LS1 Tech seems to be the best place to ask about 4L60E issues - so here goes...

I have a freshly built up LS trans and custom low stall speed torque converter. The trans is controlled with a USShift Quick1 (Baumann Optishift). It's working pretty well except for a harsh vibration that happens whenever the lockup clutch is engaged.

The vibration is not just momentary when the clutch is engaging but is there the whole time the TCC is locked up.

There is no noticeable slippage when the TCC is locked. The vibration does not change significantly with load. In fact, it is just as bad decelerating as it is under load or at light cruise. It's a little less harsh at higher speeds but is always present until the TCC releases.

The trans controller allows me to adjust the TCC firmness and line pressure. Changing those parameters doesn't have much of any noticeable effect.

TCC solenoid? PWM valve? Faulty lockup clutch?

Any insights, suggestions or advice are welcome.

 

My best guess would be driveline vibration magnified when the torque converter goes into lockup. Perhaps the converter has excessive hub runout, converter improperly centered to the crank, loose flex plate bolts, incorrect pinion angle and so on. There are many variables.

-Brian

 

Additionally to what Brian said, you will need to check this:
- are you getting engine misfires during lockup...?
- are engine RPM and trans TIS (view with scantool) equal during lockup...?
- what does scantool show for TCCSLIP during lockup...?

 

We have even seen a poly trans mount cause interesting vibration issues.

-Brian

 

Hey guys, thanks for the replies.I don't believe it could be magnified driveline vibration. It just doesn't have that sort of feel to it. When the vibration occurs it sounds and feels like running over those rumble strips that are sometimes cut into the side of the road. It's loud and 'sharp edged' shakes the whole car. Also, the frequency of the vibration is maybe 2-3 times higher than engine rpm. At 60 mph and in 4th lockup the motor is turning 1500 rpm. That's about 25 Hz. The vibration feels more like 50-100 Hz, maybe higher. As I remember it, the frequency does not increase with rpm or road speed. I am not 100% sure about that but will pay specific attention next time I take it out on the road - which won't be until next week.

The converter is a custom made Circle-D unit. Chris hooked me up with it last fall but I've only got the car out on the road this week. The center boss is pretty snug in the crank. I measured .003" clearance in the initial test fit. Didn't see anything that looked like it could be a problem during test fitting and installation.

Transmission and motor mounts are the standard black rubber variety.

I don't understand what 'incorrect pinion angle' refers to. Can you explain? Is it something I can check?Definitely not a misfire. The motor is a GMC 6.5 diesel. Diesels don't really 'misfire' like a gas motor can. I can't get any scantool data. The project car is way too old to have OBDII which is one reason I'm using the USShift controller to manage the transmission.

Keep the ideas coming.

Can anyone tell me approximately what frequency the PWM valve pulses at? My best guess at this point based on the feel is that the PWM valve is 'hammering' the TCC and not allowing it to fully lock. Is that even possible?

 

Bump?

 

When you say you can adjust TCC firmness and line pressure, can you elaborate more. I assume it still a PWM apply and you are adjuring the min/max values like HP tuners?

If you crowd the throttle when locked any noticeable flare or slip?

Chris

 

The Quick1 controller has a table where you can adjust shift points, line pressure and TCC "firmness".

The firmness is a chart line with 0-100% throttle position in the horizontal scale and 0-255 in the vertical scale labeled firmness. You can shape the TCC firmness line by moving points up or down. The default line was a curve starting out relatively high (200ish) in the low throttle openings and tapering down to less than 50 nearing WOT. I don't know exactly how the controller accomplishes this. There are also separate settings to tell the TCC what speed to engage and what speed to release when the throttle is closed. As well as whether the TCC can engage in 3rd, or 2nd.

Line pressure is a similar chart line, adjusted in the same way. The vertical 0-255 scale is labeled current. If I set the line pressure too high (over 125 at any point) I get an over-current error code from the display on the controller.

I don't have any experience with HP tuners so can't comment if it is similar.

No matter how hard I am into the throttle I can't detect any noticeable amount of slip when the TCC is locked. Also, getting on or off or feathering the throttle does not affect the intensity of the vibration.

I should mention that at the end of a couple hours of driving spent dialing in the shift points and trying to have some tuning effect on the vibration the TCC quit locking (even thought he controller indicator showed locked). I'm guessing whatever the vibration problem is may have overheated it. It was back to locking up (and vibrating) the next day.

 

If your Quick1 is controlling a 4L60E or 4L80E, be aware that line pressure goes up as current goes down... you have to be careful when moving this curve.

Post pics/screenshots of your various tables.

 

Hmm... I have not been able to turn up much info about how to (or how not to) work with the line pressure curve. The error code explanation does state that if it sees an over-current error it attempts to override it with some default values.

I'll post some pics next week, as soon as I get back to my laptop.

 

Overcurrent implies that line pressure is being commanded too low (insufficient for clutches to hold).

 

OK, that explains the ski slope shape of the line pressure curve. Less current at higher throttle openings.

So, moving the curve downward on the chart will increase line pressure. Is there anything to watch out for by lowering the line pressure curve too far?

 

Looks like the only way to answer my last question is to install a gauge and adjust the line pressure according to the gauge readings.

I've read elsewhere that line pressure on the 4L60E should not exceed 240 psi. Does anybody disagree with that? What would be the risks of running slightly higher?

 

^ not sure

 

The first image shows the up and down shift curves with the line pressure curve.

The second image has the TCC firmness added in.

 

One issue is that the 3/4 clutch can begin to "cone" because the backing plate is only held by the snap ring on the outside edge. This is one reason the Sonnax Smart Tech input drum has a very solid bolt-in backing plate.
I've also heard trans builder tell me they have seen pump problems and blown seals/gaskets when the pressure reaches close to 300 psi.

 

May also cause torque converter ballooning issues (which will mess with crank thrust bearing).