losing OD while cruising

[gore]

Hey,

I just joined this forum. Good to have a place to discuss these engines and transmissions.

I recently bought a 94 Olds CUtlass Supreme with a 3.1 and a 4T60E automatic. It is a well cared for car overal, but the tranny is losing its overdrive.

When the engine and tranny are cold, the tranny will shift into OD like it is supposed to. However, after it is good and warm it usually slips out of OD and will not shift back into it. It doesn't matter if I stop and turn off the ignition. The only thing that will get the OD to work again is to allow it cool off for a while.

Several factors influence how long the OD will function on any given day. The biggest factor seems to be how warm the ambient air temp is. On hot days I may only get 30 miles of OD. On cooler days, like 60* F and cooler, it may work fine for 200 miles. Secondly, the amount of load on the engine affects it. Pushing a strong headwind and driving at freeway speed will shorten the time OD will work. Climbing long hills and accelerating hard also shuts off the OD.

Not sure what the deal is here. I have worked on and rebuilt many TH350 and TH400 transmissions, but never a transaxle. Any input on this is appreciated. I get a lot of windshield time at work and having MPG drop to 18-20 w/o OD from 28 or 29 with OD really sucks with gas prices what they are.

Thanks.

[PCGUY112887]

How many miles are on it?

Sounds like a classic dieing 4T60E

Could try some additive such as Lucas, or could have a trans shop look at it. Sometimes it's just an easy solenoid that is going bad, but usually it's more.

[gore]

It has almost 160k. I have no problem with rebuilding it, but I am not what exactly is causing this problem. Any ideas?

[19Cutlass94]

How is the fluid in the tranny? color? is it burnt? and whats the level?

[gore]

The fluid is fine now. I flushed the tranny and changed the filter shortly after I got it since the fluid was a little dark and nasty. I wouldn't say it was burnt, just dirty. It didn't smell burnt.

There was very little debris in the pan/on the magnet so I assume it isn't in that bad of condition.

The new fluid seemed to help somewhat to keep the OD working longer. A few days ago I added a 12oz bottle of CRC transmission fluid additive (snake oil IMO, but maybe worth a try) to it, but it didn't seem to have any effect.

The tranny doesn't leak and the fluid level is where it is supposed to be. The 12oz of additive didn't seem to affect the fluid level noticeably.

I should mention that when the OD decides to quit, the tach will slowly creep up 300-400 rpm or so, like it is trying to stay in OD, and then it will "let go" and the engine will jump about 1000rpm when the tranny downshifts into 3d gear.

When I had the pan off, I noticed the valve body appeared to be made of aluminum. After doing a little research on this tranny, it turns out that some people have had trouble with the aluminum wearing and not sealing the trumpet valves. I'm not sure if this is the case here or if the valves in the valve body are directly responsible for supplying fluid to apply OD or not.

PCGUY112887 mentioned a bad solenoid as a possible culprit. What function do the solenoids perform in these trannmissions? Just a hunch, but wouldn't a solenoid either work or not work? That is to say, I wonder why OD works sometimes, but not others, and for various lenths of time based on different driving conditions and temperatures. I'm speculating here, but it seems like worn out hard parts (like the valve body) or a band or clutch or something.

Again, I don't have any experience with this type of tranny. Just brainstorming.

[sharkey]

the solonoids are for shifting. there is no govoner or throttle bable on this tranny, instead the computer uses the tps , map, and vss to figure engine load, and the computer controlls the solonoids and commands the tranny to shift. you also have a lockup solonoid to controll the converter clutch. line pressure is controlled by the modulator, just like a turbo 350.

what you need to do is determine if you have an internal transmission problem or a controll issue. the best thing to do is get a hold of a scan tool with a data stream. the idea here would be to watch the commanded gear and see if when its falling out of OD if the computer is commanding 3rd or 4th gear. if its commanding 4th, you have an internal transmission problem, if its commanding 3rd, then you need to find out why. a couple things that could cause this would be a faulty or misaligned MLPS (manual lever position sensor), the pcm may be getting a signal that its in 3rd gear, so it will downshift. another cause could be a if your map or tps value suddenly changes.

i myself would lean towards an internal problem. generally, if its worn /hard seals, it would not have OD when cold. i wouldnt lean towards clutches/band as it would slip all the time. im thinking more a valve body issue. the valve body is aluminum and some valves are steel, aluminum expands more, and can cause leaks between the bore and valve. now you can get the valve body off in the car, it is a big job, but possible.

[gore]

Thanks for the info. Very helpful. It seems more and more like a valve body issue.

What is the fix for this? Is there a vendor that sells a new or rebuilt valvebody for this tranny or does one have to sleeve or bore the existing valve body?

Tango mike...

[sharkey]

there are a lot of sonnax valve out there for the 4t60e. another option would be a reman valve body, best thing to do would be to talk to a local tranny shop about this.

[SinisterZ26]

same problem as gore

http://60degreev6.com/forum/showthread.php?t=38304&highlight=Transmission+Modulator

im having the same problem!!! i took out the modulator and theres tranny fluid in it!!! i thought to myself how can this be since theres really no seal to pervent t-fluid from leaking where the mod is imbeded. is there supose to be t-fluid in this mod? if not where is the fluid coming from?
i also noticed in pics that there is a seal around this mod and i dont have a seal on my orig mod
also when i took out the mod and got the best part of the fluid out of said mod. OD worked fine (on a hot as ballz day) but the next day same prob. but she isnt slaming back into gear after i come to a stop then accelerate again. i was told that this might be a front pump prob.
FEEDBACK PLEZZZ!!!

respectfully,
Phil

[IsaacHayes]

When I pulled my modulator to put on an adjustable one it had some trans fluid in it, not a lot. There is a rubber o-ring that seals the modulator into the trans. The stock one is black rubber with orange coating on it.