Clutch bolts

Yes you can use grade 8 bolts.

The automotive OEM’s use what it needs to be safe and nothing more since there is a difference in cost between grade 5 and grade 8 (or metric 8.8 and 10.9). Since the OEM’s manufacture millions of vehicles each year, the difference in a few cents per fastener adds up to a lot for them.

 

I've always swapped out the grade 5 for grade 8. Never had any issues.

 

Just because a bolt is harder doesn’t make it better for the application. The softer Grade 5 are used because they have a higher sheer quality than the harder grade 8 bolts that have a better clamp (or hold down) quality.

 

According to this chart, grade 8 has better shear capability.

 

Never go wrong with grade 8 standard and 10.9 metric on any engine parts I've ever seen. Stock one type in the shop bins and done. OEM fasteners is the best bet especially with flanged head fasteners. When it comes to clutches I always replace the lock washers as they are most often flat. Bolts I reuse unless there is an obvious issue with overtorque or damaged threads. Always tap out flywheel holes to clean threads as you never know weather your using the old holes or not.

 

That's what I've been doing for a while now...went to all grade 8 in the bins. I also swapped to a lot of stainless although still grade 5, for certain work that isn't critical just for the longevity of the fastener and ease of removal down the road.

I found in my experience anyway, that using a stainless bolt with a mild steel nut like a nylock for instance...you can take them apart later on trouble free. Whenever I use a stainless bolt with a stainless nut, I never can get them apart and have to cut them apart. For some reason they gall after they are tightened and the threads get distorted, so a stainless bolt/regular nut or vice versa usually solves the issue.

Like my new grill surround trim I put on last week. I bought a bunch of 1/4" x 3/4" stainless phillips cap screws and mild steel Nylocks to put the grill pieces in with. The stainless won't rust on the outside, and the nuts are inside where it doesn't matter nor are visible. Nice, clean look, no hex heads outside to grab the wash mitt or my knuckles on anymore.