Ford Differentials: How To Rebuild The 8.8 And 9 Inch Manual Book

[AgileYeti]

Does anyone have a copy of Ford Differentials: How To Rebuild The 8.8 And 9 Inch Manual book you no longer need or want to get rid of? I hear it’s a must read before any rebuild.

162973

Thanks!

[NAZ]

If you don't get a copy of the book you're looking for, this may help you. https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTM-4209-8.PDF

[AgileYeti]

Thanks, Naz! That’s some really good documentation you have there! I really appreciate you sharing it with me.

All the best,
Yeti

[NAZ]

Here’s some info on the 9” you may find interesting: https://www.diyford.com/ford-9-inch-differential-guide-third-member-assembly/

I learned the correct way to overhaul a Ford 9” when I was 18 at the Ford Engineering Center during my Ford Service Tech training. Since then, I have rebuilt a wide variety of rear ends and angle drives from small import cars to large industrial drives that you could physically crawl inside the housing once you remove the ring gear and carrier.

Large or small, all are very similar in set-up. The Ford 8.8 is very similar to the Ford 9”. Rebuilding them is not difficult but you do need some special tools and resist taking shortcuts – attention to detail is required to get it right. A hydraulic press, bearing pullers & installers, good quality torque wrenches including an inch pound dial type for pinion pre-load, a dial indicator and way to hold it. If you want to rebuild Dana Spicer rear ends (used by Ford in many truck models) you may also need a case spreader as they use shims to set backlash so the carrier can be a tight fit.


Good luck and have fun.

[AgileYeti]

Large or small, all are very similar in set-up. The Ford 8.8 is very similar to the Ford 9”. Rebuilding them is not difficult but you do need some special tools and resist taking shortcuts – attention to detail is required to get it right. A hydraulic press, bearing pullers & installers, good quality torque wrenches including an inch pound dial type for pinion pre-load, a dial indicator and way to hold it. If you want to rebuild Dana Spicer rear ends (used by Ford in many truck models) you may also need a case spreader as they use shims to set backlash so the carrier can be a tight fit.


Good luck and have fun.

Thanks again! I picked up a 96 GT 8.8 at the local pick and pull. Owner rear-ended someone and totaled his car. But the back half was pristine. 3.27 gears too, I almost hate to change them, but think 3.55 might suite me better since I won't see much highway time. I have been accumulating tools over the last 6 months for this. I still need to get/make a pinion flange bracket and come up with a 1/2" breaker bar with some leverage...or a good cheater bar so I can get my torque down right.... and maybe a few sets of crush washer in case of emergency ;) I am sure taking somewhere would be much easier, but I am real excited to sniff some 30 yr old friction modifier and see if I can set a proper lash. I did find a local shop who agreed to check my work for me for a few hundred dollars. I'll probably take them up on that just to be safe. I need to get a build thread going so those interested can help me learn.

Send over all the tips you can! Sounds like sage advice

[Jacob McCrea]

The Ford manual NAZ posted should tell you just about everything you need to know. Here are a few tips I learned from rebuilding two 8.8 and a Dana 44, which is about the same thing as an 8.8:

1. I set the pinion preload with a little bit of gear oil on the bearings.
2. You'll be surprised by how easy it is to overshoot the pinion preload. Take it very slowly when you get near the minimum breakaway torque. I use a 1/4 Park Tool beam type torque wrench - certainly not the ideal tool but affordable.
3. It may be tempting to use Loctite on the pinion nut, but don't do it: it will probably "lock tight" before you get the preload set.
4. If you get into changing pinion bearing races, head to the fish market and get some dry ice to shrink them down. You can heat up the case a little with a propane space heater placed under it. You can grind a few thousandths off the old races and make them into a tool to tap the new races into place.
5. I seem to remember that black plumbing pipe and a cap/plug will make a cheap tool for pressing the rear pinion bearing. Heating the bearing in a crock pot full of hot gear oil will make it slip on nicely - especially if you have the pinion chilled in dry ice.
6. I'd replace all the fasteners. Trick Flow and ARP make nice main bearing cap studs.
7. The pinion seal is aggravating and if you find a good seal driver for it, buy it.
8. If all the measurements and the pattern come out right, I would save the hundreds of dollars and just trust that you have done it right. That sounds like an awful steep charge to check the backlash, pattern and rotating torque of the assembly.
9. The Lube Locker gaskets are really convenient and priced right.

Good luck!

[NAZ]

I'll echo what Jacob said about replacing fasteners. Critical fasteners should not be reused.

