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what are the chances...***now a question about tranny modulator****

rudeguy

rudeguy

Lifer
My Grand Prix has been having trouble starting in the mornings and sometimes stalls at idle. Check engine light came on so I figured it was a sensor. I stopped at Autozone to get the code read but they said they couldn't do it since my car is a 95.

So I'm pulling out of there and it won't shift out of first (its an automatic). I could start in 1 and go up to 3 just fine but it wouldn't shift on its own. I added some tranny fluid hoping that would help but it didn't.

So my car is on a hook up to the shop. Just for shits and giggles...what do you think the chances are of the two symptoms being related?

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Starting problem was vacuum related. The tranny they thought was another vacuum issue but that didn't fix it. They said it could be the vacuum modulator but they weren't sure since I didn't take it to a place that usually does tranny work.

So my question is...how much does a modulator usually cost for parts and labor? I don't want to keep dumping money into this if it gets too much more expensive.
 
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i am not a mechanic, but the first could be a problem with the ignition/electronics/fuel system, while the second is clearly (IMO) a transmission issue
 
Vacuum problem for the stalling tranny is still screwed. They said it may be the module(?)

Anyone know how much that would run?
 
I came in here to say check vacuum on the starting and stalling, but you've already found that out. And which module? The PCM?
 
transmission modulator. I wasn't sure until I looked it up. I took it to Pep Boys because I trust them more than a tranny shop. They said that it could be the modulator and that they COULD do it...just that they didn't usually.

I checked Rockauto and it looks like a cheap part, but what about labor? Its a disposable car and I already dropped $300 between the tow and the work I had done. Any more than a couple hundred more and it would make more sense for me to sell it off and just pick up another one.
 
Tranny modulators on the old RWD's simply screwed in to the side of the trans. and had an adjustment screw in the center. Considering all it does is move a linkage rod I wouldn't think yours is much different. The only hang up would be putting a hand on the dumb thing if it was buried.
 
Found some general info:

Governor, Vacuum Modulator, Throttle Cable
These three components are important in the non-computerized transmissions. They provide the inputs that tell the transmission when to shift. The Governor is connected to the output shaft and regulates hydraulic pressure based on vehicle speed. It accomplishes this using centrifugal force to spin a pair of hinged weights against pull-back springs. As the weights pull further out against the springs, more oil pressure is allowed past the governor to act on the shift valves that are in the valve body which then signal the appropriate shifts.
Of course, vehicle speed is not the only thing that controls when a transmission should shift, the load that the engine is under is also important. The more load you place on the engine, the longer the transmission will hold a gear before shifting to the next one.
There are two types of devices that serve the purpose of monitoring the engine load: the Throttle Cable and the Vacuum Modulator. A transmission will use one or the other but generally not both of these devices. Each works in a different way to monitor engine load.
The Throttle Cable simply monitors the position of the gas pedal through a cable that runs from the gas pedal to the throttle valve in the valve body.
The Vacuum Modulator monitors engine vacuum by a rubber vacuum hose which is connected to the engine. Engine vacuum reacts very accurately to engine load with high vacuum produced when the engine is under light load and diminishing down to zero vacuum when the engine is under a heavy load. The modulator is attached to the outside of the transmission case and has a shaft which passes through the case and attaches to the throttle valve in the valve body. When an engine is under a light load or no load, high vacuum acts on the modulator which moves the throttle valve in one direction to allow the transmission to shift early and soft. As the engine load increases, vacuum is diminished which moves the valve in the other direction causing the transmission to shift later and more firmly.


http://www.familycar.com/transmission.htm


Edit: Just looked at a picture. They might have to drop the pan to unhook it at the valve body.
 
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LTC8K6 said:
I would have bet a paycheck that there wouldn't be a vacuum modulator on a 1995 car.
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Damn! I would have taken you up on that bet. 😉

It does have a modulator but it does not have anything to do with shift timing. The modulator is used to control pressure line rise. You should take it to a shop that has the ability to scan a GM vehicle with an ALDL connector. Determine if there are problems with the shift solenoids or possibly a QUAD Driver. It could be something as simple as a blown fuse not allowing power to the transmission.
 
herm0016 said:
what engine? shouldent that car be obd2 and be able to be read??
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ODDII was not standard until '96. Some cars were equipped prior to that time with it but may or may not have full access to all diagnostic functions through that connector
 
so it would be worth it to take it to a tranny shop? I'm scared as hell to take it to one of those places. All I have ever heard is about how they overcharge and charge for stuff that doesn't need to be done.
 
You need to take it to a reputable transmission shop. I know it sounds like an oxymoron but there are some of us out there.

Ask people that you know about who they would recommend. Search for shops online in your area and read the reviews left for them by other customers. I guarantee people will leave bad reviews a lot faster than good ones. I've seen some shops with dozens of bad reviews and hardly any good ones.

When you find a shop with a good reputation you know that they probably earned it and don't want to lose it.
 
If you register at auto zone, you can enter your car type and engine, and then get info on what's involved in replacing that modulator, to give you an idea...
 
LTC8K6 said:
If you register at auto zone, you can enter your car type and engine, and then get info on what's involved in replacing that modulator, to give you an idea...
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No need to register with them I can tell him how. Remove vacuum hose> remove bolt from modulator bracket> remove modulator and bracket. Reverse to reinstall. Takes about 2 minutes if you're smart and do it while the engine is cooled down. 😉
 
TonyH said:
No need to register with them I can tell him how. Remove vacuum hose> remove bolt from modulator bracket> remove modulator and bracket. Reverse to reinstall. Takes about 2 minutes if you're smart and do it while the engine is cooled down. 😉
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I could have told him that too, except I wasn't sure it was that type of modulator. I'm still not sure... 🙂
 
did you check the flux capacitor... perhaps you shuld buy the tranny a beer first?

**Sea Moose goes back to ATOT where he belongs 😛**
 
uggh....looks like they already tried the modulator. I had it towed back there because it was still stalling out today. I figure if I paid them $250, I should at least get something out of it. Think its too much for them to at least wash it for me so I get something for my money?
 
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