Corvette servo way too harsh on 1-2 shift

[CDeeZ]

I put a Vette servo in my daily driver a 2004 GMC Sierra.

Stock truck. I wanted to do the Vette servo after reading about it being a good upgrade for the 4L60. Not trying to do anything crazy, just looking to wring the most miles out of this vehicle as possible.

The 1-2 shift is very harsh SOMETIMES. Usually it is too harsh IMO. When I'm towing a trailer, it feels OK. But just light throttle cruising around it often shifts into 2nd gear in a manner that I personally feel is way too harsh.

What can I change to soften the 1-2 shift??? I have found this thread, but since it's so old, it seems that some of the parameters are in a different location with a different name??

https://forum.hptuners.com/showthrea...ed-Change-tune


I have tried copying some of the trans shift settings from a stock vette tune found on the repository. Doesn't feel like it's helped much...

I know the harsh shift can be quite subjective from one person to the next. This is MORE than a firm shift. Firm, positive shifts are good. I like them and I know they can help lengthen the service life of trans related components. But this thing is usually just too aggressive going from 1st to 2nd.

Another question comes to mind. I'm running this thing in SD. The MAF failed and I run my turbo truck in SD so I just figured why not. I have read that SOME PCMs (and I'm not clear on which ones) will command higher line pressure for the trans when in SD mode. I cannot find anything iny my tune file that would govern this, if it is present??

My tune file, the Vette tune file I am borrowing trans settings from and a short log is attached. I started logging line pressure (I think)

[bk2life]

What can I change to soften the 1-2 shift

put the stock servo back in.
is the easiest solution here

[2xLS1]

You have the MAF Fail frequency set to 0. all 3 MAF codes set to NER and a 1 bar SD COS applied. What are you trying to do with this set up?

[CDeeZ]

put the stock servo back in.
is the easiest solution here

Really? I've never ridden in a C4 4L60 car, but I can't imagine it shifted like this truck of mine does since adding the Vette servo? I guess I will go back to the stock servo if need be. But, I was under the impression that the Corvette servo, while used sometime for "performance" applications; was also a decent upgrade just to help any 4L60 last longer, firmer apply and all that?

You have the MAF Fail frequency set to 0. all 3 MAF codes set to NER and a 1 bar SD COS applied. What are you trying to do with this set up?

Do I not have the MAF set correctly to fail it out for SD?? Just last night I changed the 3 MAF codes to NER. I DID have those three MAF codes set to NO SES - MIL ON FIRST ERROR. The only reason I changed it to NER, is fro from something I read on this forum regarding the possible correlation between running in SD and the PCM maxing out line pressure... Not saying what I did was right, but trying to continue to learn.

It's been a few years since I cracked open the laptop and did any kind of tuning, so I'm a bit rusty. And, I can't say I was ever an expert by any means before that.. But, I switched it to 1 bar SD simply because I am most familiar with tuning SD. I have a 3 bar SD COS running on a 411 in my hot rod. I learned whatever I know there. So I guess, I was just trying to keep this thing simple and relative to what I know, which is SD. The MAF died on this truck and since I have had relative good luck running my hotrod in SD, I figured, why not? Mind you, I have been running this thing in SD for several years now.

The only thing I'm trying to do with this setup though, is make it last as long as possible. Stock daily driver truck. Pretty much never go past half throttle (if that far) for fear of tearing up something in the 4L60. Also, I do like the simplicity of a SD only setup.



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Of no relation to the above hard shift from the Vette servo (AFAIK)

Here's another question. I found this post with RussK talking about changing the TCC min and max tables accordingly to make the TCC behave like the old 700R4 where it is either ON or OFF. If what he says is correct, and more importantly I understand him correctly, this sounds like a change that will help the TCC live longer.

Post #6 and #8 : https://forum.hptuners.com/showthrea...odifier-tables


I have had an INTERMITTENT P1870 code with this truck for years. I can drive literally all winter and maybe set that code one time, if that. But in the summer when it's hot, it will set that code fairly often.The truck has never been abused or driven hard during the time of my owning it. It has 190K miles on it now and I've had it since about 100K miles.

Here's what I've done to try to correct that issue:


1.) I have replaced the valve body with a reman unit from Ebay from what I believe to be a reputable seller. Can I link that here or is that frowned on? The reman valve body had a new TransGo seperator plate and a Sonnax TCC regulator and isolator valve kit to fix the known problems with the TCC regulator bore. "Rebuilt in a professional shop and vacuum tested".

2.) I have installed pinless accumulator pistons for 1/2 3/4 and direct, all Sonnax parts.

3.) I have replaced the TCC PWM solenoid



I recently had the VB down to install the pinless accumulator pistons and I know that there's much of the internals that still can't be seen, but what I can see looks mint. I suppose something might be wrong the the TC itself, specifically the TCC, but I doubt it since this particular issue is intermittent.


