84CUCV
3/4 ton status
Its in a 91. from the navy. has 66k on it. now and then its shifts hard and i mean hard, whole truck jumps. any ideas what it might be? thanks
CK5
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4l80e shifting hard
- Thread starter 84CUCV
- Start date
Bring this BTT in a few hours and I'll be home to check and see if the service manual lists that "fault", if someone doesn't beat me to it.
Any other problems with the vehicle? Speedometer not-work, random power loss, issues at a particular throttle position, etc.
Any other problems with the vehicle? Speedometer not-work, random power loss, issues at a particular throttle position, etc.
I had a similar problem in my 91, turned out to be a "PCM" (not real sure what that is). 
PCM is powertrain control module.
On the early 4L80E trucks, diesel got a TCU as I recall (Transmission Control Unit) as the engines didn't have electronic controls, while the gas ones got a PCM, which controls both the engine and transmission. Vs of course an ECM, which is engine only. (and minor transmission function like TCC)
On the early 4L80E trucks, diesel got a TCU as I recall (Transmission Control Unit) as the engines didn't have electronic controls, while the gas ones got a PCM, which controls both the engine and transmission. Vs of course an ECM, which is engine only. (and minor transmission function like TCC)
I always thought it was an internal trans part. To be honest, it was under warranty with a rebuilder at the time so I didn't pay much attention - "fix it!". 
Well it could be something else too I suppose, there are a fair number of electronics to these transmissions, I'll check it out when I get home if I remember. 
neverendingproject
1/2 ton status
could be valve body. ive seen it before.
84CUCV
3/4 ton status
ok guess i will try to find a manual for it thanks
Any codes? If so, I can't check my manual tonight.
84CUCV
3/4 ton status
thanks will get back to you
Forgot last night, sorry.
Made a reminder, I'll try again this evening.
Made a reminder, I'll try again this evening.
It's most likely a bad pressure control soenoid. When they go bad they default to max line pressure which causes brutal part throttle shifts. There are 2 different designs, 91-94 take a Bosch design, 94 and later take a Holley design and they are not interchangable.
I'm a knucklehead! That's the internal part I had a problem with.
Man I'm glad I don't have one of these trans.
20 pages of symptoms and possible causes!
Anyways, erratic shift quality is the easiest: gasket (6), oil transfer hole cup plug, oil seal rings (218). The numbers unfortunately reference the 4L80E repair section, which I don't see in this manual.
There are 10 possible codes for harsh shift, so it would seem pretty likely that if there is a problem, you'll get a code.
It does break the issue into WHICH gear shifts it occurs on, if no codes that might help narrow it down as well.
20 pages of symptoms and possible causes!
Anyways, erratic shift quality is the easiest: gasket (6), oil transfer hole cup plug, oil seal rings (218). The numbers unfortunately reference the 4L80E repair section, which I don't see in this manual.
There are 10 possible codes for harsh shift, so it would seem pretty likely that if there is a problem, you'll get a code.
It does break the issue into WHICH gear shifts it occurs on, if no codes that might help narrow it down as well.
Man I'm glad I don't have one of these trans.
Did I mention, I sold mine and bought a truck with a 6spd manual?
84CUCV
3/4 ton status
i will be looking at this truck soon. at a stop. hit the gas, goes into gear hard! rest are easy shifts.
So just the 1-2 shift then? Not hard going from P-D or anything like that?
