Setting up and 8.8 rear end
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Old March 6th, 2009, 11:24 AM   1 links from elsewhere to this Post. Click to view. #1
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Setting up and 8.8 rear end


I'm always asking for help and advice in the forum, so I thought I'd finally give back a little. I just completed round 2 of a rear end set up and figured I'd pass along some info to help any other shade tree mechanics attempting this project. First things first, I used the following link, and years with hands on a wrench for the basic how to's. I mainly just want to cover some issues I had and hope it helps. Just to note. Round 2 has less than 150 miles so far, so it still may have issues, but so far so good.
CarTech, Inc.: Browsing Ford 8.8 Inch Differential Gear Swap

NOTE: I did not find this job hard, but more of an art than just turning wrenches, which led to long hrs of frustration. I've heard that most shops will do this for a couple hundred bucks, and unless you are just really curious, or have a strong desire to learn a new skill, or just have pride in doing your own stuff..... PAY SOMEONE!!!!!!! I did it for all of the above reasons, and will probably never do it again... lol, the "tuition" at this school was more than I wanted to pay. If you still want to do it yourself, I respect that, so read on, maybe it will help.

Tools you'll need and may not have to do this job are: A press, as the pinion bearing must be pressed on. A torque wrench with a needle (not a click style) that can measure small increments (10-30 IN-lbs), dial indicator, bearing/seal installation tools, axle bearing puller and slide hammer and a 3 and 2 jaw puller some of which you can probably rent at the local parts store.
Next, tricks I picked up that may help. The problems I had with round one were a shallow pinion depth and not enough preload on the the bearings. The first problem can be solved one of two ways. The easiest is a lucky guess, but I don't recommend this, b/c if you are wrong, you have to press the bearing back off (risking damage) to change shims. The next is to either buy an extra bearing (less than $20) or press the old bearing off of the old pinion. To do this you will need a bearing knife to get under the bearing to press it off of the pinion. Take this bearing and mill, grind, or file the inside SLIGHTLY, so that it will just barely slide on and off of the pinion. I also recommend taking steel wool or a scotch bright to the new pinion where the bearing sits, to get all the rough off of it. On that note...... you'll want to wire wheel the pinion flange teeth, on the pinion, and add some grease when installing the pinion flange, and test fit it on the bench, until it reaches the bottom of the teeth. If not, it may bind during install and prevent proper preload. With this "mock up bearing" you can install the pinion with both bearings and the diff assemble to test gear mesh pattern. Some where on the internet, I can't find it now, is an excellent description of proper gear mesh, but hear it is in a nut shell. You want the pattern in the middle of the ring gear teeth. If the pattern is toward the inside of the ring gear, you need less shim. If its on the outside, you need more shim. Also, the backlash here needs to be close, but not perfect at this time. You do not need a crush sleeve or pinion seal at this time. Just make sure the pinion flange is seated so that there is NO slack in the bearings or pinion.
Now for problem two, improper preload. Once you have the proper shim for the pinion depth, you can press on the good pinion bearing and install the pinion with the front bearing and pinion seal, and crush sleeve. The pinion flange should go on with some resistance, but not too much, then you'll hit the crush sleeve. It will be very stiff at first (in the area of 150 ft/lbs) but will then collapse and the tension will ease up some. This is where you use that torque wrench to start measuring drag, b/c it will tighten up quickly. NOTE: the should be NO slack in the pinion flange assembly. The info I have says about 20 inch/lbs of rotational drag. I never could get my hands on a proper torque wrench, so I used a 12 inch bar, and, believe it or not, a fish weight scale to measure the amount of drag. It should be about 1.6 ft/lbs. HOWEVER, I do NOT recommend this, b/c I'm not sure of its accuracy and I may have overloaded mine just a touch... time will tell. Just one of those things you come up with at 11 pm and improper tools. One other note. the crush sleeve that came with the second set of gears was very thick walled compared to the one that came in the rear end rebuild kit. Watch out for this b/c that heavy one is a son of a gun to get seated.
I found backlash fairly easy to adjust, and actually was fortunate to be able to use factory shims to obtain .013. this may be slightly loose, as the info I have says .008-.012, but that's pretty close and I've HEARD that under .015 is good. Also, if using FRPP parts, they have a tech line 1-800-367-3788. So, good luck and hope this helps!!
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Old December 29th, 2013, 10:26 PM   #2
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This is long overdue...