I think this truck might have been a lemon or flood damage truck or something becuase aside from the already super long post I've made here, I have had a bunch of odd electrical issues with it that I have had to find "creative work arounds for"

I got nearly 400k miles out of my last daily driver pickup. Original engine, transmission, rear-end, T case etc.... I was hoping to do similar here. Thus the reason for any changes I have made or thought about making to this vehicle specifically.

[Russ K]

Return trans tables 15140 & 15141 back to stock.

Russ Kemp

[bk2life]

Really? but I can't imagine it shifted like this

i was under the impression it shifted fine, and then you install the new servo and it shifted bad.

vette or billet servos increase the hold when shifting, which improves life of the trans.

most poeple like cadillacs and want that slow smushy floaty feeling. crisp hard shifts isnt cadilac

[CDeeZ]

Return trans tables 15140 & 15141 back to stock.

Russ Kemp

Thankyou Russ. I have done what you advised. Will drive it tomorrow and report any changes.

i was under the impression it shifted fine, and then you install the new servo and it shifted bad.

vette or billet servos increase the hold when shifting, which improves life of the trans.

most poeple like cadillacs and want that slow smushy floaty feeling. crisp hard shifts isnt cadilac

In relation to the first part of my last post, and, the original reason for starting the thread, yes the 1-2 shift was OK before the vette servo. The only reason I installed a vette servo a few years ago was because of reading it to be a potential longevity upgrade for the trans yes.

That P1870 code and the accompanying SUPER hard shift into 2nd is (apparently) an unrelated issue that I was also curious to ask about in my last post.


I think what I'm saying is I have two issues.

1.) Ever since installing the Vette servo the 1-2 shift has been pretty harsh. Not firm, or crisp but just harsh. It does seem that the 1-2 shift has gotten more harsh since I originally installed the vette servo a couple or 3 years ago. Not sure how or why?

-and-

2.) This truck has a tendency to set the P1870 code primarily in the warmer months. And when it does, it shifts into 2nd so hard it feels like someone crashing into the back of the truck. And to reiterate, this problem has been present BEFORE AND AFTER the vette servo.


I swapped in a rebuilt VB like I wrote above. And, the only reason I installed the vette servo then was one of those deals : " well, I'm already in here so let's upgrade this".


To reiterate: This truck has had an intermittent 1870 code for I think a literal decade at this point. And when it sets that error code, it will absolutely SLAM into 2nd gear.

When I clear that code, and when driving around without the code being set, IT STILL feels like it's grabbing 2nd gear too harshly for light throttle. I suspect this is because of something not dialed in with regards to the vette servo.

The more throttle you give it, the better the 1-2 shift feels. Makes sense, with more throttle, you would be getting a firmer and quicker apply into 2nd gear I would think, aka more "agressive". But if you just barely give it throttle, very light cruising, it just shifts into 2nd too damn hard for that condition of engine load I think is what I'm trying to say.

[edcmat-l1]

You're not setup correctly for speed density. You have to set the P0101, 2, 3 to MIL on first error.

Some PCMs will command max line pressure when they have MAF codes. The way you have it setup may be causing high line pressure. I'd turn the MAF back on and see if the harsh shifts don't go away. A Corvette servo doesn't all by itself cause harsh shifts in a stock Corvette 4L60. Jacked up line pressure will.

[twenglish1]

Have you measured the 2-4 band clearance with the vette servo/pin assembly? Are you using a new servo assembly? The tip of servo pin often needs ground to set the band clearance. Could be issues there. Also why is the control module voltage reading 17.2V? Confirm this is correct with a meter, not sure what issues this could cause but it cant be good for the PCM along with the battery and other electronics. Add more transmission channels and record more data

[CDeeZ]

You're not setup correctly for speed density. You have to set the P0101, 2, 3 to MIL on first error.

Some PCMs will command max line pressure when they have MAF codes. The way you have it setup may be causing high line pressure. I'd turn the MAF back on and see if the harsh shifts don't go away. A Corvette servo doesn't all by itself cause harsh shifts in a stock Corvette 4L60. Jacked up line pressure will.

I had those 3 codes set to MIL first error No SES up until a few days ago. It shifted into 2nd harshly either way. I disabled those codes entirely a few days ago to see if that made any difference and it of course didn't.

I flashed the completely stock tune back in and it definitely shifts into 2nd much less harshly. This leads me to believe that this PCM was in fact commanding high line pressure from being in SD. Though, as far as I'm aware there is no setting within the tune to disable high line pressure b/c of SD. Perhaps not defined and therefore not visible?

