C2 (2 1/2") Exhaust Clamps --- Again---

[Bill L.]

HI:

There has been a ton of traffic here on clamps but I still wanted to get some opinions...

Which (if either) of these 2 1/2" clamps are correct?

Screen Shot 2016-04-25 at 3.10.22 PM.jpgScreen Shot 2016-04-25 at 3.06.42 PM.jpg

Thanks in advance for any input on this----

Regards
Bill

[Alan D.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

I'm used to the one on the right which I use on mine. Now if you can find one with a part number that may answer the question.
So the part number for the 2 1/2 clamp should be the one for HP/FI, poor picture but one can read if you down load and enlarge.
And here is some more information on these from GM sources I have been saving, it may be a little tough to follow;

middle clamp
63AIM Sec 8 sheet 6.00 regular exhaust
64AIM Sec 8 sheet A2.00 regular exhaustU Bolt exh pipe clamp (3/16-18) 3824283
63-64 Corv w/H/Per Sp. H/Per, FI (exc PG) U Bolt front exhaust pipe clamp (3/16-18) 3824528


63-64 Corv w/H/Per Sp. H/Per, FI (327) Clamp UnitClamp UnitU Bolt exh pipe clamp (3/16-18) 3824283
63 Corv w/H/Per Sp. H/Per, FI (exc PG) U Bolt front exhaust pipe clamp (3/16-18) 3824528




Gary Beaupre, ncrs, 11/3/12
Do anyone know if any of the repro 2.5" clamps have a 5/16" thread?




66 – 67 nut is flanged pn 1359887 replaced Sept 79 to 271184
1359887 is Gr 8.917 HFH (5/16 – 18 13/64 286M PC

[Bill L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Thanks Alan:

This is some good documentation ---

One of the things that I have been told about the clamps is they need to be fine thread --- and the 2 1/2" stamping is inside a circle --- like the clamp on the right. I have a few in my collection but I have never had anyone tell me definitively what all of the markings and measurements are.

I tend to go with the one on the right as well but only because of the 2 1/2" stamp being inside the circle... otherwise these seem pretty similar.

However, I will also say the the depression is different on both clamps... the one on the right is much deeper and more pronounced than the one on the left.

Thanks!!!
Bill

[Gene M.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Thanks Alan:

This is some good documentation ---

One of the things that I have been told about the clamps is they need to be fine thread --- and the 2 1/2" stamping is inside a circle --- like the clamp on the right. I have a few in my collection but I have never had anyone tell me definitively what all of the markings and measurements are.

I tend to go with the one on the right as well but only because of the 2 1/2" stamp being inside the circle... otherwise these seem pretty similar.

However, I will also say the the depression is different on both clamps... the one on the right is much deeper and more pronounced than the one on the left.

Thanks!!!
Bill

No, mid year clamps are 5/16 -18, which is course thread. The solid axle cars were using 5/16 fine thread. I think original supplier was Arvin. Your callouts for thread size (3/16-18) must be typo.

[John D.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Alan, Nice presentation. My '63 has the right clamp on Lucia's. Course thread for sure.
Jorjorian has a bunch for sale on Ebay right now. Not sure if they are correct though. John

[Bill L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Thanks Gene:

This has been frustrating to say the least --- the issue of fine vs. coarse has become problematic....AND:

For what it's worth, the NEW '67 AIM (page 204) calls out ... "fine thread hex flange nuts"-----

Given what I am seeing in the way of original and NOS clamps --- and what you are indicating -- I am thinking its coarse thread !!!!

Thanks!!
Bill

[Jim S.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Thanks Gene:

This has been frustrating to say the least --- the issue of fine vs. coarse has become problematic....AND:

For what it's worth, the NEW '67 AIM (page 204) calls out ... "fine thread hex flange nuts"-----

Given what I am seeing in the way of original and NOS clamps --- and what you are indicating -- I am thinking its coarse thread !!!!

Thanks!!
Bill

If you need correct clamps contact Greg Thompson at gt66duntov@gmail.com

[Bill L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Thanks Jim...I will contact him.

Regards
Bill

[David L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

The 2 1/2" U-bolt clamp on the left (below green box) has 3/8"-16 threads (length of threads measures 1 5/8") and is made by Versatube Corp., Troy Michigan. There are no stampings.

