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22 GEARSSeptember2007
I ts a rare day that the ATRA Hotline doesnt get a call about a
transmission thats back on the bench for the second time because
its missing a gear. It can be no reverse, first, second, third or
even eighth gear. It could be a combination of miss-ing gears, but
doesnt slip or flare. Of course, it cant be no forward and no
reverse at the same time; that would be no engagement or no
movement.
Here are a few things you can look at that can make it a little
easier to find those missing gears.
Would You Look at That?When I ask the tech if he has
looked at this part or that part, the answer is always the same:
I dont see any thing wrong. I believe him. Lets face it: If he
could see the problem, hed have fixed it and we wouldnt be talking
about it.
Just looking at the parts again and again hasnt helped find the
problem, so what do we do next?
Plan on Taking New StepsWhat we need is a new plan. The
new plan must be more than just look-ing at a part lying on a
workbench. We need a step-by-step plan, with tests along the way,
and when possible a test with results that can be measured.
Usually no testing was done before or after the rebuild, so we
usually have little more than symptoms to work with. And now were
really in a tight spot, because by now the car has been in the shop
for three days or more and the customers getting antsy. We need to
work with a fast, step-by-step plan to identify the general problem
area.
Step Right Up to SuccessHere are 6 simple steps you can
use to help find a missing gear or gears on most
transmissions:
Step 1: Check the turbine shaft splines. Feel or look for sharp
or stripped splines on the front of the shaft. Replace the shaft if
its worn or damaged.
Missing Gears: Tips for
Tough Stuffby J Weldon Barnett
Figure 1: If you feel or see metal shavings or clutch material,
replace the converter.
Figure 2: If you hear, feel or see stripped splines, replace the
converter.
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24 GEARSSeptember2007
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Step 2:
Checktheconverter.Slowlypourallofthefluidoutoftheconverterintoyourhand.Ifyoufeelorseemetalshav-ingsorclutchmaterial,replacetheconverter(figure1).
Step 3: Check the internal turbine splines in the converter
(Figure2). Clamplockingplierstotherearoftheturbineshaft
andinstalltheshaftintheconverter. Withonehandlifttheshaftabout
off the bottom of the converter. Withyourotherhandusethepliers
torotatetheshaftwithveryquick jerks clockwise and counter
clockwise. If you hear, feel, or see stripped
splinesorbrokenpartsreplacethe converter.
Step 4:Ifyouhavetheunitoutforthesecond time, use another
case;moreontheoldcaselater.
Step 5:Assemblethetransmissionbutdont install
thevalvebody.Testall
theclutchesandservoswithabout55PSIofregulatedairorfluidpressure(Figure3),unlessanotherpressureisrecommendedby
theOEM.Listen and feel for cross-
leaks.Forquickandmoreaccuratetesting,Irecommendyouuseatestplate;oneofthetestmachinesthatareonthemarketisevenbetter.
Step 6: Checkforclutchengagement. Attach lockingpliers to the
inputandoutputshafts
(Figure4),insuchawaythattheyllletyouturnthe
Missing Gears: Tips for Tough Stuff
Figure 3: Use a test plate to check for leaks and apply
problems.
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GEARS September 2007 25
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shafts without hitting the case.
Get someone to help you apply the clutches with air or fluid
pressure hoses.
Apply all the necessary clutches for the gear thats missing.
With the gear applied, turn the input shaft with the locking
pliers. Does the person at the rear of the trans have a hard time
holding the output shaft from turning?
Lets use an example of no reverse: Is the output shaft rotating
in the opposite direction? In other words, do you now have a good
solid reverse apply, or is the output shaft just rotating due to
frictional drag? If you have reverse at this
step, its extremely unlikely the problem is in the assembled
parts up to this point on most transmissions.
You may not know where your problem is yet, but you can have a
very high degree of confidence that the box is okay, and wont need
to come back out of the car if you still have problems. At this
point you should be looking for a prob-lem in the valve body or the
computer control system, but the box isnt a suspect anymore.
Figure 4: Attach locking pliers on the input and output
shafts.
You may not know where your problem is yet, but
you can have a very high degree of confidence that the box is
okay, and wont
need to come back out of the car if you still have
problems.
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26 GEARSSeptember2007
Are You Overdriven? Only Your Ratios Know for Sure!
Lets look at another example: What if you think youre missing
5th gear on a Mercedes 722.5, but cant tell for sure if it is 4th
or 5th, because the ratios are so close together. Build it up quick
and test the ratios; heres how:
Look up the ratios for the trans.
Use air or fluid pressure to lock the transmission into 4th
gear.
In this case the ratio is 1.00:1 that would be turning the input
shaft one complete turn for one complete turn of the output shaft.
Fifth gear is 0.75:1, which would be of a turn, or 0.75 for the
input shaft to one turn of the output shaft. This type of testing
gives you measurable results.
NOTE: See page 58 in the January/February issue of GEARS for
several ratios all in one place.
Oh, By the WayI didnt forget about the case in
step 4. Besides all the usual case inspec-tions, such as looking
for stripped holes and checking flatness, test the case for cracks
in the worm track area; heres how:
Drag a sharp, single-edged razor blade across the case surface
(Figure 5), to see if it snags on the surface. If it does, examine
the area for signs of a crack. Sometimes when a wall cracks, it
bends over; then the main casting and the cracked part no longer
line up, so the razor blade may snag on the crack.
Sometimes you can see the gasket has been scraped back and forth
as the pressure moves the wall back and forth. Then again, maybe
not; by this time the unit may have been though several gaskets, so
there may not be much to look at. Also the gasket may have a bit
more aluminum scuffed on to it in the broken area.
Cracks seem more likely to occur on the outside walls of the
worm tracks.
Most case cracks are so obvious they never make it to the ATRA
HotLine. Inspection of the gasket, separator plate, and case is
about a 10-minute project.
If you suspect a crack but arent entirely certain of it, pop the
case into your parts washer for about 20 minutes to heat it up, and
see if it reveals the crack. If you dont find the crack, youll know
you need to keep testing, because you havent found the problem
yet.
If you cant find any other problem and decide to replace the
case, tag the old case with a date and the repair order number. If
the car comes back next week for the same problem, the original
case from that car is probably okay. If you dont see the car for
three months, send the old case to the smelter.
As with so many other transmis-sion troubles, sometimes
identifying a missed gear just takes a little time and some careful
testing.
Figure 5: Test the case for cracks in the worm track area.
Missing Gears: Tips for Tough Stuff
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