Discussion Forum - Northstar Chevelle Club

jim larson · 2K+ Club

Correct flexplate

Bobs_Place · Vice President

Jim

Good to here from you!!

As I recall, if your flex plate has 6 converter mounting holes, same as the summit, 3 are for the T400 and the other 3 are for T350, the plate is universal. Measure the mounting holes, you should find 3 of them are closer to center.

Lost in the 60s · President

I did a direct swap from TH350 to the 200r4 in my '38 and never changed the flex plate, shift linkage, driveshaft or speedo cable.

dashboard · 2K+ Club

Lost in the 60s wrote:
I did a direct swap from TH350 to the 200r4 in my '38 and never changed the flex plate, shift linkage, driveshaft or speedo cable.

Side Bar

Mitch, how did the T350 length compare to the 200r4? Same driveshaft?

Good to have you back Jim.

jim larson · 2K+ Club

Should have explained more. The flexplate that came with the car was 153 teeth and had a SB straight pattern starter.

I am going to a 168 tooth flex plate, a HT starter for the 168 tooth flexplate with the staggered pattern.

I have a used flexplate for that; but dont trust it. Thus considering a new flexplate.

jim larson · 2K+ Club

Kevin, I am using the same driveshaft that was for the powerglide, and then used with the 350TH swap.

jim larson · 2K+ Club

Lost in the 60s wrote:
I did a direct swap from TH350 to the 200r4 in my '38 and never changed the flex plate, shift linkage, driveshaft or speedo cable.

Mitch, I will be using the same driveshaft and speedo cable. I was thinking I would need a different shift linkage as it. Appears to have been modified Somewhat.

Lost in the 60s · President

dashboard wrote:
Lost in the 60s wrote:
I did a direct swap from TH350 to the 200r4 in my '38 and never changed the flex plate, shift linkage, driveshaft or speedo cable.
Side Bar
Mitch, how did the T350 length compare to the 200r4? Same driveshaft?

Good to have you back Jim.

Yes, same everything, except the relocation of the crossmember rearward. The 200 is physically the same size as the TH350, but the mount is moved back on the main housing.

Bobs_Place · Vice President

jim larson wrote:
Should have explained more. The flexplate that came with the car was 153 teeth and had a SB straight pattern starter.
I am going to a 168 tooth flex plate, a HT starter for the 168 tooth flexplate with the staggered pattern.
I have a used flexplate for that; but dont trust it. Thus considering a new flexplate.

I think there are only two converter to flex plate bolt patterns for these engines.

I have two 168 tooth flex plate, both have two converter patterns, the smaller bolt pattern measured 9.25" c to c on two of the mounting holes. The différance between the two patterns is not much, the bolt holes for the small pattern are about 3/8" closer to center. One of my plates look just like the Summit plate with both patterns except it is for a 454 externally balanced. Not easy to see the differance in the picture.

Have you compared the two plate you have to see if the converter holes line up or place the plate up against the new converter.

Summit says that plate will fit 11.5" and 10.75" converter bolt patterns.

jim larson · 2K+ Club

Bobs_Place wrote:
jim larson wrote:
Should have explained more. The flexplate that came with the car was 153 teeth and had a SB straight pattern starter.
I am going to a 168 tooth flex plate, a HT starter for the 168 tooth flexplate with the staggered pattern.
I have a used flexplate for that; but dont trust it. Thus considering a new flexplate.
I think there are only two converter to flex plate bolt patterns for these engines.
I have two 168 tooth flex plate, both have two converter patterns, the smaller bolt pattern measured 9.25" c to c on two of the mounting holes. The différance between the two patterns is not much, the bolt holes for the small pattern are about 3/8" closer to center. One of my plates look just like the Summit plate with both patterns except it is for a 454 externally balanced. Not easy to see the differance in the picture.
Have you compared the two plate you have to see if the converter holes line up or place the plate up against the new converter.
Summit says that plate will fit 11.5" and 10.75" converter bolt patterns.e

Don‘t like the elonged bolt holes on the summit plate. Would like the plate to fit the converter. One of my plates is an original 66 plate, does not fit. The other one has both patterns; but it is drilled such that the holes are one directly under the other.

