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4l70

ajswenson

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ajswenson Enthusiast

ajswenson

Posted
Posted

Hey guys I have a Vmax with the 4L70 in it. Plans for it include CAI, exhaust, and a tune for sure and that is probably it engine related. Anyway, I was wondering what your thoughts are on putting vette style servo in and leaving it at that. I put an HD2 kit in my old 5.3 and the shifts were pretty harsh, not sure it is what I am looking for. I really don't care about having the harsh racing shifts, I just want to make sure my tranny doesn't go out from removing the TM. Would there be any benefit from doing just the servo? If i understand it correctly the servo and the SK apply more pressure to the clutches in turn decreasing slippage and ultimately prolonging the life. (the servo is easy and i'm not sure I feel like pulling apart the valve body again it was kind of a pain in the ass)

Rat4go Enthusiast

Rat4go

Posted
Posted
Hey guys I have a Vmax with the 4L70 in it. Plans for it include CAI, exhaust, and a tune for sure and that is probably it engine related. Anyway, I was wondering what your thoughts are on putting vette style servo in and leaving it at that. I put an HD2 kit in my old 5.3 and the shifts were pretty harsh, not sure it is what I am looking for. I really don't care about having the harsh racing shifts, I just want to make sure my tranny doesn't go out from removing the TM. Would there be any benefit from doing just the servo? If i understand it correctly the servo and the SK apply more pressure to the clutches in turn decreasing slippage and ultimately prolonging the life. (the servo is easy and i'm not sure I feel like pulling apart the valve body again it was kind of a pain in the ass)

 

 

 

The Vette servo will give you firmer 1-2 shifts and influence how your 2-3 shift (and 3-2 shift) happens.

 

Keep in mind that the 2-3 (and 3-2) shift involve 2 clutches (or actually a clutch and a band) with one coming on and one going off. If you mis-time how they work due to your changes, bad stuff happens. On a 2-3 shift, if you let go of the 2-4 band too soon before the 3-4 clutch is applied, you get a moment of 'first gear' before the 3-4 clutch grabs and pulls engine down to 3rd. You're working the 3-4 clutch harder to pull the engine down from the momentary first gear state. If you grab the clutch before the band lets go completely, you get a moment of 4th gear before the band loses capacity and you get third for real. Now you're trying to use the 3-4 clutch to basically go from 2nd gear engine speed to 4th gear engine speed for a moment. Both situations can work the 3-4 clutch more that if the 'handshake' between the band and clutch is timed correctly.

 

From what I've read, the trans hardware and TM both work to help that timing be correct. At low power levels, you probably won't hurt anything too bad if it's a bit off, but at WOT, you run the risk of roaching things (sooner) without the TM if the trans hardware is set up assuming the TM is there.

 

Maybe I'm just gun shy, but I'd be reluctant to remove the TM on a newer vehicle that you were planning on keeping for a while. On an upshift, you're going from a faster engine speed to a slower one and the clutches are what's slowing the engine down...it seems to me that TM might help get the engine to the slower speed 'quicker' that if you didn't have the TM.

 

Think of it this way.....For upshifts, clutches are like the brakes on your truck when you're towing a trailer, and having engine mods that make more power is like towing a heavier trailer. Truck brakes are there to slow things down and so are the trans clutches.

 

TM is like having a brakes on the trailer, too...you could slow the truck down without the trailer brakes, but the truck's brakes will wear quicker or they'll need to be upgraded if you don't have the trailer brakes to help slow things down. Tow heavy without trailer brakes and you're really asking for brake issues. Run higher power without TM and you're asking for clutch issues.

 

Because TM only happens during the shift, I'd be suprised if TM cost you any significant performance on a WOT run. You might see it on the strip, but in normal driving, do you really notice the performance improvement, or is it just a 'feel thing'?

 

If it's just the firmer shift feel during normal driving that you're after, there are cleaner ways to accomplish this in the 4L60/70 without risking the durability of the clutches, but you need to know what shifts you're going after, and under what conditions (light throttle, medium throttle, WOT, etc). This means you have to do some homework to figure out the right way to do it (or just let someone else do the homework and live with what they decide is an OK risk/reward for your truck).

 

I killed 2 sets of 3-4 clutch plates in the 4L60 in my carb'ed big block Camaro before I pulled out the shift kit from a 'big name company' and did my own targeted mods. I have another 30,000 miles on my Camaro and a whole bunce of strip passes, and all is good. I got less than 5000 miles total on 2 sets of 3-4 plates with the shift kit. They said they tested their kit in a trans behind a 550+ HP big block, and since I wasn't making that kind of power, I'd be OK. Apparently, their 'testing' was a few strip passes to make sure it didn't blow up. Needless to say, I'm done trusting others as they aren't the ones pulling my trans and replacing my burnt clutches.

 

Interesting note....most if not all of the 'new' 6-speed truck transmissions use the '2 clutches involved' methodology for all the shifts. Gone are the days when you could just boost line pressure and drill out a couple spacer plate holes to get firm durable shifts. Now you better trust the guy doing your 'tune' and have him warranty his work from a trans durability perspective if you plan on keeping your truck for a while!

pj5454302 Enthusiast

pj5454302

Posted
Posted

Well i rarely race my truck and when i do i shift fast enough to stay a head of automatic versions of my truck. I prefer manual to automatic anyways beacuse you have less problems with them so there. :confused:

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