Transmission Downshift

[John Robinson]

About 4 weeks ago I took a short 40 mile drive in hot weather and when I came off the interstate I manually downshifted my 4L60 into second gear and the car just freewheeled no compression braking. the car has 112 K on it. However the transmission behaves normally in every other respect. All the shifts are normal it downshifts has good tip in and tip out on demand from the throttle. I have been to three transmission specialist in my area and one tells me the sprag gear is going bad. The second guy had no glue but said to just drive it. And the third guy called me a liar about it being a 4L60 Transmission until I lifted the hood and he could see the TV cable. As I drove away he said I should change the oil (He did not look at it) All this happened just prior to my having to make a 700 mile trip in one day with the car.

I have made the trip with no problems and the car ran great. Since nobody around here has ever seen anything like this I have hesitated to make this Thread but got to thinking (Gets me in trouble every-time)that maybe this was not unique and that someone may know what is happening.;help

 

[93Rubie]

Check your FSM section on the auto transmission. There should be a sytmphon chart specifically see if you can find the apply chart. The apply chart will show you what is doing what in any certain gear. Also, is your linkage adjusted properly? When you manually shift into 2nd or any gear you move the manual valve body, this sends fluid in different directions. If it is off a little or so, could cause a problem. Did it do this once or can you get it to do it again and again? Sounds like those tranny shops are idiots, it is a freaken 4L60, GM only made a billizion of them.

My Ford Focus has a 4F27E in it and once in a blue moon will act like it locks up for a second with a big jerk. Usually, happens on very light accerlation and between 2 and 3. Like it is hunting for a gear and cannot decide which one. It has done this since I bought it with 59K on it now has 107K. I attribute it to just being confused for second.

 

[John Robinson]

I have looked at the section on the transmission in my FSM. The best I can determine is that there is a electrically operated solenoid that controls the stator lockup. Which may have a piece of dirt or glaze in it. But as stated in my first post the transmission works just fine in every other respect. As for the fluid in the transmission it is clear almost to the point that you can not see it on the dip stick and it does not have a burnt smell at all. I have been told that a simple filter and oil change would fix the problem because in the tellers op-ion that would free up the stuck solenoid previously mentioned. I also have looked at the Seafoam transmission additive that says it will clean up glaze and varnish but am hesitant to use it with the oil looking as if it were new before I bought the car at 67K.

 

[Hib Halverson]

If you pull the shifter into "2" and get no compression braking, the transmission is faulty and may need an overhaul.

You can try "Seafoam" or other "mechanic-in-a-can" remedies or you can try a fluid/filter change, but my guess is you're going to be opening up the trans for repairs.

 

[boomdriver]

I have looked at the section on the transmission in my FSM. The best I can determine is that there is a electrically operated solenoid that controls the stator lockup. Which may have a piece of dirt or glaze in it. But as stated in my first post the transmission works just fine in every other respect. As for the fluid in the transmission it is clear almost to the point that you can not see it on the dip stick and it does not have a burnt smell at all. I have been told that a simple filter and oil change would fix the problem because in the tellers op-ion that would free up the stuck solenoid previously mentioned. I also have looked at the Seafoam transmission additive that says it will clean up glaze and varnish but am hesitant to use it with the oil looking as if it were new before I bought the car at 67K.

yes, when the TCC solenoid is working right there is good solid decelleration engine braking until its down to 1400 rpm OR until you touch the brakes...whichever comes first.

I can see where a sticky TCC would free-wheel if the trans was downshifted. Is there a chance that the brake was momentarily applied as it was downshifted I wonder? That would explain the lack of engine braking with otherwise normal operation.

 

[Hib Halverson]

If this trans can be downshfted manually into second and no compression braking occurs, the TCC is not the problem. The TCC never "freewheels".

When the TCC is enabled, the driveline and the trans are locked and spin at the same rpm. When the TCC is disabled, the driveline and trans are not locked but are still coupled through the torque converter.

 

[93Rubie]

John did it do this only once or has it happended again or multipile times? If it did it only once, I would not go out and get a trans. rebuild based on a one time thing. However, if it has done this mulitiple times or you have noticed other things going on, then I would start shopping around. See page 7A-15A-37 for manual 2 description. Says overrun clutch is still applied to allow engine braking when needed. Overrun clutch is still applied in 3 and 1 so if they are ok, well then....

 

[John Robinson]

John did it do this only once or has it happended again or multipile times? If it did it only once, I would not go out and get a trans. rebuild based on a one time thing. However, if it has done this mulitiple times or you have noticed other things going on, then I would start shopping around. See page 7A-15A-37 for manual 2 description. Says overrun clutch is still applied to allow engine braking when needed. Overrun clutch is still applied in 3 and 1 so if they are ok, well then....

