G56 Clutch replacement advice

The South Bend Con-OFE clutch that I installed in my 2005 G56 12 years ago is finally slipping. Despite throw out bearing noise and a jerkier engagement from the Con OFE discs, it has been a decent clutch until I inadvertently (read distractedly) slipped it going up a steep hill with a heavy load in the wrong gear. It now slips when towing when I apply anything but the gentlest power on the gentlest hill, so its definitely time for a new clutch.

I do tow 15k to 20k fairly regularly and need a clutch that can support and handle the extra beans.

I am gathering information to help me decide between resurfacing the flywheel and replacing the clutch with another Con-OFE (feramic and organic single disk) ...

...or upgrading to the SBC Dual Disc Organic kit to get smoother engagement and more holding power at the likely expense of more clutch noise.

I would love to hear real world feedback on dual disc noise increases as well as feedback on their potential smoother engagement versus an upgraded single disc.

Also I am open to using Valair clutches if their dual disc strapping noise reduction system is an actual improvement over SBC's multiple neoprene inserts.

TIA !!!

 

How many miles did that clutch log? Also, is the, "I do tow 15k to 20k fairly regularly" your combined weight, or just the trailer weight? Last question - what is the horsepower / torque of your engine?

Personally, I would stay with the organic material whether or not I went with a single or dual disc clutch.

- John

 

The SBC Con OFE clutch went in only about 75k miles ago.
Thats pretty much combined weight which occasional combined loads to 22k.

 

Something don’t smell right here.

 

That's correct...it smelled pretty bad when I accidentally slipped it with too much power going up a STEEP hill with a HUGE load of green redwood 10 x 10 x 24' beams.
THAT load could easily have been 30k combined, but it is rare for me to pull so much,.

 

Speaking from experience, the South Bend Dual disc will hold more, but that about the only pro. The clutch will be slower and noisier than any single disc. You will "have" to double clutch your down shifts if you don't already because of the time it takes for that mid plate to slide for a shift. The Dual disc "hates" down shifting. The Dual disc will rattle pretty badly as well.

If you compare the South Bend Dual Disc to something like a Class 8 Eaton Dual disc or triple disc clutch the South Bend in terms of engineering is about as primitive as it gets, the clutch drivability and nosiness reflects that. Likewise for the Valair clutches, "This Quiet version will eliminate the floater plate rattle when the clutch pedal is pressed in. It will not get rid of gear rollover noise."

I'm sure this is due to proprietary rights of design. If you can get a single disc to work for your application I'd recommend that over a dual disc.

 

@seafish I don’t see anything in your sig that indicates you could overpower that O-FE clutch with only 75K miles on it (that assumes non abusive driving). Is something missing from your sig?

I ran an O-FE for years in my 05 (75K miles on it when I sold it). I generally maxed out at 23K but I did but 30K GCW a time or two, with 415/850 to the rear wheels and it was never an issue.

I did consider a slight detune to run the O-HD as I preferred it it the O-FE, and to any dual disk I had driven.

 

^^^ Thank you....That is very helpful info...

I didn't think about any of the effects of a dual disc clutch would have on downshifting... and of course driivng where and how I do, I downshift ALOT, though even with the Con OFE (Feramic/Organic discs) I often need to double shift.

 

@AH64ID Yes your observation is well noted and well said and I also will consider the O-HD as a possible replacement.

 

One of the biggest single issues of clutch kit installs, by the owner or shop, is they will use the pressure plate bolts from the kit. They are inferior to oem and can strip.

Years ago, I lost a clutch hub in my Ford Conversion. I was on the road loaded and had to have a shop fix it. They stripped my flywheel with the pressure plate bolts. On my test drive, 3 days and two clutch's later, (they both slipped) I crawled under the truck and found the problem. It has a large inspection cover on the bottom.

At 210k I replaced my oem on my '01 with this clutch from Sachs and had the flywheel surfaced. I am at 156k with it. On level five, I am at 400/900, never slips. I generally run level 3.

