Speedo Jump

[LVMarauder]

Leaving the gym today i got onto a big stretch of wide street and floored it with o/d off and right about at the 1-2 shift i looked at the speedo , it read about 40 and when it shifted the speedo jumped to 50 then fell to 40 then FLEW to 60 all really quickly . then stabilized, didnt happen on the 2-3 or 3-4 . just a little odd.

[TripleTransAm]

Sounds like wheelspin on the 1-2 upshift.

[jspradii]

Yep! Ditto TTA.

[LVMarauder]

whats tta? is its traction control im an early 300 A , thus no traction control, It was a violent move ment of the speeeo, but if u guys have seen it.

[gilby04]

LV,

TTA = TripleTransAm

[TripleTransAm]

Most likely the upshift was harsh enough that the engine was able to overcome the contact friction of the tires before it was slowed down due to the next gear.

Think of it as riding your 10-speed bike in a really low gear. You leap off the line, pedaling madly, while reaching for the gear shift lever. Imagine that your legs are so strong that as the bike jams into the next gear ratio, you overcome the sudden deceleration of your pedalling that would have come with the new gear ratio, and the rear tire has no other choice but to spin, since your legs manage to keep pedalling at close to the same speed. Eventually, the tire grabs and your pedalling slows to match the proper speed for that gear.

In the above analogy, your engine is the legs doing the pedalling. The nice solid bang gear shift is the 4R70W shifting with more aggressiveness due to the Microtuner's settings. More than likely, your engine is stout enough to resist the slowdown of the gear shift, and the driveline shock of the upshift broke the tires loose... momentarily.

[LVMarauder]

now THAT is the type of explination I am most grateful for. that makes sense, i just hope im not tearing up my tranny doing that. Thanks for the tech talk TTA.

[gilby04]

TTA,
Well said.
Contact friction is difficult to overcome by pedalling...unless downhill.

[SergntMac]

I hope I'm not starting ANOTHER tranny thread, please hold your thoughts for the best thread on transmissions.

LV...As long as your speedo is showing this jump, your tranny is fine. You "got a patch" at the 1-2 shift, thats all. Remember, these BFGs do not make a lot of noise when they spin. Now, if your Tach was doing this, I'd say your tranny is slipping, or, heasitating as it will do from time to time. Slow filling accumulator pumps are something you can address if it's a consistent problem.

Tuning from a Reinhart chip, a Jerry Dyno tune, or, the SCT hand held programmer can only improve the electronic side of 4R70W transmission behavior. Shift timing and punctuation can be manipulated with very positive results. However, there is a limit, a physical limit to this tuning inside the tranny.

There are 3 accumulator pumps playing a serious role in shifting by filling with fluid and releasing that to force the shift. How fast the pumps fill and release is a physical mod inside the tranny, and I suspect that improving this function, is one of the reasons the '04 gets the refined 4R75W tranny.

Tuning by chip will bring you to the point where the pumps need to be modified to further refine shifting. How these modifications can be had is talked about quite a bit in other threads, and I don't want to start another discussion here.

Watch for more good 411 from Brad (BBOCKSTANZ) from Pande's Performance, one of our vendors here, and post your questions to him, please. I've met Brad and Pande face to face, and they are an asset to us MM owners up here in the MidWest regions of the country. They also mail-order parts and kits. Out west, there is Art Carr, and in the east, Performance Automatic, both familiar with the MM tranny and it's unique behavior, but they are not vendors here. Dennis, of course, does it all.

Trannies...Getting to be a piece of cake, eh?