4TH to 3RD Shift Switch

[rjwest]

Well , I finially got the 4th gear switch working.

First the reason why: I do not like letting the
truck downshift under load, especially with the
TCC locked ( TCC Lock up sw ). Therefore I manually downshift to 3rd ( while unloading the engine )prior to the PCM commanding a shift.
IT was a real pain though, lifting and pulling.

SO: I put a sw into the 'B' cmd line and it controlls the down/up shift between 4th and 3rd gear, so far it seems to work, mounted the sw down on the center console where I rest my arm.
Real easy to shift back and forth between gears.

Might try a remote RF sw mounted to the steering wheel. ( anyone know of a cheap unit ).


Getting ready for Maine hunting trip with the Truck camper, see how it works out...

Note: next is to figure out to control 2nd gear, a little more envolved, need some logic devices to ensure it does not mess up 'N' 'R' if you forget to return sw's to normal...

Any one have an old Pressue sw off of the transmission ( the sw on the side with the cable ).

[MTTwister]

rj - naturally , we'll want a complete how-to : both install and Use... After you're through testing, of course. Hmm, I'm running out of places to install switches, tho'.

[trbankii]

Sounds like what you need is a manual transmission! I don't seem to have the problem of it shifting when I don't want it to... smile.gif

[rjwest]

Standard shift Diesels VERY hard to find...

Got a Code today " P1810 "

I left the 4th gear lock out sw on ( open), When I started engine it set the code, Wrong Transmission code at start up, Have to rember to have switch in normal mode when shuting down...

Need to work on a " Logic " lock out so it only works in " D " position,,,

[MTTwister]

RJ - resurecting this thread - you should be back from hunting by now I assume. So how'd it go? Both the hunting, and the switch?

Also - was wondering today - the 4l80e is a 4sp with overdirve - 5 sp total - correct? If so, how does the average Joe keep it in 4th ( 1-1 final ratio) - and not engage Overdrive ( .75'ish)? Thanks.

[stingthieves]

like this???
http://www.picturetrail.com/gallery/view?p=999&gid=7515073&uid=3320954

[JohnC]

Originally posted by MTTwister:
- the 4l80e is a 4sp with overdirve - 5 sp total - correct? No, a 3 speed with OD. 3rd is 1:1. The "5th gear" is the torque converter lockup.

[adamcortell]

Stingthieves

Loved your picture trail Stingthieves. Good descriptions. Electronics has never been my strong point. With a little clarification on the wiring of the switch and resistors onto board I would be able to recreate what you have done. Next question would be how does it work once I have it installed in the truck? Which switch position for what response at what speed, etc, etc... Is this the switch for the 3rd 4th shift or TCC lockup?? Trying to puzzle it all together. Thanks for any further clarifications.

Adam

[stingthieves]

Not my picture trail Adam - I found it here - posted by one of the kind members that are willing to share. I just want to say thank-you and please continue> I did not wish to claim credit. Rick

[adamcortell]

After another look I see that picture trail is for the shift switch. I still would appreciate more details on how it all works.

Thanks
Adam

[MTTwister]

atom_c - First - do a search on those 2 topics - you'll find a lot of threads discussing both. ( Search is in the uppper right corner)

The "shift " switch basically affects the transmission line pressures for firmer shifts. It's easy to make, just be sure you have the board orientated in the right direction when you connect the resistors . ( DAMHIK)

The TCC lockup switch fools the Computer in to thinking there is High Tranmission Fluid temp (TFT) and locks the TCC. Simple to make - kinda tricky to use - RJ has some how-to's written up.

JOHN C - Thanks for the clarification - ( ummm duh!) So, awaiting the road trip results report.

[MTTwister]

Another BTTT - so RJ How is this working out? and the HOw-To's, if it is... thanks

[rjwest]

JUST GOT BACK, Hunting bad, operator error,

Truck good, Switch works great, EXCEPT,

Can not forget to leave it it 4th gear lock out,
gets a code and high pressure shifts when eng starts,

code must be reset with Sacn tool, high pressure shift resets itself, workin on interlock
to prevent code problem,

Works really great on the back roads where 3/4 shifts occur, leave my hand on arm rest and flick the switch to 3rd and back. I use it with the TCC lock up switch, like driving a std shift, match rpm with speed,

I am looking into how to build a lock out version,
something that will only allow operation when
shift lever is in 4th, thereby preventing the ;code, problem,

Lastly: I did get a " defuel" condition,
"loss of power without code" do not think it is related to shift switch, except that the 3rd to 4th gear shift ( 3000 rpm with TCC locked )
gives me a spike of boost,

Will keep posting as progress is made...

OH: to shift from 4 to 3 and back, a switch goes in series with the 4th gear position indicator line to pcm , opening line causes a down shift to 3rd.. when in park, pcm senses illegal shift indiactor and sets code. Thats why I need to build a lock out for 4th gear position only..

need some logic and a relay,,, in progress..

[GMC Hauler]

That picture from my picturetrail account was for a shift kit.

I did notice once, when I broke the connector on the thermostat crossover for the temperature sensor, that it would not go into overdrive. So, if you open this line, it would cause it not to go into overdrive.

Try disconnecting the sensor and running like this... it may not set a code. The only thing, the PCM will think the engine is cold.

I thought of doing this, but like the man said... too many switches. I am working on a trick switch panel that would be real nice for all of those switches, and not very visible.

If someone wishes, I could take a look at a scmeatic and figure out how to do this.

[rjwest]

GMC Hauler, thanks,

I wanted to keep the normal shift operations except
being able to shift 4-3-4 without moving lever.

Working on 4-3-2 also, a little more complicated..

Learned to live with the TCC lock up High pressure,
Use throttle to control harhness of shifts..

Note: if I use the TCC lock up on acceleration,(
Freeway merge with the truck camper ), the
acceleration is much improved.

Hold second gear with lever, at 30 , Lock up TCC,
Really pulls to 3000 rpm, ease of throttle a tad shift to 3rd, pulls to 3000 rpm, by than at road speed. That is why I am trying to get 2nd 3rd 4th
control by switches..

[MTTwister]

RJ - you may not remember that when I had mine wired incorrectly ( as in - always on), I eventually had some really wierd engine surges! I had made it over to Michigan, and it was probably about a week or 2 into the mis-wiring, when it started to act up. You may not want to leave it "on" all the time. Or if you do, see if you replicate my problem ( cost me Dealer Time to resolve my screw-up).

[rjwest]

I do recall, I try to turn off the TCC lock up when stopping and back on when needed ( at speed)

( I assume you was using the Resister between temp sensor and ground , not forcing the TCC solenoid to ground)

Have left it on at times, just shifts a little hard. But the PCM does seem to learn some smoother shifts after time. Have not had any SES lights but the P code is present when temp/ sw engaged.

I have had a few " defuel " modes set that would not reset with the computer " clear " command
, not the same as the overboost 'defuel' which was
resetable with the computer..No eng surges though.

I have noted a real differance in performance from day to day. After several hours of driving on
60 +degrees days power seems to fall off.
I alyways attributed it to " heat soaked engine and higher Input air temps. On last trip it was
about 30 degrees overnight, after 20 minutes warm up, Eng was making major power,had over 15 lbs of boost, was running 75 with the truck camper,
did so for about 1.5 hours untill oil temp came close to 200, backed off, and after a few more hours, all the super power was gone,,,
sure can't figure the PCM , must have had a good nights rest..