From: tonygull (tonygull@ozemail.com.au)
Date: Wed Sep 18 2002 - 03:32:44 PDT
Well now i know my my truck had a clanking sound..the TX case had worn
mainshaft
bearings.
After rebuilding the front axle, I took it the GMC for a drive, braking
was much better with parallel wheels, however a clanking sound has worried
me ever since i got the truck..I gave the drive shafts a hand test and found
substantial free-play in the short tranny to TX case shaft, upon removal the
front
bearing was shot, i pulled out the thrust washer and found about 10 of the
32
needle rollers in the mainshaft bearing were missing.
Luckily I acquired a TX case soon after buying the truck, an inspection of
the
visible beraings and oil seals showed them to be shiny and new. I bought
this and other parts from Transfield in Sydney, they were all nice and dry
and rebuilt looking in a shipping container...the service manager, who had
40 years experience on there fleet of
literally hundreds of GMC, told me the TX case was a major weakness in these
trucks.
Others have told me this is not so, but looking inside I think the main
problem is
twofold, in that the entire gear train is working cause they are 1.15 to 1
in
direct drive, meaning the the drive goes thru the mainshaft, idler gears,
rear
axle drive and back up thru the mainshaft. Also the mainshaft is right at
the
top of the case, the oil is at the bottom, the Gear Oil was like mud, and
there was considerable corrosion inside..anyway i fitted the replacement
case and
it drove very nice and quiet after that..pretty rotten job...the case is
HEAVY,
about 250lbs, and fits very tight into a recess were it has 8 bolts. To
replace
it I sat it on a wooden board, nailed 2 battens to stop it falling back or
to
one side, and using 4 jacks, one on each corner of the board, lifted it up
into place.
I then stripped the old case down as i would like to retain a
replacement...they are
apparently hard to come by..one of the few available sold fro $800 recently
the mainshaft bearings were pretty sad, everything else seems acceptable.
I do have a question tho and it is VERY technical, so GMC experts..
??There is a bearing between the mainshaft and mainshaft gear that is Hyatt
1307TS
it is a roller bearing with 13 rollers, it is fitted into a recess in the
mainshaft gear and a spigot from the mainshaft fits into its ID, like a
flywheel pilot bearing/gearbox-spigot arrangement (OD is 3.1496 "). It
is retained in the mainshaft gear recess by a large circlip...instructions
to remove
this bearing are to remove circlip and bang gear on solid block of wood,
well guess what..it doesnt want to come out..the rollers and inner cage just
fell out,
but the outer race cannot be budged...is this normal? for the inner race and
rollers to be easily removed? or should they not be seperable?
Is there a method for removing the outer race? Has anyone struck this?
I can get the bearing, but I also know of a broken case that might be a
better bet
cause my mainshaft has damaged threads were the castellated nut fits to
retain the yoke.
There are five bearings in the mainshaft..one is OK, the needle roller one
is rebuildable.
I suppose I could reassemble the Hyatt bearing, I have a new rear bearing,
and I can
buy a new front bearing.
When i put the new case in the front axle declutch was very stiff, and damm
me
but the cast lever arm that connects the the control rod to the TX declutch
shaft,
fractured about the link pin, it appears this might be a weakness also, as I
noticed its companion, the high/low range arm had been previously welded,
anyway, I recovered the fractured pieces luckily, and welded it all back
together,
but I am a bit nervous that it wont last as the casting is thin at that
point,
less than 1/8", also i will grind the arm recess back a tad so that my
slightly
reinforeced lever is hopefully less likely to break, other than that, a bit
off
a wrecked one i suppose.
Another other thing I noticed is that all the yokes had spot welds on them,
near werw
the dust cover is, that is 4 on the old case and 4 on the new..so either
this is
factory or they all break?
Sorry for the long post, technical and boring for non-CCKW persons, but
tecnical
info is what I am hear for...bye the way "Band of Brothers" had lots of CCKW
sitings, as well as tanks and Jeeps..I am probably way behind USA viewing
fot this
TV series.
Tony
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