Launching with a 4L60E

The 4L60E has a serious "design flaw" that GM blessed us with. When you launch a car with one, the whole weight of the vehicle is on the input sprag. The input sprag is a one way clutch. In the late 700R4s, GM switched manufactuerers of the sprag elements. This changed their design to a much weaker style. We upgrade ALL of our 4L60Es to the Borg Warner "dual cage" 29 element sprag. While these will take much more abuse, the sprag is still a weak area, especially in heavy vehicles.
In a stock (or most BUILT transmissions), there is a way to help keep the sprag alive. If you pull a 4L60E to manual 1st or 2nd, you bring the over run clutches on. The over runs hold the over run hub of the input sprag, which takes some strain off the sprag itself. You're launching on the sprag AND the over run clutches. While this helps the sprag, it brings up a few other issues. Most stock (And even many modified) 4L60Es don't like to be manually shifted...Especially at high RPMs. A stock 4L60E is designed to start dropping pressure at 5000 RPMs. Obviously, if you launch in manual 1st, you have to make atleast 2 manual upshifts. If you launch in manual 2nd, it will make an automatic 1-2, but you'll still have to make a manual 2-3. This is applicable in MOST vehicles, but some are set up to start in 2nd gear if the shifter is in manual 2nd. This is a computer tunning thing. Now, if you're pulling alot of gear, you may have to use O/D in the quarter mile. That means one more manual upshift.
Most build manuals list the over run clutch as being applied in manual 3rd. This is partially true, but is deceiving. The over runs ARE NOT on in 1st or 2nd...They come on in 3rd...When you DON'T need them...LOL This also makes the over runs a "timed engagement" which isn't good for them.

So, how do we fix this? Our "Pro Race" transmissions are modified so that the over run clutches are applied in manual 3rd. This means you have sprag protection, and you can race the car in D. We do have several customers pulling alot of gear and running alot of MPH so some are making a manual 3-4 upshift.

Frank

Made this a stickie. Very good info Frank. A good way to eduacate our fellow members.

question: I have an early 700r4 that has been converted to full manual valve body, and is set to keep constant pressure. Is this sufficient to protect the sprag? And what risks would be posed launching the car in second over first gear?

If this is getting to far off topic I will delete and start a new thread.

Great information, thx for posting.

These all need to be merged and pinned to the top, lot of good info here. Its good to see some of this "witch doctory" stuff explained. When I look at a transmission I'm looking for the rated HP and price tag. Frank you might just talk me into a 60e yet!

Edit: thanks for the sticky!

Quote:

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Originally Posted by Ray@NitroDaves.com

question: I have an early 700r4 that has been converted to full manual valve body, and is set to keep constant pressure. Is this sufficient to protect the sprag? And what risks would be posed launching the car in second over first gear?

If this is getting to far off topic I will delete and start a new thread.

Great information, thx for posting.

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Actually, the 700 is different. The over run clutches are applied in manual 3rd. Does your manual VB still have engine braking? It's best to launch in 1st gear. Leaving in second is hard on the band.

Frank

Yes it still has engine braking

Quote:

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Originally Posted by Ray@NitroDaves.com

Yes it still has engine braking

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If you notice, you should have engine braking in manual 1st, 2ns and third. The over run clutches are what give you engine braking.

Frank

That's what I thought, just wanted to make sure, I plan on leaning on the transmission a lot harder this year than I have in the past.

Frank,

You said above some are running a lot of gear and MPH and having to make the 3-4 shift, what kind of gear are you talking? We're running 4:10 in the rear and through the traps ET was 11.82 @ 114.3 this weekend with a 1.58 60'. The cars been getting quicker through the season. RPM was very high and I had to make the 3-4 shift between the 1000' and 1/4. The trans is stock and has a 3000 stall. There is some slippage, probably 500 passes on the converter and who knows on the trans, was in the car when purchased. Was thinking about putting in a built TH350 that we have but maybe we should have you rebuild the 4L60e? Any thoughts?

Thanks
Dan

Quote:

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Originally Posted by Dannyac500

Frank,

You said above some are running a lot of gear and MPH and having to make the 3-4 shift, what kind of gear are you talking? We're running 4:10 in the rear and through the traps ET was 11.82 @ 114.3 this weekend with a 1.58 60'. The cars been getting quicker through the season. RPM was very high and I had to make the 3-4 shift between the 1000' and 1/4. The trans is stock and has a 3000 stall. There is some slippage, probably 500 passes on the converter and who knows on the trans, was in the car when purchased. Was thinking about putting in a built TH350 that we have but maybe we should have you rebuild the 4L60e? Any thoughts?

Thanks
Dan

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Dan, This also depends on max engine RPMs. I was making a 3-4 shift in my Z when I had 4.10s in it, crossing the line at 112 MPH, but my shift light was set at 6000 RPMs. Another example is the 9.91 B-Body we built the trans for. He's running 4.10s and crossing the stripe at 139 MPH but his shift RPM is substantially higher.

Frank