transmission help


chevyguy93
11-13-2006, 06:15 PM
I got a 91 cutlass, and the transmission is acting really goofy. When you drive, it doesnt want to shift out of first. And when it finally does, it shifts through the other gears rough and kinda sluggish. Already changed the filter, and oil, not sure what to try next.

maxwedge
11-13-2006, 07:27 PM
Make sure you have good vacuum the modulator, lower l/s of trans facing the forward.

chevyguy93
11-13-2006, 07:30 PM
and what does this thing look like? does anyone have a picture?

caddyman379
11-13-2006, 10:33 PM
http://www.timgilles.com/photogallery/Engines/5.7vacuummodulator.jpg
Thats not for your engine but, it's similar to that, except yours would be black. From the front of the engine, to the right, look directly below the air cleaner tubes and you should see it. It screws into the tranny I believe, and has a vacuum hose on the end of it. The vacuum should be around 13-17 otherwise it can cause hard/soft or late shifts.

chevyguy93
11-14-2006, 07:34 AM
alright thanks alot. I will look for it after work today.

chevyguy93
11-14-2006, 04:10 PM
Well. I went and i took a look. According to a manual, this is it

http://i28.photobucket.com/albums/c216/timpropeg/vacuummodulator.jpg

just a picture i snapped of it. Its in the middle of the picture. I felt around the hose and it didnt have any cracks in it at all. Could the modulator itself be shot?

Also. Before I took the airbox and stuff off (i know you dont have to do that to get at it, I just wanted more room) i had taken it for a ride. And it seems it just didnt want to shift out of first. After i was poking around down there, i unhooked the connector above it, and made sure it was on properly, etc. I took it for another ride. When accellerating slow, it seemed to shift fine into 2nd (just a little late i would think because the rpms were a little high) and when i got to 44km/s, the engine revved up and acted as if the car was in neutral. i floored it a few times, and it eventually started going again. And I also found that if you floor it while accelerating, it doesnt act like it's in neutral like when you are accelerating slower.

Sorry if some things arent explained well, I tried to do it the best i could without trying to confuse anyone hehe.

Also, my father seems to think it may have something to do with the governor. Could that also be a thing to check?

maxwedge
11-14-2006, 05:02 PM
When you pull the vacuum hose off the modulator do you have good vacuum? This starting to sound like an internal problem, Next step may be a scan of the trans functions at a trans shop or dealer. Is the fluid burnt?

chevyguy93
11-14-2006, 05:14 PM
i didnt actually pull the vacuum line off, in fear that i would have snapped it haha. And the fluid is not burnt. I didnt know that a transmission could be scanned. I only thought the engine could, and only when the check engine light was on. ?? Thats very interesting. Is there any place in particular that does this scan?

Ian Szgatti
11-14-2006, 09:57 PM
1. Does this condition exsist no matter what the trans tempreture is?
2. Is there any check engine light on that you may not have mentioned? ...you might have assumed that engine sensor problems are indicative only of engine problems.
3. when the trans does shift into second finally, does it kick hard, or smoothly engage?

You did identify the vac modulator in the picture correctly. You should really check that line all the way up to the intake manifold. By the look of it, you should replace it anyway.
As far as other components that could contribute... sounds like problems with the governor assembally. when vehicle speed increases, the pressure developed by the governor is directed to a shift valve.
Looking in a text book here, and it sounds like a very reasonable assumption. Please keep us posted!!

chevyguy93
11-14-2006, 10:53 PM
thanks for the reply

1. yes the condition stays pretty much the same with the temperature.
2. no the engine light is not on
3. when it does shift, it doesnt shift hard because the rpms are way up, so its a smooth shift.

As for the governor, is it replacable? Or is it just something that needs cleaning.

Ian Szgatti
11-14-2006, 11:50 PM
The governor consists of components that must be replaced. The governor assembally is driven by the trans output shaft, sences road speed, and sends a fluid pressure signal to the valve body to either up-shift or down-shift. As speed increases (and therfor pressure), the spring tension and throttle pressure on the shift valve are over-come and the valve moves. This action causes an upshift. Likewise, a decrease in speed results in a decrease in pressure and promotes downshift.

Vac Modulator metioned by Maxwedge:

Now... the vaccume modulator mentioned earlier uses engine vacumme to change trans pressure. The governor will change your gears.. but the vac modulator knows how much load is on the engine. (i.e, going up a hill means your on the throttle more, therfor the throttle plate is open farther, lowering engine vac) It allows for an increase in pressure when vacumme is low (acceleration), and decreases when vaccume is high (closed throttle).
If the vacuum modulator has a hole in its diaphragm, the valve body thinks that the throttle is wide open, and the shift valve will move into the lower gear position. This will result in harsh, late shifts, if the transmission upshifts at all. When there is a hole in the diaphragm, the engine can experience several things. First, there is a vacuum leak. This can result in a rough, slightly higher idle and a flat spot (hesitation) during take-off. Also, the hole in the diaphragm means that the transmission thinks that the engine is under full load, even though the car might be barely cruising. The result is that the transmission shifts really late, if at all.
The key to diagnosing a faulty vacuum modulator is that the transmission is probably using ATF, without leaking externally.
A low fluid level is usually caused by a leak. A leaking vacuum modulator will also result in an internal leak when ATF is pulled into the intake manifold where it is burned.
When burned, ATF causes white smoke out of the exhaust.
The modulator should be able to hold approximately 18 in. Hg (457 mm Hg). If transmission fluid is found when you disconnect the line at the modulator, the vacuum diaphragm in the modulator is leaking and the modulator should be replaced.
If the vacuum source, vacuum lines, and vacuum modulator are in good condition but shift characteristics indicate a vacuum modulator problem, the modulator may need to be replaced or adjusted.If you can perform these tests with a vaccume gauge, it will greatly decrease diagnostic time in a trans repair shop. If you require a shops service, be picky, and document your findings to relay to them. You want to let them know that you know whats going on. Personally I don't trust many shops. I hope this helps somewhat. Let us know what you find.

