2008 5.3/4l60e 3-2 downshift flare. Corvette servo? Extended servo pin?

[Dustin Jackson]

2008 5.3 4l60e 3.73 gears 180,000 miles lifted about 3 inches with 32 inch Ko2 tires

Hello gentlemen,

When I purchased the Blackbear tune for my motor and trans I was very unsatisfied with the transmission performance and I went back and forth with Justin and loaded a few different tunes he sent me but ultimately I was never happy with the trans but I didn't want to put it on blackbear, they said the trans is probably worn. The trans is old but still works great so I didn't want to push the issue.

Problems I had with the blackbear trans tune: harsh 1-2 shift until warmed up, very short 2-3 (happened very soon and didn't feel like it is in sync with engine speed), and 3-2 downshift flare (RPMs will raise high and then the gear engages and RPM drop back down as it goes into gear. almost like dumping the clutch, feels very concerning)

I will say that these problems probably existed before the trans tune but were amplified by the tune bringing them to my attention or were masked by factory trans tuning.

To solve the short 2nd gear problem I asked Justin to extend the duration of the 2nd gear but this basically got rid of 4th gear for me, my truck would go from 1st, 2nd, to 3rd to overdrive and only hit 4th gear under certain situations, I only ran it like this shortly before deciding this isn't a good solution and reverted back to stock trans tune in 2022.

This spring 2023 I reinstalled the first trans tune from Blackbear and have found parts of it enjoyable but the passing aspect when going uphill or passing on the freeway when I need that 3-2 downshift really is a problem.

This morning I came across this post that outlines someone else journey in solving this same problem: https://ls1tech.com/forums/automati...2-downshift-flare-any-4l60e-experts-here.html

Here is an album the poster made that includes the original problem, some servo testing and then another video explaining their fix and showing the results: https://photos.google.com/share/AF1...?key=MTh2MjR3bmQzY3o0RHlYRS1YSGUyallEQnAtZVB3

All this being said, it seems that the fix is to extend the length of the servo pin by welding a bead to the tip. This helps tighten the 2-4 band in turn eliminating the 3-2 dpwnshift flare.

Now my question is what do I do? I don't weld, is there a longer aftermarket servo pin I should use? Would a corvette server work? Do I get an extended servo pin AND a corvette servo? Can I run a corvette servo and trans tune at the same time?

- Signed by a man looking to milk every mile out of this transmission while drinking a lot of coffee this morning.

 

[Trey Hardy]

2008 5.3 4l60e 3.73 gears 180,000 miles lifted about 3 inches with 32 inch Ko2 tires

Hello gentlemen,

When I purchased the Blackbear tune for my motor and trans I was very unsatisfied with the transmission performance and I went back and forth with Justin and loaded a few different tunes he sent me but ultimately I was never happy with the trans but I didn't want to put it on blackbear, they said the trans is probably worn. The trans is old but still works great so I didn't want to push the issue.

Problems I had with the blackbear trans tune: harsh 1-2 shift until warmed up, very short 2-3 (happened very soon and didn't feel like it is in sync with engine speed), and 3-2 downshift flare (RPMs will raise high and then the gear engages and RPM drop back down as it goes into gear. almost like dumping the clutch, feels very concerning)

I will say that these problems probably existed before the trans tune but were amplified by the tune bringing them to my attention or were masked by factory trans tuning.

To solve the short 2nd gear problem I asked Justin to extend the duration of the 2nd gear but this basically got rid of 4th gear for me, my truck would go from 1st, 2nd, to 3rd to overdrive and only hit 4th gear under certain situations, I only ran it like this shortly before deciding this isn't a good solution and reverted back to stock trans tune in 2022.

This spring 2023 I reinstalled the first trans tune from Blackbear and have found parts of it enjoyable but the passing aspect when going uphill or passing on the freeway when I need that 3-2 downshift really is a problem.

This morning I came across this post that outlines someone else journey in solving this same problem: https://ls1tech.com/forums/automati...2-downshift-flare-any-4l60e-experts-here.html

Here is an album the poster made that includes the original problem, some servo testing and then another video explaining their fix and showing the results: https://photos.google.com/share/AF1...?key=MTh2MjR3bmQzY3o0RHlYRS1YSGUyallEQnAtZVB3

All this being said, it seems that the fix is to extend the length of the servo pin by welding a bead to the tip. This helps tighten the 2-4 band in turn eliminating the 3-2 dpwnshift flare.

