Flywheel dilemma

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Flywheel dilemma

Postby gjz30075 » Wed Dec 07, 2016 7:18 am

Hi all. I'm looking to change out my extremely heavy clutch in my 66 GT350. The car was an automatic and the PO changed it to a T10. I now noticed the
bellhousing is a C5AA type, ie, 164 tooth flywheel. I'd like to change it back to 157 tooth flywheel but my research shows I'll need a hipo flywheel, ie, 30 oz imbalance
vs a normal 28 oz imbalance. I'm making some assumptions here because it hasn't been pulled apart yet but, is it possible the 're-imbalance' the 164 tooth flywheel to
30oz? Assuming they didn't, should I feel vibrations of imbalance? Motor revs fine up to 5k without issues. Haven't tried 6k yet.

If I get a hipo flywheel, would I be 'good to go' without rebalancing? I really don't want to pull the motor and take it apart for this.

Another alternative would be to simply get a different clutch for the current flywheel. But it, too, may be 'imbalanced'. Ugh.

Another thought: Is it possible to imbalance a 28 oz flywheel to 30 oz?

Thanks!
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Re: Flywheel dilemma

Postby zray » Wed Dec 07, 2016 8:09 am

I've used the stock 28 oz balance flywheel on a a '66 GT350 and a couple of early K codes. The motors didn't have any more vibration at 6,000 + rpm than they had before the switch. That's not a scientific conclusion. And your experience may vary.

Clearly the right path would be to rebalance the entire rotating assembly. But I dont think that many people go to the trouble to do that.

Z

PS. When I installed my first vintage Paxton in a '66 GT350 about 20 years ago, I changed the the original clutch out for a Cemterforce Dual Friction clutch thinking I needed more holding power. After all, with the supercharger I did have considerably more horse power, and fun ! But I grew tired of the on-off type engagement so I tried the basic Centerforce I clutch. To my surprise it held just fine and was much easier on the leg.

BTW, when I changed to a diaphragm clutch I left the underdash spring in place and never had any trouble with high rpm shifting making the clutch pedal hang up in the down position as others said have reported. So I'd leave it alone unless an issue develops.
Last edited by zray on Wed Dec 07, 2016 8:21 am, edited 2 times in total.
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Re: Flywheel dilemma

Postby Texas Swede » Wed Dec 07, 2016 8:20 am

I would take it apart first and make sure it's an 164 type flywheel and make sure the 289 HiPo has the correct damper and the
counterweight behind the crankshaft sprocket and go from there. Also, original HiPo flywheels had 160 teeth.
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Re: Flywheel dilemma

Postby gjz30075 » Wed Dec 07, 2016 9:55 am

Thanks guys. Z, you give me confidence because I know many 66 Hertz cars were changed to sticks and I've wondered if the owners really chased down a hipo flywheel. Probably
not.

You're right Swede, I've not taken it apart yet, only assuming the C5AA bell (and corresponding hammer dents in the headers (argh!)) would lead to a 164 tooth flywheel. This motor has ARP'ed hardware to death, even using ARP head studs in place of the bolts, so I'm wondering if the counterweight had been left in. Is there ANY way I can tell if its installed?
Perhaps a scope through the pan drain plug?

BTW, the damper looks correct but has what I think is a date code of L1.
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Re: Flywheel dilemma

Postby C6ZZKGT » Wed Dec 07, 2016 1:51 pm

The C5AA bell housing will only work with the 164 tooth flywheel. If it had a 157 or 160 tooth flywheel, the starter would not engage as the C5AA bell housing moves the starter out to match the 164 tooth flywheel. Yes, the original smaller flywheels had 160 teeth but Ford found that the 157 tooth configuration lasted longer with the starter drives. Somewhere around 1968 Ford changed over to the 157 teeth on flywheels and replacement ring gears. The part numbers did not change, just the number of teeth.

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Re: Flywheel dilemma

Postby C6ZZKGT » Wed Dec 07, 2016 1:55 pm

If your engine seems to have a proper balance at this time, I would take both flywheels to a reputable balance shop. They should be able to match the two flywheels for balance. I have had this done in the past.

A change of clutch should not affect engine balance as the clutch should be neutral balanced.

