99 LTZ 3.8 tranny question...

OK, here goes. Does anyone know if the 3.8 had a vacuum modulator on it? I know the 3.1s did. And, according to a dealership, this thing IS supposed to have one. But, I've already seen 2 lumina 3.8s and none of them have this. As for my car, when I tried to find the Modulator, all I found was a broken bracket and a missing modulator. Can I pull one off a a 3.1 and use it in my 3.8?

Another question. Could a missing vacuum modulator cause my transmission not to shift into 3rd and 4th gear.

Thanks

I don't think so. They usually only affect the 1-2 upshift. 3-4 is solenoid controlled. I don't know for sure if yours came with one or not. I kinda doubt it.

post the last 8 digits of your vin and I'll run it for you and let you know.

The easiest way to tell is look on your SPID label located in the trunk under the lid or on the back of the spare tire cover. Look for M13 on one of the data lines. If M13 it is a 4T60E with vacuum modulator. If it says M15 or MN3 then it is a 4T65E which is totally controlled by the PCM.

On your lack of overdrive (4th) what typically causes that problem is a bad 4th gear clutch spline which may mean a rebuild. This problem is common on 4T65E trannies.

Even if you had one, a defective vacuum modulator will not cause a lack of upshifts or your problem.

3800 LTZ's are m13 transmissions 4t65e, no modulator. Trans need to be scanned for shift/solenoid commands and slippage errors for proper diagnosis.

3800 LTZ's are m13 transmissions 4t65e, no modulator. Trans need to be scanned for shift/solenoid commands and slippage errors for proper diagnosis.

Max, ole buddy, are you sure M13 RPO code is correct? According to my GM RPO codes listing M15 is the 4T65E and M13 is the 4T60E.

Have you made any decision to get that new Buick yet?

I don't know if you recall I traded my '96 Lumina in for a '01 Regal GS. Nothing like an old fart mobile. :bigthumb:

I would almost bet a 99 LTZ does have the 4T65E. the easiest way to tell is how the transmission connector is placed. And of course the lack of a Vacuum modulator! 4T60E have the connector coming out of the front ( facing the radiator) which is right next to the modulator. 4T65E have it coming out so it faces the driver side tire. As for not having 4th, how many miles do you have on the car & how hard do you pound on it? the 4th shaft will strip if a heavy foot is applied to gas pedal. The splines are weak cuz GM didn't harden them. A quality replacement one such as a Acdelo the splines are now hardened. The mod should be interchangeable our aftermarket ones are. If your were missing the modulator you would be hemorrhaging ATF and you will need to get the little valve that’s behind the mod also cuz it probably gone.