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Geo Auto trans trouble
http://www.teamswift.net/viewtopic.php?f=9&t=51191
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Author:  blue_can [ Thu Jun 16, 2011 8:15 pm ]
Post subject:  Re: Geo Auto trans trouble

mikemetro wrote:
@ blue_can

Tbut the spring between the down shift plug and the throttle valve leads me to believe that when steady pressure is applied they ( the down shift plug and the throttle valve) move together. But under rapid excelleration the spring compresses.


I don't believe the way it works varies whether you move the cable fast or slow. Either way the spring has a tension so in order to move the throttle valve the downshift plug needs to overcome this tension by an opposing force. Whether this force is applied quickly or not should not matter and end up having the same effect which is to modify to increase the line pressure in response to the throttle.

Not sure why it is called the downshift plug as it does not control shifting. Could be a left over term from the days when it was indeed also controlling the shifting. It's been a few years since I looked at the close up details but I do have some more info around on Toyota transmissions which explain the details on how this assembly works. Since the MX17 was made by the same company (Aisin) the VB and the gear assembly and structures was very similar. I will see if I can dig out that info.

Author:  KCCats [ Thu Jun 16, 2011 8:45 pm ]
Post subject:  Re: Geo Auto trans trouble

Ok Now Im more confussed!

Author:  blue_can [ Thu Jun 16, 2011 9:02 pm ]
Post subject:  Re: Geo Auto trans trouble

KCCats wrote:
Ok Now Im more confussed!


Sorry for confusing you. Probably the bet thing would b to test the trans as suggested and post back the results.

Author:  blue_can [ Thu Jun 16, 2011 9:19 pm ]
Post subject:  Re: Geo Auto trans trouble

Mike - here is the description of the throttle valve from the ATSG manual. Somewhat short but essentially says what I said before which is that it controls the boost pressure under high throttle conditions.

I had forgotten the details but I looked over the hydraulics and essentially this is a summary of how it works.

The spring coupling between the shift plug and the TV converts the linear motion of the cable to a non-linear motion of the TV. This is due to the fact the as a spring compresses you need more force to compress it (Hooke's law). The exact characteristics is not clear due to the fact there are two springs plus the several removable shims behind the TV. But essentially the idea is to convert a straight linear movement of the gas pedal to a more complex movement required to regulate boost pressure.

The TV itself has an inlet from the oil pump. The raw pressure of the oil pump is very high. The TV generates throttle pressure by opening the oil pump pressure to the throttle pressure outlet. This passage is then fed into the base of the primary pressure regulator. The primary pressure regulator generates line pressure by opening the oil pump pressure to the line pressure port and the throttle pressure serves to increase this by moving the regulator an additional amount.

That's the basic explanation of the how the pressure regulation works. It is certainly possible to remove the springs and characterize them to figure the exact response and plot a curve. I have an interesting book from ATRA on valve body design and it shows how to design and modify springs in the VB to obtain different shift characteristics using basic physics.

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Author:  mikemetro [ Fri Jun 17, 2011 6:05 am ]
Post subject:  Re: Geo Auto trans trouble

KCCATS - Sorry to confuse you. Got wrapped up in the detail. I attached PDFs with the testing procedure( See Below). Hope it helps
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Blue. Thanks for the info. The TCU Gets info from the VSS and TPS to select gears. Just to verify that it was an old left over term I unplugged the TCU (vehicle Stays in 3rd while in the D selector) No kickdown. Its sole function is to control pressure.

KCKATS - Make sure this cable is adjusted properly once you work out all your other issues. If it is loose or not functioning properly pressure within the tranny may be too low causing it to slip

Author:  KCCats [ Fri Jun 17, 2011 6:21 am ]
Post subject:  Re: Geo Auto trans trouble

OK is there a spec on adjustment?

Author:  mikemetro [ Fri Jun 17, 2011 6:29 am ]
Post subject:  Re: Geo Auto trans trouble

KCCats wrote:
OK is there a spec on adjustment?

Yes. Unless someone gets back to you before i do I'll upload it. Might have to wait till i get back. Check solenoids first. Then clean Then check TCU. Then make final adjustments. Post results after each. Dont want you to replace any parts that are not broke.

