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Re: [GMCnet] Reviving the Cad 500 [message #163608 is a reply to message #163589] Tue, 20 March 2012 08:09 Go to previous messageGo to previous message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma:
Senior Member
Adrien,

You, like most, IMHO, misunderstand the term "ballooning the TC". I
struggled with the concept for a long time myself until I came to realize
that the only way "ballooning" can be considered a problem is to think of a
flying balloon, NOT a static one:

The pressure inside a torque converter does indeed cause its housing to
expand like a balloon. But that's a very small amount -- no where near
enough to cause the problems I, and so many others, have experienced. It's
probably only a few thousandths, and the TC should have about 0.125" free
play fore & aft -- as mine does.

Where the axial pressure on the crankshaft comes from is the different
areas of the front and back of the TC -- that is, the area of the opening
in the TC hub. According to numbers I've found recently, that amounts to
about 2 square inches -- about what I'd have guessed at a glance.

If we assume that the transmission pumps 100 psi ATF into the torque
converter, it matters not what the area of the front of the TC is, so call
it X. The forward force will be 100X. But that force will be balanced by
the rearward force of 100X-2. So only the 2 is left to worry about -- that
means 200 lbf forward force on the crankshaft through the flex plate.
According to one reference, the Chevy 454 is rated for only 210 lbf
forward crankshaft force -- the 455 and 500 are probably about the same.
Thus the cautions about not creating conditions that cause excessive
transmission pressure.

Both Manny and Bill Bramlett told me of pressure checks they've run and I
considered doing them myself as soon as I reassembled my engine. But after
finding the distorted flex plate and other symptoms, I thought I'd found my
problem. Of course, I hadn't, so now I'll have to do those tests because I
can think of NO reason, other than excessive ATF pressure, for the second
thrust bearing failure.

Ken H.



On Tue, Mar 20, 2012 at 12:17 AM, Adrien Genesoto wrote:

> ...
> I wonder how much axial expansion a TC does per lbs of oil pressure. How
> much pressure would be required to balloon the TC?
>
> If the TC has internal problems that normal internal pressures cause it to
> expand (balloon) picking up the axial free play plus (?). That could put
> pressure on the thrust bearing.
>
> I wonder if oil pressure built up between the TC and the oil pump, may be
> thrusting the TC forward. Just thinking out loud.
>
> If the thrust bearing is worn on the rear side (flex plate end side), I
> think it would make the TC a strong candidate to consider.
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
 
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