shoehorn_hands

Hey folks, I'm swapping an Olds 350 into a 1985 Monte Carlo with a 200-4R. I realized that the flexplate I pulled from my trashed Chevy 305 won't bolt to an Oldsmobile crank, so I grabbed my Olds flexplate......and it won't bolt up to my 200-4R. What a pain.

So, I tried to source a flexplate for an '85 Cutlass with a 307, but none of them seem to be compatible, and customer service at Summit Racing told me that model is listed with a TH400 in their books??? I thought all 1985-88 G bodies had a 200-4R but I guess I was wrong?

Anyway, my question is does anyone make a flexplate to mate an SBO to a 200-4R and if so what models do I need to look at to find one in a parts catalog?

I'm very frustrated with this, I can't move any further on this project until I have that part. I suppose I could swap in a TH350C but this car is going to be my daily driver and I REALLY want it to have overdrive.

Thanks. Ryan

svnt442

My guess would be the torque converter is the issue you are having because the 200 4R was behind a ton of 307's.

oddball

What precisely is the problem with the Olds flexplate?


The normal problem is many Olds flexplates used a pretty wide balance weight which interferes with the Chevy-style torque converter mounting lugs. The simple solution is to use longer bolts and two or three hardened washers between the TC and the flexplate. Just enough to get it to mount solidly, but make sure the TC is still pulled forward from fully seated. It needs to be able to expand back towards the tranny. If the spacing is so bad that the washers keep the TC fully seated then you'll start breaking parts.


Anyway, this is pretty normal. The nicer solution is to use a TC with olds-style mounting pads - that's why TH350 and TH400 TC's are listed as Olds vs Chevy - but those are pretty rare for the 200r4.


Your flexplate should have a usable pattern in it for the TC lugs. If it doesnt' then you can drill the appropriate holes in the flextplate.

shoehorn_hands

Basically my bolt patterns won't line up.

The old motor is a 1986-87 Chevy 305 with a small bolt circle on the crank. The new motor is a 1970 Olds 350 with a 1977 Olds 350 crank and a larger diameter bolt pattern on the end of the crank.

So, I have a flexplate for each engine BUT the one that came with the Olds motor came from a 1977 R-code Firebird with a TH350 and it doesn't have the appropriate bolt holes for a 200-4R torque converter, they are not far enough out.

What about this? Do you think this one will fit a 1977 SBO crank and a 1985 200-4R torque converter? Does the TH400 use the same bolt pattern? Should I just order it and see?

https://www.jegs.com/i/PRW/228/18455...276+4294828792

OLDSter Ralph

I think there is another thread about the 200-R4 and flexplates out there. It is fairly recent........in the last week or so. Joe P had some info on this subject.

olds 307 and 403

I used a 1976 Olds 350, a 78 Olds 403 and a 83 Olds 307 flexplate with stock and aftermarket 2004R torque converter's, all with the factory lug style torque converters. The only issue I had was the converter pulled out to far and caused a big leak with an aftermarket converter. Heck I even bolted up a 76 Olds 350 to a 94 4L60E in 4x4 truck. Double check everything, it should bolt up just fine.

oddball

Well, you have to use the Olds flexplate. That's a given. The balance is different between Olds and Chevy, as well as the mounting dimensions.


Every Olds flexplate I've seen has both bolt patterns for the TC. On that Jegs listing see the dual holes along the outside? A larger and smaller diameter circle? If your flexplate only has one (and not the right one), you can drill out the holes you need by hand (doesn't have to be machinist precise), or just pick up a stock flexplate from someone here. Or the SFI one from Jegs.

joe_padavano

You were "wrong" when you believed the Summit Tech Line answer about anything having to do with Oldsmobile...


The only automatics offered in the 1985 Cutlass were the three speed TH200 or the four speed 200-4R, period. Nearly all 307s came with the 200-4R. There is no fuzz on that at all.

matt69olds

shoehorn_hands

I'm an absolute idiot, I just went out and double checked the flexplate from my donor car and it DOES have dual bolt patterns. One of them lines up with my new torque converter. I don't know how I missed that, maybe because when I checked the first time I was expecting to use the same bolt holes again, maybe I thought they were for balance or something. Sorry for wasting everyone's time

oldolds88

never an idiot for missing anything.this is called the learning curve.

OLDSter Ralph

We have all overlooked things or made mistakes. It doesn't make you an idiot. Thank you for letting us know what happened, it can help others.

olds 307 and 403

That is why I mentioned it, we all miss stuff. I have run a bunch of mid 70's to mid 80's Olds V8 and all the flex plates had dual holes. Either way you saved some time and money. By the way, Iove an Olds V8 into a chebby. The chebby guys say GM is GM until you swap an Olds V8 into a chebby body. Then the crying starts.

therobski

OMGosh. If you only knew what I thought were stupid mistakes on all of my Old's builds, I could write a book titled " Basic Oldsmobile Builds for Dummies" Hey, if an Old's was easy build like (Chevy) everyone would build one and most do!....This Club is very knowledgeable, dig in and learn! Robski, over an out....

shoehorn_hands

You're right, I can't wait to take this thing to a show and see the looks I get

Thanks again guys