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Discussion Starter #1 (Edited)
I do not believe it is a tranny problem, but I have to start somewhere.
I have done a few Mods on my wife's 1995 Tbird lately. I recently replaced the 3.08s with a 3.27 tloc. I also updated the 95 intake to a 96/97 style. When I took it out for a test drive all seemed well except downshifting at highway speeds. It seems the car refuses to do a 4-2 downshift. I do not drive her car often and she has no clue what a 4-2 downshift is so I'm not sure when it started.

Since then I have cleaned the valvebody, done a Jmod on the 4R70W I drilled the seperator plate for the mild/gear setting and updated the accumulators, the 1-2 accumlator is using a Blue top spring and no bottom spring, 2-3 accumulator has no springs, I installed a larger OD servo and updated to a 96 trans pan. I torqued the valvebody to 90 in/lbs 3 times. The transmission shifts fine with the exception of 4-2 downshift.

Just as a test I did a manual 4-2 shift, I know it is not recommended. It shifted from 4 to 3 then to 2.

What inputs tell the 4R70W to do a 4-2 downshift?

I figure the engine load is determined by the TPS and MAF and those inputs go to the EEC and the EEC orders the 4-2 downshift.

Any insight would be helpful.


Thanks,
Todd
 

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Discussion Starter #2 (Edited)
Well I replaced the TPS that did not fix my no 4-2 downshift.

The only code I have is a P1000.
That is from when I disconnected the battery.
 

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Did you change the speedo gear in the trans when you switched differentials? If so the relationship between speed and load being sent to the computer may be off, causing your problems.

-Miller
 

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The Parts Guy
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Roadhawg said:
The 3.27 Tloc and the 18 tooth speedo gear came out of a supercoupe. :rolleyes:
An 18 tooth speedo gear is not the correct gear for 3.27's with stock size tires. :rolleyes:

-Rod
 

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Discussion Starter #8
racecougar said:
An 18 tooth speedo gear is not the correct gear for 3.27's with stock size tires. :rolleyes:

-Rod

The factory original gear for the 3.08 gears was a 17 tooth................

an 18 tooth for 3.27 gears seems about right
 

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Hey Todd, take off the intake tube and then have someone push the pedal to the floor and see if the throttle plate opens all the way. Maybe after the intake swap you just aren't getting a full engagement of WOT for some reason.

And even though there aren't adjustment slots in the TPS, it is still recommended to check the voltage and you may have to drill the holes larger and adjust it properly. I had to do it to mine after having it off a few times. Here is an article:

http://www.blueovalchips.com/tech/throttlepos/throttleposadj.php

And that setup calls for a 17.6 tooth speedo gear. We all know you can't get one of them...lol. So 18 is the way to go.
 

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The Parts Guy
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With a stock size tire (26.6" tall), 3.27's, and a 7 tooth drive gear, you'll need a 17.4 tooth driven gear. A 17 tooth gear would be the closest.

SCCOA's speedo gear calculator

-Rod
 

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Discussion Starter #11
Tony said:
Hey Todd, take off the intake tube and then have someone push the pedal to the floor and see if the throttle plate opens all the way. Maybe after the intake swap you just aren't getting a full engagement of WOT for some reason.
I checked the throttleplate and it is wide open with the pedal to the floor. I also checked and I have no codes. The car drives fine other than no 4-2 Forced downshift. It was suggested by someone that it maybe a sticking control valve in the valvebody. I do have an extra valvebody from a Mustang that I can swap in and I know the transmission that VB was in had a good 4-2 forced downshift.
 
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