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Torque Converter Bolts

16K views 12 replies 10 participants last post by  Fred Ficarra 
#1 · (Edited)
I purchased a B&M holeshot 2400 torque converter for my TH350 that came today. I had picked up some ARP converter bolts in 3/8-24 assuming that was the correct size, I was wrong. It came will 3/8-16 bolt, but they are only grade five. ARP does not have a 3/8-18 converter bolt so I was wondering what would be the next best thing? Should I just get some grade 8 bolts from the hardware store? Will the head on a normal grade 8 bolt stick up to far, the ARP bolts have a shorter head? Thanks
 
#4 ·
Actually if you research fastener hardware you should see discussion on shear strength vs pull or clamping strength. I believe the grade 8 are better for clamping applications vs shear load application (torque converter) It has something to do with the hardness of the fastener. check it out good luck
 
#6 ·
Hardened steel is tough to wear resistance, but it is brittle. A non-hardened bolt CAN be stronger. It all depends on useage. A torque converter bolt that is hit hard, at lets say a drag strip can easily snap. Now lets say on a road course - more constant stress on the bolt a heat treated bolt may work well. I vote for the grade 5 bolt as it is kind of in between a hardened bolt and a non-hardened.
 
#7 · (Edited)
As a grade 8 will have 190,000 (?) tensile strength (straight pull) and a grade 5 at 120,000 (?) yet when side loaded the grade 8 will break where the 5 will bend first.

We have 20" screws moving tons of rock 24-7 and use grade 3's to 5's.
 
#12 · (Edited)
Grade 3? are you sure? Are you reading 3 radial markings on the head as a grade 3? There is no such thing as a grade 3. ;)

As for grade 5 bending before breaking.. In a shear application (which this is), there won't be any bending of the bolts prior to failure. A grade 5 bolt will simply shear under less load than a grade 8. A grade 8 is superior (150,000psi), yet may not be required depending on the amount of loading.
OE Powerglide and TH350 are 3/8-24 Gr5. (GM 3799830) However, Ford use larger 7/16-20 Gr8 in the same application, so "overkill" is not really matter here. Just make sure you torque according to both diameter and grade.

Let me go check my COPO torque converter bolts. Be right back,,,
Grade 8. There's six on mine. But my Super Street Fighter only uses 3 grade 5's. (35 pounds torque) Go figure?
Fred, the amount of torque used to preload the bolt has nothing to do with it's shear strength. The shear strength of a 3/8 Gr5 is still ~7700lbs per bolt (plus ~5" of leverage they have over the crank centerline. Basically, it's a lot! :p)
Being such a short fastener, the type of bolts used in this application are "place bolts" that use the head of the bolt to apply most of the preload when torquing.
You will note that these bolts have radial slots in the heads or like ARP, have dimples in the center.
These slots and dimples are to allow the head of the bolt to flex at a specified torque (35ft/lbs in your example) for bolt retention.
These bolts are really too large in diameter and too short in length to stretch properly.

http://www.rockcrawler.com/techreports/fasteners/index.asp
 
#8 · (Edited)
My understanding is the idea of the higher grade fastener is to utilize the increased clamping pressure to hold the parts together and eliminate movement between the parts not rely on the bolt's sheer strength. The higher grade fastener must be tightened to the correct torque spec to achieve the higher clamping pressure - Grade 8 torque spec is about 50% higher than the Grade 5 and so is the clamping force when torqued to spec. I don't think a bolt in this application is intended to be a shear pin, although in some applications they are to protect more expensive parts and prevent extended downtime. We have some applications at work where this is exactly the case on machine drive couplings.
 
#9 ·
Let me go check my COPO torque converter bolts. Be right back,,,
Grade 8. There's six on mine. But my Super Street Fighter only uses 3 grade 5's. (35 pounds torque) Go figure?
 
#13 ·
Yep, very big heads. Kinda like some people I know.;)
 
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