Unsprung clutch disks in street cars (newer twin disks)
02-13-2012, 09:30 AM
#1
Unsprung clutch disks in street cars (newer twin disks) Whats your take on these? I'm pretty experianced with transmission rebuilds, rears, clutches, etc so I'd like to keep this as advanced as possible. I notice a lot of twins are using them and I have been considering a twin from ACT or Mcleod which both have solid hub disks. I know on some import cars I've seen the splines wear on the input shaft from unsprung disks on the street so I'm a little unsure what I want to do. I know the weight is kept down with them and they will shift at higher rpm, but if they cause extra wear on the input shaft thats no good.
This will be going in a vette so it does have a driveshaft with rubber couplers in between the clutch and trans which should help absorb some of the vibration, etc. Not sure about you guys with a standard trans layout and unsprung disks. Anybody have spline wear from these unsprung disks on street cars?
This will be going in a vette so it does have a driveshaft with rubber couplers in between the clutch and trans which should help absorb some of the vibration, etc. Not sure about you guys with a standard trans layout and unsprung disks. Anybody have spline wear from these unsprung disks on street cars?
02-13-2012, 10:42 AM
#3
The main purpose of the damper springs in the disk is to reduce the shock (when you dump the clutch) to the tranny input shaft as well as every other component all the way to the rear end. By going with a springless disk or disks, there will likely be some additional stress and possibly wear to all of the components making up the drive train. I have seen posts with street twins causing extra wear of the T56 input stub and if I had to place the blame, I would blame the springless disk. Not sure about your vette rearend but a run of the mill 10 bolt would be subjected to a sooner death due to a springless disk.
As you have already mentioned, losing the springs makes for a much lighter disk that will allow for much faster shifting under performance due to the disk being allowed to change its speeds faster (less inertia). Also there is less chance for disk explosion with a springless disk or disks.
If its a street ride, I would keep the springs if given the option as to maintain the greatest reliability possible. Another way of lightening the disk is to address the friction surfaces. Some clearly weigh more than others. I had a Spec 3+ disk and it was around 2 pounds heavier than the stock disk and it was apparent when high speed shifting.
As you have already mentioned, losing the springs makes for a much lighter disk that will allow for much faster shifting under performance due to the disk being allowed to change its speeds faster (less inertia). Also there is less chance for disk explosion with a springless disk or disks.
If its a street ride, I would keep the springs if given the option as to maintain the greatest reliability possible. Another way of lightening the disk is to address the friction surfaces. Some clearly weigh more than others. I had a Spec 3+ disk and it was around 2 pounds heavier than the stock disk and it was apparent when high speed shifting.
02-13-2012, 11:16 AM
#4
Yea, pretty much what you said, but the sprung disks also eat up a lot of the torsional vibration as the engine rotates. Certian engines (4 cylinders, etc) have different vibration traits that might be worse or better (depending on rpm) so it hard to say in our applications. Corvettes have a driveshaft (torque tube) between the engine and transmission that has rubber quibos which might help absorb some of the vibration. Having that driveshaft in front of the trans also adds extra load on the syncros, hence the reason corvettes have double and triple cone blocker rings, etc. I figure the standard transmission configuration would take more vibration, but it's hard to say without measurments.
It would be nice to hear from people that have been using unsprung disks (single or twin) for extended periods on the street. I like the idea of light disks making fast shifting, but a twin has two disks that are a little smaller in size so the MOI should be less. When you have two disks it's ahrd to say how they would compare to a larger single disk. Seems like most guys love how the Mcleod rxt/rst and ACT feel on the street so I'm most concerned with input shaft damage over time.
It would be nice to hear from people that have been using unsprung disks (single or twin) for extended periods on the street. I like the idea of light disks making fast shifting, but a twin has two disks that are a little smaller in size so the MOI should be less. When you have two disks it's ahrd to say how they would compare to a larger single disk. Seems like most guys love how the Mcleod rxt/rst and ACT feel on the street so I'm most concerned with input shaft damage over time.
Last edited by slowride; 02-13-2012 at 11:22 AM.
02-13-2012, 11:50 AM
#6
Is it a newer RXT/RST or the older twin? Are they toast or just worn some? Input shafts are hard to come be for vettes also which stinks (Like a $500 part at the dealer). The ls9 twin disks have a sprung hub, but are quite expensive for a factory part. The only time I've seen a factory car use a unsprung disk is when the flywheel is dual mass as it takes up some of the impact/vibration.
