My first automatic tranny car; my question when drag racing do I use drive or overdrive at the tree. The car has 3.73 gears.
Thanks in advance.

 

For racing I would say regular D so you don't hit overdrive down the track. OD will slow you down in my opinion. Use OD on the street for fuel economy.

 

I have stock 3.23's and I wasn't even close to shifting into OD at the end of the 1/4, should have tried D but I honestly don't think it would have effected anything, especially on a stock'ish car.

 

just drive

 

Your transmission will not shift into OD at WOT. Just put in OD.

 

true story

 

If your talking about a 4L60E then I would put it in Drive, when the shifter is placed in the D position the over-run clutches come on and help the sprag out.

 

Problem is on a stock 4L60E, they don't come on until 3rd gear, so as soon as it tries to shift to 3rd, it also takes some of the oil away to apply the over-run clutches. The 3-4 clutches already have a tough life. Leave the shifter in OD on a stock 4L60E.

 

The 2 overrun clutches are on, applied, and holding anytime the shifter is in Manual Low, 2nd, and 3rd.

 

I have seen that chart in e.g. the ATSG manual, and I think it is wrong.
The GM HMTG (Hydramatic 4L60E Technicians Guide) has the correct table and in the [D] position the overrrun clutch is NOT applied in 1st and 2nd gear, only in 3rd gear.

And, Sonnax makes a 2-3 shift valve which adds overrun to 1st and 2nd gear in [D].

http://www.sonnax.com/system/announcement/77754-41.pdf

The table Sonnax shows on that page is the correct one.
In other words, if you want the "common" table that WRT posted, you have to install the Sonnax valve.

I will update this thread later today when I have the HMTG manual in front of me.
(Believe it or not, I run an Internet/software company, not a trans shop <grin>).

 

^^^^nice info^^^^

 

I never new about that part from sonnax but I am sure its out there. If you read thru the power flow in the HMTG that gm puts out starting on page 66B you will see that it says on the individual reference charts the over run clutches are applied in manual 3rd, 2nd, and 1st. But then in the overall range chart it does not show them as being applied. I can't find an explanation for this either.

Now I am sure they have always been applied in the 700r4 unit in 3rd, 2nd, and 1st. There may have very well been a shift strategy change for the 4L60E but all the charts except for the one on page 72 of the HMTG manual has always shown them to be applied. That said there is a reason why sonnax developed this valve I will have to talk with Greg or Robert at sonnax next week and get their opinion on this.

 

Thanks for the additional info!
If you have access to an expert knowledge at Sonnax that would be great to share here.
I don't feel like testing this myself (I recently ruined one valve body with my experiments). Also my current trans has the Sonnax valve installed.

 

That chart is incorrect as stated.

The Sonnax piece is an almost mandatory upgrade IMO.

 

Thank you for the confirmation Jake that this "common" chart is incorrect.
I installed the Sonnax valve because I want the overrun clutch applied the entire drag strip run to reduce the load on the forward sprag.

The correct chart has the Overrun Clutch "Off" in D for 1st and 2nd gear. This is correctly documented on page 11 of the GM HMTG manual:




Without the Sonnax valve, it is debatable whether D or OD is better for a drag strip run, although the concern about having to apply both the Overrun and 3/4 clutch during the shift to 3rd in D seems valid.
With the Sonnax valve, it it clear (to me anyway) you want to run in D and not OD.

 

I agree, Running in D3 is preferable with the Sonnax valve.

I've been doing some in depth 4L60E hydraulics R&D lately. I may have a REAL solution to help the 3-4 clutches as far as the 2-3 shift but it's all concept form at the moment.

I do have a 4L60E transbrake functioning though

 

I have a 3500 stall, b&m shift kit, yes it is a 4L60E.

 

What is the Sonnax valve, where can I buy one, thanks.

 

Its about $30:
http://www.transmissionpartsusa.com/...-007775441.htm

You have to remove the valve body and mod it by drilling a hole between two passages; so there is no going back.

WRT mentioned that the 700R4 definitely had the overrun clutches engages in D3 for all gears. I suspect that GM changed this in the 4L60e to "soften" the automatic downshifts in D3 as the car was slowing. I think we would all prefer the tighter feel of having the overrun clutches engaged in D3, plus it puts less strain on the forward sprag.

 

What will sonnax do for me as far as performance and durability? Thanks I'm clueless with autos, does it effect DD?