I noticed after installing my transgo hd2 shift kit the trans does what I can only describe as a double downshift, it seems to do a mild downshift before doing the main downshift. Is this normal? I actually like how it does it but not really sure if its meant to happen but it must be normal because I 100% did everything as perfectly and methodically as you could possibly do it.

 

Is this occurring from 3rd gear to 2nd gear?

Which Servo are you using for the band?
What is the Band clearance?
What is the 3-4 clutch clearance?

What is the 3rd Accumulator orifice size?
What is the 3rd Exhaust orifice size?

 

No, it is not normal. We don't want there to be excessive slippage as that quickly wears out components. Hence vorteciroc's question to you. Do you have a trans pressure gauge? If not, it might be a good time to order one - AT5550 on Amazon for $35.

 

I'd say it happens from 3rd gear to 2nd gear yes.

Never touched the servo because I had no access to it so skipped that part. Servo is stock. And didn't touch the band clearance either.

Not sure what you mean by the 3rd accumulator orifice size are you talking about the separator plate hole sizes?

I just installed the kit exactly as the instructions said. Also installed the transgo hardened separator plate, all new solenoids (except epc), and a new pressure manifold switch (updated design with white plastic on one side)

Everything was installed very carefully and double checked, nothing was rushed or forced. The kit was installed with transmission still in vehicle.

 

By slipping do you mean when you try to accelerate and the rpms just go up high and the car either barely accelerates or doesnt accelerate at all like its in neutral? because this transmission has never done that. it just does a very quick mild downshift before it does the main downshift kinda feels like the trans has an extra gear and is "stepping up" and should have mentioned that it doesn't do this all the time mainly on steep hills it will do it.

The transmission functions exactly the same as it did before I installed the kit except for firmer shifts and this "double downshift" which doesn't bother me at all but just curious why it does it.

 

It would be very helpful to know the band clearance. While holding a small ruler next to the servo cover, press on it with crowbar and tell us how much it moves. 1/16" to 1/8" is correct amount; much over 3/16" indicates a worn band.

I'm not being critical here, but...
You say "I just installed the kit exactly as the instructions said", yet the instructions do specify changes to the servo and you did not make them. The mods to the servo are designed to work with the mods to the separator plate.
Again, not being critical - you have done more work on your trans than even 95% of mechanics would attempt themselves. Be proud of it!

The trans is in either a gear or in neutral. There is no "mild downshift" and "main downshift"; these sounds like slippage or even a bind.

 

I think I understand exactly the condition that the OP is describing. Many years ago I had a "built" 4L60E that did the same thing; it would rarely complete a 4-1 downshift as a single event. Instead, it would complete a 4-2 downshift and then a 2-1 downshift as a separate event immediately after the initial downshift (what the OP is describing as a "mild" or soft downshift). This would happen at speeds when the proper command was in fact a direct 4-1 downshift, and the previous trans had no problem executing the task. I lived with this for about a year before the trans began to have other issues, and then I replaced it with a much better unit. The new "built" unit did not have any problems in this regard at all, further indicating that it was not an issue related to tuning, etc.

Unfortunately, upon tear down the old trans revealed many problems and premature wear to several items, so there is really no way of knowing which part (or combination of parts) were responsible for this behavior. But I just wanted to indicate to the OP that I was familiar with this condition and it started happening immediately after the first "built" trans unit was installed, much like his condition began immediately after installing the shift kit. There could be more than one cause for such a condition, but if yours unfolds anything like mine then it's not a good indicator of future transmission durability (though there still may be time to correct yours if it was just a kit install error of some sort).

 

for anyone reading...please PLEASE do not do 4-1 downshifts

unless you want the reverse input drum to to eventually cut the case in half

no...I'm not exaggerating

 

The factory tuning does allow for this, it's especially noticeable on the 2.73 geared cars where a downshift to 1st will occur at up to ~37mph (which is already into OD if TPS % is low enough). I suppose this is a more critical concern as power level increases. On my '02 Z28, which was just a stock daily driver, I allowed this factory setting to remain for the full ~110k miles that I owned the car and the original trans showed no signs of failure. Have you frequently seen this sort of outcome even at stock power levels?

