Clutch fingers and bellhousing
03-14-2014, 01:26 PM
#1
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Clutch fingers and bellhousing This has been discussed in other threads, but curious what you all think of my situation.
I'll try to keep this simple.
Hyd. clutch release bearing gap between bearing face and fingers should be between .1 and .2 determined by subtracting trans face to bearing face (at fullly compressed position) measurement from the fingers to bellhousing trans mount surface.
Most everyone knows that an LS has a .4" shorter flywheel mounting surface which I made up for using the recommended .4" thicker flywheel from McLeod. I'm also using a Quicktime bellhousing that is the same depth as an old school bellhousing 6.290" that mates a TKO 600 to an LS, a McLeod RST twin disc clutch, and an extended pilot bearing.
The problem is that the measurement from the fingers to the bellhousing is only 2.53" which is shallower than what it would be if this were a SBC which is the whole point of using the thicker McLeod flywheel. To get the clutch disc to ride the input shaft where it would if this were an older style engine.
When I do the calculations using the shortest bearing I could find, my A - B measurement = .0325.
So at this point, I'm not entirely sold that I needed the .4" thicker flywheel contrary to several articles and discussions out there.
Ideas? Thoughts? Similar experiences?
I'll try to keep this simple.
Hyd. clutch release bearing gap between bearing face and fingers should be between .1 and .2 determined by subtracting trans face to bearing face (at fullly compressed position) measurement from the fingers to bellhousing trans mount surface.
Most everyone knows that an LS has a .4" shorter flywheel mounting surface which I made up for using the recommended .4" thicker flywheel from McLeod. I'm also using a Quicktime bellhousing that is the same depth as an old school bellhousing 6.290" that mates a TKO 600 to an LS, a McLeod RST twin disc clutch, and an extended pilot bearing.
The problem is that the measurement from the fingers to the bellhousing is only 2.53" which is shallower than what it would be if this were a SBC which is the whole point of using the thicker McLeod flywheel. To get the clutch disc to ride the input shaft where it would if this were an older style engine.
When I do the calculations using the shortest bearing I could find, my A - B measurement = .0325.
So at this point, I'm not entirely sold that I needed the .4" thicker flywheel contrary to several articles and discussions out there.
Ideas? Thoughts? Similar experiences?
03-14-2014, 03:10 PM
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03-16-2014, 10:34 PM
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I never thought that the longer flywheel was needed. I used a 621 bellhousing on my L92 with a LS7 clutch and flywheel with a Richmond 6spd and a Quarter Master TOB. I had plenty of room for the bearing and just used the supplied spacers to get my gap right. Details are in my build thread.
Andrew
Andrew
03-17-2014, 07:46 PM
#7
I never thought that the longer flywheel was needed. I used a 621 bellhousing on my L92 with a LS7 clutch and flywheel with a Richmond 6spd and a Quarter Master TOB. I had plenty of room for the bearing and just used the supplied spacers to get my gap right. Details are in my build thread.
Andrew
Andrew
Not to 'jack this guy's thread, but do you happen to remember the depth of your 621 bell? I have an old-school (6.5" deep) BBC scattershield, SPEC stage II clutch, Howe hydraulic bearing and Jerico 4 speed going behind my L92 block. I believe my "stack" is too short and will require at least a 1/4" spacer between the box and bell...
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03-17-2014, 09:34 PM
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Andrew,
Not to 'jack this guy's thread, but do you happen to remember the depth of your 621 bell? I have an old-school (6.5" deep) BBC scattershield, SPEC stage II clutch, Howe hydraulic bearing and Jerico 4 speed going behind my L92 block. I believe my "stack" is too short and will require at least a 1/4" spacer between the box and bell...
Not to 'jack this guy's thread, but do you happen to remember the depth of your 621 bell? I have an old-school (6.5" deep) BBC scattershield, SPEC stage II clutch, Howe hydraulic bearing and Jerico 4 speed going behind my L92 block. I believe my "stack" is too short and will require at least a 1/4" spacer between the box and bell...
I never measured the depth of my 621 bellhousing but the "standard" GM bellhousings were 6.25". Remember that the old school Muncies and other transmissions (my Richmond and your Jerico, and the TKO included) all had an input shaft length of 6.66".
I can't imagine that you would not have enough room unless the clutch your using is extra tall. Keep in mind that the clutch fingers will move towards the engine as you tighten the pressure plate. I used quite a bit of shims to get my air gap right on my set-up. Here is a picture will the shims installed:
If you look carefully there is a mark on the splines, that is where the edge of the disk was. The other mark at the tip was where the input shaft engaged with the LS7 pilot bearing.
Andrew
03-18-2014, 08:02 PM
#10
Russ,
I never measured the depth of my 621 bellhousing but the "standard" GM bellhousings were 6.25". Remember that the old school Muncies and other transmissions (my Richmond and your Jerico, and the TKO included) all had an input shaft length of 6.66".
I can't imagine that you would not have enough room unless the clutch your using is extra tall. Keep in mind that the clutch fingers will move towards the engine as you tighten the pressure plate. I used quite a bit of shims to get my air gap right on my set-up. Here is a picture will the shims installed:
If you look carefully there is a mark on the splines, that is where the edge of the disk was. The other mark at the tip was where the input shaft engaged with the LS7 pilot bearing.
Andrew
I never measured the depth of my 621 bellhousing but the "standard" GM bellhousings were 6.25". Remember that the old school Muncies and other transmissions (my Richmond and your Jerico, and the TKO included) all had an input shaft length of 6.66".
