How to install your own gears!!!

Discussion in 'SN95 4.6L Mustang Tech' started by Slider, Feb 24, 2004.


  1. Slider

    Slider Founding Member

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    Well I took the plunge last week and decide to install my own gears, and I thought that I would share my experience. First off I just wanted to say that this project is not hard, but it is very time consuming and requires several very specific tools. I do not suggest that you attempt to do this on you car if you “have to” drive it everyday to work or school. There are several things that can pop up that may require more time then you have allotted. This project is a project for the mechanically inclined, and not for the occasional wrench turner that only knows how to change spark plugs. You do not need to be a car god to do this job. It just requires patients and a lot of elbow grease.

    I am not going to do a full right up on how to install gears, but what I would like to do it simply add my observations and experience. I am including a zip file that has several gear install articles and a jpg of a chart that shows you how to read gears. The info I am presenting is simply my experience and should not be taken as gospel. The most important document to look at is the one titled “Installing Gears based on shim thickness.” This is the article that real makes installing the gears a very doable project for the home mechanic.

    gear_install.zip

    For my project I rebuilt the whole rear end with FMS 4.10 gears, Superior Axle 31 spline axles, and an Eaton posi. I used a Superior Axle master overhaul kit that contained new bearings, seals, and shims. This install can be split up into 2 main parts: 1) the gear install and 2) the seal and bearing install. The gears can be installed with out installing all new bearings and seals. It is recommended that if you car has some pretty good mileage on it that you do since the cost is very minimal. However, I will warn you that removing and replacing all of the bearings greatly complicates this project, which I will go over.

    - Installing New Bearings and Seals -
    If you are going to install all new bearings and seals then I must warn you that this is possible the hardest part of upgrading you rear end. This will require the use of several special tools. You will need to go to Autozone and borrow their 2/3 jaw slide hammer. This tool is used to remove the axles bearings and the bearing races for the pinion gear. You need to put a about an $80 deposit on the tool, but you get it back when you bring the tool back. This tool simply looks like a gear puller that is attached to well a slide hammer. You use it to pull out the bearings. Now this may seem easy, but the axle bearings are a major PITA to get out. I hammered on those thing for about a half and hour before the came out. I had to basically bust out all the bearing to get it come out. Your hands will be very sore when you are done so make sure you have a good set of heavy duty gloves to help cushion the impact from the slide hammer. You will have to use some much force that you will think that the car is going to fall off the jack stands. Luckily the pinions bearing races are much easier to get out. The problem with them is that it is hard to get the slide hammer up under the car to get them out. I am sure it can be done. I however had the whole rear end out of the car so this was a simple step for me.

    When installing the new bearings you will need access to a hydraulic press for the carrier bearings. The axle bearings can be driven into place using a large socket or washer. I used the biggest socket I had and bought a very large washer at the hardware store. I simply duct taped the washer to the socket, and pounded the bearing in. It is a good idea to let the axle bearings in the freezer over night to easy installation. The bearing races for the pinion need to be driven in also. I again put them in the freezer over night to easy installation. The problem with these bearing races is that they are very large and a socket or washer will not be big enough. I used a very large piece of round stock aluminum that was about the right size for each race. Used the old races as a buffer between the alum and the new races. I then simply hammered the races in. I have also heard that you could simply use the two-race trick and a punch to seat the races. You would simply work your way around the race with a hammer and punch to seat the bearing. How the main pinion bearing goes on I will cover in the gear install section, and all the seals can easily be pride out and hammered in. To remove a seal simply get a screwdriver under the lip of it and work the screwdriver around its edge. It should come out with relatively little effort.

    - Installing a New Ring and Pinion -
    This is actually not that hard. You will probably spend more time dealing with removing and installing all the bearing then this step. If you rear end is in good shape and you do not need the bearings, then this project will go much faster and easier.

