Flexplate delema

[61BT409]

I installed a 168 tooth flexplate SFI approved on my 409, only to find insufficient clearance between the flexplate torque converter mounting pads and the mounting lugs on the torque converter. I believe the condition may be caused by the flexplate not sitting flat to the crank flange due to the countersink on the flexplate and the "non-round" design of the 409 crank flange, which is forcing the flexplate out of alignment. My question is, can I install the flexplate "backwards" to eliminate the effect of the countersunk flexplate, and by doing so, I will gain clearance at the T/C mounts as the raised mount pads on the flexplate are facing the opposite direction? Or is this just asking for more problems by installing the flexplate backwards?

[petepedlar]

I just ordered shims from Show Cars for mine. You need two .025 shims from what I understand.

Dave

[fatride]

What torque converter are you using? Make sure the pump drive is engaged before bolting up tranny. Is the SFI flexplate the same dimensions as the stock unit?

[Dond409]

I had the same problem as you. No converter clearance. I even sent the converter back to have it cut and rewelded to narrow it some.They wouldn't do that. Said the converter was to spec. They did machine the pads a bit. I ended up making a .062 shim to go between the engine and transmission. I ended up with the clearance I needed. I even got a different flywheel that I didn't need to use shims with. You have to have clearance to allow the converter to expand. The first transmission lasted about 2 months. Took out the low reverse clutchs.

[gearhead409]

this is a problem that most don't think about. GM had this same problem with its first 62 alum powerglides. i have fixed this problem by putting a rubber expandable freeze plug in the converter hole and grinding some off the end. note, must burr it very well as not to cut front seal.

[tripower]

Or you could switch to a 4-speed...:clap :clap :clap

[61BT409]

The torque converter is in the trans all the way - 1" from converter mounting lug to straight edge across bellhousing. I bought & installed a .050 flywheel shim from parts store today, which now allows flexplate to sit flush with crank flange, but the converter will only turn freely until it meets the "raised" t/c mount pads on the flexplate, at which point there is no clearance. The tranny is a TH350, if that make a difference, converter is a B&M holeshot. Not sure what else I can try?

[Dond409]

You can call a converter company and explain what you need. You need a converter that is an 1/8 to 3/16 thinner than a regular small block converter. They might already have something along those lines or they may not. It could also be very expensive. Do not run a converter without at least 1/8 clearance!! That's the bottom line. I've given you some suggestions, and also how I solved the problem. Please keep us informed on how you make out.

[fatride]

The torque converter is in the trans all the way - 1" from converter mounting lug to straight edge across bellhousing. I bought & installed a .050 flywheel shim from parts store today, which now allows flexplate to sit flush with crank flange, but the converter will only turn freely until it meets the "raised" t/c mount pads on the flexplate, at which point there is no clearance. The tranny is a TH350, if that make a difference, converter is a B&M holeshot. Not sure what else I can try?

I ran a 2400 stall B&M converter with my 350 in back of a 348 engine with no issues, Go figure :scratch I wonder what the difference is?

[models916]

I took a grinder to the crank flange. Minor alteration required. TH400 and convertor fit correctly. I can see where grinding the convertor and the front pump drive will do the same thing.

[61BT409]

Problem solved!!! I bought a new CSR flexplate (CSR200) yesterday after seeing a post on here that someone else had good luck with the CSR. Went with the CSR even though it was more $$, because it is flat which eliminated the shim between crank flange and flexplate. Got the 1/8" clearance I needed. Turns out the flexplate that the dyno shop gave me to replace the good I had and they lost, turned out to be an offshore piece of crap. Thats for the input!! Now I can slide that engine in place and start reassembling the car.