Now my question is what do I do? I don't weld, is there a longer aftermarket servo pin I should use? Would a corvette server work? Do I get an extended servo pin AND a corvette servo? Can I run a corvette servo and trans tune at the same time?

- Signed by a man looking to milk every mile out of this transmission while drinking a lot of coffee this morning.

Try either a corvette servo or the slightly better sonnex servo that may help.
I had to go back and fourth with my tuner when I done the Tahoe it was super sluggish then would shift too hard whenever stabilitrac would go off we tuned that out tweaked it some more and she’s perfect now I ended up not using the vette servo in it and ended up throwing it in my Silverado

 

[Dustin Jackson]

@Trey Hardy Does installing a corvette servo solve the same problem of the servo pin not being long enough?

 

[Dustin Jackson]

Update: I found some more information that would suggest my harsh shift from 1-2 would also be caused by the 2-4 band... It seems that I can kill multiple birds with one stone of solving this servo/short servo pin situation.

"The harsh 1-2 occurs by allowing the 2-4 band apply oil pressure to be re-routed to the 4th gear servo apply piston"

4L60E Harsh 1-2 Shift - Transmission Digest

Let us have a look at the systems and potential problems in a 4L60E that can cause a harsh 1-2 shift.

www.transmissiondigest.com

 

[iamdub]

2008 5.3 4l60e 3.73 gears 180,000 miles lifted about 3 inches with 32 inch Ko2 tires

Hello gentlemen,

When I purchased the Blackbear tune for my motor and trans I was very unsatisfied with the transmission performance and I went back and forth with Justin and loaded a few different tunes he sent me but ultimately I was never happy with the trans but I didn't want to put it on blackbear, they said the trans is probably worn. The trans is old but still works great so I didn't want to push the issue.

Problems I had with the blackbear trans tune: harsh 1-2 shift until warmed up, very short 2-3 (happened very soon and didn't feel like it is in sync with engine speed), and 3-2 downshift flare (RPMs will raise high and then the gear engages and RPM drop back down as it goes into gear. almost like dumping the clutch, feels very concerning)

I will say that these problems probably existed before the trans tune but were amplified by the tune bringing them to my attention or were masked by factory trans tuning.

To solve the short 2nd gear problem I asked Justin to extend the duration of the 2nd gear but this basically got rid of 4th gear for me, my truck would go from 1st, 2nd, to 3rd to overdrive and only hit 4th gear under certain situations, I only ran it like this shortly before deciding this isn't a good solution and reverted back to stock trans tune in 2022.

This spring 2023 I reinstalled the first trans tune from Blackbear and have found parts of it enjoyable but the passing aspect when going uphill or passing on the freeway when I need that 3-2 downshift really is a problem.

This morning I came across this post that outlines someone else journey in solving this same problem: https://ls1tech.com/forums/automati...2-downshift-flare-any-4l60e-experts-here.html

Here is an album the poster made that includes the original problem, some servo testing and then another video explaining their fix and showing the results: https://photos.google.com/share/AF1...?key=MTh2MjR3bmQzY3o0RHlYRS1YSGUyallEQnAtZVB3

All this being said, it seems that the fix is to extend the length of the servo pin by welding a bead to the tip. This helps tighten the 2-4 band in turn eliminating the 3-2 dpwnshift flare.

Now my question is what do I do? I don't weld, is there a longer aftermarket servo pin I should use? Would a corvette server work? Do I get an extended servo pin AND a corvette servo? Can I run a corvette servo and trans tune at the same time?

- Signed by a man looking to milk every mile out of this transmission while drinking a lot of coffee this morning.

If the problem is wear, there's nothing you can do to reverse it. It's worn and, as they do from new, continue to get worse. Just wanted to get that out there first. It's like the mentality of people doing all kinds of tricks cuz they want their abused and clapped-out 300K-mile engine to have all teh oil pressures on the gauge to make them feel like it's not worn.