    The article I pointed out above (Installing Gears based on shim thickness) is what you really need to understand completely before you start this part. The concept is very simple. First off you WILL NEED A PRESS to get the old pinion bearing off and to reinstall it. Actually you might not need it to install it if you freeze the pinion and boil the bearing in hot water, but while you are getting the bearing pulled off you might as well use the time to press the new one on.

    To set the right pinion depth you simple adjust the pinion shim based on the length of the pinion headed of the new gear verses the old gear. Note this only works for Ford gears. I suggest using a 2” or larger micrometer for measuring the pinion head length. Calipers will not give you an accurate enough reading for what you need. Makes sure that you take measurements around the entire pinion head, and then average them to get the pinion heads thickness. The thickness of the pinion head will most likely vary +- 0.001”. When I did this my new pinion was an average of 0.001” longer then the old pinion. From what I have gathered by reading about others doing this with ford gears it is very common for the two pinions to have this close of a spec. Since this was such a small difference I simply reused the shim from the old pinion.

    The really hard part of installing gears is the setting of the preload on the bearings via the crush collar. The crush collar is a small collar/sleeve that goes between the 2 bearings on the pinion. What needs to be done is that the pinion nut needs to be tightened down enough that this collar starts to deform or crush. The collar will start to decrease in length as it is crushed, and causes the two bearings to move closer to each other. You keep tightening the pinion nut until you get a preload on the bearings. This will cause drag on the pinion shaft. This is what the inch*pound torque wrench is used for. You are measuring this drag on the pinion to determine when the bearings are set properly. Just as a note the pinion nut is 1 1/16”. You will most likely only find this socket in ½” drive, and the torque wrench will be 3/8”. That means that you will need an adapter to convert the between the two. This can bought at the autoparts store for about $5 or $10.

    The concept of doing this is really simple, but there is one massive catch. The amount of torque required to crush the collar is extremely large. You will need at a minimum a 3 to 4 foot extension for you breaker bar to turn the pinion nut. This is no joke, and even then it will be hard to turn the nut. On top of this you should only move the nut about a 1/8 of a turn or so, and then check the drag on the pinion. If you over do it you will have to get a new crush collar and start over.

    Once you have taken care of the pinion you can move on to the ring gear. This is actually more time consuming, but it is relatively easy. You simply added and remove shims from the sides of the differential until you get the right amount of backlash in the gears. You will need a magnetic base and dial indicator for this. I bought mine from Harbor Freight for about $40. There are two important things to make sure of when shimming the differential. First, I would suggest running as little backlash as possible. The specs are from 0.008” to 0.015”. It is best to error on the low side because as the gears wear the backlash will increase. Not to mention 0.008” will cause the pinion gear to run more towards the center of the ring gear, and this is where the gear is the strongest. This is will result in the competition gear pattern as shown the jpg in the zip file. Also, you need to make sure that you added enough shims to both sides of the differential so that it requires you to hammer it back in with a mallet. Any play in the differential is bad news.

    I actually had to re-shim my differential after 2 days of driving. What had happened to me was that I originally shimmed it to 0.011” and over the 2 days as the bearings seated properly and the gears started to wear in the lash moved out to 0.016”. The gears were quite, but when I shifted gears the extra play in the gears combined with the play in the transmission would cause a clunking noise. I also found out that the differential was not shimmed tight enough. It should require a good amount of effort to get it out, and when I went back in it did not take much effort to get it out. I think between the seating of the bearings, wear of the gears, and not enough shim preload on the differential cause the lash to be out of spec. I then added another 0.012” shim, and readjusted the shims to give me a backlash of 0.007”. Now that is a little tight, but I checked the contact pattern with the chart, and it looked very good. Look exactly like the competition pattern. I took the car out for a drive and NO WHINE and NO CLUNK. The car just hauls a$$, and is as quite as stock.