Have you measured the 2-4 band clearance with the vette servo/pin assembly? Are you using a new servo assembly? The tip of servo pin often needs ground to set the band clearance. Could be issues there. Also why is the control module voltage reading 17.2V? Confirm this is correct with a meter, not sure what issues this could cause but it cant be good for the PCM along with the battery and other electronics. Add more transmission channels and record more data

I have not measured 2-4 band clearance. Perhaps that is a source of the harder than expected shift with the vette servo? I will log more transmission channels and get some more logs.

I hadn't noticed the PCM voltage until you caught it. I just looked at a log for this same truck from 4 years ago and it also shows PCM voltage at 16.5+ volts. Battery voltage with a meter is ~14v when idling. Like I said in an earlier post, I think this truck is a lemon or something. I have had a TON of unexplainable electrical issues with it. I'll explain some below:

1.) This truck used to refuse to start. You would drive somewhere and stop the engine and then when trying to start it again, it would refuse to crank. Wait 15-30 minutes and it would start. I checked the usual stuff, VATS long since disabled. What I found, was that for whatever reason the PCM and BCM (not entirely sure of the order of operations here) would NOT allow the "request start" signal from the relay under the hood to energize the starter. If I remember right, the security light would flash on the cluster. There is no chip/resistor in the key, but if I remember correctly, some of my research led me to measure the resistance with something pertaining to the ignition switch. I determined said resistance and made a resistor pack and installed it inline in one of the wires under the steering column. This was years ago at this point when I was trying to "fix it the right way". I researched everything I could and studied wiring diagrams.... I even took it to a shop and they couldn't figure out the intermittent no start issue either. Frustrated, I finally gave up trying to "fix it the right way" and cut the wire from the started enable relay that energizes the starter after checking with the PCM, BCM and whatever other over-engineer electronic horseshit and just wired it into a bypass switch. I did that 7 or 8 years ago. It's worked fine ever since even though it wasn't the "right solution". Field expediency.

2.) The A/C compressor also refuses to turn on sometimes. IIRC it was almost the exact same case as the no start issue. IIRC the A/C request signal is managed by the BCM, maybe the PCM and a relay on the same relay block under the hood where the starter enable relay is located. I did the same thing, I just cut the wire going to the compressor after identifying the correct one that energizes the mag-clutch on the compressor and wired it to a toggle switch. When the truck refuses to run the A/C normally; the way GM designed it, I simply flip the switch and FORCE the compressor to kick on.

3.) This truck was originally a clutch fan. I installed an electric fan and ran that for a while. I copied the fan settings from a friends truck 1 year newer that came factory with Efans. Same story as the above 2 points; USUALLY, the fans would come on and off as calibrated in the tune and there was no issue. However, when the truck wouldn't start normally, and I had to use my bypass starter switch, the fans WOULD NOT OPERATE AT ALL.........

4.) When all of the above 3 issues would happen, I would also get that shift into 2nd where it feels like someone crashed into you. Would set code 1870 . THIS WAS WITH OR WITHOUT THE VETTE SERVO.

None of this makes any logical sense. That's why I suspect something electrically wrong with this truck from the beginning. Perhaps the BCM I don't know???

In summation: when I had to use my starter bypass switch, I also had to use my A/C bypass switch, and when I still had Efans I had to also use my manual fan switch and finally, the trans would shift into 2nd so hard it felt like someone crashed into the back of the truck. Given the electrical issues this truck seems to have in general, it might be that a vette servo just isn't workable in this specific application.

I only ever installed the vette servo because I thought it to be a longevity improvement mod for a stock 60e in a stock daily driver. However, given the electrical maladies I have described above, it seems that simply going back to a stock servo might be the best solution for me.

I apologize to everyone for the expansion of the scope of my original post. I think some of this information is relevant. I feel it is. I appreciate everyone weighing in so far and I hope you all find it at least somewhat interesting like I do.

[edcmat-l1]

I had those 3 codes set to MIL first error No SES up until a few days ago. It shifted into 2nd harshly either way. I disabled those codes entirely a few days ago to see if that made any difference and it of course didn't.

You're not reading what I'm saying and interpreting it right. The fact that the codes are set to mil on first error WILL CAUSE HIGH LINE PRESSURE AND VERY AGGRESSIVE SHIFTS in some applications. Yours doesn't have the DTC disable switches like the P01s do. And, setting them to "no error reported" can cause the PCM to do the same thing, possibly. Some DTCs when disabled will not turn the light on but will have the same side effects as if the code is actually set. That's why I said re-enable to MAF and set the codes back the way they're supposed to be set and see what happens.

Turning the maf back on temporarily is the easiest way to see if that's the issue. The other thing you could do is put a pressure gauge on it. But like I said before the Vette servo shouldn't be the cause of it all by itself. Not overly aggressive shifts. My money is on line pressure because it's in speed density.

max line pressure dtc disable.jpg

[Alvin]

I've not encountered a GEN 3 that would max out line pressure in SD mode that didn't have the switches to turn it off in the trans diag section.

