396 Flywheel...calling Joe Lucia

[John O.]

I'm almost ready to reassembly my 396 and have hit a snag. I have what should be an original flywheel but my engine man says may not be so. Joe, or someone can you please tell me what the correct part # for this should be and it's diameter and metal composition. Also, a description of any other unique characteristics would be greatly appreciated.

As always, thank you!

John Osterholm

[Bill W.]

Re: 396 Flywheel...calling Joe Lucia

John I dont have a picture of your flywheel or the casting # Im sure Joe will have it . This flywheel is unusual looking it is a iron lightweight 10 1/2" .The outside is cut away to get rid of extra weight and just has "nubs " left to hold the clutch on.It was only used on 65 396 Corvettes & 67 L88s. Im also told it was used on 302 Z28 Camaros ? There is a picture of one in an old Dobbins 63-67 fact book under L88s.I have seen a few of them at swap meets but they are worn out.Bill

[Joe L.]

Re: 396 Flywheel...calling Joe Lucia

John------

The flywheel for your application was originally GM PART #3866735. This is a 12-3/4" nodular iron flywheel with a 153 tooth steel ring gear. It is of "lightweight" design and 15.8 pounds weight. I can't confirm the casting number for this piece, but I believe that it may be GM #3856579. In addition, most original flywheels of this part number had six 15/32" flywheel-to-crankshaft mounting holes which were stamped. Five of the holes were stamped with a small "v" and one of the holes was stamped with a "w". Unfortunately, these markings may not have been on all original flywheels but, if they're there, it pretty much identifies this as an original flywheel.

The above-referenced flywheel was used exclusively on 1965 Corvettes with L-78 and 1967-69 Corvettes with L-88.

For 1970-72 Corvettes with ZR-1 and 1970-72 Camaros with Z-28 a virtually identical flywheel was used. This flywheel was GM PART #3991406. I believe that it also used casting number 3856579. I don't know if this particular part number had the stamped mounting holes, or not. The GM #3991406 flywheel became the SERVICE replacement flywheel for the GM #3866735 when that flywheel was discontinued from SERVICE in October, 1971.

The best news is that a "direct descendant" of the GM #3866735 and the GM #3991406 remains available from GM to this very day. In fact, I believe that it still carries the 3856579 casting number, but I can't guarantee that. In any event, it is identical as to functional specifications and it is the direct replacement for the original. It carries GM PART #14085720 and is probably the best 12-3/4" flywheel that GM ever offered.

If I were building or rebuilding an internally balanced Chevrolet V-8 with a 12-3/4" flywheel for a street application, this is absolutely the flywheel that I would use. Would I use an old, re-surfaced flywheel in order to have an "absolutely original" unit when this virtually identical NEW one was available? NOT A CHANCE!

By the way, what is the casting number of the flywheel that you have and does it have the stamp markings at the mounting holes that I described?

[Mike M.]

Re: 396 Flywheel...calling Joe Lucia

joe: i'm looking at an old GM flywheel, cast # 3856579 that is cast dated E 18 5. i've had it 20 plus years and got from a friend who said it came out of a 65 396. i just glass beaded the old girl looking for the V and W near the flywheel to crank mounting holes. can't find the letters on either the front or back surface in vicinity of flywheel to crank bolt holes. mike

[John O.]

Re: 396 Flywheel...calling Joe Lucia

Hey Guys,

Thanks for the responses. Well I'm way off. The one I found has casting number 3988999N on it. And it's got to weight more than 15 pounds. I've also got an after market High Perf one that works on it but requires a shatterproof housing. By the way what is 3988999N for?? Joe, I'll take your advice and get the GM part. Also, does GM still carry the clutch disk/pressure plate, if not them who is good for this?

Thanks again,
John

[Joe L.]

Re: 396 Flywheel...calling Joe Lucia

Mike-----

Check the periphery of the flywheel for other holes that might have the stampings next to them. My recollection is that it was the flywheel-to-crank mounting holes that had the stampings but it might have been other ones.

[Joe L.]

Re: 396 Flywheel...calling Joe Lucia

John-----

I don't know what the 3988999 is. However, if it's a 12-3/4" flywheel, then I expect that it's one of the casting numbers used for the 63-68 small block flywheels. Although never originally used on a big block, they can be used on internally balanced big blocks. This flywheel is a "standard weight" unit (about 25 pounds, or so).

The pressure plate assembly and friction disc for your application are long-discontinued from GM. This was a diaphragm-type unit and the pressure plate and friction disc were the same as those used for 63-68 Corvettes with small blocks (but NOT the same as those used for 1967-69 L-88s, which, as I previously mentioned, used the same flywheel as L-78).

A Luk/Sachs replacement will be just fine and should perform as well or better than the original. Also, you could go with a Centerforce I or II.

[John O.]

Thank You For The Responses *NM*

[Mark #28455]

Re: 396 Flywheel...calling Joe Lucia

If I remember correctly, this same flywheel was also used on the 5 speed vettes and camaros prior to going to the one piece rear main seal (different balance - have a visible weight on the back) many jet boats also used this flywheel with the 350's.