Gearing/Clutch Chatter BBC-T56
 

Hello Everyone,

I'm having a problem with my clutch chattering when the clutch and engine are cold. When they aren't it still seems like I have to slip the clutch quite a bit and then I smell hot clutch. It occurred to me this weekend that maybe I have gearing issues.

The engine is a 454 BBC with a T-56 transmission. First gear is 2.66. I haven't touched the rearend, but was told it had something like a 3.09 rearend gear. The Camaro's that this transmission came with usually had a 3.31 or 3.55 rearend. I'm wondering if mine is geared too high. I think the torque of the BBC is overcompensating so its sort of working.

Would this cause my chattering and having to slip the clutch problem? 6th gear is almost useless right now. Doing 80MPH it tachs about 1700RPMS, if that.

Thanks for the help!

I'm thinking I have some oil on my clutch disc and that I need to resurface the flywheel.

My gearing isn't optimal, but that shouldn't be the chattering. I'm planning on pulling the trans to inspect and fix this problem.

Tim,

Clutches truly have there own personality. Every manufacture is using a different recipe in the friction material and design. A compromise in clamping force to hold horsepower and maintain smooth engagement for driveability. My experiance lately has been mixed, we used a dual friction kevlar based friction on one side of the disc made by spec and mcleod and the spec was horrible, chattered like crazy, all with a brand new engine, well balanced fresh cut flywheel and new mounts. The mcleod was ok, but had a slight chatter when hot, needed to be slipped slightly. We ended up using a stock LS7 clutch and it had fantastic engagment, it appeared to be some kind of organic mix on both sides. Also had good expeiarances with the centerforce dual frictions smooth with good clamping force. If your trying to harness over 600 hp and launch the car agressivelly then just go with a dual disk.

You didnt mention what your using. Heres some tech on how those little springs and center wave plate between the frictions help dampen and prevent chatter.

Clutch linings. The linings of the disc used to be made of asbestos. They're now made of fiberglass or other materials that do not contain asbestos due to the effects of asbestos to our health. However, asbestos provides superior cushioning and better wear than the newer materials at this time. The linings contain copper and/or bronze metal strands to aid heat dissipation and to help prolong disc life. The linings have grooves cut in their faces for air ventilation and to help prevent lining dust build up. Dust build up causes chatter and slipping due to the slip/grab action of the dust. The 6 to 9 springs around the disc hub may range from loose to tight. Not to worry, the looseness/tightness does not affect the operation of the disc. They're there to asborb shock and help eliminate engine pulsations (lumpy cams). By far the most critical element of the disc in eliminating chatter is the "marcel". This is the term given to the crimped plate, or wafer, between the 2 clutch linings. The purpose of the marcel is to prevent clutch chatter by giving the clutch disc some "give" during clutch engagement. The marcel also helps prevent the lining from sticking to the flywheel and/or pressure plate (due to the spring effect of the marcel) when the clutch is being disengaged. The marcel thickness (the distance the linings are held apart by the marcel when the disc is not under compression) will vary depending on the type of use the disc is designed and built for. Basically the thicker the marcel, the smoother the clutch will engage and the spongier it feels to your foot. The absence of marcel makes the clutch grab, but makes for a much more postive lockup (less slippage and ability to handle more horsepower). As the marcel thickness increases, it will require more clutch lever travel to engage/disengage the clutch. A pure drag/race car clutch marcel will be from 0.000" to 0.010" since engagement is quick and abrupt and chatter is not a problem. Truck clutches use marcels in this area also. A street/strip clutch will generally have marcels from 0.015" to 0.025". Pure street clutches will use marcels in excess of 0.025". A super soft clutch uses marcel in the neighborhood of 0.030" to 0.040". Mine is 0.025" and works well with no slippage and no chatter. When the marcel gets up to 0.030" and more, it may require as much as 60% of the clutch travel to engage. In 1949 or so, Ford advertised a "cushione clutch" in the Mercs and Lincolns. With the newer disc materials the marcel thickness has increased to 0.050" to 0.060" since there is little cushioning affect of the harder materials. When marcels are used, the linings are riveted. When they aren't used, the linings are bonded or riveted and bonded.

Hope this helps- Rich

I did a similar install with a clutch disc rated at 650hp (semi rigid flex plate between input spline and friction disc material). Just as 67Rag mentioned, each disc has its own characteristics and some of those will jump up and be more obvious than others depending on the application and use.

On the install I did, the rear end had 3.08s. However the system worked for hard driving, especially if you hammered it hard, because the flexing portion of the disc and marcels did not have time to viberate and cause wierd noises. The only main problem was that is was a little annoying for the street. And yes the customer could not basically use his 6th gear even at highway speed due to the 3.08 gears. At low torq and RPM roll ons - or highway speed in 6th gear, and especially from 1st gear, the disc would clunk and rattle like there was a gear problem in the T56. It basically was the disc having harmonic viberations in the flex plate and marcel area.

Good info 67Ragtop

If you need to replace the clutch and want pedal pressure like a Honda that can hold the power look at the McLeod twin discs. They are a big more expensive than a single disc; however you will not be worried about it holding the power in ANY environment. They have ones rated at 800-1000hp flywheel.

One of the nicest clutches I've ever driven that holds the power. An LS7 clutch beyond about 500rwhp in a heavy car simply doesn't take the abuse well. They do drive nice though :)

[QUOTE=Tim@TMI;451256]I'm thinking I have some oil on my clutch disc and that I need to resurface the flywheel.

[QUOTE]
thats what iam thinking too. how did it feel when it was new?