C4 Automatic Trans Downshift

[ljbest]

Hi,

I have a 1996 stock C4 Coupe (70,000 miles) with 4L60E Automatic transmission. The trans usually behaves normally, but once in a while I get what I believe is a missed downshift. This usually occurs when cruising at 50-60 MPH and slowing down to 35-40 MPH for traffic or a turn. If I give it moderate acceleration, it takes a second for the trans to get in the right gear - and by that time, I can be near the red line or on the rev limiter. This occurs infrequently, and has happened more often when taking hard right-hand turns. The fluid level is normal, and I am not getting any OBDII codes that indicate any issue with the trans.

Since this occurs infrequently, it's difficult to diagnose. I had the fluid and filter changed (Chev dealer) about 3000 miles ago. Before I take this in, I'd like some guidance on what the possible issue may be, or how I can best describe the problem. I have looked at some related threads, and have seen references to electrical problems that may contribute to shift problems. As I said, this occurs randomly and infrequently, does not appear related to temperature, and the car is a week-end driver.

 

[tlong]

Something is amiss. There are relays for the trans and settings in the ECM that handle all of that. In other words I don't have a clue how to help but someone will soon. Not sure as well what if any codes would be thrown. The right hand turn occurence may help with the diagnosis.

 

[ljbest]

Thanks for the update. Yes, something is amiss, and it's more aggrevating than operational. I meant to add that this situation occurs when you 'punch it', vs. just pushing on the throttle like you would in slow traffic.

Thanks,

Larry

 

[redc4corvette]

Try driving the car in drive not over drive see what it does.
Let's see said the blind man?
Well cheap check replace the map sensor on the intake manifold by the throttle body has wires and a vaccum hose that controls the up shift for 3rd and 4th gear.

Get out your level and find a flat piece of ground and check the trans fluid hot.
The 4L60E hates to be over filled or low even a little.

Now this should be the first test stomp on the gas and the trans should be
in o-drive.
If the car shutters when it shifts into 3-or 4th not good .
Now put the trans in 3rd gear not o-drive and try the same thing,if it shutters very little then the presure regulator selonid is going bad.
Spend the money now or later.:cry

 

[ljbest]

Thanks for the info. I'll try the tests for shuddering tonight. I did not mention it in my original post, but I did change the MAP sensor already. That did not really have any effect. I thought that I should also change the rubber seal (not part of the AC Delco kit) since I did not think the original had that great of a fit. I was leary of using silicone on it, given the trouble it can create with the O2's.

As far as the potential for a flakey pressure regulator solenoid - that is exactly the sort of isolation I am trying to achieve so that I have a chance if I take this to the dealer. I know that trans is very electronic, and other posts and searches on the web typically point to simple fixes being electrical. Since this thing pulls up through the gears under normal throttle behavior, I'm hoping it's not a major rebuild.

As referenced in another post, I had some leaks that seemed to stop when I removed about 1.5 pints of fluid. After a fluid and filter change, the level (hot) was about an inch aboove the 'S' in the dipstick - way overfilled by the marks on the stick.

Thanks again,

Larry

 

[tkrphxr]

Trans problem

I had what sounds like the same problem with my 2000 Silvrado.(same trans) He suggested changing fluid and filter and adding a bottle of Lucas Oil trans additive. Worked great for mine. No further problems. Mine had 75K on it when this happened and I have put about 10K on it since. Good luck

 

[redc4corvette]

Just so you know my trans is in the shop now I got a year out of it by adding justice brothers trans addative and using a power programmer lowered rpm on the shift points until it blew 3 and 4 gear.
Trans guy said 3-4 always blows in these trans.
I had a shift kit and racing clutches installed,I'll get it back on friday,not bad I blew nos 125 shot in it for a year.My case was also cracked ??? saw it but I wounder??
Good luck on yours.$2,000 to fix .