    - Odds and Ends -
    Here are just some random tips. Make sure you get yourself several pairs of rubber/latex gloves. Gear oil is very “smelly”, and you really do not want to be putting your hands in it. Not to mention the oil will most likely have metal shards in it from when the gears wore in, and you do not want to get these in you skin. Also, I found out that several rolls of high quality paper towels can be very helpful. Working on the rear end is very messy and you are bound to get oil all over. Cloth towels work ok, but they get messy fast. I used some rally nice paper towels (not the cheap Wal-mart specials), and they worked amazingly well. I used them a lot, and would not want to do it with out them. Also, make sure you have the disk brake tool for depressing the caliper piston. To get the brakes back on you need to push the piston back in some. The brakes are not the old school ones that you can simple push back in with a clamp. You need the funny looking cube tool to do it that allows you to push and turn it at the same time. Just go buy it if you do not have it. It is only $10.

    Well that about covers it. If you have any questions feel free to ask. If I remember anything else I will added it.

    Michael :nice:



    PS here is the above in Doc form.
  2. hognutz

    hognutz New Member

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    I will give you little tip on the axle bearings if you ever have to do it again. get a long piece of pipe that will slide through you rear end housing. run it from one side of the housing to the other, then hammer on the pipe and drive them out. they will come out so easy it will make you feal stupid. I was doing what you did an my old man showed me the trick.

    the setup just takes patience. $50-$60 an hour always gives me patience even though I don't really have any. ha ha.
  3. DarkHorse01

    DarkHorse01 New Member

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    Is this the same on a 97 GT. I have 3:55 gears I want to install..
  4. Slider

    Slider Founding Member

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    This should pretty much cover any Ford 8.8" for any year.

    The only difference maybe the disk brake part I mentioned at the end. I do not no when Ford switched to the new style disk brakes.
  5. Slider

    Slider Founding Member

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  6. COramprat

    COramprat Drone Driver Mod Dude

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    I did my axle bearings myself and I know what you mean about driving those suckers out. But now that I know how to do it it wouldn't take me nearly as long. Bump while we're at it.
  7. crankin

    crankin New Member

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    what size pinion shim did you end up using? I'd like to install my 373's but don't know what shim to start out with
  8. Kilgore Trout

    Kilgore Trout Fried or Broiled ?

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    That is an excellent writeup :flag:

    One of the best tech threads ever :nice:
  9. loosescrew79

    loosescrew79 New Member

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    Great write up. I have gears for my car and have been contiplting the change myself. With this info I might actually go for it.

    My car already has 3.73s, so can I just use the same amount of shims for the 4.10s???
  10. bakos24

    bakos24 I find there is nothing better than a tasty wiener

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    One of the best, oldest tech threads. :nice:
  11. timeless2

    timeless2 Vi Veri Veni Versum Vicus Vici Admin Dude

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    Good one. It's going in the Tech sticky thread.
  12. Pearl02

    Pearl02 Member

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    I'm going to say no. You can start with the shims you have now. You'll probably have to add or remove shims when you measure your backlash. Pearl02.
  13. mn moose

    mn moose New Member

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    does anyone have that gear zip file that slider posted??? im in dire need of it and the link is broken.

    thanks guys
  14. mixedbreed02gt

    mixedbreed02gt Banned

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  15. BobHyatt

    BobHyatt New Member

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    One note. The rear ABS sensors can sneak up on you. With them in place, you can't slide the axles in enough to remove the c-clips to remove the axles from the carrier. Remove the ABS sensors and things work flawlessly...
  16. HaynStang

    HaynStang New Member

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    Great post, but does anyone know if that zip file still exists somewhere?
  17. rabidscoobie

    rabidscoobie Member

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    I believe that zip file is the exact same thing he originally made as his opening thread,just copy/paste into notepad/wordpad and you basically have that zip file...unless im misunderstanding something.
  18. jorgegt500

    jorgegt500 New Member

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    hey i need help im putting 373 gears in when i put it back in the ring and pinnion dont spin when i tighted the side clamps??

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