75-76 Aluminum 833 4 speed Overdrive trans questions ?

I don't have a problem with the different friction materials, or even the dual friction disc, they just need to be matched with a pressure plate that provides an appropriate amount of clamp pressure for that friction material and application.

The problem is the typical aftermarket manufacturer doesn't give you many choices when it comes to clamp pressure, they instead generally adjust torque capacity by varying the friction material. Since there are only a few common friction materials available, the step from one to another can be pretty big.

The typical aftermarket 10.5" diaphragm pressure plate has around 2800lbs of clamp.
......with an organic disc that's ballpark for around 500ftlbs.
......with a typical dual friction, now it's ballpark for around 650ftlbs.
......with cerametallic or iron disc, it becomes ballpark for around 820ftlbs.

So what do you choose if you have a street/strip car making say 550ftlbs, more than what the organic disc can reliably take? The next step up is dual friction, which has about 30% more clamp pressure than what is ideal for 550ftlbs. If you go for the cerametallic or iron disc it's even worse, about 64% more clamp than what's ideal for 550ftlbs.

Excess clamp pressure is what makes clutches act like on/off switches. The more excess you have, the worse it gets. The more excess you have, the more bog/spin you get, also the harder it beats on your drivetrain. Excess clamp pressure means higher than necessary pedal effort as well.

To me it would make more sense if we could choose the friction material for the application first, and then choose the clamp pressure to suit the application. Street applications would most always get organic single disc up to about 500ftlbs to keep pedal effort acceptable, organic dual or triple disc above that. Street/strip could step up to more aggressive friction materials that would be less street friendly but last longer under extreme conditions.

Diaphragm clutches are easier to operate for a given clamp pressure, and the clamp pressure stays in a tighter range over the life of the disc. Wouldn't it be nice if someone made diaphragms available in 200lb increments from 1200-2800? Not likely to happen.

They do make adjustable clamp Diaphragm, Long, and B&B pressure plates, so that's an option if you can find one with a suitable range.

What do I do? I'm a guy that likes to get more than expected out of common affordable parts. For my street/strip applications I take the common 2800lb PP, and then use my clutch hit control products to make that 2800lb pressure plate initially hit like a much softer 1800-2000lb unit, then transition to hold like a 2800lb unit. Softer hit on the drivetrain without giving up any of the holding power.

Grant


I agree. The issue I’ve had is most of those metallic discs (not the sintered iron) don’t do well when the clutch is being slipped.

The stuff balls up and gets gooey.

I‘m hoping that guys learn and understand that you have to have some way to control the application of the clutch. The cars will always be quicker and faster plus they don’t break parts when you get a handle on it.

I can’t count how many guys have told me over the years they quit running sticks because they broke everything. You find out what they had for clutches and you’re like all hell yeah it broke stuff.

I‘m old enough to remember (and to have used) one of the Direct Connection “green” cover pressure plate. Bought one in 1981. Actually two of those junkers. One for myself and the other for a buddy. I bought them the Friday before the Super Bowl and we changed out both as we listened to the Raiders beat the Eagles.

That thing SUCKED. Way too much plate load even for a rag disc. My friend bolted on some cheater slicks and promptly **** the driveline right out.

Of course, we were both proud as hell because we thought man, now she’s hooking and making power. It was a slow pig but a little bite and that clutch broke the driveline first and then we got that all beefed up it **** the 8 3/4.

And that was the start of parts destroying clutches over the years until I figured out you can’t just make the clutch a toggle switch.

So something needs to control the application of the clutch.

EDIT: I forgot to ask what disc you are using for your car.