[dataway]

I'm getting close to mating the transmission to the engine ... my 68 GTO to my knowledge has never had the re-enforcing plate that I have seen on some flex plates. The one that goes under all the flex plate to crank bolts on the back side of the flex plate.

Was it only used on certain models or years? Seems like a good idea, is it necessary? Will the standard OEM bolts still work with the additional thickness? Any clearance problems to torque converter?

[Stripes]

Great question. Mine had one on it and we still use it.

[dataway]

There seems to be a lot of confusion about where and when they were used.

[400 Lemans]

http://vi.raptor.ebaydesc.com/ws/eBa...11400000&ver=0 Run it.

[abefromen]

Originally Posted by 400 Lemans

http://vi.raptor.ebaydesc.com/ws/eBa...11400000&ver=0 Run it.

"What does the shim plate do? Our understanding is that it is for sound dampening".

Say what?

[dataway]

Not talking about the shim ... I'm asking about the re-inforcing plate that goes on the transmission side of the flex plate, under the bolts.

[Half-Inch Stud]

Crank Flange
thin shim ( all applications )
Flex plate
Reinforcing plate ( HO engines)
Longer bolts when using Reinforcing plate

[stevep]

I think they used them in regular engines until 1970 or so.

[Goatracer1]

My 1965 Cat with 389 2bbl had one.

[dataway]

Yep ... it seems to be all over the place when and where they were used.

Mine from day one, 68, first time I tore it down ... no plate and obviously marks where the bolts had been seated on the flex plate from the factory. YS 400.

[chrisp]

Have the plate & longer bolts if needed .

[dataway]

That's kind of the question .... I don't KNOW if it is needed or not.

I should probably just go by what H.I.S. posted, he's usually right.

[PAUL K]

Originally Posted by dataway

That's kind of the question .... I don't KNOW if it is needed or not.

I should probably just go by what H.I.S. posted, he's usually right.

It's not needed. I'm not sure what purpose they serve but imagine they were designed for a "reason". We've put over a thousand horsepower through the stock flexplate for years without using the support and never had an issue. However, if I had the support plate, correct bolts (they are longer) and was using a stock torque converter....I would use it.

They were used on all Pontiac engines I've seen that were original from the mid 60's and seemed to disappear late in that decade. Not nescessarily HO engine only applications.

[dataway]

That's enough for me .... I'll be making about 350 hp.

Mine is a very late (July) 68 model .... so that would jive with them disappearing late in the decade.

Perhaps improvements in steel or flex plate design during those years .... or perhaps just a legacy part that was deemed unnecessary.

[PAUL K]

Originally Posted by dataway

Perhaps improvements in steel or flex plate design during those years .... or perhaps just a legacy part that was deemed unnecessary.

Possibly, or maybe it was a part carried over from earlier transmission designs and it turned out the TH350 and TH400 didn't need it.

[Scarebird]

Did the bolt head design change concurrent with the plate deletion?

[PAUL K]

Originally Posted by Scarebird

Did the bolt head design change concurrent with the plate deletion?

No just the length

[dataway]

Curious situation ... considering, when you think about it, that area is the focal point of all the HP an engine makes, and at some point it did seem to serve a purpose. Wonder if it was as simple as being easier to assemble during manufacture than six individual washers. (Assuming they thought washers were necessary during the dates it was used)

Has anyone ever noticed at any time that 50s-60s Pontiacs were cracking at the bolt holes?

[stevep]

Originally Posted by Scarebird

Did the bolt head design change concurrent with the plate deletion?

It may have. The later bolt may have a "built-in" washer on it.

[Half-Inch Stud]

I've never seen crack propagations start at the bolt holes...!

The Reinforcer ring looks great on paper and in practice (for holding the converter weight under acceleration and under high TQ transfer. But not a must-have in the 1/4 mile huh.
--> did 73-74 SD with TH400 also used them?

My studies showed that the Reinforcer ring &bolts never hit Factory TH400 Converters, but i have had AfterMarket Converters interfere with the Reinforcer ring.

My experience with a factory 4L80 Converter showed the Reinforcer ring setup interferes with the Clutch converter during dry-fit. After shimming the 4L80 Converter for good excursion centering, The last photo reveals the Reinforcer ring would probably clear when sitting idle, but would land on the Converter face during converter swell under load, and Gring up the Thrust bearing. So I left the Reinforcer ring out. Notice the 4L80 converter shape is different fron TH400 Converters.

As for,Thrust bearing protection, the Converter does move for/aft with rpm and acceleration, showing the flexplate does inded flex. The Converter needs to have some for/aft play to protect the Thrust Bearing & Front Pump Gear face from metal bind, but i've never seen a factory spec for that excursion.

We all "shim the converter" to what we think is fine & good.