gear change

January 25, 2006, 10:03:19 AM

hey guys, anyone know of a good write up on how to change gears in a 7.5 trac lok? goin to put 3.45's in and i just kinda need a know how to.
thanks, Joe

gear change

Reply #1 – January 25, 2006, 02:21:25 PM

Its rather easy, took me about an hour to do mine. I'll try to write up the procedures for you. I wish I would have written them all down when i done it.

gear change

Reply #2 – January 25, 2006, 02:28:19 PM

Hope this helps................

For this job you should have:
1) Puller set, or stock to make your own or steel drift and heavy hammer.
2) Your ring&pinion set, new or used
3) Bearings, 4 cones, 4 cups, for pinion and differential
3a) this would be a good time to do the wheelbearings too!
4) Pinion seal, having at least 2 is a good idea (can return if unused)
4a) this would be a great time to relace the wheel bearing seals too!
5) Crush collar for the pinion, or shims for its bearing preload.
6) Spider-gear pin lockscrew with sealer (often comes with it from dealer)
7) New pinion yoke nut, also with sealer on it.

RTV silicone sealer for sealing everything back up
9) new lube, 2-4 quarts
10) dial indicator OR soft thin "electronics" solder
10a) measuring, micrometer caliper or accurate verniers often useful
11) rags, cans of Brake-Clean, regular tools
12) grinder of some sort, mini-grinder or die or bench grinder will do
13) gear marking paint, white lead or other greasepaint will do.
14) a selection of pinion and side shims would be nice

You may be pulling the pinion out and reshimming it, so having extra
crush-collars, pinion seals, spider-pin lockscrews and yoke nuts on hand
may be a good idea. You can return them later if unused.

Your main concerns are:
1) Pinion depth, centering up the pinion on the ring-gear teeth.
Usually set by rear pinion bearing shims (front being the yoke).
2) Ring gear backlash, the clearance necessary to prevent excess
friction.
Usually set by side shims or (hopefully) screw adjusters.
3) Pinion bearing preload, like adjusting front wheel-bearings.
Usually set by progressively tightening the yoke nut against a
crushable collar to get the proper clearance and tension,
usually measured by amount of drag with a inch/pound torque wrench.
4) Ring gear bearings preload, usually set by shimming the side bearings
a given amount past where they contact or additionally turning the
screw adjusters a given amount past contact.

TO GET THE REAR AXLE APART
The axles come out first, easy on non-"C"clip axles like the removable
carrier types and full-floating axles like on most 3/4 ton and 1 ton
trucks. Remove the wheels, the drums or brake calipers too, undo the bolts
and slide the axles out. Some hammering may be needed to get them out.
Unbolt and carefully pry off the differential carrier.
Often hard to get it off the first time, I used to do "weekend warrior"
gear swaps in 20 minutes with practice.

"C"clip axles require you pull the rear pan off (catch the oil!),
heat and remove the lockscrew and spider-gear pin. Then push the axles in
and wiggle out the "C"clips inside the differential out of the grooves on
the ends of the axles. See below how to remove the pin.

Front axles require you to learn about disassembling front hubs...

REMOVING THE SPIDER GEAR PIN AND ITS LOCKSCREW
The lockscrew is usually retained with "Locktite" or some other sealer.
Heat up the differential where the threads are with a propane or welding
torch until the oil starts to smoke a bit, then unscrew the pin.

Rotate the ring-gear 180 and hammer the pin in a bit, not too much
or it won't rotate and you'll REALLY be screwed! Once it is in about
3/4 of an inch, spin it around, put a nail or bolt through the spider
gear pin hole and pry it out any way you can.

When you go to re-install the pin you'll have to line up the spider
gears and you should use a new lockscrew with sealer (usually on the
bolt from the dealer).

Remove the "C" clips if this axle has them, slide out the axles if
you haven't already and unbolt the bearing caps. On some axles it may
take some dedicated prying to get the differential out. Dana recommends
using a special case press but I have never had to use it. Just get a
bar in there and pry it out.

