Clutch size
 

Going to be swapping my clutch out on my 77 Trans Am 400/4speed. Mild build, well under 400hp, and I just wondered what your thoughts were on 10.5” clutch vs 11”. I’ve run both, with the 10.5 being in there now. Both sizes I’m looking at are roughly the same cost too.

Thanks.

Is your flywheel drilled for both sizes? If so i would go back with a 11 inch over the 10 1/2.

I believe it is from memory

Are you running the OE iron flywheel? Might be a good time to upgrade that too?


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No, I replaced the flywheel already.

EDIT: long version is I pulled my engine last year and decided it was time to replace the clutch, PP and flywheel I’d installed probably 8 or so years ago when I converted the car from an auto to manual. I’d taken the car to a shop (big mistake) to fix a botched transmission rebuild and at some point they did something to cause the old clutch setup to chatter. I was better off walking away than trying to fight with them on the chatter issue. I just dealt with it until I pulled the engine last year.

So, at that time, I replaced the items above and still have some chatter issues. I didn’t think I needed to have the new flywheel surfaced but I’m hoping not doing so is at least a contributor to the chatter so I’m pulling the trans again, replacing the clutch kit and having the flywheel resurfaced at an attempt to stop the chatter. When I bought the last clutch kit I didn’t realize I’d gotten a 10.5” nor have I noticed much difference but I thought I’d ask opinions on the 11” vs 10.5”

You can get rid of the "Chatter" by glass beading the clutch disc on both sides and by
cleaning the flywheel surface and pressure plate surface with tide soap and water or with
gasoline BUT do the cleaning away from the garage.

Parts will last for many years. The chatter comes from the clutch resins boiling to the clutch disc surface and allowing the flywheel/ pressure plate/ and disc to not do their jobs.

Tom V

Tom, I seem to recall you saying previously to lightly glass bead the disc. What do you mean by that. Don’t have a blaster but I’m going to pick up a small one and some media to give this a try. Only thing it’ll cost me is some time and some extra time if it happens to not work and I need to pull it all apart again.

Why does this happen with the resin? I haven’t seen any other reference to this occurring.

Learned this from the Engineers at the Manual Transmission plant years ago.

The resin is used to bond the clutch disc material together when the part is created.
The resin gets hot after installation (of a new disc and guys beating on the parts)
and puts a film of resin on the surface of the disc and the flywheel and pressure plate.

Course the hot rod guys speed up the process of the resin boiling off the disc
material and on clutch parts. Then the clutch starts slipping and chatter.

So they remove the disc and install another part or parts. Same deal again. Reason why is no one is paying attention to
why the parts were slipping.

But the fix is to clean off the pressure plate and flywheel of resin and use a glass bead cabinet to "glass bead machine" the disc with walnut shells, etc to remove the excess resin on the clutch surface.

NOW THE DISC HAS BEEN HEAT CYCLED and the excess resin boiled off and the parts are all clean and fresh for re-installation.

I have run (and beat on HARD) the clutch parts on my GTO with no slippage whatever for years.
I will be glad to take any 11" clutch discs that Pontiac guys remove and then install new parts again.
Tell me what the shipping cost is. I usually give the parts to a bunch of short track racing friends or Bonneville guys.

So that is HOW and WHY it works. I really like the LUK 11" clutch parts.

Tom V.

Lots of experienced parts changers, not very many "This is WHY it happened" guys.

Thanks for the explanation. As it happens, my clutch setup is also a LUK. I took your mention of “glass bead” literally though and although I haven’t purchased any media yet, I planned to used glass bead. Do you recommend something different such as the walnut shells?

I’m hoping this takes care of my issue and will report back. I seem to recall the chatter occurring from the start of the new flywheel and clutch instillation but I could be mistaken.

Good info here. I'm also doing a clutch in my 77, and was looking at the LUK brand setups.

Seems we're in the same boat lol

My first LUK setup worked great until the stupid trans shop did whatever they did to cause the chatter at that time.

I would, for sure, use the "alternate media" vs glass bead as that just gets buried in the disc. Even fine clean sand would work better than glass bead. Walnut shells would be my 1st choice.

Tom V.

Thanks for the clarification

Glad to help.

Tom V.

Haven’t had much time to dig into the car lately till recently. Wife got covid then our 6 month old got sick at the same time. Got the trans out and PP/clutch off. Before I continue on my path, anything stick out to anyone? Seems ok to my uneducated (inexperienced) eye.

I tried listing another reply with the pressure plate but it won’t let me. Trying again

Small update is I took my flywheel to get resurfaced and afterward I noticed something I hadn’t before. This flywheel, which was advertised as a replacement for external balance and pictured with a portion of material drilled out for that offset balance, is missing the drilled portion. I called where I bought it from and after sending pictures and some back and forth they advised all of their on the shelf flywheels of the same part number have the drilled portion so mine must have escaped without it.

I never noticed a vibration but was able to confirm with my engine builder from 6 years ago my rotating assembly and stock flywheel was balanced and required no change.

The place I bought the flywheel from us me return the defective one and they are sending me a new one. Can’t complain seeing as I bought the other one almost a year ago but I slowed me down on getting everything back together this weekend like planned. Plus I ate $50 on the resurface but oh well. I’m sure I’ve spent more on worse.

Well worth the time to check stuff. Glad you got it figured out.

Tom V.

Man that's weird. Good on them for fixing the situation. Sucks about the waste of a resurfacing, but lok at it like you're getting a new flywheel for $50.

Just gotta blast that clutch disc and get everything back together to see if I’m back in business. Will post an update. Hoping to get the new flywheel by this weekend.

72, you’re not wrong. Definitely could’ve been worse and I’m grateful they were willing to make it right. Not their fault I resurfaced the faulty flywheel.