 

The issue is that the Reverse-Input Drum has to violently start to accelerate (to 3 times engine RPM) in the opposite direction of engine rotation, from having been at a complete stop.

 

As this condition is sure to occur under certain circumstances when going WOT, is there a recommended mitigation technique such as manually downshifting to D (3rd) before going WOT in that speed range (thus prompting a 3-1 auto downshift vs. 4-1)? The only other way to avoid it would be with custom tune changes to shift speed tables, which may not be part of the plan for folks with otherwise stock vehicles, or to not ever go WOT from a steady cruise state in certain speed ranges.

 

vortec hit the nail on the head...not surprisingly!

At a minimum, pull the shifter into d3...preferably on any rebuilt unit, you install the sonnax HD 2-3 shift valve

and Yes, I've seen a stock 5.3 in a truck literally cut the case in half until it was leaking all around the case. It towed small car trailer alot and made endless 4-1 downshifts.
When I got it apart, a swift "pop" with the dead blow and the case opened up along the seam that was cut. Just the valve body casting was holding it together

I've seen signs of this in many other cases. Most of the time it's not bad, but the lugs will be flared and you'll see some "witness marks" that they have been rubbing the case

 

This is why you see the fingers on some drums flared out ?

 

Yep precisely
It happens on 4-1 downshift because the input sprag is not holding and when the band releases, under power, the sprag "slips" before it holds
that allows the drum to over-rev and the lugs flare

having the sprag in a "holding" situation in 3rd (especially with the overruns applied if using the HD 2-3 shift valve) will save alot of headache

 

I forgot to mention the OEM/ Stock 1 - 2 Shift Valve-Train design of the 4L60E Transmission Family...

The PCM and 1 - 2 Shift Valve-Train allow for an Up-Shift from 1st to 2nd Gear; when the Gear-Selector is in the Manual 1st-Gear Range.
In many scenarios, this is a good thing... as it helps protect both the Engine and Transmission from Over-Speed/ Revving.

The TransGo 4L60E HD2 "Shift-Kits/ Reprogramming-Kits" , provide a replacement 1 - 2 Valve-Train that does away with the Stock-Function/ Safety Feature that I mentioned above.
This is what TransGo means, by saying that 1st-Gear can now be held to any RPM (engine speed).
The TransGo 4L60E HD2 1 - 2 Valve-Train does have its place... I do like to use it when I convert the 4L60E to a Full-Manual Forward-Shift Valve-Body without the use of any Shift-Solenoids. I do Retain the EPC solenoid that operates with a TPS.

I bring all this up, because in some situations... pulling the Gear-Selector down to the Manual-1st Gear-Range from OverDrive...
The Transmission will not actually go into 1st-Gear... But instead go into 2nd-Gear, until the vehicle speed decreases.
So here again; this is a benefit of the Stock 1 - 2 Shift Valve-Train.

When Down-Shifting from 4th-Gear to 2nd-Gear... The Reverse-Input Drum remains held by the 2-4 Band/ Servo...
Simply the 3-4 Clutch releases.
This is a far better scenario, than a 4th to 1st gear change.

 

And the pretty silver pearl flake left in the trans fluid. It really sparkles in sunlight.

If you’re boosted, say 10-12psi on a PD blower, you can expect to get 2, maybe 3 4-1 downshifts before the tangs/tabs start cutting into the case.

Ask me how I know?

 

Understood, and great insight as always.

But a downshift to 1st gear is sure to happen with stock tuning when going WOT up to a certain speed, including from OD in some circumstances. So, based on this...

...it seems that the better option would be to manually select D3 prior to WOT when at speeds where a downshift to 1st is expected to occur. Is this the general consensus?

 

Yes.

 

Will get the servo measurement in next few days. Am still planning on installing the corvette servo, found out if I unbolt trans from rear mount I should be able to lower it just enough to be able to take the servo out. The reason I call it a mild downshift is because that's exactly what it feels like, it physically feels like a downshift but just softer and then the real downshift comes right after it.

 

I've got another question that i'd appreciate if someone could answer for me, when I was drilling separator plate holes my instructions didn't say to drill this hole in the top right corner but everyone elses instructions shows to drill it. I assumed transgo has modified their kit or maybe i got dud instructions? can post picture of my instructions it has no mention or arrow pointing to that hole