PULLING (AND INSTALLING) BEARING CUPS FROM AXLE HOUSINGS
First of all, swapping a R&P often involves replacing the press-on
bearings which usually involves using pullers or a hydraulic press.
It can be done with a hammer and punch but it is much more work and
is very likely to damage the bearings or their mating surfaces unless
you are careful. For a one time job, hammering is cheaper if careful.
If you are going to buy pullers, buy the best you can. There is a world
of difference between SnapOn and MadeInChina.

The bearing cups are hard to get seated and are pr0ne to getting little
bits of foreign matter jammed behind them. This will pen 15 them and mess
up their alignment. Brass drifts tend to shatter into bits that do this
so try to use mild steel drifts. If there is no sign of unusual wear it
is often best to leave the cup in place, just replace the cone&rollers.
Doing a poor job of installing the cup is much worse than not replacing
a high mileage but good condition one. Do a good visual inspection.

A puller to remove the bearing cups from the axle housing can be made up
from heavy bar stock cut and ground to just fit behind the bearing, and
pulled by means of heavy threaded rod, a nut and a big wrench. This will
install the new cups as well, pulling from the other side.

I have done this but usually carefully beat the cup out with a long
steel drift and 5-lb hammer. You have to carefully beat from one side to
the other taking care not to pen 15 the shell or mar the bore it fits in.
For installing the new cup, use the old one to protect it from your blows.
Make sure you install it facing the right direction!

PULLING (AND INSTALLING) BEARING CONES FROM PINION AND DIFFERENTIAL
Getting the old bearing cone off the pinion so that you can access the
shims can be a real pain. The cones (that hold the rollers) become almost
welded in place with time. I usually plan on replacing them as a matter of
course so I do not try to save them. I cut the roller cage with heavy
wire-cutters and grind a groove almost through the cone with a
mini-grinder, die-grinder or bench grinder. A couple smacks with the 5-lb
hammer and maybe a chisel will usually crack the cone and it will slide
off easily.
WEAR SAFETY GLASSES FOR THIS! Chips of bearing do fly off with speed.

A press is the best way to install the cones, without exception.
You definately can hammer the cones on if you need to.
Again, use the old cracked cone to protect the new bearing from your
blows.

PINION DEPTH
(Swapping shims from old pinion method)
Usually most ring&pinions are manufactured to very close tolerances.
Most of the axle housings are not. Usually the shims that came with the
axle housing will work with any new set of gears. Some gears may be marked
"+0.008" or "-0.025" on the end of the pinion to indicate deviations from
norm. Do the math and follow this indication to add 0.008" shims or remove
0.025" on the pinion to correct the depth as needed. If both pinions say
nothing, just remove the shims from the old pinion and put them on the new
pinion for trial fit. "Running a pattern" will be the final determination
of correct pinion depth.

(Measuring pinion depth from ring-gear bearing seats method)
If you have the specification for the actual pinion end depth from the
ring-gear centerline, you can physically measure this by placing an
accurate bar (drillrod?) across the ring-gear bearing bores.
This is the way the factory recommends setting up the pinion but they use
a special proprietary jig that makes it easy. Unless you have this jig
this method is complicated and assumes you have Machinist quality
measuring skills and tools.

With integral carrier axles like the Dana44, GM Corporate and Ford 8.8"
axles you have to put the depth shim behind the first bearing cone on the
pinion. A real pain if you later have to correct it as you have to pull
the bearing cone back off to replace the shims, ruining the crush collar,
locking yoke nut, seal and the pinion bearing preload setup. Usually the
old shims will be fine, but if you have any serious reason to believe you
are going to have problems with the depth setup you may be advised to
leave the crush collar and seal out and use the old yoke nut and spider
shaft lockscrew until you run a pattern that suits you. All this can be
replaced without disassembly if you get a good pattern.