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Well . . . I would first point out that DBM's clutch is a NV5600 if I am correctly recalling from his transmission threads (not sure that it matters but thought I would point it out). I have an SBC dual disc organic in my G-56 and engagement is smooth and I do not recall there being any down shifting issues or other noise while shifting. As to noise I do get the throw-out bearing noise when the clutch is depressed (which is a good reminder not to have the clutch depressed any more than necessary) and I will get gear rollover noise if my shift points drop below 1800 rpm or so. Otherwise, it's quiet and holds my power which I have been advised should be 400+. I have not got the motor on a dyno to know better HP and torque numbers but it's pretty stout.

 

Great info...when did you install it and how many miles are on it ??
Would also like to hear about your GCW and how often you tow as well as the terrain you tow in.

TIA

 

Installed clutch at 189,000 miles. Threw in a new throw out bearing, pilot bearing and clutch fork at 207,000 when I had the motor out for rebuild. Currently has 215,000 miles on truck so about 26,000 on the clutch. I'm new to towing but the truck has been weighed at approximately 10K and the trailer wet is somewhere between 10K and 12K. I need to get everything weighed on a scale to know for sure but those are good estimates. I'm learning how to tow with my current set up and find when I get on upgrades I need to down shift into 5th to keep the EGT's down going up hill. On a couple of down grades I have also down shifted to control decent (no exhaust brake). All downshifting has occurred without any issues including noises that I can recall.

 

The G-56 or the NV5600 transmission with a single disc clutch or a dual disc clutch should perform equally well. They all should shift smoothly, whether upshifting or downshifting (assuming that all parts are in good working order).

When driving trucks with manual transmissions, it is always a good practice to match engine rpm's to road speed when shifting the transmission (up or down). Both the G-56 and NV5600 are fully synchronized transmissions. The synchronizers make up the difference in engine to road speed matching (through the transmission) when the operator does not make the effort. These synchronizers are designed to work with the mass and weight of a single clutch disc and pressure plate. The life of the synchronizer will be determined by the operator. Because the synchronizers are so effective, an inexperienced operator can shift as smoothly as an experienced operator. Also, the synchronizers allow for the OEM clutch to be single-clutched during shifts.

When a single disc clutch and pressure plate are replaced by a dual disc clutch and pressure plate, considerable rotating mass / weight has been added. Any mismatch of engine rpm to road speed will now exceed the capability of the synchronizer (especially if the rpm mismatch difference is significant during the shift), resulting in a rough or gear grinding shift. This is where the difference between an inexperienced operator and an experienced operator presents itself.

The primary purpose of double-clutching is to allow the operator to use the engine throttle to control the rpm's of the clutch discs, transmission input shaft, and transmission counter shaft while the transmission gear selector passes through neutral. This control can only happen WHILE the gear selector passes through neutral AND THE CLUTCH PEDAL IS RELEASED. It is at this precise moment that the throttle can be used to match the engine rpm's to road speed. If the clutch pedal is depressed while the gear selector is passing through neutral, the connection from the engine to the transmission input shaft will be lost - the operator will not be able to match engine rpm's to road speed. Consequently, the synchronizers, which are not up to the task, will be forced to do the work.

Typically, the operator doesn't have a problem with upshifting with a dual disc clutch using the single-clutching technique. This is because the engine rpm's fall when the throttle is released and the transmission input shaft rpm's naturally fall, as well. The upshift can be completed smoothly just by timing (or feel).

Driveability problems occur during downshifts because the operator needs to bring the transmission input shaft up to speed by using the engine throttle. This is when the double-clutching technique and throttle control are necessary and are effective for smooth shifts.

Personally, I use a modified double-clutching technique. At the beginning of each shift, I unload the gear by using the throttle and then pull the gear selector into neutral (no clutching). I then finish the shift as explained above.

- John

 

I found this video. Interesting. The sound as he is pulling into the garage is the sound I was describing with the clutch pedal depressed. I too have the hesitation going onto second gear. I have not noticed it on the other gears.