Quick Q: Grade 8.8 bolt enough for rear suspension bolt?

[evilnickwong]

I need to replace the rear suspension bolts which are M12,1.5,65 bolts.

Are 8.8 enough or do I have to look for 10.9?

[Ant_e30]

If original spec are 10.9 I'd stick to that, are they marked or anything?
It shouldn't be hard to get 10.9 at a fastener specialist however are you sure they're 12-1.5? Standard coarse pitch for 12mm is 1.75 and Fine is 1.25 so 12-1.5 is pretty odd

[evilnickwong]

I didn't check the existing bolt on my car. Reason being those bolts seem to be the wrong length (there's extra space even when installed) which is the reason I am replacing them. I just asked cause I read an old thread where someone mentioned 10.9

I got the spec from bmwfans.info, the hex bolt is mentioned as "M12X1,5X65"

[immajackuup]

I think all cars use Grade 8.8

[evilnickwong]

Anyone else has any confirmation? I don't want something untoward to happen when I hit a big bump. :)

Some random googling seemed to mention that when in doubt, look for a 10.9
My issue is that so far, most of the bolt shops near my place only have 8.8

[KenC]

Which rear suspension bolt? Lower shock bolt, I wouldn't go below stock spec on.

[KenC]

I think all cars use Grade 8.8

Some bolts are higher grade. Flywheel bolts are 12.9

[evilnickwong]

Yeah lower rear shock bolt, part #3 here:

http://bmwfans.info/parts/catalog/E30/4-doors/Europe/318i-M40/RHD/M/1991/browse/rear_axle/single_components_for_rear_spring_strut/

That page only specs the size tho, not the strength grade, so I don't know what the stock grade is.

[Ant_e30]

i wrote a big response theorizing but then just decided to go out and crawl under my car and have a look as my car is totally stock 89 E30 318i.

i work in marketing for a fastener company and used to work at a branch on the counter for a couple of years so i thought i should resolve this one!

my car has 8.8 grade bolts as the lower shock mount bolts. they are marked as such on the head and are yellow zinc coated (as most auto bolts are, aftermarket tend to be silver zinc coated in 8.8 ). i'm confident these are the original bolts so get your 8.8 and you'll be sweet :)

[nando]

you guys are confusing SAE grade 8 with metric 8.8/10.9/12.9

not the same thing. a metric 8.8 is a mid grade bolt (similar to SAE grade 5) and 10.9 is close to an SAE grade 8 bolt.

[Kvasi]

Dont really understand the problem, if ur gonna buy new bolts anyway use the xtra cents and get some u trust.

[Hellabad]

Buy them from the dealer. They are cheap, excellent quality, and you are assured they are not China counterfeits (which is a HUGE problem, especially internet bolt sales.

Most dealers will have them in stock.

The stock fastener is a 10.9 BTW, we are assuming you are talking about the lower shock bolt.

[evilnickwong]

I'll try the dealer, but most of the parts shops in my area here where I usually buy my spares have no stock for things like bolts.

That's why I started looking at just getting a suitable grade bolt from a bolt shop.

[Ant_e30]

Nando - i know the difference between Metric & SAE, although i sometimes interchange the 'class' and 'grade' wordings without thinking which i guess is an oversight. Saying that, how is anyone confusing it? If it is a Metric fastener (M12-1.5 x 65 apparently) then we are talking Metric Class gradings not SAE. Thus the fastener would either need to be stamped 8.8 or 10.9.

My bolts are definately stamped '8.8' which is class 8.8 Metric grading...if it had 6 lines/marks on the head it'd be SAE Grade 8 which i agree is closer to 10.9 but you don't get Grade 8 Metric since thats combining the two!

I suppose it is correct to say that 8.8 is 'mid grade', however it is still high tensile. Low tensile for Metric is class 4.6. 8.8 is high tensile, 10.9 is, for want of a better term, 'very' high tensile.

It is worth mentioning too that it isn't always best to go for the highest possible tensile as the fastener becomes more brittle the 'harder' it is. It depends on where the loads are distributed in the joint. For example it'd be better to have a bolt that may bend in some situations rather than just snap clean.

Hellabad - as i say my bolts are definately stamped 8.8. My rear shock absorbers are red which may not be factory, so perhaps someone changed my bolts somewhere along the line, but my car is dead stock and 2 older owners so it seems odd. I guess you have observed for yourself in doing installs that the bolts are stamped 10.9 on the head?

[AndrewBird]

It is worth mentioning too that it isn't always best to go for the highest possible tensile as the fastener becomes more brittle the 'harder' it is. It depends on where the loads are distributed in the joint. For example it'd be better to have a bolt that may bend in some situations rather than just snap clean.

THIS right here. Higher grade bolts are harder and while they do have a higher tensile strength, they are more brittle and can break easier in certain situations. Strong does not always equal better.

On a shock bolt, an 8.8 should be fine. It isn't support the weight of the car, only the resistance of the shock, which really is not that much, even under sudden movement.