The Ford removable carrier axles are a little better in this respect.
The pinion bearing preload can be set up independently in its own little
"nose-piece" and then this nosepiece is shimmed to get depth.
Did I mention that I really like working on these Ford 9" rear axles?

PINION BEARING PRELOAD
Most pinions now use a little crushable collar between the two tapered
bearings to take up the space between them. You tighten the locknut on
the yoke end of the pinion to crush this until the clearance is taken up.
Then you crush it a bit more to put a little "preload" on the bearings.
The amount of preload is measured with a small "inch/pound" torque wrench.

New bearings are set up to drag at 30in/lb or so to give the bearings a
chance to seat, old bearings don't need this and can be set up to drag at
15in/lb or so, just enough to take up the clearance. It takes a lot of
force to turn the locknut enough to collapse the crush collar, about 150-
250 ft/lbs of torque, so be sure you have a secure means of holding the
yoke from turning. I either use a bar with holes drilled for the U-joint
bolts or wait until the ring-gear, axles and brakes are installed and have
someone hold their foot on the brake.

REMOVING AND INSTALLING THE RING GEAR
Remove all the bolts from the old ring-gear, set it on its end in
a vise or suitable support and with a smaller diameter steel drift
bottomed in the bolt holes give a mighty smack in a back and forth
pattern like you were tightening headbolts or wheelstuds. The ring gear
will slowly work its way off, don't get it pen 15ed. Inspect for burrs or
dirt, start a few bolts to assure they line up and press the new ring-gear
on to the differential. NEVER use the bolts to draw it in place, you will
end up with ruined bolts and runout problems. A press is best but the
the ring-gear can be hammered on if you put a mild steel bar over the
teeth to protect them. Please excuse all this "hammer mechanic"
technology, it goes against most of what I was taught in Machine and
Mechanical Tech School but it is the only thing that will work without a
press. This is how the 3rd world does these jobs or you can do them in
your driveway or the woods or desert if you have to. One wrong blow can
ruin a bearing or a ring-gear, so it takes careful work.
A press is always better.

LOW RATIO GEARS, TOOTH BLOCKING THE PIN
Some low gear sets in some differentials have the ring-gear teeth get
in the way of the spidergear pin. The pin won't go in, they block it!
In some cases you need a different differential with a revised pin
position to handle gears lower than a certain point. I believe the Dana44
is this way. If you jump from 3.55 gears to 4.11 you need a different
differential. Time to upgrade to a TruTrack, ARB, limited slip or locker!
In many cases the interferance is minimal, and merely grinding a flat
along the side of the differential pin (spider gear pin) will give you the
clearance you need to install it. Some factory pins come with this flat.
In some cases you may need the flat AND to grind a bit off one tooth on
the ring-gear. It it only one non-load bearing end of the tooth that gets
ground and just as minimally as possible. Installing 4.56 gears in a
Ford 9" is one example of this.

DIFFERENTIAL SIDE BEARINGS
Three methods are used to locate the differential and its bearings:
1) threaded adjuster nuts, the easiest setup.
2) shims on the outside of the bearing cups, easy but you need the shims.
3) shims on the inside of the bearing cones, EGAD, I hate these!
The bearing cones have to come off to do the many adjustments needed
and they don't come off easy. It does squeeze into the carrier a bit
easier than the shims on the outside however...
(screw adjusters)
The screw adjusters are a dream! Back off the adjusters, drop in the
differential and its bearings, close up the adjusters until the ring-gear
contacts the pinion and then close up the bearing clearance on the the
other side. Play with the adjusters to get the right backlash, then
tighten them to get the right bearing preload. Easy!
Did I mention that I really like the Ford 9" axle????

(shims)
With shims on the outside of the bearing you throw the differential and
its bearings in place, then slide various shims in to get your backlash
and take up the bearing clearance. To preload the bearings you install
slightly larger shims (see manufacturers specs) on both sides and
press/pound the differential back in place. Not bad, but since the shims
are about $10 apiece you either want to have a selection of old ones on
hand or be prepaired to wait several days as the dealer orders the right
size in for you.
You can fiddle with the shims that you have, shimstock, big washers,
"1/4"coldrolled" stock or whatever to get in the ballpark but I always
find I never get it perfect in the first try.

