break in a but the backlash opens up a tiny bit to the middlish range.
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Old 05-05-2013, 06:25 AM
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On a budget right now otherwise i would def go with a new and larger cover for cooling. I def think i got the shims in pretty tight. I used a little wedge to help push the carrier to one side while tapping the shims in lightly with a dowel. Even without the caps on the carrier sat in place with the shims in. Thanks for all the help. Its good to hear a shop is setting on the tighter side and it loosens a little after break in. I torqued the caps to 80 ft. lbs. Hopefully with a light load break in period i should be good after that. Now waiting for the friggin axle shaft o-rings, the big o-rings that go around the shaft near the flange. Ordered from quad4x4 and shipping is 14 days on 3 o-rings????
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