BudH

iTrader: (3)

Like the title says, why not if the tranny is built for it?

Also, what parts are really stressed (will break) by WOT shifts into OD?

radz282003

iTrader: (1)

My understanding is there is not enough strength in the clutches to hold the power. When I was at the dealership, I had seen trucks and vans come in, with mid-sized trailers, pulling in overdrive, and burnt the tranny up. I have seen most builders add discs in these clutches to add strength and in fact, a 4L65E has more clutches, among other things, to accomidate extra power and higher loads. Overdrive is designed for lower wear-and-tear and better fuel economy. It' s not there to go faster.

spy2520

iTrader: (3)

i think the stock OD clutches are some weak paper ****. and you dont hit OD until pretty high on the speedo in most cases anyway...

Camaroz

iTrader: (2)

I've only shifted into overdrive at WOT once and it was a good kick but i know its a weak gear so I left off.. I didn't even know how fast i was going until it shifted.. suprised me pretty good

BudH

iTrader: (3)

FYI, the 4L60 shifts to OD on the Band, not with clutches. The clutches are used for the 2-3 shift. The power flows thru the 3rd gear clutches but they are already fully engaged at the 3-4 shift. I've already replaced the 3-4 clutches with a Rabestos Z-Pack. The band I'm using is a Rabestos Kevlar band shifted by a billet 4th gear servo. Line pressure is about 15 percent above normal.

Also, the shift speed would be around 115 - 120! I hope to trap about 128 - 130 this year. I have upped the boost by 2 lbs and don't want to rev the motor as high (too much boost there). I'm trying to decide whether to change my rear end from 3.73s to 3.42s so the tranny won't have to shift to 4th or run it as is.

Rock-On

iTrader: (-2)

I don't know...I tell my guys to drive the car...we see higher pressure in 4th with less of a pressure drop, and faster pressure recovery on the dyno in 4th versas 3rd...this is a built tranny i'm useing for my comparison...hope this helps Dave

SSHOTROD

iTrader: (5)

have you considered running a larger tire? my second choice would be lower gears

chris718

the 3/4 clutches are on in 4th gear and if they werent with band applied it would go back to second.NOW here is how the 700 works:first gear front planet is on in reduction,second gear front planet is still on but overdriven by the rear planet,third gear by driving the reaction tube and rear carrier the pinions cannot rotate thus the front and rear sets are locked together.fourth gear the rear planet produces overdrive ratio by once again holding the rear sun gear as in second except the front planet is inneffective as the reaction shaft drives the rear carrier causing the pinions to rotate in the rear carrier around the grounded sun gear thus driving the rear ring gear and output shaft.so with this known it would infer that the rear sun gear and drive shell are stopped instantly on a wot upshift and this can cause spline strippage without the use of a premium type shell.also power transmittal through the pinion gears from stationary in third to power transmission when overdriven can cause chipping.the reaction shaft is already in motion so it does not recieve a shock load.remember overdrive in general without the technical end is to provide an output speed faster than input .on the 4l60 not the 4l60e even with perfornmance valve bodies (except for a few)you cant auto shift into 4th at wide open throttle without backing out of the throttle enough to close the detent hole in the plunger that feeds the tv upshift circuit its shift delay oil (regulated from 0psi at closed throttle to 90 psi wot ).this allows the goverer psi to win the fight against modulated tv upshift oils influence in shiftvalve position at the tv upshift sleeve by reducing it to less than governer (also shift land diameter and a calibrated shift valve spring.with the new gm 5 pinion planets ,our heat treated reaction tube,e4340 output shafts ,and proper valve body calibrations id say your safe to about 450 horsepower with a genuiene wot upshift into 4th.this is with a functioning 4th accumulator circuit and one with the proper accumulator spring in the valve body for the application as well as finding a SMALL accumulator valve and bushing.ckperformance

blind527

iTrader: (8)

So If I want to drive "fast" on the street OR in the track and not caring about gas mileage, keep it on 3, and not D *D is obviously OD.* But keeping it in 3 will kill the tranny faster? This is with a 4L60E.

black 2001Vette,Nightmare

BadAzz...you gotta love HP transmission builders! I gotta lot of respect for people who are on top of their game!

