4l70e no second gear on fresh trans
10-22-2016, 11:13 PM
#1
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4l70e no second gear on fresh trans I have 60 easy miles on this fresh transmission. I’ve been sorting out this LS2/4L70e transplant with light throttle, nothing more than 30 to 40%. Originally had all 4 gears and TCC. Today it will not shift to second, stays in 1st until 3rd gear shift point - even when commanded with HP Tuner. I pulled the pan and its clean.
Picture of band “wiggle clearance” when I originally assembled it.
Complete kit from Probuilt 4L60E Rebuild Kit Street/Strip 1997 & Up
Including:
1 Borg-Warner Hi-Energy 2-4 band
2 Corvette servo with Viton sealing rings. (with the Transgo gold shim)
3 I added a new GM rev input drum
Log file attached with “TransLine” pressure in kPa. See 1st 1_2 shift attempt at 12:15:48, although the shift never happens, until 3rd gear at 12:16:09. The second shift attempt at 12:16:24 was commanded with HP and same result.
Line press is about 90psi at the 1_2. (Convert the kPa to PSI by multiplying by 0.145)
All interweb searches lead me to worn band, but that can’t be the case here. I appreciate your help and let me know if I can provide further info.
Thanks!
Picture of band “wiggle clearance” when I originally assembled it.
Complete kit from Probuilt 4L60E Rebuild Kit Street/Strip 1997 & Up
Including:
1 Borg-Warner Hi-Energy 2-4 band
2 Corvette servo with Viton sealing rings. (with the Transgo gold shim)
3 I added a new GM rev input drum
Log file attached with “TransLine” pressure in kPa. See 1st 1_2 shift attempt at 12:15:48, although the shift never happens, until 3rd gear at 12:16:09. The second shift attempt at 12:16:24 was commanded with HP and same result.
Line press is about 90psi at the 1_2. (Convert the kPa to PSI by multiplying by 0.145)
All interweb searches lead me to worn band, but that can’t be the case here. I appreciate your help and let me know if I can provide further info.
Thanks!
10-23-2016, 09:59 AM
#2
Moderator
Despite your new band, I would start by checking the servo end play - estimate how much the cover moves when you press on it with e.g. a crowbar. Spec is between 1/16" to 1/8".
If within spec, remove the servo and check the seals again on the 2nd gear servo piston.
I don't know if a broken 1-2 accumulator piston could cause this - it would allow the 2nd gear circuit to leak into the accumulator circuit - but is easy to check.
If your servo end play is OK, the problem is almost certainly in the servo or VB area and not internal to the trans.
If within spec, remove the servo and check the seals again on the 2nd gear servo piston.
I don't know if a broken 1-2 accumulator piston could cause this - it would allow the 2nd gear circuit to leak into the accumulator circuit - but is easy to check.
If your servo end play is OK, the problem is almost certainly in the servo or VB area and not internal to the trans.
10-24-2016, 08:01 PM
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Yes on the shim...
"2 Corvette servo with Viton sealing rings. (with the Transgo gold shim)"
All the seals on the servo look perfect. Picture of entire servo with Transgo springs / gold shim.
"2 Corvette servo with Viton sealing rings. (with the Transgo gold shim)"
All the seals on the servo look perfect. Picture of entire servo with Transgo springs / gold shim.
10-25-2016, 09:58 PM
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Is it time to pull the pan again? ... and look at the 1-2 accumulator?
It has the aluminum one in the Probuilt kit:
"Modified second accumulator piston, new "hardened" (RC52) pin, & seal with matching accumulator springs (allows for a very smooth 1-2 part throttle shift)"
The accumulator housing number was 937 with Orange-Red Inner spring, White Middle spring and Orange Outer Transgo Springs.
It has the aluminum one in the Probuilt kit:
"Modified second accumulator piston, new "hardened" (RC52) pin, & seal with matching accumulator springs (allows for a very smooth 1-2 part throttle shift)"
The accumulator housing number was 937 with Orange-Red Inner spring, White Middle spring and Orange Outer Transgo Springs.
10-27-2016, 08:46 AM
#7
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Sorry, I'm at a loss of additional suggestions.
Checking the line pressure is always a good diagnostic tool.
If it were me, after checking line pressure I would check the 1-2 accumulator and if that looked OK, install a spare valve body (VB). I realize that only shops and enthusiasts like me have spare VBs, but I'm still confident the problem is in the servo or VB.
Of course, I could be missing something, even something obvious.
Perhaps one of the pro builders has some other suggestions.
Checking the line pressure is always a good diagnostic tool.
If it were me, after checking line pressure I would check the 1-2 accumulator and if that looked OK, install a spare valve body (VB). I realize that only shops and enthusiasts like me have spare VBs, but I'm still confident the problem is in the servo or VB.
Of course, I could be missing something, even something obvious.
Perhaps one of the pro builders has some other suggestions.
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10-27-2016, 09:44 AM
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I appreciate your response... I had checked the pressure, it was in the HP log file I had attached. TransLine(kPa)
Is 90PSI enough at 5% pedal for the 1_2?
It completes the 1_3 shift with 87PSI. I'm just not familiar enough to know if that's adequate pressure. Anyway - dropping pan and going in to inspect!
Thanks again MrVedit!
Is 90PSI enough at 5% pedal for the 1_2?
It completes the 1_3 shift with 87PSI. I'm just not familiar enough to know if that's adequate pressure. Anyway - dropping pan and going in to inspect!
Thanks again MrVedit!
10-27-2016, 11:44 AM
#9
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I appreciate your response... I had checked the pressure, it was in the HP log file I had attached. TransLine(kPa)
Is 90PSI enough at 5% pedal for the 1_2?
It completes the 1_3 shift with 87PSI. I'm just not familiar enough to know if that's adequate pressure. Anyway - dropping pan and going in to inspect!
Thanks again MrVedit!
Is 90PSI enough at 5% pedal for the 1_2?
It completes the 1_3 shift with 87PSI. I'm just not familiar enough to know if that's adequate pressure. Anyway - dropping pan and going in to inspect!
Thanks again MrVedit!
Also, the numbers 0 - 94 are not the line pressure, but correspond to a control line pressure. "0" means minimal pressure, typically around 60psi (but around 80psi if a larger boost valve is installed) and "94" means max pressure, typically in the 200-240 psi range.
10-27-2016, 12:32 PM
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I am logging line pressure with an 5V external transducer and read thru the ac pressure transducer channel into the ECM. I take the AC PRESS VOLTS and have a linearized calibration equation to convert to kPa. It is in my HP log file as "TransLine". I could have just as easy displayed this in PSI. A picture of my set up attached. I have a 3 pin extension harness to reach down to the line pressure port (not shown).
Is 90PSI enough at 5% pedal for the 1_2?
Is 90PSI enough at 5% pedal for the 1_2?