Auto ransmission resistor mod's: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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March 18, 2009 2:35 p.m. 4cylndrfury Reader

Ok, I have an idea that might make my slushbox blues clear up a little. Over on G20.net, I read about a mod that basically bypasses a resistor regulating autotrans line pressure, and essentially nets you full line press resulting in redlines before shifts and faster ETs in a straight line and cute little birdy noises when you do finally shift. Now, this piqued my interest, but I got mixed signals about the effect this has on a 10 yo trans with 115k on her. Some say this is better becasue firmer shifts have less slipage and generate less heat, but AFAIK, full line press is essentially a neutral bomb every time you shift right? I was always taught this is transmission suicide. Not to mention, bypassing this resistor ticks off the ECU and it throws a CEL code...annoying etc etc

Anyway here is my idea. pictured below a re 2 REEAALLLY crude diagrams. The top is the current design...pos wire into the resistor, neg out. Without knowing the actual amount, lets just say this resistor is rated at 20ohms, and is there basically to reduce pressure and produce more comfortable shifts...hence the "C" on the resistor.

The bottom diagram is my mod, which wires a switch and a resistor rated with less resistance...lets say 10 ohms,, which following logic, will produce 2x the line press resulting in only half the slippage and 50% firmer shift right? I have the smaller resistor marked as "S" for...wait for it...Sport. Clever right?!? The switch is the black box where the red pos wire splits.

OK now for the questions:

A. is this wiring setup legit? I can solder my joints and mount the switch in the cabin, Im just no wiring guru and am not sure if this setup is valid...i.e. will it send crrent somewhere bad and make my car exploderate or something?

B. is my logic as far as the resistors sound? Does anyone have any background/experience with this?

Thanks for your help oh forum of cheap car magic!!
March 18, 2009 2:51 p.m. Strizzo Dork

i heard somewhere that putting a shift kit in an auto transmission is like putting a hammer in there, its just going to go around and bang on things until it breaks something.

although i heard this before a lot of people started swapping out valve bodies and the like in the modern transmissions, but even with those i've heard of front pump failures due to the higher demands of running the line pressure way high
March 19, 2009 6:20 a.m. 4cylndrfury Reader

bump...anyone?
March 19, 2009 8:18 a.m. Grtechguy SuperDork

not to hijack, but is this basically what the "Power Mode" is on my Aurora's Transmission?
March 19, 2009 8:57 a.m. Gearhead_42 Dork

I would just unplug the resistor in my S14 for events
March 19, 2009 12:08 p.m. xci_ed6 Reader

Install a potentiometer? Then you have adjust ability from stock to firm.
March 19, 2009 12:09 p.m. 4cylndrfury Reader

Gearhead_42 wrote:

I would just unplug the resistor in my S14 for events

sounds tempting, but I dont want full line press, maybe just like 85%.

anyone recomend the design I posted up earlier or have any suggestions for improvement on it?
March 22, 2009 7:59 a.m. 4cylndrfury Reader

ok, so I did some poking around and now I need to know about rocker switches. will a single pull-double throw take current from one source and split it 2 ways depending on what position the switch is in?

And also, will it hurt for me to just solder the neg wires (black wires in the pic above) back together after the resistors?

Thanks again for everyones help.
March 22, 2009 2:05 p.m. Hal HalfDork

4cylndrfury wrote:

ok, so I did some poking around and now I need to know about rocker switches. will a single pull-double throw take current from one source and split it 2 ways depending on what position the switch is in?

And also, will it hurt for me to just solder the neg wires (black wires in the pic above) back together after the resistors?

Single pole - double throw is what you want. Don't get one with a center-off position. I don't think it would be good to have a situation where neither resistor was connected because someone accidentialy bumped the switch.

You can solder the negative wires back together after the resistors with no problem.
March 22, 2009 2:14 p.m. 4cylndrfury Reader

thanks a bazillion...my auto electricians liscense is still backordered at the printers...the clown college I got it at hasnt paid their bill from 2004 yet lol

OK, so then Im gonna work on this during the week, and report back with what I find. I will make it a pic heavy post, and anyone else whos trans is set up with a resistor that controls line pressure can follow suit.