1990 k1500 with 460le trans problem

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ErnieHaycraft

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I have a 1990 k1500 silverado that's been mistreated. I'm slowing bringing it back. It will shift fine through every gear no sluggish problems, but when I hit fourth gear it randomly wants to jump inbetween 3rd and 4th. When it should be in fourth. I flush the fluid and changed filter seem to help a little, but still does it. Wondering if it could be a selenoid? Any suggestions ?
 

Schurkey

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Perhaps a moderator will move this to the TRANSMISSION section instead of the TRANSFER CASE section.

The only solenoid in the '90 4L60/700 transmission is for the lockup torque converter. Are you sure the problem is between 3rd gear and 4th gear, and not the torque converter locking and unlocking?

If the torque converter is locking and unlocking, it MIGHT be normal. You could verify the adjustment of the Throttle Valve (TV) cable. Connect a scan tool, see what the computer is commanding for torque converter clutch operation. My torque converter unlocks above 75 mph, lower speed if there's a headwind, a heavy load, uphill, or I'm accelerating. If this is really 3rd gear--4th gear problems, I'd be wondering about the 2--4 band or the 4th gear servo / accumulator part of the 2--4 servo assembly. The band and servo seems to be a weak point of this trans, but there's other possibilities.
 

ErnieHaycraft

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I really don't know much of anothing about this transmission but ill take a look at that cable for sure. My pops actually suggested that as well. Thank you for your input. I really appreciate it.
 

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Absolutely. Heavier load disengages the TCC; and I hit that load limit at ~75--78 mph. Less, as I said, if I'm on the throttle due to trailer-towing, too much weight in the bed, incline, acceleration, etc.
 

AuroraGirl

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Absolutely. Heavier load disengages the TCC; and I hit that load limit at ~75--78 mph. Less, as I said, if I'm on the throttle due to trailer-towing, too much weight in the bed, incline, acceleration, etc.
I bet gearing and rpm and MAP are used or something to determine engine load and the PCM will decide based on the calibration on it what to do such that there may be a above 75 lock idk
 

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I know that Corvettes and some Camaros had shift valves that allowed heavy-throttle 4th gear operation; but I don't know of any OEM tuning that kept the converter locked.

But then, I never studied that either. It'd be nice to have converter lockup at highway speed.
 

PlayingWithTBI

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Absolutely. Heavier load disengages the TCC; and I hit that load limit at ~75--78 mph. Less, as I said, if I'm on the throttle due to trailer-towing, too much weight in the bed, incline, acceleration, etc.
That is due to the TPS vs MPH tables and min CTS value. There is a "Scalar" which will lock the TCC based solely on MPH. The post above shows that, in this case it's 80 MPH but can be adjusted to whatever you want with a tune. Yours may be set to some irrelevant speed like 100 MPH.

Here's where we were discussing TCC lockup and unlock. You can see the TPS/MPH goes higher than just 75 MPH.
https://www.gmt400.com/threads/sniper-efi-conversion.51562/post-1210523

I bet gearing and rpm and MAP are used or something to determine engine load and the PCM will decide based on the calibration on it what to do such that there may be a above 75 lock idk
Yes, just TPS/MPH. This is on TBIs with 700R4 (4L60). IDK about electronic controlled trans PCMs.
 

AuroraGirl

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That is due to the TPS vs MPH tables and min CTS value. There is a "Scalar" which will lock the TCC based solely on MPH. The post above shows that, in this case it's 80 MPH but can be adjusted to whatever you want with a tune. Yours may be set to some irrelevant speed like 100 MPH.

Here's where we were discussing TCC lockup and unlock. You can see the TPS/MPH goes higher than just 75 MPH.
https://www.gmt400.com/threads/sniper-efi-conversion.51562/post-1210523


Yes, just TPS/MPH. This is on TBIs with 700R4 (4L60). IDK about electronic controlled trans PCMs.
i suppose that makes sense since the ECM just has the authority over allowing the transmission to do its thing (lockup) by energizing or de-energizing, and there are, i believe, range switches inside that tell the ECM what gear its iin. So a simple allow-disallow makes sense

440t4 had something similar i believe but the cars had more features so i think more executive "off" situations could occur
 
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