Carefully consider your final drive ratio as this makes a significant impact on performance and driveability. I ran a 28" tire with 3.55:1 final drive and a TKO600 driven by 500+ HP & 500+ lb ft. The car was not a slug by any means but was certainly acceleration challenged for a 2,500lb car. Also, consider running a Truetrac LSD, these are seamless and way better than the clutch type LSDs. I've run them on the street and on the drag strip. My Ford Raptor has essentially the same LSD in the front axle and that truck is built to run at high speed across the desert. https://www.eaton.com/us/en-us/catalog/differentials/eaton-detroit-truetrac-differential.html

[AgileYeti]

The Ford manual NAZ posted should tell you just about everything you need to know. Here are a few tips I learned from rebuilding two 8.8 and a Dana 44, which is about the same thing as an 8.8:

1. I set the pinion preload with a little bit of gear oil on the bearings.
2. You'll be surprised by how easy it is to overshoot the pinion preload. Take it very slowly when you get near the minimum breakaway torque. I use a 1/4 Park Tool beam type torque wrench - certainly not the ideal tool but affordable.
3. It may be tempting to use Loctite on the pinion nut, but don't do it: it will probably "lock tight" before you get the preload set.
4. If you get into changing pinion bearing races, head to the fish market and get some dry ice to shrink them down. You can heat up the case a little with a propane space heater placed under it. You can grind a few thousandths off the old races and make them into a tool to tap the new races into place.
5. I seem to remember that black plumbing pipe and a cap/plug will make a cheap tool for pressing the rear pinion bearing. Heating the bearing in a crock pot full of hot gear oil will make it slip on nicely - especially if you have the pinion chilled in dry ice.
6. I'd replace all the fasteners. Trick Flow and ARP make nice main bearing cap studs.
7. The pinion seal is aggravating and if you find a good seal driver for it, buy it.
8. If all the measurements and the pattern come out right, I would save the hundreds of dollars and just trust that you have done it right. That sounds like an awful steep charge to check the backlash, pattern and rotating torque of the assembly.
9. The Lube Locker gaskets are really convenient and priced right.

Good luck!


Jacob, those are some great tips! I never would have thought about the crockpot and dry ice! You always see heat come out, but dry ice? That will be fun and allow for some cool science fun with my daughter afterward. I picked up a similar torque wrench, but ft/lb and 3/8". Now that I think of it in/lb might have been a better move to sneak up on things. I'll have to remember to just take my time.
I am fortunate my local O'Reilly store has a race and seal driver set for loan. I am hoping it will do the trick to help me keep things square. Plus calling in a favor from a friend to come over and use his shop press one weekend.
Great idea on replacing those bearing cap bolts! I will order a set from ARP today. I picked up a Yukon rebuild kit which has new bolts for the housing cover. Thanks a ton for those suggestions! Just the kind of thing to make a tough job much more bearable. You rock!



I'll echo what Jacob said about replacing fasteners. Critical fasteners should not be reused.

Carefully consider your final drive ratio as this makes a significant impact on performance and driveability. I ran a 28" tire with 3.55:1 final drive and a TKO600 driven by 500+ HP & 500+ lb ft. The car was not a slug by any means but was certainly acceleration challenged for a 2,500lb car. Also, consider running a Truetrac LSD, these are seamless and way better than the clutch type LSDs. I've run them on the street and on the drag strip. My Ford Raptor has essentially the same LSD in the front axle and that truck is built to run at high speed across the desert. https://www.eaton.com/us/en-us/catalog/differentials/eaton-detroit-truetrac-differential.html


What gear ratio did you land on Naz? 3.73? Or was it only challenged because you had to shift so quickly? Thanks for the suggestion on the LSD. Hopefully, it won’t be too bad, but I already snagged a Yukon Dura Grip LSDs on a super sale back on Black Friday. I have a new 3.55 Yukon pinion/ring, Dura Grip LSD, and a rebuild kit with Timken bearings just waiting for me to muster up the bravery to go out in the cold and work on things. I am a bit space challenged at the moment but hoping to line that out in the coming weeks after a bit of a garage sale. I am hoping that will all play nice with the Mosier 31 spline axles. I won’t have quite that much HP (more like 300hp maybe) so hopefully, that will help. My clutch is Kevlar/ceramic so might be something completely different than I am used to.

I greatly appreciate both your input. Definitely gave me some great ideas and guides on how to make things go smoother.

[Jacob McCrea]

I'd be surprised if a 3/8" drive, beam-type torque wrench gives an accurate enough reading to set the pinion preload. The acceptable range for new bearings is between 16 and 28 inch pounds and I set them as close to the middle as possible - which is under 2 foot pounds. Even my 1/4" beam wrench can be tough to read accurately because it will indicate a little high before the pinion moves, then the reading will drop an inch pound or so when the pinion gets moving. I use the "moving" reading provided that the higher "break-loose" reading is well within spec.

And yes, for press-fit bearings a crock pot and dry ice go together like cake and ice cream. The crock pot will expand the bearings while ensuring you don't get the metal anywhere near hot enough to affect the heat treating. Good luck!