Where does this bolt go? Pressure plate to flywheel?

Also, why the slots?

 

3/8" bolt? Fine or Coarse thread?? Length??

Guessing, I think some 3/8" bolts with this head were used to bolt the torque converter to the flywheel on PG cars. NOT SURE, so the experts may have to give you the real scoop.

 

The Paragon bolt chart shows it 3/8-24x1" but I can't find the number they list for it on their website.

As unique looking as it is I would think somebody would know what it is for easy.

 

Sound like 3/8-24 is right, but 1" seems long. I'll go to the shop and see what I can find to jog my memory. How may do you have???

 

I think it was six.

 

I don't know where goes, the slots show it is a grade 8 bolt.

Bill

 

Went out to my bolt bin of hundreds of old bolts and found one 3/8-24x1/2" long. Checked a PG torque converter and flex plate and found it takes the 3/8" bolt. Pretty sure this is the application as the thin head is installed on the block side of the flex plate and a nut on the converter side. PIA to get a wrench on the bolt and nut. Guessing the thin head is to prevent interference with the starter nose??

I also found a couple of 5/16 fine thread x 3/4" long. So now you have me wondering where they go???

 

Looks like the flywheel to crank bolt.

 

Finally a correct reply.............

Larry

 

nope, they are 7/16" NF x about 1".

 

R66:

We need to have OP put a dial caliper or mic on the bolt to get the exact diameter. I agree that flywheel bolts to crank are 7/16-20 and 15/16 long (from Paragon book).

But the look of the bolt heads, fine thread, length, grade 8, and number of bolts (6) make it almost certain to be flywheel to crank.

Let's have OP measure the bolt shank.

Larry

 

The flywheel to crank bolt are definitely 7/16" NF whether for a standard flywheel or a auto flex plate and six are required. Those bolts also have a thin head to clear the clutch disc. Not saying GM didn't use that style head on those crank bolts, but none that I have from the 60s era have the configuration his picture shows.

I know 3 ea. 3/8" NF are required for the torque converter to flex plate on a powerglide. I believe they did have that head configuration, but then again I am getting older and don't remember like I used to.

A verification of the diameter might be in order if he did not already do so.

Also, the OP is asking if they fit the PP to flywheel. All 6 of the pressure plate to flywheel bolts are 3/8" NC and have a shank that fits into the recess of the holes to help align the PP and help prevent shearing I believe.

Ron

 

The slots are not a grade marking on these bolts, they are functional. They were, as I recall, there to lend some sort of resistance to loosening, maybe extra stretch, given that the grip length of the fastener (i.e., the part of the threaded shank that stretches) was so short. I'd don't know of a use other than flywheel attachment, ever, for such parts on GM vehicles, but there could have been one or two.

Mike

 

depends on length,size and threads, some early calipers used bolt with that type head 66racer

 

My 1967 brake calipers halves had bolts with that head marking........but I don't think OP bolts are brake caliper bolts. Maybe because he felt they belonged to the flywheel/clutch/engine areas of the car and because of the number (6) and grade (8) of the bolt.

OP needs to provide additional bolt details to go any further.

Larry

 

Nah, they are not caliper bolts. And, as I said earlier those grooves are not head markings; head markings always stand proud of the surrounding surface. Those are functional grooves, used only on flywheel bolts.

 

In the 50's & 60"s Ford used tons of that style head in several different places to include manifolds and such.

I have hundreds of them in various sizes out in the shop.

Bill

 

I got a basket car and these bolts were attached to the flywheel, and since they have a unique design that I haven't seen anywhere else on the car I thought they would be easily recognizable.

 

Your initial proposal is probably the correct answer.........pressure plate to flywheel.

According to Paragon, the typical Chevrolet PP bolts are 3/8-16 x 15/16 inch long with a shoulder and a lock washer. Typically are also Grade 5.

Your bolt is a nominal 3/8 inch diameter. It appears to have the course thread of 16 TPI. Bolt length is measured to the underside of the head and not the top, so if I subtract the head thickness, you appear to have 15/16 to 1 inch length.

I cannot tell if the bolts have a shoulder or not from the photos you posted. They should have to index/locate the pressure plate better to the flywheel and minimize looseness. Do they??

If so, I guess that is your answer. More photos or detail initially would have minimized this discussion.

Larry

EDIT: AMC used bolts with your headmark for flywheels and flex plates back in the late 1960's and early 1970's. I used them on my AMX 390 car. They might also have used bolts with this headmark for clutch PP as well......I just can't remember all of them, but I know flywheel and flex plate for sure. http://www.ebay.com/itm/AMC-Rambler-...JXC-5E&vxp=mtr AMC and Chevy took the same PP back then, so they might have come from an AMC car sometime in the past. I also saw this headmark on the bolts holding the caliper halves of my 1967 Corvette. Again, same headmark, but different diameters and lengths.

 

OK, here's the real scoop. LOOK AT THE BOLT HEAD. If it came off of a GM car and has six radial GROOVES, it is most likely a "Place" bolt, a very specialized part, GM used only on those flywheel-type applications. The grooves are not an identifying "head mark", they are functional.

On the other hand, if it has six radial lines that are raised above the flat surface of the top of the head,, like the 67 caliper bolt, it is NOT a place bolt. It is Grade 8 machine bolt, the strongest variant normally used on GM cars of that period. The 1967 caliper bolts referred to above had six radial lines raised above the bolt head flat surface. They were not "Place" bolts, though, they were normal Grade 8 bolts.

It much more difficult to create dies to make a fastener head with grooves, so anytime you see it, it means someone went to lot of trouble, for a reason , not just to mark the bolt