It's worth a shot.. but I don't think that is going to be it.

I think the problem is from him copying stuff from a Vette tune into this. Although the only thing that looks out of wack is the shift pressure modifier stuff. Also the way he has the trans setup I'd expect it to have a slip bang feeling shift. Shift times are huge, lots of TM still, and the line pressure is ran up from copying over from a vette tune.

I'll bet it feels like huge pauses for the shift then a quick bump or bang into gear.

[edcmat-l1]

I've not encountered a GEN 3 that would max out line pressure in SD mode that didn't have the switches to turn it off in the trans diag section.

It's worth a shot.. but I don't think that is going to be it.

I think the problem is from him copying stuff from a Vette tune into this. Although the only thing that looks out of wack is the shift pressure modifier stuff. Also the way he has the trans setup I'd expect it to have a slip bang feeling shift. Shift times are huge, lots of TM still, and the line pressure is ran up from copying over from a vette tune.

I'll bet it feels like huge pauses for the shift then a quick bump or bang into gear.

I didn't look that deep.

I agree I'd start with the vehicle's base file settings instead of copying over anything. That's never a good idea.

[CDeeZ]

You're not reading what I'm saying and interpreting it right. The fact that the codes are set to mil on first error WILL CAUSE HIGH LINE PRESSURE AND VERY AGGRESSIVE SHIFTS in some applications. Yours doesn't have the DTC disable switches like the P01s do. And, setting them to "no error reported" can cause the PCM to do the same thing, possibly. Some DTCs when disabled will not turn the light on but will have the same side effects as if the code is actually set. That's why I said re-enable to MAF and set the codes back the way they're supposed to be set and see what happens.

Turning the maf back on temporarily is the easiest way to see if that's the issue. The other thing you could do is put a pressure gauge on it. But like I said before the Vette servo shouldn't be the cause of it all by itself. Not overly aggressive shifts. My money is on line pressure because it's in speed density.

max line pressure dtc disable.jpg

I have gone back to the stock tune, MAF and all, with the exception of the TCC min and max tables being modified per the thread I mentioned from Russ.

It IS slightly less harsh shifting into 2nd. But it's STILL harsh.

If you're saying that is not correct way to setup SD for a P59 because of the possibility of high line pressure, then what is?? I found this thread here for setting up SD on either P01 or P59. Line pressure is not mentioned a single time.

https://forum.hptuners.com/showthrea...488#post575488

I've not encountered a GEN 3 that would max out line pressure in SD mode that didn't have the switches to turn it off in the trans diag section.

It's worth a shot.. but I don't think that is going to be it.

I think the problem is from him copying stuff from a Vette tune into this. Although the only thing that looks out of wack is the shift pressure modifier stuff. Also the way he has the trans setup I'd expect it to have a slip bang feeling shift. Shift times are huge, lots of TM still, and the line pressure is ran up from copying over from a vette tune.

I'll bet it feels like huge pauses for the shift then a quick bump or bang into gear.

The only reason I tried some of the vette stuff was to see if it made it any better. It did not. The harsh shift into 2nd has been present since installing the vette servo. I only recently tried to incorporate some of the other vette settings to see if that made any difference and it did not.

I don't believe I ever changed any shift times. I tried reducing some TM at some point in the past and that in fact did not help but made it worse.

With all the things I have tried, it has never felt like a slip bang shift. Just bang. A hard/harsh bang into 2nd. You can hear the dash creak and the brake pedal bounce around sometimes when it grabs 2nd.

I only ever tried some of the vette settings for the transmission paramaters a few days ago. I went back to what the original tune file had immediately after deducing that it was no improvement and perhaps making the problem worse.

I didn't look that deep.

I agree I'd start with the vehicle's base file settings instead of copying over anything. That's never a good idea.

Like I said above, back to completely stock tune file minus the TCC changes I mentioned. Running it in MAF seems to have softened the 1-2 shift a bit compared to when it was SD. But, it's still on the harsh side. Probably just going back to stock servo.

stock tune with TCC slip eliminated. ON or OFF basically.hpt

[edcmat-l1]

Like I said above, back to completely stock tune file minus the TCC changes I mentioned. Running it in MAF seems to have softened the 1-2 shift a bit compared to when it was SD. But, it's still on the harsh side. Probably just going back to stock servo.

stock tune with TCC slip eliminated. ON or OFF basically.hpt

That's not at all surprising. But the only way to know for sure is to put a pressure gauge on it and check it both ways. I'm sure you don't wanna invest that time. You can just switch back to the stock servo and be done with it.