Chat­ter Stop

Cen­ter Plate Snub­bers Bring Quiet to a Twin-Disc Clutch

Diesel Power - - Contents - Words by BRUCE W. SMITH + Pho­tos by BRUCE W. SMITH

Cen­ter plate snub­bers bring quiet to a twin-disc clutch

EVEN BE­FORE the cus­tomer shut off the en­gine and walked into Mo­bile Diesel Ser­vice’s of­fice, the tech­ni­cians in the South­ern Ore­gon shop knew what the is­sue was with his ’13 Ram 3500. The noise and dis­tinc­tive rat­tle when the clutch was dis­en­gaged could be heard above the sound of air guns and shop com­pres­sors. The truck’s twin-disc clutch was in dire need of some TLC. By the sound of it, the most likely cause of the ca­coph­ony could be at­trib­uted to the an­ti­rat­tle snub­bers be­ing shot and no longer do­ing their job.

A year and a half ear­lier, the same rig had a slip­ping stock clutch. Mo­bile Diesel up­graded the 6.7L Cum­mins–pow­ered pickup with a South Bend Clutch G56OK-HD twin-disc to han­dle the ad­di­tional power gained from an ex­haust, ECM tun­ing, and other mod­i­fi­ca­tions, which most likely con­trib­uted to the stock clutch’s early demise.

Ac­cord­ing to the owner, the rat­tling noise be­gan sev­eral months ear­lier and had got­ten pro­gres­sively louder. Ruben Vil­lalo­bos, an MDS tech­ni­cian who spe­cial­izes in such mat­ters, put the Ram on the rack and pulled the clutch. Sure enough, he could clearly see the hard plas­tic anti-rat­tle snub­bers were

miss­ing from the cen­ter plate of the clutch. Hence, the pri­mary cause of the ob­nox­ious rat­tling when the clutch pedal is de­pressed.

All twin-disc clutches make noise as a di­rect re­sult of the cen­ter, or “floater” plate, which is the in­ter­me­di­ate fly­wheel be­tween the clutch discs, vi­brat­ing against the lo­cat­ing notches in the fly­wheel when the clutch pedal is de­pressed. There are nu­mer­ous meth­ods used by clutch man­u­fac­tur­ers to damp the noise gen­er­ated by the in­her­ent move­ment of the floater plate. South Bend uses hard, but­ton-like neo­prene snub­bers, one on each side of the four lo­cat­ing ears.

Why these snub­bers fail is dif­fi­cult to pin­point. “A clutch is a wear­able prod­uct, so it re­ally comes down to how the truck is be­ing used and how it’s driven,” says Man­seil Wash­burn, the head of the South Bend Clutch diesel divi­sion. “Snub­ber fail­ure in this in­stance could be at­trib­uted to the truck be­ing hooked up to a trailer all the time. But it’s more likely hard jolts to the driv­e­train, such as when spin­ning tires sud­denly get trac­tion, that flat­ten out the snub­bers pre­ma­turely.”

Man­seil says the loss of the tiny in­ter­nal noise dampers can also be caused by one or more of them not prop­erly fit­ting in the holes in the ears of the cen­ter plate, caus­ing them to loosen pre­ma­turely. They may have also got­ten hot from slip­page, which can hap­pen when back­ing up a trailer. Ex­ces­sive heat leads to the plas­tic snub­bers fall­ing out or dis­in­te­grat­ing. Or it could be a com­bi­na­tion of all of the above.

One thing that is al­most cer­tain when one fails is the oth­ers will soon fol­low. The miss­ing piece causes the cen­ter plate’s vi­bra­tion to in­crease, which places even more force on the re­main­ing snub­bers. The good news is they are easy to re­place once the clutch is out. South Bend typ­i­cally sends a packet of the “Neo­prene Anti-Rat­tle Cen­ter Plate Snub­bers” (PN MV11-1) to cus­tomers free of charge.

“We haven’t made a change to those [snub­bers] in a cou­ple of years, but the new­est ver­sions have a lit­tle ta­per on the pro­tru­sion that fits into that cen­ter plate, so they’re go­ing to be stronger

ini­tially be­cause they fit the hole bet­ter,” Man­seil says.

As you see in the pho­tos, Ruben re­places the snub­bers and throw-out bear­ing (PN N070SA-HD), which also shows signs of wear. The rest of the clutch assem­bly still looks new—even after 70,000-plus miles. In the end, six hours of rack time and $60 worth of parts is all it takes to make a Ram’s ob­nox­iously loud clutch whis­per quiet.

2. Mo­bile Diesel Ser­vice tech­ni­cian Ruben Vil­lalo­bos uses a hy­draulic trans­mis­sion jack to do a lot of the heavy lift­ing when work­ing alone, in­clud­ing re­mov­ing the ’13 Ram 3500’s trans­fer case cross­mem­ber and the two-piece rear drive­shaft.

1. Re­move the plas­tic trim and six 5/16-inch bolts that se­cure the shifter to the G56 six-speed man­ual trans­mis­sion, so the gear­box can be taken out eas­ily. Note: Shift the trans­mis­sion to Neu­tral to ease re­in­stal­la­tion.

PRO TIP:Be­fore pulling the trans­mis­sion, the elec­tronic trans­fer case is shifted into four-wheel drive. This al­lows the front out­put yoke on the trans­fer case to be turned by hand, mak­ing it much eas­ier to align the trans­mis­sion in­put shaft with the clutch dur­ing re­in­stal­la­tion.

5. Be­fore low­er­ing the trans­mis­sion/trans­fer case/clutch assem­bly, Ruben un­hooks the frame clips that hold the DEF wiring har­ness so he can slide it up and over the trans­fer case with­out ac­tu­ally hav­ing to dis­con­nect all the wiring.

6. Pro tip:Rent or bor­row a 33-inch-long, ½-inch drive ex­ten­sion for your air-im­pact gun. The long ex­ten­sion re­ally makes get­ting to the up­per bolts that hold the bell­hous­ing to the block a lot eas­ier.

4. With the G56 six-speed man­ual trans­mis­sion/trans­fer case assem­bly bolted to the jack, Ruben pulls out the four 15/16-inch bolts that hold the cross­mem­ber to the frame. Make sure you have a stout jack, be­cause there’s about 450 pounds sus­pended above your head.

3. The hy­draulic clutch slave cylin­der is re­moved.

10. Here’s the cause of most of the clutch racket: miss­ing anti-rat­tle snub­bers on the twin- disc’s cen­ter plate, or “floater plate.”

11. Once the South Bend twin-disc clutch is taken apart, the old snub­bers fall out. All are in dif­fer­ent stages of dam­age and de­te­ri­o­ra­tion. Ruben in­stalls new snub­bers from South Bend (PN MV11-1), along with athrow-out bear­ing.

9. Be­fore re­mov­ing the clutch assem­bly, Ruben shows us where the man­u­fac­turer marks the po­si­tion (red paint) of the com­po­nents after ev­ery­thing is bal­anced. It’s crit­i­cal the clutch goes back to­gether with the parts in the same lo­ca­tion.

8. With the trans­mis­sion down, in­spect­ing the throwout bear­ing is easy. This one is bad, so it is be­ing re­placed. Rid­ing the clutch or sit­ting with the clutch pedal de­pressed for long pe­ri­ods of time will shorten any throwout bear­ing’s life.

7. The trans­mis­sion is then low­ered and moved out of the way.

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