If shimmed, the differential is rather hard getting back in the carrier.

Just as you had to use a bar to get it out, you may need a soft hammer
to get it back in. Make sure the shims are centered on the ends of the
bearings as you push the diff in place.

BACKLASH
Two methods of checking backlash, the best is a dial indicator on the
ring-gear teeth, but not everyone has one. The other method is using soft
thin solder and running it between the gears. It tends to chip up, and
gives readings a bit higher than an indicator so make sure the housing is
grease free and well cleaned afterward, and look for a measurement on the
high side.
Most differentials look for backlash in the 0.006" to 0.018" range.
Tighter IS NOT better! I destroyed one gearset with my machinist's
"tighter is better" mentality by going for minimum clearance on a small
diff used on a 300+HP car. Looser is better for hard use. It allows less
friction and more oil to cool the gears.

If you have a dial indicator, use it to check the ring-gear for runout.
Less than 0.004" would be nice, any more and you should try remounting
the ring-gear in a slightly different position.

After all this care for precision, I will calm your worries that for
most purposes being within 0.005" is plenty accurate enough in most
measurements. If you aim for perfection you have that much "forgiveness"
build into most diffs. This will allow for a bearing that wasn't perfectly
seated, too tight or loose a feel on the preload bearings, or a ring-gear
that for some reason settles back in use. Set it up to be perfect, but
if on later inspection something is out 0.005", don't worry. It's OK.

RUNNING A PATTERN
Here comes the part where you find if your measuring and guesses and
suppositions (it is a "black art" isn't it?) all come together.
Paint the ring-gear with some greasepaint (white lead was perfect but
is now extinct) and spin the pinion, using the airgun is fastest.
Put some drag against the ring-gear, perhaps with a screwdriver and watch
the shiny spot appear on the gearteeth. Roughly described, it should be
centered on the ring-gear tooth, but best to get a book that has picts of
what to look for and how to correct it, although I can go into great long
descriptions! After all this work it is a real downer to find the
pattern is wrong. There is a real tendency to say "ta heck with it" and
leave it as is, DON'T! Take the time to correct it, that is why you bought
the extra seal, crush collar and pin lockscrew. Leave them out until you
have it perfect. Now is the time to get it right or you will be cleaning
metal filings out with the lube in a few weeks.

Use a torque wrench to put it all back together. A little Locktite is
prefered by some but if the torques are right I have never had one loosen
up. Silicone RTV works OK instead of gaskets, I break in on regular lube.

BREAK IN
I take it easy for the first while, only short trips and no high speed.
I feel the diff for temp for the first while. Heat means trouble!
If all feels well I increase the trip times and speeds. If it gets too hot
I pull the thing apart and find out why. After a week or two or a few
hundred miles I like to pull it apart again to double check the preloads,
backlash, bolt torques and replace the lube with fresh synthetic stuff.

gear change

Reply #3 – January 25, 2006, 07:53:22 PM

dude!! now thats a book, but some great knowledge!!!!!!! is it really that time consuming and all that trouble?? never done it before but i do want to make sure its right. i have read some people on here where it only takes them a hour or two. mthanks for the info, and yes i did make a copy of it, thanks, Joe

gear change

Reply #4 – January 26, 2006, 08:33:24 AM

I did mine my self first time took 2 hours, once you start taking it apart you'll see its reall not that bad. Make sure you have someone there to help you, at least to hand you tools and so forth.

gear change

Reply #5 – January 26, 2006, 02:23:16 PM

yeah after i heard all the rap about it i was kinda afraide to do it to, but iv done it 2x now and no problems yet. its simple, it makes it easier to that all the ford parts are basicaly the same "sizes" as far as shims go. technicaly you can use ford racing gears and put em in and not worry about shims because it should come out to be the same. but you should always check, i used a dial indicator.