Lost in the 60s · President

I noticed the elongated holes too and wondered if it was just poor photography ? I wouldn't want elongated holes either.
This TCI has round holes and should be correct for your application. The reviews do indicate some people were told to elongate the holes for converters that didn't line up well. Must be a common thing with these, as the one you posted says GM went to that for variations in converter bolt hole pattern.
https://www.summitracing.com/parts/tci-399273?rrec=true

jim larson · 2K+ Club

Lost in the 60s wrote:
I noticed the elongated holes too and wondered if it was just poor photography ? I wouldn't want elongated holes either.
This TCI has round holes and should be correct for your application. The reviews do indicate some people were told to elongate the holes for converters that didn't line up well. Must be a common thing with these, as the one you posted says GM went to that for variations in converter bolt hole pattern.
https://www.summitracing.com/parts/tci-399273?rrec=true

Thanks Mitch. I think I will have to try my original gm sbc flexplate to see how it fits on the converter John installed, that should tell me if the converter has the correct bolt pattern.

jim larson · 2K+ Club

The. Original SB 153 tooth plate fits the converter perfect. After reading a lot of reviews it seems there always some flexplate that have to be sent back for some reason like runout or balance.

looks like you have to just order one and have it checked out.

Enganeer · Mega Poster

A quick check on flex plates, is that that a 153 tooth flexplate (12.75" dia) typically uses the straight bolt pattern starter while the 168 tooth flexplate (14" dia) uses an angle / staggered bolt pattern starter. Both flex plates (aftermarket) may have the same converter bolt circle. 153 tooth flexplate has a 10 3/4-inch bolt circle but a 168 tooth flexplate uses a 11 1/2-inch bolt circle from factory.

-- Edited by Enganeer on Friday 9th of April 2021 10:29:07 PM

Lost in the 60s · President

jim larson wrote:
The. Original SB 153 tooth plate fits the converter perfect. After reading a lot of reviews it seems there always some flexplate that have to be sent back for some reason like runout or balance.
looks like you have to just order one and have it checked out.

Or buy an OEM plate. You don't need an SFI spec plate for what you have there.

jim larson · 2K+ Club

Lost in the 60s wrote:
jim larson wrote:
The. Original SB 153 tooth plate fits the converter perfect. After reading a lot of reviews it seems there always some flexplate that have to be sent back for some reason like runout or balance.
looks like you have to just order one and have it checked out.
Or buy an OEM plate. You don't need an SFI spec plate for what you have there.

Looks like the TCI plate you recommended has the highest ratings (4.5) and is ordered by most people. Seems all the cheaper plates (around $65). Have the elongated holes for the converter. Thinking I done need SFI plate; but for $30 more, why not?

Lost in the 60s · President

jim larson wrote:
Lost in the 60s wrote:
jim larson wrote:
The. Original SB 153 tooth plate fits the converter perfect. After reading a lot of reviews it seems there always some flexplate that have to be sent back for some reason like runout or balance.
looks like you have to just order one and have it checked out.
Or buy an OEM plate. You don't need an SFI spec plate for what you have there.
Looks like the TCI plate you recommended has the highest ratings (4.5) and is ordered by most people. Seems all the cheaper plates (around $65). Have the elongated holes for the converter. Thinking I done need SFI plate; but for $30 more, why not?

Yep, for only another $30, may as well get that one.

jim larson · 2K+ Club

Also free shipping if order is $99 or more.

Lost in the 60s · President

jim larson wrote:
Also free shipping if order is $99 or more.

If I need a part that doesn't meet the minimum, I keep a list of other things I'd like in my "wish" list just to bring a total up to $100...