Also, a page from my 1969 Chev. Parts Catalog.

My 1963 Chev. Parts Catalog lists GM # 237616 for the 2 1/2" CLAMP UNIT for the 63 Corvette w/HP, SHP, and FI. This appears to be a misprint as it was corrected in my 1964 Chev. Parts Catalog as GM # 2378616.
My 1965 Chev. parts catalog lists GM # 2378616 for the 2 1/2" CLAMP UNIT.
GM # 2378616 was replaced with GM # 9784420 in Feb. 1968 which was then replaced with GM # 3633128 in June 1970 as per Chev. Parts History.

Dave

[Alan D.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Interesting -- "No, mid year clamps are 5/16 -18, which is course thread" The number that David Liukkonen posted below of 2378616 is used throughout GM. If the clamp under that number was either a fine or course would think the pn would change however I find a few old catalogs listing it as a 5/16-18 thread. Also the diagram of 63 corvette exhaust calls for 5/16-18 nuts on multiple clamps. So the story is not over yet, is it? By the way David also found the number 237616 in two cat, P&A Feb 61 and P&A Oct 62

[Gary B.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Guys,

Via an inspection of a '66 Bowtie car and based on supporting evidence from the '66 AIM I can tell you that the U-bolt and nut thread for the 2.5" clamp at the center clamp of '64-'67 is 5/16-18. The '66 AIM calls out part #1359887, which is still sold by GM for a list price of $4.56. I purchased some and I can confirm they are 5/16-18, which is the coarse thread.

Gary

[David L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Interesting -- "No, mid year clamps are 5/16 -18, which is course thread" The number that David Liukkonen posted below of 2378616 is used throughout GM. If the clamp under that number was either a fine or course would think the pn would change however I find a few old catalogs listing it as a 5/16-18 thread. Also the diagram of 63 corvette exhaust calls for 5/16-18 nuts on multiple clamps. So the story is not over yet, is it? By the way David also found the number 237616 in two cat, P&A Feb 61 and P&A Oct 62

GM # 237616 appears in my 1963 Chevrolet Parts Catalog (Oct. 1962) but GM # 2378616 does not.
However, GM # 2378616 (Gr. 3.708) does appear in my Chevrolet Dealer Parts and Accessories Price Schedule (Oct. 1962) with list price of $0.60. GM # 237616 does not appear in this same price schedule so I truly believe that it is a misprint.

Dave

[David L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Guys,

Via an inspection of a '66 Bowtie car and based on supporting evidence from the '66 AIM I can tell you that the U-bolt and nut thread for the 2.5" clamp at the center clamp of '64-'67 is 5/16-18. The '66 AIM calls out part #1359887, which is still sold by GM for a list price of $4.56. I purchased some and I can confirm they are 5/16-18, which is the coarse thread.

Gary

Gary,

My GM English & Metric Standard Parts Catalog (Oct. 1978) lists GM # 10008001 in Gr. 8.917 as a 5/16-18 Hex Flange Nut, grade 286M, Phos. Org. Finish while my GM Standard Parts Catalog (Oct. 1988) lists GM # 1359887 in Gr. 8.917 as a 5/16"-18 Hex Flange Nut, grade 286M, Phos. Finish with a thickness of 13/64".

As per my GM Parts History Catalog (Jan. 1982 to Jan. 1990) GM # 10008001 was replaced with GM # 1359887.

GM # 1359887 also appears in my 1966 Corvette AIM (UPC 8, sheet A2) as you mentioned.

GM # 1359887 is not listed in my Chevrolet Dealer Parts and Accessories Price Schedule (Oct. 1966).

Dave

[Gary B.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Dave,

So what's the difference between 10008001 and 1359887? They sounds near identical to me.

Gary

[David L.]

Re: C2 (2 1/2&quot Exhaust Clamps --- Again---

Dave,

So what's the difference between 10008001 and 1359887? They sounds near identical to me.

Gary

According to the Standard Parts Catalog the thickness of the 1359887 hex flange nut is 13/64" (or 0.203").
Maybe the 10008001 nut was a different thickness.

What is the difference between "PHOS." and "PHOS. ORG."?