I can't imagine that you would not have enough room unless the clutch your using is extra tall. Keep in mind that the clutch fingers will move towards the engine as you tighten the pressure plate. I used quite a bit of shims to get my air gap right on my set-up. Here is a picture will the shims installed:
If you look carefully there is a mark on the splines, that is where the edge of the disk was. The other mark at the tip was where the input shaft engaged with the LS7 pilot bearing.
Andrew
My old 70's scattershield is exactly 6.5" deep...
03-18-2014, 11:00 PM
#11
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I like your t/o bearing better than the Howe. On mine, the lines are on the part of the cylinder that push/pulls the actual bearing so the lines are constantly flexing. I did my initial mock up by bolting everything together (including torquing the clutch) and needed 2 shims. But since taking everything apart, a guy over on hotrodders.com who has the exact same parts, needed the spacer just to get his stuff together. I may still be OK, I'm inclined to trust my measurements over someone unknown to me but I'll have to wait until I can get things together again. This time, I have my master cylinder so I can actually operate everything on the floor before installing. Don't know about your QM, but the Howe needs some slack to "adjust" for clutch wear unless I want to be pulling it apart to remove shims as the clutch wears...
My old 70's scattershield is exactly 6.5" deep...
My old 70's scattershield is exactly 6.5" deep...
The QM bearing is similar to the Howe in that the actually bearing is pressed on the body which is the part that moves. The piston fits over the bearing retainer and is stationary, so the lines move with the bearing. I haven't experienced any issues with this. The Howe does have the snap ring that keeps the bearing from being over extended, which is a nice feature. I've over traveled the QM bearing and that's no fun.
i think both the Howe and the QM bearing need about a .150-.200" air gap between the clutch fingers and the bearing surface. I think I set mine up with about .180" clearance.
Andrew
03-19-2014, 12:22 PM
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Good to know that the howe bearing has the retainer to prevent over extension. I was worried about that. I still plan to use a pedal stop. U using one as an extra safety?
03-19-2014, 12:44 PM
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Yeah I just got off the phone with howe. Not very helpful and they informed me that I would have to pull the trans occasionally to make adjustments as the clutch wears. No thanks! Lol
03-19-2014, 06:48 PM
#14
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The tech is confused. The whole purpose of setting up the bearing with a .200" air gap is to accommodate the movement of the spring fingers as the clutch wears. So as the clutch wears, the amount of free play at the top of the pedal will decrease because the fingers are now closer to the bearing face, but there should not be any periodic adjustment needed. The tech doesn't know what he is talking about.
One of the reasons that I like the LS7 clutch is that it has a self-resetting mechanism that maintains preload on the disk as the disk gets thinner, so the above problem isn't even a concern.
Andrew
03-19-2014, 08:17 PM
#15
Sorry for the misunderstanding. The Howe bearing is the one that has the retaining clip to prevent over traveling, not the QM.
The tech is confused. The whole purpose of setting up the bearing with a .200" air gap is to accommodate the movement of the spring fingers as the clutch wears. So as the clutch wears, the amount of free play at the top of the pedal will decrease because the fingers are now closer to the bearing face, but there should not be any periodic adjustment needed. The tech doesn't know what he is talking about.
One of the reasons that I like the LS7 clutch is that it has a self-resetting mechanism that maintains preload on the disk as the disk gets thinner, so the above problem isn't even a concern.
Andrew
The tech is confused. The whole purpose of setting up the bearing with a .200" air gap is to accommodate the movement of the spring fingers as the clutch wears. So as the clutch wears, the amount of free play at the top of the pedal will decrease because the fingers are now closer to the bearing face, but there should not be any periodic adjustment needed. The tech doesn't know what he is talking about.
One of the reasons that I like the LS7 clutch is that it has a self-resetting mechanism that maintains preload on the disk as the disk gets thinner, so the above problem isn't even a concern.
Andrew
03-19-2014, 08:34 PM
#16
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How's that work? I've got a SPEC stage II, how is this different from a factory clutch? I'm with you on the free-play, the more you can dial in at the start, the less you have to pull the trans & reset shims. And the play can be adjusted for if you have an adjustable pushrod. Or a Wilwood reverse-hung 2-pedal like I'm running...
http://www.google.com/patents/US4924991
All of the aftermarket companies use the old style diaphragm style pressure plates, presumably because of the Valeo patent.
There is a fine balance between having enough air-gap to allow for some room between the spring fingers and bearing and having too much. If there is too much free play, then the bearing can run out of stroke before the clutch is fully released. This is especially critical with the QM bearing that only has about .500" or travel. The Howe bearing is supposed to have .750" of travel, but I don't have any first hand experience with it.
The play at the top of the pedal travel can only be adjusted if there is a spring to pull the pedal up to the top. I don't have a spring like that, so I don't have a lot of free play in my pedal on my GTO. Other pedal arrangements will obviously be different, so as they say, "your mileage will vary."
Also, it is always a good idea to run a pedal stop. I don't run one but do as I said and not as I do...LOL I learned this the hard way and it is the reason that I overtraveled my bearing and had to drive home from the track by starting the car in gear and shifting by rev-matching. Not fun. Supposedly with the Howe bearing this is not a concern, but again, I don't have first hand experience with it other than holding one in my hand.
Andrew
03-20-2014, 09:05 AM
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I didn't like the howe vibe. Probably going with the McLeod bearing and a pedal stop. Good customer service and tech support plus I'm using a McLeod flywheel and their RST twin disc clutch.