It now does this all the time when I manually downshift it freewheels. I can put the car in 1st when stopped and pull the car up against the brakes to over 1500 RPM and there is no slippage. I am going to have to put the car on jack stands and try to check the voltage to the electrical connector on the tail shaft. From reading the selection you referenced I am wondering if the manual valve is hanging up causing my problem. If I understand it right it has to open to re leave pressure so the transmission can shift to 2nd gear.

On my retirement income a rebuild is the death of the car for me and I would have to almost give it away. It has been my life long dream to have a Corvette just as my father had his 1960 and put 250k on it. For that reason I am trying to see if this is something I can live with.

Another option I have is to have the transmission serviced and see if there is any shavings in the oil or filter. I still can not believe that this is fatal since as I have said before the transmission works beautifully except for this new anomaly.

 

[Hib Halverson]

In four weeks, if this problem has gone from once, to occasionally and now regularly, it won't be long until the transmission fails.

As I said earlier, you can try a fluid and filter change, but my guess is this is not an issue relating to fluid/filter contamination. It's likely a problem with failed parts. When you pull the pan, if you find more than about a "dime's worth" of chips or metal powder, you need an overhaul.

Sorry to be the bearer of bad news.

 

[John Robinson]

I have not been clear about one thing. This has not been a slow progression to not working at all it started immediately and has never changed. Once it happened I have not been able to get the manual downshift to work. Since it started I have driven the car 1k with a 700 mile trip one day in 85 degree weather.

 

[gmjunkie]

I have not been clear about one thing. This has not been a slow progression to not working at all it started immediately and has never changed. Once it happened I have not been able to get the manual downshift to work. Since it started I have driven the car 1k with a 700 mile trip one day in 85 degree weather.

Assembly #648 Sprag assembly is Shot (Brokey,Ka Putt,Bit the Big One,Like in History),John,Sorry!~!!

May go 2,000,5,000.20,000,50,000 miles and not get any worse! Or it could just self destruct at anytime!~!! :ugh
The only difference in a automatic transmission and a milling machine is about .010 thousandths!~!!
My turbo 400 in my Olga truck has had a bad sprag for the last 35-40,000 miles and will freewheel in 2 nd,It's kinda skeerie with 17-20,000 lb heading down a 3-5 mile 6-7 % grade!eek:eek I've not had to hit a runaway truck ramp yet,But it does raise the pucker factor!~!!

See Attachments below.....

 

[Hib Halverson]

I have not been clear about one thing. This has not been a slow progression to not working at all it started immediately and has never changed. Once it happened I have not been able to get the manual downshift to work. Since it started I have driven the car 1k with a 700 mile trip one day in 85 degree weather.

Sorry. I misread the OP.
That changes the situation somewhat in that, I agree with Junk...your transmission reliability may plateau for a while or it may continue downhill.

 

[John Robinson]

Assembly #648 Sprag assembly is Shot (Brokey,Ka Putt,Bit the Big One,Like in History),John,Sorry!~!!

May go 2,000,5,000.20,000,50,000 miles and not get any worse! Or it could just self destruct at anytime!~!! :ugh
The only difference in a automatic transmission and a milling machine is about .010 thousandths!~!!
My turbo 400 in my Olga truck has had a bad sprag for the last 35-40,000 miles and will freewheel in 2 nd,It's kinda skeerie with 17-20,000 lb heading down a 3-5 mile 6-7 % grade!eek:eek I've not had to hit a runaway truck ramp yet,But it does raise the pucker factor!~!!

See Attachments below.....

Thanks Junk you have confirmed what the first transmission shop told me and they quoted $1600 to fix.

I guess I will just drive it tell it blows. It won't change what I could get for it that much and maybe it still will outlive me.

 

[John Robinson]

Would an administrator please pull this thread it no longer is of any use to me and my problem.

As a side bar I retired from a GM transmission plant after 30 years. I was responsible for the scheduling of the prototype build. But that still does not make me able to know what is wrong with my transmission because I did not actually disassemble or build them. There were actual people who could tell you what was wrong just by hearing the symptoms of a failure and I hoped there might still be some of them around and on this forum.

Junk and Greg are those kind of men. I would always listen to them because they have the grease of a lifetime of working on cars under there nails.

 

[Mac]

Taken care of, John.

-Mac

ps: I'm glad we were able to maintain the diagnostics and useful information for future reference. The other stuff... :eyerole