Transmission & converter guru's, I have a couple of questions

[gregh]

History of my first thrust bearing failure

I changed the crank, had the converter checked & thought everything was good to go this fall when I parked the car for the great winter sleep.

This spring I got it fired up & was looking for the source of a bad oil leak when I discovered that I'd installed the wrong rear main seal(line honed SB 400, I didn't know they used a different seal than every other SBC out there).

I pulled the engine to fix the leak & discovered that the new crank had eaten the thrust bearing too after about 200 miles.

Round 3.

The crank is repaired, new bearings & the proper seal is installed. I get my TH350 back from the builder tonight after a checkup & freshen & I just picked up a new B&M 3000 Holeshot converter. When I was reading the instructions for the B&M, it mentions to check a converter for balloning by hooking the inner gear & lifting up, you should have 0.050 or less of end play.
I checked my new converter & it's 0.045" & then I checked my old unit, 0.128".
I phoned the converter builder & they won't give me a straight answer,

yes it should be 0.050 or less but if it's at 0.128 it won't kill the thrust bearing unless the converter pilot surface bottoms out in the crank end.

That doesn't make sense to me.

My old converter shows that the snout was about 1/4" inside the crank but wouldn't it be able to transfer enough forward thrust through the flexplate to take out the bearing?

Is this excessive play in the converter OK or not?

 

[10secZ28]

sorry to see you get the run around Greg!?Is that a used crank?If it is used,was it used with a 4-speed,cause 4-speeds had a pilot bushing\bearing,and if it still in the end of the crank,it might not be letting the snout of the converter sit in there properly.Just another suggestion.Man it sounds like your pulling your hair out on this one,don't lose too much sleep on it,you'll get it Greg!..SteveP.S.-K.I.S

 

[gregh]

Both cranks were brand new, out of the box Scat 9000 series units. No pilot bushings for sure.

 

[myclone]

Both cranks were brand new, out of the box Scat 9000 series units. No pilot bushings for sure.

FWIW Ive had two scat cranks cause issues as far as thrust surface bearing wear. Traced it down to the hub where the flex plate bolts to was too "thick" combined with some wear on the stator support splines/new torq converter pushing the crank forward. The scat cranks located the flex plate ~.018" further rearward.

Might be worth comparing a GM crank to one of the scats to see if youre in the same boat as I was (comparing the two with mic's is how I found it).

HTH

 

[gregh]

But if the converter to flexplate distance is OK, the crank hub thickness measurement is meaningless, no?

 

[myclone]

But if the converter to flexplate distance is OK, the crank hub thickness measurement is meaningless, no?

Taking into account the front pump stator support spline and tc stator spline wear as well as the thicker hub made it all came togeather just right to close up the thrust clearance which wiped the rear main thrust surface out. TC to flex plate clearance doesnt take into account any wear in the splines on the stator in the tc or stator support on the front pump of the trans. If the stator support would have been brand new or zero wear which wouldnt have pushed the crank forward under load the thicker flange wouldnt have been a problem (BTW, Ive never seen a 700R4 that didnt have some stator support spline wear that had a few miles on it).

Two scat cranks in a row that had a "thick" mounting flange tought me to mic them all from now on.

 

[gregh]

Interesting.
Does anyone have a stock GM crank kicking about that they can measure?
I'll mic my spare Scat when I get home from work today.

 

[gregh]

I measured the rear flange on my spare Scat crank, .511. Is that close to a stock GM crank?

 

[myclone]

Interesting.
Does anyone have a stock GM crank kicking about that they can measure?
I'll mic my spare Scat when I get home from work today.

Ive got a fresh GM crank that I'll mic in the morning and post it.

 

[jakeshoe]

Just measuring the thickness of the rear flange is meaningless.

You would have to measure the distance from the thrust bearing surface to the rear of the flange to get any meaningful information.

Excessive trans pressures can cause a ballooned converter and wiped thrust.
Not running a modulator, most full manual VB's do this and it can (but does not necessarily) create problems.