G56 Issue

[Clay]

So, this weekend I had my oil changed to 5w40 since it's starting to get cold up here and the below 0 tempts are quickly coming and I had the differential fluid changed as well. I noticed an issue afterwards, and I don't know if it's related to the service or not, but I didn't want to hold back any info. In first, second and reverse I don't feel very much torque from idle to about 1. 5k rpm. After getting into third gear it drives like normal, but in those lower gears it feels and sounds like I'm revving the engine in neutral or have the clutch partly pressed in. Is my clutch slipping? I only have around 32k miles on my truck. Or is this something else? Thanks.



Clay

 

[AH64ID]

Are the rpms increasing faster than wheel speed?

 

[JLeake]

Sounds like the clutch may be slipping. Is it adjusted properly? AH64ID's question and the answer will help you figure it out.

 

[GCroyle]

Sounds like the clutch may be slipping. Is it adjusted properly? AH64ID's question and the answer will help you figure it out.

The factory hydraulic system does not have an adjustment.



The Self Adjusting Clutch does just what its name says, Self Adjusts w/o any directed input from the driver. It adjusts as necessary to compensate for a change in disc thickness. You cannot even access the SAC with the trans installed to try to adjust it. The only time I have found any reference to adjusting an SAC is if the worn disc ONLY was being replaced, there is a process to reset SAC's to a starting position, but it is a rare situation.



AH61D's comment about a disproportinate increase in engine RPM vs. MPH = slippage is valid. Tach should not spike like an A/T would when you accelerate hard. Prolonged slippage is very detremental to any clutch systems life and would most likely be detected as a nasty smell, a bit like hot drum brakes.



Your hydraulic system has a device in it just before the slave cylinder. It is between the elbow and the line, held in with wire clips. This device we feel is a pressure sensitive varible orfice. It is built with two "pistons" and springs. If you had some debris in the orfice IT MIGHT slow down the return of fluid and act as if you foot was on the pedal, possibly even gradually allowing the pressure to equalize and finally return to ZERO PSI which is normal with your foot off the pedal. This might be a real interesting case where applying a pressure gage between the slave cylinder and the rest of the system to see if you are experiencing residual hyd pressure.



If I'm anywhere close on that one, I'll be the first one to be suprized, but I have taken several of those flow restrictors apart, might be gummed up a bit.



Good luck.



Gary

 

[NIsaacs]

That is weird, normally a slipping clutch will work in the lower gears and not in the higher ones. I can't see where it is related to the oil changes.

Nick

 

[GCroyle]

Test Drive Idea

Clay,



We haven't heard from you in a bit, but this one has me puzzled. Suggestion.



The next time the truck behaves as you describe, find an isolated road or even open parking lot. Drive like normal, shift 1-2-3 or when it feels like it is not delivering engine torque completely just back off of the throttle a little bit, no acceleration. Hold in this mode for several seconds or even a bit longer. Now accelerate w/o touching the clutch pedal. Does it slip or hold? If it holds after you have a dwell time with your foot completely off of the pedal before accelerating, this might isolate the hydro's as holding residual temporary pressure. You are normally only in 1 or 2 or 3 for a very short time I F the hydros are holding pressure rather than allowing full release of pressure and permiting clutch engagement, well its just a test drive and might tell us something.



A stock G56 clutch and hydro's has a very soft pedal feel, almost like an import car with a longer pedal travel. Pedal effort is had to quantify and might best be compared to an identical setup. Any aftermarket G56 non self adjusting clutch system will NOT have the same pedal effort.



Good luck.



Gary