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Re: Flywheel dilemma

Postby gjz30075 » Wed Dec 07, 2016 2:10 pm

Thanks Fred!
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Re: Flywheel dilemma

Postby Texas Swede » Thu Dec 08, 2016 8:19 am

Thanks Fred,
Didn't think about the starter's location. When I restored my 65 GT350 the engine which is original including the flywheel,
counterweight, and clutch were professionally balanced. When this was done in Denver, CO, I used the Ford HiPo clutch already in the car when I bought it. A couple of months later I found a NOS HiPo clutch and wanted to use it instead. The balancing company
had used the clutch and marked the location with red paint. Took the new clutch to the balancing company and they balanced
it the same way and marked it so I could place it the same location.
It makes sense to have the clutch neutral as it will always have to be changed at some point. Maybe that's what the balancing company was doing, i.e. made sure the clutch was neutrally balanced.
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Re: Flywheel dilemma

Postby C6ZZKGT » Thu Dec 08, 2016 11:58 am

Texas Swede wrote:Thanks Fred,
Didn't think about the starter's location. When I restored my 65 GT350 the engine which is original including the flywheel,
counterweight, and clutch were professionally balanced. When this was done in Denver, CO, I used the Ford HiPo clutch already in the car when I bought it. A couple of months later I found a NOS HiPo clutch and wanted to use it instead. The balancing company
had used the clutch and marked the location with red paint. Took the new clutch to the balancing company and they balanced
it the same way and marked it so I could place it the same location.
It makes sense to have the clutch neutral as it will always have to be changed at some point. Maybe that's what the balancing company was doing, i.e. made sure the clutch was neutrally balanced.
Texas Swede


When I have engines balanced I always specify to leave the clutch out of the overall balance so that the clutch can be swapped without any issues. The first time that I had an engine balanced I ran into the situation you had where they marked where the clutch was to match the flywheel.

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Re: Flywheel dilemma

Postby gjz30075 » Mon Jan 02, 2017 10:42 am

Hi guys, just another quick question. The flywheel I have is a C3OZ 6375 B, which only takes a 10" clutch. I noticed in the Tony's Hipo book (ver 3) that the suffix on the
flywheel is a 'C' and the clutch, of course, is a 10.4". Hence, a different pp and disc, with a stronger clamping force and 8 springs in the disc vs the 10" 6 springs, per the book.

I'm a little leary about installing the smaller clutch assembly. Would I be better off getting a 5.0 flywheel for the bigger clutch?
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Re: Flywheel dilemma

Postby C6ZZKGT » Mon Jan 02, 2017 12:38 pm

gjz30075 wrote:Hi guys, just another quick question. The flywheel I have is a C3OZ 6375 B, which only takes a 10" clutch. I noticed in the Tony's Hipo book (ver 3) that the suffix on the
flywheel is a 'C' and the clutch, of course, is a 10.4". Hence, a different pp and disc, with a stronger clamping force and 8 springs in the disc vs the 10" 6 springs, per the book.

I'm a little leary about installing the smaller clutch assembly. Would I be better off getting a 5.0 flywheel for the bigger clutch?


Why does your flywheel only take a 10" clutch? The 10" and 10.4" clutch have the same bolt pattern.

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Re: Flywheel dilemma

Postby gjz30075 » Mon Jan 02, 2017 1:28 pm

Hmm, interesting. I just had the flywheel resurfaced at a clutch repair place and I indicated I wanted a 10.4" pp. He said it won't fit. I certainly trust you guys more than
this clutch guy. I will continue forward and purchase a 10.4" pp and disk. Thanks Fred!
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Re: Flywheel dilemma

Postby zray » Mon Jan 02, 2017 2:13 pm

I would ask your guy WHY he thinks it won't fit .


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Re: Flywheel dilemma

Postby C6ZZKGT » Mon Jan 02, 2017 2:42 pm

gjz30075 wrote:Hmm, interesting. I just had the flywheel resurfaced at a clutch repair place and I indicated I wanted a 10.4" pp. He said it won't fit. I certainly trust you guys more than
this clutch guy. I will continue forward and purchase a 10.4" pp and disk. Thanks Fred!


The clutch that will not fit that flywheel is an 11" unit.

-Fred-
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