Anyway, what you CAN do is adjust for the wear to help restore some of the original operation to make the most out of the clutch material, etc. that's left and possibly slow down the wear a little since the loosed tolerances contribute to slip, which contributes to wear. I used a Corvette servo, Sonnax Super 4th servo and a GM "Long Pin". I measured the travel in the apply piston and it was at the maximum (loosest) limit. The pin, installed as it came outta the package, put the travel at the minimum (tightest) spec. My heap has 222K miles and I've owned it since 147K. I have no idea if the trans is original, but I treat it as if it has all 222K miles on it. It seems to be doing fine. I've noticed no adverse characteristics hinting of failure. Since the engine work and tune, I almost always manually downshift with a throttle blip (rev-matching, yo!) to get it in the lower gear but not under hard throttle. It just makes me feel like l'm doing all I can to keep it alive.

IMO, it's worth a shot. Supposedly, there are different length pins. At my mileage, I decided to get the longest and trim it if necessary. I read somewhere that the inside of a common washer has the correct radius for the tip. I don't recall what size washer, but we can research that if necessary. Anyway, you cut the washer in half and shave the tip of the pin down a hair at a time, maintaining its contour by comparing it to the halved washer as a guide.

I thought I took pics and posted them and details in my thread, but I'm not finding them.

The Corvette servo is, IMO, a standard item. The Sonnax Super Hold 4th servo might've been a splurge. But, it a good "while I'm in there" thing.

I believe I got my pin and stuff from Oregon Performance. Here's the pin and Corvette servo as a package and here's the pin by itself. I got my Sonnax Super 4th servo from Amazon (This). Also, this looks interesting. I'd like to summon the expertise of @NickTransmissions.

 

[Trey Hardy]

@Trey Hardy Does installing a corvette servo solve the same problem of the servo pin not being long enough?

I’m not sure it’s supposed to have a stronger hold on the 2-4 band that’s about all I know lol

 

[Fless]

@NickTransmissions might be a good one to weigh in here.

 

[NickTransmissions]

2008 5.3 4l60e 3.73 gears 180,000 miles lifted about 3 inches with 32 inch Ko2 tires

I'm at a family barbeque ATM but will review and provide a more in-depth response sometime tomorrow morning.

Only thing I'll mention now is I generally advise against messing too much with the factory tune on these transmissions. If you want the transmission to shift a certain way, you do it mechanically (spacer plate feed hole sizing, 2-4 servo band clearance, 2nd and 4th gear servo selection, 3-4 clutch clearance adjustment, clutch and band friction material selection (stock, high energy, red/blue plate etc), forward dr clutch piston return spring selection and accumulator mods/adjustments.

@Trey Hardy Does installing a corvette servo solve the same problem of the servo pin not being long enough?

No - a longer servo pin or shim does that.

Will explain more in the AM.

 

[Dustin Jackson]

@iamdub Thank you for the response, I think the information you provided validates that I am heading in the right direction.

Here is the guide that references the 3/8" washer being the right size for grinding the pin tip, for your future reference: https://www.jegs.com/installationinstructions/500/555/555-603300.pdf

I don't race or drive fast in my Tahoe so I don't think the Sonnax Super 4th Hold is my style but I agree that the Corvette server and longer pin kit are calling my name. Most of my driving is daily and low RPM action, merging and passing on the freeway is the most action this thing sees.

How do you recommend a shade tree mechanic measure the servo travel distance? I plan on using a drill and angle grinder to shave the pin if I need to.


Thank you Nick, enjoy the BBQ we can pick up on this tomorrow. For the tune I didn't get anything crazy, just requested recommend quality of life changes from Black Bear, if you think I should tune back to stock let me know.

I think the reason I re-installed the trans tune was because the shifts are super soft and I understand that the soft shifts come at the cost of clutch material and I thought that having the trans shift more firm would extend the life of it.

 

[iamdub]

Here is the guide that references the 3/8" washer being the right size for grinding the pin tip, for your future reference: https://www.jegs.com/installationinstructions/500/555/555-603300.pdf

Funny thing is I originally wrote 3/8" washer but then thought that was way too big so I edited it. Good job finding the specifics.

https://www.jegs.com/installationinstructions/500/555/555-603300.pdf

How do you recommend a shade tree mechanic measure the servo travel distance? I plan on using a drill and angle grinder to shave the pin if I need to.

I put a socket on the center of the cover and stuck a large prybar up in the trans tunnel with the curve of the bar against the socket. This gave me lots of leverage to easily and smoothly depress the cover just until it bottomed out. I used the depth gauge part of my digital caliper to measure how far the cover pressed in. It's just a cheap Harbor Freight caliper but does what I need. >THIS<