Vibrations when lockup occurs???
Vibrations when lockup occurs??? When driving in OD around 2K rpms and around 45mph i start to get some vibrations. These vibrations don't happen in any other gear. Is the lockup function in my converter causing this? Just had a new driveshaft installed but it still does the same thing.
does it only do it until 35-40 mph like mine??? lol ive had this problem for a while and theres no fix for it, its like putting a manual in too high of a gear when ur not going fast enough. just leave it in third until u hit 40 mph then shift to OD, so for around town driving where u really dont go faster than 40 leave it in third, then on highway put it in fourth. hope this helps at all...
if the engine is built, you prob have to raise the rpm or speed the converter locks up-as said, kind of like a stick car straining in to high a gear, your brain tells you to downshift, now the pcm has to tell it to
on my Compushift controller, i played with the lockup feature and eliminated the shudder by trying diff lockup throttle % and speeds, makes a huge diff
on my Compushift controller, i played with the lockup feature and eliminated the shudder by trying diff lockup throttle % and speeds, makes a huge diff
set lock up higher at a higher speed such as 50 to 55 mph
Greg
Greg
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Brett Foote from what i have heard lockup occurs in OD only. While i was modding my TCC table i saw that the 3rd gear and 4th gear settings were exactly the same. dont know if that was causing an issue. anyway i raised all the OD values by 10mph. fixed the problem but i didnt get up to the new quicker speed values to see if the vibration was still there.
If it's bucking, that wants MPH raised (or fix the AFR
and timing). I can lug pretty well down to 1500RPM
on mine, and it's not that mild (though not *****-out
either).
But a higher frequency vibe may be clutch chatter
and that might respond well to putting TCC PWM
to 99% full time, and maybe bring up the low-load
line pressure (TCC applied steady state trans pressure
adder, or force motor if that's not available in your
OS / tuning software combo).
Look at a scan and see if TCC slip RPM is nonzero
but TCC is applied, when the vibe is going on. That
will tell you where to go.
and timing). I can lug pretty well down to 1500RPM
on mine, and it's not that mild (though not *****-out
either).
But a higher frequency vibe may be clutch chatter
and that might respond well to putting TCC PWM
to 99% full time, and maybe bring up the low-load
line pressure (TCC applied steady state trans pressure
adder, or force motor if that's not available in your
OS / tuning software combo).
Look at a scan and see if TCC slip RPM is nonzero
but TCC is applied, when the vibe is going on. That
will tell you where to go.
Last edited by jimmyblue; Oct 22, 2009 at 08:07 PM.
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Joined: Jan 2004
Posts: 315
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Mine is doing something similar to this now. It doesn't shudder for the first 5 minutes, but once the fluid is almost hot enough for lockup to occur, it starts chattering/shuddering at around 2000 rpms. I very rarely hear it at any other rpm. It does not matter what gear I have the car in either. Sometimes it will do it idling at a stop light. It also seems to only happen in cold weather, where lockup does not occur for the first few minutes of driving.
I have daily driven the car for several years with no issue and put about 10k on the converter. Any ideas?
thanks
I have daily driven the car for several years with no issue and put about 10k on the converter. Any ideas?
thanks
Mine is doing something similar to this now. It doesn't shudder for the first 5 minutes, but once the fluid is almost hot enough for lockup to occur, it starts chattering/shuddering at around 2000 rpms. I very rarely hear it at any other rpm. It does not matter what gear I have the car in either. Sometimes it will do it idling at a stop light. It also seems to only happen in cold weather, where lockup does not occur for the first few minutes of driving.
I have daily driven the car for several years with no issue and put about 10k on the converter. Any ideas?
thanks
I have daily driven the car for several years with no issue and put about 10k on the converter. Any ideas?
thanks
had to get my 2-3 clutch pack changed went out fairly quickly after i bumped up my lockup mph. i bumped up my lockup mph because the vibes were only in OD around the lockup points. my tranny guy hooked it up to the scanner and he said he saw line pressure dropping on the 2-3. he asked me if i had made any changes to the tune and i let him know about the lockup issue. he was like that might have caused the burning up of the clutches as everything was mechanically sound in the tranny. anyway i set my lockup tables back to stock. havent driven to car to see if the vibes have come back.
I think you want more line pressure at light loads,
and you may have some compounding problems like
tune settings or sensor skews that tell the PCM that
load (airflow/RPM) is less than it really is (trans line
follows load, but can be on the wrong side of "just
enough" GM profile, if calibration is not as-stock).
Too little pressure, holding or during shift, will glaze
clutches.
I know nothing much about LT1s but you might want
to work over the force motor table, after pulling some
logs that show you delivered torque, line% and force
motor current. On my car I could see that even on
uphill grades at steady cruise, PCM commands 0% line
and this is where I was getting TCC slip & groaning.
Pulled back the 0%-column force motor current from
stock to something like 900mA, and blended it more
aggressively to zero current by 200lb-ft, and got a
fair bit better (but by then the converter clutch had
been pretty trashed, eventually replaced it).
You can monitor both TCC slip (straight RPM) and
"gearbox" clutch slip by the input/output shaft ratio
divided by the current-gear ratio - anything not 1.00
shows friction slip and is bad news (except for some
momentary, transition slip). If your in/out ratio does
not snap down to the target within a few frames you
are seeing a line-starved (or pre-cooked) clutch pack
or band.
and you may have some compounding problems like
tune settings or sensor skews that tell the PCM that
load (airflow/RPM) is less than it really is (trans line
follows load, but can be on the wrong side of "just
enough" GM profile, if calibration is not as-stock).
Too little pressure, holding or during shift, will glaze
clutches.
I know nothing much about LT1s but you might want
to work over the force motor table, after pulling some
logs that show you delivered torque, line% and force
motor current. On my car I could see that even on
uphill grades at steady cruise, PCM commands 0% line
and this is where I was getting TCC slip & groaning.
Pulled back the 0%-column force motor current from
stock to something like 900mA, and blended it more
aggressively to zero current by 200lb-ft, and got a
fair bit better (but by then the converter clutch had
been pretty trashed, eventually replaced it).
You can monitor both TCC slip (straight RPM) and
"gearbox" clutch slip by the input/output shaft ratio
divided by the current-gear ratio - anything not 1.00
shows friction slip and is bad news (except for some
momentary, transition slip). If your in/out ratio does
not snap down to the target within a few frames you
are seeing a line-starved (or pre-cooked) clutch pack
or band.