Late Model Transmissions

[Texas1911]

My friend's 4.8L 2000-ish model GMC has eaten through a number of transmissions thanks to a healthy nitrous shot and some bolt-ons. If I were to open the motor up with a decent cam, intake, and header back exhaust would I be really pushing the transmission?

 

[Texas Jim]

I am assuming 1/4 mile and maybe some street racing...correct me if I am wrong.

Do you have a "GOOD" high capacity trans cooler?
Has the shift points been changed from stock?
Has the LINE PRESSURE been raised to enable quicker, firmer shifts?
Have the clutch packs been replaced with performance versions?
Has the transmission pan been replaced with a higher capacity pan?
If so...Does it have cooler tubes in it?

You say he has gone thru "SEVERAL" transmissions...
What has been done to the trans to try to increase it's life?

You/he, may want to consider a "BUILT" transmission to handle the extra power with out having it break so often.
And put a good cooler on it.

You are generating a tremendous amount of heat when running it hard, and heat is the major enemy of automatic transmissions.

You absolutely have to be able to get rid of the heat, or they will continue to fail...no matter WHAT kind of automatic transmission you use.

I like big, oversized Hayden or B&M transmission coolers.

 

[Texas1911]

His were stock transmissions, maybe a B&M cooler on it. Not sure.

I would plan to run an upgraded trans cooler, and not jack with the line pressure. I would probably change the shift points, but that would depend on the cam. Odds are, without replacing the heads, I'd stick with a moderate street cam.

He has a built transmission right now, and is planning a low boost single turbo setup.

 

[Alljackedup408]

what is it? 4l60e im assuming?

 

[Texas Jim]

A moderate street cam and a good set of long tube headers sound like an excellent idea.
Shorties wouldn't even by on my list for consideration.
Long tubes or keep the stock manifolds.

A turbo setup is going to increase the power a lot.

Upgraded transmission cooler is also a good idea.
You may want to also check into an oil cooler if you are going to be running it hard.

Who built the trans?
Was it built for performance?
If so, it probably already ahs a shift kit in it, but..if not...
A good quality "SHIFT KIT" would probably do wonders for the longevity of the transmission.

The reason I mentioned line pressure, is that a moderate increase will reduce the amount of time it takes to completely go from one gear to another gear.
The entire time it is actually SHIFTING GEARS...it is slipping when coming out of one gear and slipping going into the next gear.

This generates a lot of heat, especially when you are increasing the HP over stock.

A shift kit will take care of a lot of that.

I am sure that you know this already...but...
When it shifts from 1st to 2nd...the bands and clutches start to DISENGAGE from 1st gear.
At the same time, the bands and clutches start to ENGAGE for 2nd gear...the entire time, as it is going from one gear to the next...it is slipping, generating heat and causing wear on the bands and clutches.

The more power the more slippage and heat.

Making it shift QUICKER and FIRMER will reduce the slippage accordingly.
On the other hand...you don't want it just BANGING into gear every time it changes either.
That will also break parts due to the SHOCK of making it just BANG into the next gear.

It is also not very enjoyable to drive one on the street that shifts TOO HARD.
BTDT...didn't like it.

One more thing...don't overlook the extra heat generated by the torque converter when POWER BRAKING it before a run.

 

[Texas1911]

I'm not going to bother with power braking and all that mess. I just want to build a fun street truck. If it's going to replace my M3, it needs to sound good and be somewhat quick.

I've had only one automatic car my entire life, I don't really like them, but manuals in a truck aren't quite the same as in a car. I'm kinda leery of jacking with the transmission; one of the reasons why I prefer manual.

 

[Texas1911]

what is it? 4l60e im assuming?

Believe so.

 

[Alljackedup408]

if yah dont wanna take the transapart.. then jim nailed it. BIG cooler, perferably with its own fan, line pressure.. theres a solenoid on the valve body, its got a torx screw on the back of it, crank it about 1/8 to 1/4 turn. Itll boost the pressure and the trans will shift alot firmer. Stick a good 2 - 4 servo in it.. which is right on the outside of the case. A transgo shift kit would do the trans good as well. and put a bigger pan on the transmission, the more fluid the better.

 

[Zembonez]

Rear end gears are a biggie in making a 4L60 live under a little added power. Going with 4:10s instead of OEM gears lessens the load on the trans at launch where a lot of transmission damage occurs.

Gas mileage is going to SUCK.

 

[Texas1911]

Rear end gears are a biggie in making a 4L60 live under a little added power. Going with 4:10s instead of OEM gears lessens the load on the trans at launch where a lot of transmission damage occurs.

Gas mileage is going to SUCK.

My friend installed 3.73s in his truck and it woke it up quite a bit.