4L70E with a bad, sometimes, 1-2 shift
Thread Starter
Teching In
Joined: Feb 2014
Posts: 22
Likes: 0
From: Montana
4L70E with a bad, sometimes, 1-2 shift I have a 4L70E trany in my '80 vette with a LS3 engine. About 1/3 of the time on the 1-2 shift it will shift so hard that it barks the tires. And I am not even on it. Why does it do it sometimes and not all the time? Had the trany pulled out and rebuilt and it still does it. Makes you start flinching when you know the 1-2 shift is about to happen. Again, sometimes it does and sometimes it doesn't (shift hard enough to bark the tires).
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
The ECM might be detecting an engine sensor problem, such as a bad TPS, and is then commanding max line pressure to the trans which results in the very firm shift. Various engine and trans codes will force the max line pressure.
Have you scanned for codes?
A good scanner like HP Tuners would likely show the commanded line pressure when the firm shifts occur.
Pity you had the trans rebuilt when it might be a engine sensor, ECM/TCM or tune problem.
Have you scanned for codes?
A good scanner like HP Tuners would likely show the commanded line pressure when the firm shifts occur.
Pity you had the trans rebuilt when it might be a engine sensor, ECM/TCM or tune problem.
