Whats worse in roll racing?4L60E
03-06-2015, 09:48 PM
#1
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Whats worse in roll racing?4L60E So people talk about roll racing and autos and everyone has their different approach. Leave it in od, d, shift manually. I get that you have choices.
Id like to hear from the trans guys. Ive been out of the trans rebuilding game for a while. When you physically put the car in 2nd gear going about 40 mph would that be better than lets say leaving it in d and letting the trans do a harsh downshift? After wot in 2nd I would click it back to d to let the trans shift on its own
From a trans builders view and from someone who knows whats actually going on in there what is better?
Thanks
Id like to hear from the trans guys. Ive been out of the trans rebuilding game for a while. When you physically put the car in 2nd gear going about 40 mph would that be better than lets say leaving it in d and letting the trans do a harsh downshift? After wot in 2nd I would click it back to d to let the trans shift on its own
From a trans builders view and from someone who knows whats actually going on in there what is better?
Thanks
03-07-2015, 02:36 PM
#3
Moderator
+1 ^
Several pro trans builders have told me and posted that 4->2 downshifts are especially hard on a 4L60E, particularly on the already marginal 3/4 clutch.
Several pro trans builders have told me and posted that 4->2 downshifts are especially hard on a 4L60E, particularly on the already marginal 3/4 clutch.
03-07-2015, 08:21 PM
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Right I never do anything in od. I am between leaving it in d for 30 to 60 mph rolls or manually putting it in 2nd then shifting to d as soon as I hit it
03-07-2015, 11:36 PM
#5
There may be other factors that I'm not aware of, of course. But I've been involved in other threads on this topic over the years and haven't gotten a satisfactory answer as to why the 4>2 is so bad.
Other than that, in roll racing situations, the only way to go 4>2 automatically is to go WOT. I would do as you suggest - manually select 2nd, rev matching, of course, and then go WOT.
03-08-2015, 12:52 AM
#6
I've heard this said, but I don't understand it. Since the topic is what's happening internally, on a 4>2 downshift, the 3-4 clutch pack is released. On a 3>2 downshift, the clutch pack is released and the band engaged, which is certainly a more complex if not failure-prone process.
There may be other factors that I'm not aware of, of course. But I've been involved in other threads on this topic over the years and haven't gotten a satisfactory answer as to why the 4>2 is so bad.
Other than that, in roll racing situations, the only way to go 4>2 automatically is to go WOT. I would do as you suggest - manually select 2nd, rev matching, of course, and then go WOT.
There may be other factors that I'm not aware of, of course. But I've been involved in other threads on this topic over the years and haven't gotten a satisfactory answer as to why the 4>2 is so bad.
Other than that, in roll racing situations, the only way to go 4>2 automatically is to go WOT. I would do as you suggest - manually select 2nd, rev matching, of course, and then go WOT.
You go from over-running the forward sprag in OD, to locking it on a 4-3 shift. You also go from the rev input drum and sun shell being static in 4th, to spinning up to engine speed (input shaft speed actually) in 3rd, almost instantaneously. This can cause the tangs on the sun shell to expand from centrifugal force, they get into the case, case gets sawed in half, explosion or something close occurs.
3-2, the opposite occurs. Rev input and sun shell go from spinning engine speed to slamming to a stop.
Automatic transmissions generally work on these principals but the 4L60E has some odd powerflow relatively.
03-08-2015, 12:58 AM
#7
Also on a 4-2 or 3-2 downshift, the 3-4 clutches have to release, which means as they are trying to exhaust, so is the inner portion of the servos. You never get a clean release of 3-4s on a 3-2 downshift because there's too much volume to exhaust, and it has to time with the band. You get to "perfect" the upshift timing of the 2-4 band release, and the 3-4 clutch apply on the 2-3 upshift, but you don't get to perfect the downshift too. It's along for the ride. Whatever you do on the upshift calibration (feed hole and exhaust hole sizing, servo size, band size, 3-4 friction area, 3-4 clutch return springs, servo release capsule, servo spring) all has a play on the release too.
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03-08-2015, 07:22 AM
#8
You go from over-running the forward sprag in OD, to locking it on a 4-3 shift. You also go from the rev input drum and sun shell being static in 4th, to spinning up to engine speed (input shaft speed actually) in 3rd, almost instantaneously. This can cause the tangs on the sun shell to expand from centrifugal force, they get into the case, case gets sawed in half, explosion or something close occurs.
What's the difference between the driver doing the downshifting and the computer doing the same thing?
03-08-2015, 10:38 AM
#10
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Thanks to Jake for a good explanation of the issues.
03-08-2015, 10:52 AM
#11
TECH Junkie
I'm glad this topic was brought up again, I have read many threads on this and always get turned around lol
So to try and get a definite opinionated answer.......
