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Hi folks. A simple question has turned into quite a discussion here, so grab a beer and think about this one. What size (diameter) clutch plate should you use on a Pontiac 400? While one might assume that all 400s are essentially the same, at the parts stores they have different part numbers available for different years from different places. They offer various different size clutch plates (10", 10.5", 11", etc.). I've actually made some phone calls to tech support at a couple of clutch manufacturers and get very different answers, most reps obviously unsure of what they're telling me. Best bit I've been given is to "use the largest one that will fit such that more surface area means quicker cooling." I could go on.

Separately, but along those lines, in previous threads some have said that for street driving always go with a stock clutch. So just where do you get a "stock clutch"? Especially when you have a Frankenstein rebuild with say, a '74 block, '67 heads, and the rest from whatever other year 400 you cannibalized? For grins I walked into a NAPA store and asked for a clutch for a Pontiac 400. I thought their head would explode. They almost got mad when demanding a year, make and model of the car. I advised that I just had the engine that wasn't in a car and wanted a clutch that would work. No dice. (I'm old enough to remember the days when auto parts guys would LOVE it when someone came in with these situations....)

So what size clutch plate?

Shooter
 

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First, since you are mixing/matching parts, make sure your crank is drilled for a manual transmission. Most are, but if not, you won't be able to fit the input shaft into the back of the crank.

Stock Pontiac disc is 10.4", but the 10.5" is what you will find/use when using the factory cast iron flywheel. If you use an aftermarket steel flywheel, like Hays, they are drilled for both the 10.5" and 11" pressure plate/disc set-up.

Make sure you get the correct flywheel-to-crank bolts. Use the incorrect ones, and the heads of the bolts are too thick and will hit the center hub of the clutch disc - ask me how I know. LOL There is a set for the automatic flywheel and one for the standard trans flywheel.

You want to make sure you get the correct length throw-out bearing. There are three sizes, long, short, and intermediate. They also have different faces to match whatever style of "fingers" are used in the pressure plate. McCleod sells an 11" kit with the wrong length throw-out bearing for the Pontiac. They may have corrected this in the 10 years since I had purchased my kit. Had to shell out more money to get the correct length, so the "kit" was not so complete and I paid for the throw out bearing which was incorrect. Of course figured this out after the trans was installed and the clutch simply would not disengage no matter how I adjusted the linkage. Back out with the trans and the correct throw-out bearing installed. Worked like a charm after that.

For street, and not any killer leg pressure needed, you want to use a diaphram style pressure plate. You can use a 3-finger Long or Borg&Beck style, but these are rough on your leg as they require a lot of pressure. They have higher clamping forces, but really not needed for a street build unless you have a lot of HP. Used a Borg&Beck in one car I had, it worked great and never slipped, but even in my youth, it would wear out the left leg in stop & go traffic.

Discs have 2 different spline counts, 10 and 26. Most have 10 splines on the input shaft while a transmission like the M22 Rockcrusher uses a 26 spline input shaft. So look at yours to verify.

You want a "sprung hub" and a "marcel" between the two disc halves to absorb the shock forces - which most street clutches have.

They offer dual disc set-ups, but have never used one and don't plan on it. A single disc will get the job done.

Brand and type of disc material is open to opinion. The manufacturer will typically state the HP rating of the set-up. I see mixed choice of clutch facing materials such as organic, ceramic/organic, kevlar, etc.. Read here: Clutch Friction Materials Explained - Organic, Kevlar, Ceramic, etc. Organic is probably best for street. I had a Kevlar disc in my last build because it was recommended by my machinist. It was OK, but did chatter when letting out the clutch to take off in 1st/ Otherwise no complaints.

Year One, Ames, McCleod, and others all offer what you need. Talk/email one of these guys and you will find what you need. I would not use NAPA or other local parts suppliers to get my pressure plate and disc as they are most likely inferior UNLESS you are purchasing a brand name set-up through them.
 

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Shooter, if all you have is a Pontiac flywheel, that correctly fits your engines crank, you can measure 180 degrees apart to the furthest bolt holes tapped into the flywheel, where the pressure plate would bolt on.

-11 5/8 center to center on the holes in the flywheel is a 10.5" clutch pressure plate & disc.
-12 5/8" center to center on the small holes is an 11" flywheel & uses an 11" clutch plate & disc. Quite a few 11" cast flywheels have multiple small holes for both size clutch plates to attach.


The typical Pontiac V8 with Muncie or 2nd design T10 set-up works best with a stock style multi-finger clutch plate. These can be sourced locally, they dont have to be the cheapest Taiwan job from local autoparts store. If not ordering a McCloud clutch & pressure plate, and if you are near a major city, there will a Clutch Supply house, a local entity that builds clutches for industrial & HD truck applications. These same local companys can put together a HD clutch pressure plate/ disc in choice of either 10 splines or 26 splines for a reasonable price. They know the specs, usually at least one or two of the old timers have had a really hot manual transmision Chevelle or Camaro. Behind a really healthy high winding 413-448 Pontiac V8, an aftermarket steel flywheel & Borg & Beck style clutch setup is what I've run with. The pedal effort will be much stiffer. Would also pull the clutch pedal out & reinforce £ weld where the factory welds are up high where the square U shaped piece is spot welded on. This area commonly breaks if a 4spd car is driven hard. Best to you on getting her back together!
 

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Discussion Starter #5
To All,
I didn't forget you. Last Friday I talked to some race friends and they pointed my to a clutch shop south of town. Wanted to check this option out before I simply continues this thread. Couldn't get there for a few days due the 4th of July weekend (they were away racing). Went today and it was a sight I have never seen. This place was WAY out in the sticks, a shop set up in a guy's backyard many, many years ago that has been turned into a full fledged business. Father is now pretty much out of it and the son has taken over.

Building and grounds were meticulously kept on the outside. Walked inside and they had probably 1,000+ clutch disks sorted and hanging on the wall. Pressure plates on row after row of shelves. A pegboard of alignment tools for everything from a golf cart to a semi. 5 or 6 guys working at a breakneck pace on metal tables. Place was filthy - a grease monkey's heaven! Told the guy what I had (had the flywheel with me) and he knew exactly which parts I needed from memory. His explanation of which parts he chose mirrored exactly what each of you have said above. I had a print out of this thread and once he had the parts our on the table I went right down the list of what you guys said above. His stuff matched and he explained WHY each of those options are appropriate for me and why others would be wrong. Never tried to up-sell anything.

When the guys in the back heard it was for a '67 GTO, 3 of them came out and joined in. I learned more about clutch plates, pressure plates, Pontiac rivets, Pontiac bolts and Pontiac throw out bearings (I needed the short one by the way) than I could have ever imagined. Options for a cruiser up to a 625 hp drag kit.

$125.00 for all clutch parts (pressure plate/clutch disk/bearings/alignment tool) and $10.00 for the pressure plate bolts.

That's my idea of an auto parts store!

Shooter
 
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