Ian

chevyguy93
11-15-2006, 03:58 PM
thanks alot for the VERY helpful reply! i did notice that a few times during take-off, the car hesitated a bit, then started to go... Which as you say, could mean a vacuum leak. Hopefully when I have time, i will replace the modulator And the governor. and i just hope this cures the problem.

Ian Szgatti
11-15-2006, 06:00 PM
i am not neccesarily right about his, and if you can get a vac gauge and perform the test, it will not only familiarize you with the procedure, but confirm before you spend any money. I only say this because if I have a problem, I am open to suggestions, but I always have to confirm for myself... your welcome though. Keep us posted with your results!

caddyman379
11-15-2006, 08:10 PM
just a suggestion-before you replace either of these items, be sure that you are getting vaccum to the modulator. If you aren't or your getting weak vaccum, replacing those items wont help. If you dont have a vacuum guage then you can always pull it off and see if it sucks your finger in. Ian-Doesn't the transmission have to be removed and disassembled to replace the governor? I sort of thought that was an internal part

Ian Szgatti
11-15-2006, 09:56 PM
Ian-Doesn't the transmission have to be removed and disassembled to replace the governor? I sort of thought that was an internal part

yes it is... hopefully he won't have to do that... but at least having a rough idea will help him deal with a reputable trans shop if further mechanical inspection is needed. Im certainly no diagnostic expert, but think the modulator seems like a likey fault...
I would think there would be evidence of trans fluid in the vac line going to the modulator as well.
What I would like to know is what causes the hole to form in the diaphram of the modulator... age? brittleness?

caddyman379
11-16-2006, 03:12 AM
well my experience has been that they go because of age, they get hard and brittle and one day that vacuum, even thought its not alot, just kills it. Plus, think about all the heating/cooling cycles its subjected to.

Ian Szgatti
11-16-2006, 02:17 PM
well my experience has been that they go because of age, they get hard and brittle and one day that vacuum, even thought its not alot, just kills it. Plus, think about all the heating/cooling cycles its subjected to.

it is just a rubber diaphram, so that makes total sense

chevyguy93
11-18-2006, 02:45 PM
okay. so heres the update.
Installed a new vacuum modulator and checked the governor. Still the same problem.

While driving, it shifts a little late from first into second. When you get around 44kms/h (about time for it to shift into 3rd) it slips and goes into neutral. You have to let your foot off the gas, and slowly press it in order for it to shift into 3rd.

I believe I did everything I could. I now believe that the problem is inside the transmission itself. I'm going to be phoning around for prices on used transmissions and debating whether I should sell it as-is.

Ian Szgatti
11-18-2006, 03:40 PM
okay. so heres the update.
Installed a new vacuum modulator and checked the governor. Still the same problem.

While driving, it shifts a little late from first into second. When you get around 44kms/h (about time for it to shift into 3rd) it slips and goes into neutral. You have to let your foot off the gas, and slowly press it in order for it to shift into 3rd.

I believe I did everything I could. I now believe that the problem is inside the transmission itself. I'm going to be phoning around for prices on used transmissions and debating whether I should sell it as-is.

So you noticed no difference at all?
Before replacing, your next step should be checking the shift solenoids... you don't have to have the trans pulled for that, just have to take off the pan... that may not be entirely possible for you alone to do, but it's an option when concidering service. How much did you pay for the shift solenoid?

Chriznat20@msn.com
11-18-2006, 05:27 PM
okay. so heres the update.
Installed a new vacuum modulator and checked the governor. Still the same problem.

While driving, it shifts a little late from first into second. When you get around 44kms/h (about time for it to shift into 3rd) it slips and goes into neutral. You have to let your foot off the gas, and slowly press it in order for it to shift into 3rd.

I believe I did everything I could. I now believe that the problem is inside the transmission itself. I'm going to be phoning around for prices on used transmissions and debating whether I should sell it as-is.

Im sorry but its my experience, as the son of a trans rebuilder, that your transmission is due for an overhaul. Usually on GM FWD transmissions, especially of the era you are speaking of - the forward clutches and so forth are worn beyond any further service duty. You can buy a rebuilt unit on ebay or from a local rebuilder and R&R.

We've told customers before who dont want to spend the $$ to actually disconnect the modulator and put a screw in the vacuum hose. You "might" get a few more miles out of it this way.
What transmission model do you have (4T60E? 440T?) How many miles?

caddyman379
11-18-2006, 06:42 PM
well, that is certainly true. But before you do any of that, (this is a generic fix i know) you should check the tranny fluid and ensure its clean, and drain some and add some Seafoam. I've heard good stuff about it. I've never used it. Out of curosity, if you go down the floor from a standstill, does it redline? It's supposed to shift at or slightly below redline.

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