4L60 (700-R4) Diagnosis Fundamentals

 

 

     Lets first talk about the difference between a 4L60, and a 700-R4.  The only real difference is the name.  A 4L60 is a 700-R4.  The name only changed to better identify the transmission.  The four meaning it has four gears (1-3 plus overdrive).  The "L" for longitudaly mounted (as compared to Transverse on a FWD car).  "60" is the relative torque value.  For example, 80 is stronger than 60, which is stronger than 40, etc...  A 4L80-E can handle more torque than a 4L60-E.  The "E" you are seeing in the last sentence denotes it is electronically shifted by a computer.  Since the 4L60 is hydraulically shifted based on governor pressure and TV cable position, it is delete the "E" at the end.  With that said, lets move on.

 

     This was not intended to diagnose your tranny for you.  Diagnosing can be very complex, and even give the best of us a difficult time.  This was only intended to help you understand what is going on, and help you decide between possible causes, and rule out definite no's.  If you are unfamiliar with the 4L60, the Clutch and Band Application Chart will be your best friend.  You must first distinguish which gears are working properly, and then distinguish which are not.  Then, by using the Clutch and Band chart, you will be able to narrow down possible causes by eliminating unaffected items.  Take a look:

 

     Ok, now lets look at a common problem with the 4L60.  Here are the symptoms:

Reverse works good.  Starts out in first good, shifts normally into second,  then right before shifting into third, RPMs go soaring.  The vehicle is slipping badly.  As the vehicle slows down, it goes back into second.  Using those symptoms, lets rule out what can't be bad.

Reverse works good.  Look and see what is applied in reverse.  We now know that the reverse input clutch, and the lo-reverse clutch is OK, since we have reverse.  Cross them out.

Starts out in first good.  Go back to the chart. We can see that the forward clutch must be good, the forward sprag must be OK, and the lo-roller clutch should be OK. Cross them out.

Shifts into second normally.  Go to the chart.  We already know from first gear, that the forward clutch and forward sprag are OK, but now we have the 2-4 band being applied.  But since we have second also, then the band is OK.

Now take a look at the difference between second and third.  Remember, we lost third gear.  Notice the 2-4 band disengages, but the 3-4 clutch applies.  By using this chart, we can pinpoint that the 3-4 clutches are slipping.  Either they are burnt, or the apply piston has a blown seal, or whatever.  So by using this chart, we can also assume that we don't have fourth either.

 

This is an easy one, they get much more complex.  Shifting problems are a whole new ball game.  Because you need hydraulic schematics of the valvebody, pump, and what they control, I won't go into it.  Most shifting problems can be traced to the valvebody, and the two main factors that influence it.  The TV Cable, and the Governor.  These will come in another installment, right now, try and digest this much.

 

Think you got the hang of it?  Try this one on for size.  The symptoms:

Put the shifter in Overdrive (OD) and vehicle will not move, the engine just revs up. Reverse works OK. The vehicle will pull foward and move in Third, Second, and First, but not in the OD position.

 

Give up?  Since the car will go in revese, and pull foward in Third, Second, and First, we know the pump is good, the reverse clutches are good, the foward clutch is good, but take a look at the difference is first gears for OD, and Third.  Notice that for Third, Second, and First, the overrun clutch is applied.  The purpose of the overrun clutch in essence is to lock the sprag together, so that there is engine braking.  Because of this, we can deduce that in OD, the foward sprag was not holding like it was supposed to, but by putting it into Third, the overrun clutch applies, thus overriding the sprag allowing the car to move foward.  The sprag is faulty and needs replaced.

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