RE: [ihc] I need the rundown on the RA15 corportate axle

["Mac @ TRIAD" <mac@xxxxxxxxxxxx>]

## >> I would greatly appreciate some info on this type rear. Any
## >> help to any of these questions would be great. First I need
## >> to know how to ID the ratio without pulling the stump. Was
## >> there a tag somewhere on these or was it stamped in somewhere
## >> on the housing? Next, I need to know what kind of carriers
## >> were used in these. Was there a locker available or were they
## >> all limited slip or open? Was this the heaviest axle IH
## >> offered in an 8 lug pattern or was there a RA20 with 8 lugs?
## >> Finally, I have seen Rockwell mentioned on ads for other 1
## >> tons. Are these in actuality built by Rockwell? TIA!

okay.  first off, as Ed Sohm stated in another post, "The ratio is stamped,
in really really small print, on the end of the pinion".  i took the carrier
out and counted the teeth in mine anyway.  i had two of these RA15 axles,
and both were the 6.17 gear ratio.  as Tom M indicated in his post, he had
the "4.30 R&P - which was the tallest offered.  4.87, 5.57, and 6.17 were
also offered".

secondly, as far as i know, these were available with three different kinds
of differential sets. Tom M says they were only available in open and
No-Spin varieties, but i suspect he's never seen a Traction Equalizer (see
later).  anyway, these had the following differential options: open
differential; the Detroit Locker known in those days as a No-Spin; and a
special proprietary IH-only limited slip setup called the "Traction
Equalizer", a fairly uncommon and complicated limited-slip differential.
i've only seen one Traction Equalizer in real life, and that one was broken.
both of my RA15s and my RA20 have/had No-Spin differentials in them.  i've
never seen a clutched diff in an IH corporate axle, and i'm pretty sure they
were not available with such a thing.  by the way, i believe the "carrier"
is the housing in which the differential itself is found.  i think what
you're looking for is the various kinds of actual differentials.  as Tom
also mentioned, the entire differential carrier in both the RA15 and RA20
axles is a huge drop-out third member, and it weighs a considerable amount.
use a jack and safety straps if you're going to try to pull it out.

side note:  that drop-out third member is quite convenient.  you just pull
the axle shafts about eight inches out of the axle tubes, take out all the
bolts from the carrier, and it pops right out of the housing.  makes R&R
very simple.  you don't have to mount the truck on jackstands or take wheels
of, and you don't have to pry the R&P out of the housing the way you do with
a Dana Full-Floating (or any other type Dana) axle.  i found it quite easy,
other than the weight, to swap differentials between my two RA15 axles.
only took about an hour and a half total time, start to finish.  the
drawback to this is that there is no cover plate that you can pull to
inspect the gears like the Dana axles have.  if you need to look at it, you
have to pull the shafts and drop the whole carrier.

the RA15 was most commonly found in older 120/121/122/1200/1210 and both
older and newer 130/131/132/1300/1310 trucks, and also in the final 200
series.  there was a heavier axle, indeed the RA20, usually found only in
the earlier 140/150 and later 1500/1510 and final 500 series trucks.  i've
heard a time or two that some 1300/1310s got the RA20, but i've never seen
one of these trucks with an RA20.  i got my own RA20 out of a 1966 1500A.
mine has 6 lugs in the smaller Budd Six pattern (uncommon to say the least),
but every other of these that i've seen has had the Big Budd Five lug
pattern.  i suppose if one of these were found on a later 1300 or 1310 it
might have eight lugs, but i'm not sure about that.  as i say, i've only
ever seen my own with the smaller Budd Six, and a whole bunch with the Big
Budd Five.  Joel Furtek had a B140 recently, with the RA20 rear and matching
IH corporate front (i can never remember the FA equivalend number for the
RA15 and RA20 axles), and it has the Big Budd Five lug pattern.

lastly, my understanding is that the International Harvester Corporate axle
is in fact a licensed Rockwell axle.  IH built them, but if what i've been
told and read elsewhere is true, Rockwell sold IH the license to build these
based on the smaller Rockwell axles of the period.  i do not know if that is
absolutely true or not, but when comparing my RA15 to a Rockwell axle i
found in a boneyard about fifteen years ago, they were nearly identical.
the only externally visible differences that i noticed were the axle shaft
end cap bolt pattern (all IH axles have six bolts here, everybody else has
either eight or ten), and the drum and bearing shapes/sizes.  i could be
wrong, but it appeared to me that the IH-built axles have bigger, heavier
bearings than the axles they were licensed from.

one thing you need to be aware is, there are no spare parts for any of these
axles available new.  brake drums, differential carriers, ring and pinion
gears, axle shafts, these things are difficult at best to axquire.  i'm told
the brake drums are absolutely unobtainium these days.  i scrapped the RA15
from my B122 because i couldn't get drums for it.  at the time, the drums
for the RA20 were still available (1990), but now, those drums are also
discontinued.  if you're planning on keeping an RA15 or RA20, expect a
serious hassle finding parts for it if anything breaks.

--Mac

P.S.:  what Ed Sohm said about making an RA15 into a 2-speed isn't quite on
the money, i don't think.  no offense intended, Ed.  the RA15 and RA20
housings aren't the same size.  the RA20 is noticeably larger (i had both an
RA15 and RA20 side by side when doing the swap into the B122).  it's the
RA10 and RA15 that share a housing and differential, i'm quite certain.  the
RA10 is a semi-floating tapered shaft variant on the RA15.  the RA20 and
RA25 might share a housing, i am not positive of that just yet, i haven't
had a chance to compare my RA20 to an RA25.  however, both the RA20 and RA25
were available in a 2-speed.  the 2-speed version of the RA20 is the RA126,
and i don't remember the number for the 2-speed RA25.  to make an RA20 into
a 2-speed should be as simple as pulling the shafts and swapping
differential carriers.

if it's any consolation, Ed, i'm fairly certain you are right about the IH
corporate axles being a Rockwell licensed design as i stated above.  +)  i
can't wait to hear what Greg has to say about all this.  say Ed, have you
ever seen a Traction Equalizer diff?  i'd like to find one that isn't broken
just to see how it works, and how well.

---------------------------------------------------------------
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Krystof "Mac" MacBryghde
TyrGothi

http://master.triad.ath.cx/