missing gears: tips for tough stuff€¦ · bench for the second time because it’s missing a...

22 GEARSSeptember2007

I t’s a rare day that the ATRA Hotline doesn’t get a call about a transmission that’s back on the

bench for the second time because it’s 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 doesn’t slip or flare. Of course, it can’t 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 don’t see any thing wrong.” I believe him. Let’s face it: If he could see the problem, he’d have fixed it and we wouldn’t be talking about it.

Just looking at the parts again and again hasn’t 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 we’re really in a tight spot, because by now the car has been in the shop for three days or more and the customer’s 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 it’s 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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Step 2: Checktheconverter.Slowlypourallofthefluidoutoftheconverterintoyourhand.Ifyoufeelorseemetalshav-ingsorclutchmaterial,replacetheconverter(figure1).

Step 3: Check the internal turbine splines in the converter (Figure2).• Clamplockingplierstotherearoftheturbineshaft

andinstalltheshaftintheconverter.• Withonehandlifttheshaftabout ¼” 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:Assemblethetransmissionbutdon’t install thevalvebody.Testall theclutchesandservoswithabout55PSIofregulatedairorfluidpressure(Figure3),unlessanotherpressureisrecommendedby the OEM. Listen and feel for cross-

leaks.Forquickandmoreaccuratetesting,Irecommendyouuseatestplate;oneofthetestmachinesthatareonthemarketisevenbetter.

Step 6: Checkforclutchengagement.• Attach lockingpliers to the inputandoutputshafts

(Figure4),insuchawaythatthey’llletyouturnthe

Missing Gears: Tips for Tough Stuff

Figure 3: Use a test plate to check for leaks and apply problems.

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 that’s 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?

Let’s 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, it’s 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 won’t 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 isn’t 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 won’t

need to come back out of the car if you still have

problems.


Are You Overdriven? Only Your Ratios Know for Sure!

Let’s look at another example: What if you think you’re missing 5th gear on a Mercedes 722.5, but can’t tell for sure if it is 4th or 5th, because the ratios are so close together. Build it up quick and test the ratios; here’s 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 ¾ 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 Way…I didn’t 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; here’s 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 aren’t 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 don’t find the crack, you’ll know you need to keep testing, because you haven’t found the problem yet.

If you can’t 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 don’t 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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missing gears: tips for tough stuff€¦ · bench for the second time because it’s missing a...

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