Oh, and my advice is don't shift into OD @ WOT. I did it once while racing a Ferrari. Shifted into OD 'cause I ran out of cam/rpm...forcing me into 4th @ 6750 rpm. Instantly the DIC displayed *HIGH TRANS TEMP*. I checked my temp gauge, and it was @ 264', so I blew off the race(Ferrari already backed off at about 135mph) and slowed down to 55 mph until the temp dropped to 210...went immediately to a tranny shop...flushed the trans, in with fresh fluids...but too late...4th gear clutch was toast and the extra wide apply band I had installed was partially burned, and had to be replaced. Trans already had a billet servo, 9 red clutches, K. steels, extra wide band, and other upgrades, in case you're wondering. Bottom line...had to do a rebuild.
On the way to the tranny shop, in 4th the trans would slip up and down continuously which was driving me insane(would happen at any speed)like it wasn't locked or something. Spent a lot of time at my tuners thinking it was a programming or TC issue. We tried everything before I gave in and did the rebuild.

Hopefully my post will save you some grief.

black 2001Vette,Nightmare

Let's put it this way...when chillin' out, taking it easy, or on a road trip, or going to work 4th is a great gear to have, but when in a speed contest with lots of torque applied, and for relatively short distances, third is the preferrable gear to be in, IMHO.
Let me temper that by saying, it makes no sense to just stay in third on the highway because one is overly paranoid about transmission damage...not to mention the unnecessary rpm wear you would be accruing.

jimmyblue

iTrader: (11)

So is the 4th gear upshift a risk, but 4th gear WOT (once
shifted & settled) OK? I've seen tunes that held off the 3-4
altogether at WOT (255MPH shiftpoints in the part throttle
upshift table, at higher TPS). But supposing I really, really
wanted to go 150+MPH matted, is the trans capable of the
full torque pull once in gear? And, is making the tune require
athrottle lift to upshift a good (adequate) safety measure?

chris718

the first thought that comes to mind regarding omitting wot 3/4 ratios changes in a tune is to avoid a 3/4 ratio change at the track.this is done because a 3/4 ratio change is not needed and is counterproductive to a better time.if the car goes thru the gears that quick it is either running an improper final drive ratio or driving thru an inefficient fluid coupling in the converter.in my opinion and this is based on my years of in car testing combinations it will handle a wot 3/4 at the power levels i previously noted.after that the mechanical integrity of the internal components will be compromised.the 4l60 /e must use a throttle sensitive 3/4 accumulator circuit or you run the risk of snapping the band anchor,band anchor pin in the case,output shaft etc.many may say they have never seen these failures but they are real.we were putting 700 horsepower thru this design 8 years ago and broke everything we could.this layed a foundation for a new thought process to be implemented when building this trans for high torque loads.yes i feel it can take just as much power in 4th as it can in 2nd once the ratio change is made.i have one my my wifes 10.90 86buick gn that nets 18mpg on the hiway.ive had it in 4th on the cross bronx expressway at speeds of over 150 mphour at 28 psi of boost.

BudH

iTrader: (3)

I guess, from what I read here, that 500+ HP WOT upshifts to OD would probably be a No-No!

Thanks for the info!

buffman

iTrader: (9)

My car will actually shift into OD right around 100mph. I keep mine in third at the track. Then again I don't have a higher shift point like you F-body guys (I think the 3-4 is set at 5200rpm), and I'm running 3.73s with a 27" tall tire.

Now here's my question. Say by chance you enjoy making top speed or 120+ mph or whatever. Would it be "easier" on the 3-4 clutches if you made the shift at a lower rpm or a higher rpm?

SmokingWS6

iTrader: (1)

Oddly enough, as much as GM loves to add Torque Management they left out all related TM on the 3-4 shift. I have dumped a ton of 3-4 shift TM into my tune in hope preventing any damage. However my trans has only seen approx 5 to 10 wot 3-4 shifts in its whole life so no signs of damage have shown up.

Automatics

I have had many of my units doing WOT 3-4 shifts over the years. These are in vehicles running low 11's down to low 10's, with no problems at all. These don't see much of a gain (and you wouldn't expect to), but no loss in any case.

300bhp/ton

If there's so many problems with changing into 4th at WOT how do the guys get away with it when they run 3.73 or even 4.10 final drive ratio's.

I suppose the 3.73 would be ok if you up the rev limit, as 6000rpm is ~123mph on regular diamter tyres, so at the 1/4 mile you probably wouldn't go beyond it. But on the street (as 140mph races are pretty common) or with 4.10's how does the tranny survive??

obZidian

iTrader: (2)

When you say a bunch, how much tm are your running on the 3-4 wot shift?

jimmyblue

iTrader: (11)

I copied my 2-3 TM row to the 3-4 but I have also limited
the amount of spark pull, in the spark retard vs torque
reduction table, to 15 degrees tops and more like 10 at
the delivered torque level I produce. This makes for a
modest torque cut.