Say I'm cruising at 60mph and want to get ready for a roll race, my best option in your guy's opinion would be to slow down to say 45mph and speed match it into second instead of a wot 4-2 downshift correct?
So to try and get a definite opinionated answer.......
Say I'm cruising at 60mph and want to get ready for a roll race, my best option in your guy's opinion would be to slow down to say 45mph and speed match it into second instead of a wot 4-2 downshift correct?
03-08-2015, 12:56 PM
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Ya that sounds like the plan. I think the point is there is never really a good time to do a 4-2 downshift. If your going more than 60mph I'd say speed match down to 3rd then go wot. 30 to 60 speed match to 2nd go wot then immediately shift into d.
How does that sound?
How does that sound?
03-08-2015, 02:10 PM
#13
It's more than just the clutches/bands. You go from over-running the forward sprag in OD, to locking it on a 4-3 shift. You also go from the rev input drum and sun shell being static in 4th, to spinning up to engine speed (input shaft speed actually) in 3rd, almost instantaneously. This can cause the tangs on the sun shell to expand from centrifugal force, they get into the case, case gets sawed in half, explosion or something close occurs.
Let me raise another question. You speak in terms of 4>3, not 4>2. Is this because in the 4L60e, a 4>2 shift in effect a 4>3>2 shift? In the other words, band releases, 3-4 clutchpack releases, band re-applies. Or does the band simply stay applied? This has also been discussed with no resolution on here.
I think we're all in agreement on roll racing. You want to manually downshift rev matching at part throttle to the gear that gets you into the peak of the powerband and then go WOT.
03-10-2015, 07:26 AM
#14
Ended up over running the forward sprag, breaking OD and expaned the sun shell. From that point forward performabuilt told me to always shift the car from rolls.
03-10-2015, 03:50 PM
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Guys please don't turn this into an anti roll racing thread. There is good info here. I drag my car all the time, it has a tbrake and pulls the front wheels. But I drive on the street a lot in Chicago and some times run into stuff on the highway. That's my purpose for wanting to know how to roll race my auto properly.
Ok
Ok
03-10-2015, 05:38 PM
#18
Guys please don't turn this into an anti roll racing thread. There is good info here. I drag my car all the time, it has a tbrake and pulls the front wheels. But I drive on the street a lot in Chicago and some times run into stuff on the highway. That's my purpose for wanting to know how to roll race my auto properly.
Ok
Ok
Oh wait you're suppose to come to a dead stop on the freeway and run a realms race from a dig
Back on topic....
03-11-2015, 01:37 PM
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Alex, as your trans was built by FLT have you tried asking them this question? It's been ~10 years since I bought a 4L60E from them (that trans was my favorite part of the car), but I don't remember any specific instructions in this regard.
I agree. The expert opinions seem to range the spectrum over the years of this debate, but I've yet to see anything that has me convinced that one process is "good/safe" while the other is "bad/harmful" in comparison, in terms of 3-2 vs 4-2.
I really don't see this as necessary either, at least not for applications at or near stock power levels, considering the factory setup allows for auto downshifts from 4-3, 4-2, and 4-1. My personal experience has been such that neither manual or auto downshifting has ever caused me to lose a 4L60E prematurely, in applications ranging from stock to cammed/full bolt-ons. In fact, out of six 4L60Es, the only one that I ever lost was a poor quality "built" unit that started having issues right away with just normal street driving. For a long time I daily drove my mild bolt-on '02 Z28 a ton of miles on the expressway, doing many 4-2 auto downshifts at highway speeds. Even at ~110k miles when I sold it, the stock trans was doing perfectly fine without even the hint of an issue.
As power level and shift rpm increases, I suppose weaknesses will become more evident and then any process that can be used as a crutch to aid said weakness will be beneficial to trans life.
As power level and shift rpm increases, I suppose weaknesses will become more evident and then any process that can be used as a crutch to aid said weakness will be beneficial to trans life.
03-11-2015, 09:54 PM
#20
My personal experience has been such that neither manual or auto downshifting has ever caused me to lose a 4L60E prematurely, in applications ranging from stock to cammed/full bolt-ons. In fact, out of six 4L60Es, the only one that I ever lost was a poor quality "built" unit that started having issues right away with just normal street driving. For a long time I daily drove my mild bolt-on '02 Z28 a ton of miles on the expressway, doing many 4-2 auto downshifts at highway speeds. Even at ~110k miles when I sold it, the stock trans was doing perfectly fine without even the hint of an issue.
My point about manually downshifting doesn't pertain so much to the potential for damage, but to the best technique for roll racing. In other words, you don't want to be rolling along in a high gear, stomp it and wait for a shift. You want to already have it in the meat of the powerband, stomp it and go.