Last weekend at Tellico, it became painfully obvious that Gary really needs
hydro-assisted steering. This is a mod that’s increasing in popularity, but
so many people are afraid of the horror stories they’ve heard about drilling
and tapping their own gear boxes. I modified my own gear box for
hydro-assist a little over a year ago and I’ve done several for other people
since then, so I decided to try and de-mystify the process for those who are
interested in doing their own.
Let’s start with a standard Saginaw gear box. These come in a few different ratios,
some are 3-bolt and some are 4-bolt. The 4 bolt boxes will work in place of
the 3 bolt boxes (and vice versa for that matter). The most common ratios
are 3.5:1 (approx) and 4:1. If you are looking to make steering easier on
yourself, you’d want to find a 4:1 box.
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So ok, you have your box, you brought it home, you’re ready to get started. Keep
reading...
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At the input shaft end, there is a locking ring that’s easily removed with a hammer and
punch.
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At the other end is an aluminum cap held in with a clip. Drive a small punch or
screwdriver through the small hole in the end of the housing and that’ll
drive the clip out of it’s seat. If you have a hard time unseating it, give
the cap itself a good whack with the hammer to loosen it up a bit.
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Now remove the 4 bolts that hold in the pitman arm shaft and tap up on the shaft to drive
it out of the housing. The shaft needs to be centered before it’ll come all
the way out.
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With the end cap clip out of the way and the pitman shaft removed, you can rotate the
input shaft so that the piston pushes the end cap out.
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If you look at the end of the piston that you just exposed by removing the end cap, you’ll
see a big bolt head. Remove this bolt head with a 1” socket on an impact
wrench. You may need to stick a screwdriver or something in the housing to
stop the piston from spinning around inside the housing. Once you get that
out you’ll probably see a few ball bearings laying loose inside the piston.
These are the dreaded worm gear bearings that everyone seems to be afraid
of. Don't believe the hype! (but don’t lose those bearings either!)
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Now, keep rotating that input shaft until the worm gear is out of the piston and you
can remove the piston from the housing. Put a rag or something over the end
of the piston so you don’t lose those ball bearings. There’s a metal tube
on the piston that houses a few more bearings that may not have come out
yet, so keep that in mind as well.
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Now it’s time to get that input shaft out of there. I’m sure there’s a special tool
somewhere made specifically for removing this input shaft, but guess what?
I don’t have one. So I improvise. Find a small allen wrench or screwdriver
that’ll fit into one of those little holes next to the input shaft and use
it to lever your pry bar against to unscrew the whole input assembly.
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With that unscrewed you can pull the whole input assembly out the housing. Give the
worm gear a slight pull and it’ll separate from the input shaft. Make sure
to look down inside the housing and remove the bearing and washer that go
with the worm gear. You’ll need those during the re-assembly phase.
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If you plan to replace the seals and bearings for the pitman shaft, now would be a good
time to remove those. The seals and washers can be pried out fairly easily,
then the bearing will need to be pressed out. I used a large socket and the
hydraulic press to accomplish this.
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Finally, it’s time to get down to drilling the 7/16” holes! The first one is straight
forward, just drill all the way through at the flat spot in the housing.
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The second hole isn’t difficult, but just a bit of caution is in order. This hole
needs to hit the fluid channel that runs to the rear of the housing. I try
to line it up as centered as possible, but if you’re a little off-center it
won’t hurt.
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You need to drill this hole to the bottom of the channel, but
be careful not to drill all the way through the housing. NPT fittings are
tapered, as are the NPT taps. So if this hole isn’t deep enough, your tap
won’t cut threads deep enough to allow an NTP fitting to get started
threading into the hole. But if you drill too deep, your NPT fitting may
tighten down too far into the fluid channel and cut off the flow of steering
fluid. If you look at the first picture, the hole isn’t quite deep enough
yet. You can see that the bit has broken through into the fluid channel,
but not all the way to the bottom of it. The second picture shows the hole
after I drilled just a bit further, all the way to the bottom of the fluid channel.
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Now just tap the holes with a ¼” NPT tap. Try and keep the tap as straight as possible.
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There’s going to be a lot of metal filings in the housing at this point. Make sure you
clean them all out. I usually use brake cleaner and compressed air to clean
out the housing and blow all the material out of the fluid channel. A
magnet also works well. I also like to file down any burrs left by the tap.
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Now before you go getting all antsy about putting this whole thing back together, make sure
you can get a ¼” NPT fitting to start in the threads. It would really suck
to get it all put back together only to find out that you need to cut your
threads a bit deeper.
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OK, so that’s it for the modification, you’re all done! Now it’s time to put that thing
back together. Assembly is pretty much the reverse of disassembly and no
big deal. But you have all those ball bearings to deal with. I’ll show you
how I put them back in and you can make up your own mind how to do it.. First, take a look at them.
There are shiny ones and some darker ones. It’s hard to tell a difference, but there is a
difference of about 0.002”. These are supposed to be alternated as they are
put in, dark, light, dark, light, etc.
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Now, pack the threads inside the piston with grease and start by feeding the bearings
into the bearing tube. Once the bearing tube is full, start placing the
bearings in the threads continuing to alternate dark and light. When all
the bearings are in place, carefully put the piston in the steering box
housing.
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Sometimes the piston needs a little tap to get it to start in the hole. If you’re worried
about the bearings falling out, stick a ½” drive ratchet extension down in
the center of the piston. That will keep the bearings from falling out
while you get the piston in place. Now carefully thread the worm shaft up
through the center of the piston until the shaft is in far enough to keep
the bearings in place.
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The hard part is over! Now you can replace the pitman arm bearings and seals if you’re
going to, and put the pitman shaft back in place. You’ll need to center the
piston to get the pitman shaft to mesh properly. Now replace your input
shaft seals (those really need to be replaced if you don’t want your box to
leak) and put the input shaft assembly back in the housing where it came
from. There is a notch in the input assembly, make sure it is lined up with
the nub on the worm gear shaft, otherwise it won’t seat all the way.
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Remember the method you used to remove the input shaft assembly? Use that same method to
tighten it back down. Tighten it until it bottoms out, then back it off
about 1/8”. Now put the locking ring back on and tighten. The locking ring
should be flush with the input shaft assembly. If there are any threads
sticking up past the locking ring, you probably didn’t get that notch lined
up with the nub on the worm shaft.
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All that’s left now is to put the 1” bolt back in the end of the piston and put the end
cap back on. Tap the end cap in place and install the spring clip to hold
it in. Make sure the split in the spring clip is NOT lined up with the hole in
the housing, otherwise it’ll be a pain to get out in the future.
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And there you have it! One steering gear box modified for hydraulic fittings!
The diagram to the right shows where the high pressure areas are when you
turn, click it to see a larger version. You can see by the diagram
that the first hole you drilled will be pressurized when you turn left, and
the second hole (in the fluid channel) will be pressurized when you turn
right. Keep this in mind when you hook up your hydraulic hoses to the
ram. It's always a good idea to check and make you have them hooked up
correctly before you connect the ram to any of your steering components.
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Here are two of the seal kits you can get for this project. The small one is just
the input shaft seal kit and is the bare minimum that you want to replace.
That input shaft will most likely leak if you don’t replace the input seal.
The rest of the seals can sometimes be re-used without a problem. The
other kit is the complete “rebuild” kit and includes seals, bearings, and
new retainer clips.
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And that’s it for this week, Good luck!
Click here to see the entire photo album of this mod!
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