What are your thoughts on bolts used for pressure plates


#1

So I’ve heard some people using hardened steel bolts and lock washer on clutch pressure plates. What are your thought on that?


#2

If stock I’d use the stock bolts. If high performance I’d use what the maker recommended. Why do you ask?


#3

what I mean is bolts and Lock washers from like Ace. I ask this cause my dad from working on cars has found them on the pressure plates. I was just wonders if that was a good idea, decent idea or bad one


#4

Bolt heads used to have markings on them and if you matched those indicators you would have the right bolt. OK, when I go to Homely Depot I will be checking on bolt markings to check for grade 8 bolts or something. If your dad found them intact it may be a good idea to install anything most of the time. I have no idea these days what grade is required. I have reused the same bolts on my cars but sometimes installed whatever fits on other cars whenever a bolt was missing. Since 1969 I have probably installed a new bolt on a car but I can’t remember when.


#5

I reuse the original high grade bolts or the replacement bolts that come with the new part. If I find low grade nickel plated hardware store bolts on a part like that I replace them with OEM equivalent bolts, do these bolts ever break?


#6

no but they’re hardened steel. I also used this on my Pressure plate I got hardened steel bolts with the same thread pattern as the OEM ones got some lock washers and got them as tight as I could and called it good.


#7

There’s nothing wrong with Ace nuts and bolts as long you get Grade 5 or Grade 8. If you mean the galvanized ones in the bins those are usually Grade2 and are not meant for most automotive applications. I refer to them as “fence post bolts”.


#8

They were grade 8.8 hardened steel.


#9

Sorry, there is no such thing as grade A.

Hardened could be grade 5, 6 or 8. Or metric.

Pressure plate bolts are usually grade 8 or higher. Many don’t use lockwashers. They are meant to use LocTite or similar. Some have unthreaded areas near the head so that the pressure plate itself has a smooth shoulder to rest against.

As a general rule, don’t use hardware store bolts for things like pressure plates, flywheels, connecting rods head bolts or even harmonic balancers. These are very critical joints that often use specialty fasteners.

If you don’t understand the markings and the configuration, buy those bolts from the dealer.


#10

What happens is that people use a normal torque wrench and try to dial in the relatively low torque spec for those bolts (19lb/ft on some cars), and then they go right past the torque spec without feeling a click and after they get about 50 lb/ft on the thing they twist the head off the bolt and start rummaging through the coffee can full of random bolts so they can get the car buttoned up again.

Needless to say, this is not a good idea. :wink:


#11

I checked where we got them they are grade 8.8 hardened steel.


#12

Grade 8.8 is near the bottom of the scale but probably acceptable for pressure plate bolts. The flywheel bolts should be grade 10.9 or 12.9.

Most of the bolts in the hardware bins where I work are grade 10.9.


#13

They are NOT good enough! metric 8.8 is like an SAE (English thread) grade 5. These bolts should be SAE grade 8 or metric grade 12.9 And they should look like this. Notice the shoulder. They also have no plating and have their own hardened lockwashers.


#14

The only area where I might use Grade 2 SAE bolts and nuts would be to replace a bolt that involves body panels

I use at least Grade 5 on anything involving the frame. Installing hitches…grade 8.
Then I use grade 8 on anything involving the engine and drive train.

Sometimes it may be over kill, but the one thing to remember is that at some point you may need to remove that bolt again. The chances of snapping off a bolt, or damaging the threads is less likely with a harder bolt/nut.
I would rather use the harder bolt on even a Alternator bracket, or valve cover, rather than snap off a softer bolt next time I try to remove it. Then have to pull the radiator to be able to get a drill in there to drill out the old bolt.

I may not be the one who has to remove that bolt in the future, but I’d like to know that the next mechanic is not cussing me out that he broke off a soft bolt that I put in.

Yosemite


#15

I used to think all bolts were the same, just get what fits. I had to go to a “bolt class” and discovered how wrong I was! I’m no expert now but I know enough to get my bolt book or compare the markings to get the same bolt (except the manufacturer). That can be the most frustrating part - either getting the original bolt spec or finding it once I have the spec.

You’re best to get direct replacements, not necessarily from the dealer, but the same bolt spec. If it had an 8.8 originally, then get an 8.8.


#16

Every time I looked at any bolts involved with the clutch, they were grade 8’s (or the metric equivalent). Admittedly, these were all racing clutches, so I would expect them to use the highest quality.

And like was said above, I only used grade 2’s on the car for the body. Everything else was a grade 5 - except for the drivetrain.


#17

All the hardware stores I visit (including Home Depot) have graded bolts available. For that application I’d use whatever’s the equivalent of grade 8 myself, if the recommended replacement grade isn’t known,

Here’s a summary of the hot rod link below

For inch-sized zinc plated bolts (which I think means SAE sizes)

3 hash markings == grade 5 == tensile strength of 120,000 psi.
6 hash markings == grade 8 == tensile strength of 150,000 psi.

For metric sized zinc plated bolts

Grade 8.8 refers == 116,000 psi
Grade 10.9 is == 150,000 psi
Grade 12.9 is == 175,000 psi.

My Home Depot and the other independent hardware store (which I usually use for this sort of thing b/c they have a better selection) stocks both SAE grade 5 and 8, and Metric 8.8, and 10.9. Not sure about 12.9. For my Home Depot, these are located in the specialty fastener drawers, not on the general purpose fastener rack.

https://www.hotrodhotline.com/md/html/bolt_head__markings.php

You’d think grade 5 would have 5 marks, and 8 would have 8 marks, but that would be too logical … lol … I find grade 5 and 8 bolts all the time along road gutters on my daily walk-a-bouts and have collected a pretty good stock. Grade 8 especially are somewhat expensive to purchase new. It seems like folks who worry a lot about bolt strengths for auto repair tend to use ARP’s bolts, especially for the bolts that hold the cylinder head onto the block.

A little googling shows

1/2 inch -13 (pitch), 1 1/2 inch long grade 8, $16 for 25 pieces
1/2 inch -20 (pitch) 1 1/4 inch long grade 8, $13 for 4 pieces.