Author:  KCCats [ Fri Jun 17, 2011 7:17 am ]
Post subject:  Re: Geo Auto trans trouble

Sounds like a plan, but where do I get the solinoids? I will want to posssibly have them on hand before I tear into this? Kinda need the car right now? Or may have to wait till I get my VW turbo Diesel done?

Author:  mikemetro [ Fri Jun 17, 2011 7:46 am ]
Post subject:  Re: Geo Auto trans trouble

You have two options. A couple of guys said they had some for sale earlier in your post. Upside they are cheaper that way. Downside if you dont need them then your stuck with them. If you really want one on hand I would order one from an autoparts store or dealer (more expensive). Upside you can return them unopened. The car shifts fine as i understand if you manually shift right?? if so you can drive it like that forever. So order 1 from your choice. And when you get it in your hands open her up and start testing. The chance of both being bad is slim. Most likely a TCU (my vote) but it can definitely be either of the other 2. Out of 3 92's (that i have dealt with) with auto tranny all 3 had bad/failing TCU's. Check car-part.com for that one. Or check geo parts barn. But anyway here is the adjustment procedure.(this wont fix your shift issue IMO but its a good thing to check out)
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Author:  blue_can [ Fri Jun 17, 2011 11:09 am ]
Post subject:  Re: Geo Auto trans trouble

Good info from Mike. It just occurred to me after seeing the scans Mike posted that this site has no stickies from the FSM on the auto. On the other hand there is plenty of info on manuals. Someone a while back tried to put together a troubleshooting guide for the auto and I thought that had been a sticky but does not seem to be anymore.

Author:  mikemetro [ Fri Jun 17, 2011 11:16 am ]
Post subject:  Re: Geo Auto trans trouble

one question for KCCats. does the shift lock solenoid and turn signals work? Reason being that there is one spot to check on the wiring harness. On top of the transmission the harness is clipped to it. It has a tenancy to rub thru the jacket causing a short. Normal sign of this is a blown fuse. But not always

Author:  borshchris [ Fri Jul 01, 2011 10:39 am ]
Post subject:  Re: Geo Auto trans trouble

I could have used you guys like 7 years ago with that one. manually shifted for almost 3 months before fixing it just by luck. (blew radio fuse) Never really noticed the turn signals werent clicking, but helpful to know. Did this design span across all years? or just the mk4? just out of curiosity and knowledge. no issues with mine at the moment.

Author:  blue_can [ Fri Jul 01, 2011 9:49 pm ]
Post subject:  Re: Geo Auto trans trouble

The main internals of the MX17 transmission has not changed since 89. The main changes have been to the controls. The OBD2 models have the TCM and PCM integrated into a single unit. Also the OBD2 controls do throw out fault codes for some problems. I believe the older systems had simpler controls and the lack of fault codes.

The only other change I'm aware of is that the valve body separator plate was redesigned in the 94 and later models. I'm not sure what the issue was - possibly just to make something work better. I don't believe the actual VB design changed.

Author:  KCCats [ Sat Jul 02, 2011 6:11 am ]
Post subject:  Re: Geo Auto trans trouble

No problem with the turn signals, but I do have another question?
I have a 91(?) GTI with the Auto in it, was supposed to be a driver (NO WAY) and never came up with the title! Don't know last time it ran or even if it does? I've had it for 5 years and haven't touched it! Would it have the same trans?

Author:  KCCats [ Mon Jul 11, 2011 6:03 pm ]
Post subject:  Re: Geo Auto trans trouble

Or would the solinoids be the same?

Author:  jaguar,vettes&sprints [ Sat Jul 02, 2016 11:22 pm ]
Post subject:  Re: Geo Auto trans trouble

this thread has good bones it a shame the links are broken (sad)
still bumping it up
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.......jv&s
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.

Author:  1992Poddy [ Wed Aug 31, 2016 3:13 pm ]
Post subject:  Re: Geo Auto trans trouble

Agreed this post has been very helpful need to try and replace the solinoides in the trans I changed the fluid that was burnt black and reeked lol. So manual shifting up will not cause any problems? What about down shifting I tend to shift back into first when the car is stopped.

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