Round 2 still less than perfect. I picked up a bearing howl, and decided it was the diff carrier bearings I didn't replace. So I went in for round 3. What I didn't realize at the time was that during round two, my caps had been mixed up, and were probably not reinstalled with the original orientation which pinched the bearings.
During round 3 I installed new diff carrier bearings, but retained the cap orientation from round 2. Also, I let a mechanic convince me that the diff carrier was too tight, so I removed shim. I have since learned that the factory shim on the diff should always be retained. You can take from left and move to right and visa verse, but the total shim should stay the same. So round 3 complete I still had a bearing howl, that slowly transitioned to a gear whine. My theory is that the caps were still pinching, until the bearings seated, at which time the improper diff pre-load allowed the backlash to change, creating the gear noise. It's been over 75k miles since round 3, and still running strong, just has a little whine. Maybe some day I'll fix it.
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Old December 29th, 2013, 11:13 PM   #3
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Did you use the same gears from round 2 in round 3? Sometimes when you have to reshim old gears its hard to match the pattern on the gears from the previous install. For instance, the pattern on the drive face may be spot on but the coast side would be off and cause whining on decel or coast.
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Old December 30th, 2013, 12:06 AM   #4
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When installing gears with the axle still in the car - I never use a tool to check rotational torque on the pinion. I've always done it by feel... it's usually impossible to use a torque wrench correctly in that area and position... except on my 12" lifted Silverado lol.... Anyways never had a problem but that comes with lots of experience.

I will tell you this. ...99% of the 8.8 I've built don't have enough carrier preload with the factory thick shims. I always add more..... and you would have a VERY hard time getting enough shims in to have excessive carrier load. Most people set it up too lose then it screams on acceleration or deceleration. ...or both. Get it shimmed up tight as you can just watch the backlash while doing so because it will change as you force in.... just also realize that by not doing so your backlash is moving around just as much when you on and off the throttle.

Next biggest mistake is people that tighten then the pinion too tight then back it off without replacing the crush sleeve.... I will say I've done things like this and got away with it in my younger days but that's only if your backing it off the most very tiniest detectable amount. ... either way it's wrong.... but I also used to set up gears with news paper for backlash and grease for pattern before I had the right tools lol..none of them ever failed or made much noise though because though my methods were out there i always ended up with a good pattern and preload. ..


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Old December 30th, 2013, 11:39 AM   #5
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My whine was on throttle at about 70mph, but after the drop its more around 60 mph now. Not sure why the change (pinion angle??).

Vortek: Yes same gears. I'm pretty sure the backlash changed as the diff carrier bearings "broke in", because I did not have gear noise in about the first 5k miles or so.

Nitmare: I've learned most of that by trying to figure out where I went wrong. Just haven't taken the time to fix it, and now it would probably take a new gear set to really get it quiet, because I'm betting the current gears have a wear pattern on them. How do you measure diff carrier preload, other than the diff being a VERY tight fit?
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Old December 30th, 2013, 12:17 PM   #6
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There is no way to measure it. Gotta love it right lol
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Old December 30th, 2013, 03:12 PM   #7
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If you reused the old pinion-ring gear after round 2...then they will be noisy even if all your work is correct. Were they really shiny besides? As mentioned....that carrier pre-load has to be tight, if you can just slip the shims in by hand that will be way too loose. Tapered bearings need pre-load to work correctly. I always buy two pinion bearings and sand one down to slip on. Once I am all done with backlash and pinion depth I press on the unsanded one. Always use the old nut for all your work...then back it off...pull the yoke...now install your seal ....put the yoke on and use the new nut with the red locktite on it to wrap it up. I use about 120 ft.pds on the final torque....tight enough to hold everything, yet not so tight to crush the sleeve further. Crush sleeves are cheap, so always have a few around. If you don't have an impact to crush them...(SLOWLY and keep checking) then try getting the crush started in a vice using the old one as a guide...stop before it is even with the old one....that will get you pretty close and save a LOT of muscle if under a Mustang trying to do it. It's almost like an art setting up a rearend....but as mentioned you do learn a lot.
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Old December 30th, 2013, 03:40 PM   #8
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+1 Magna.... If I knew then, every thing I know now, it'd probably be quiet, but hey, it's all part of the experience. Who drives 60 mph anyway......hahaha
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