Suspension bolt - Grade

[RD911T]

While I was crawling around under my car diagnosing my bad fuel pump I noticed a missing bolt. It goes through the auxiliary support on the front suspension and the bracket on the wishbone that holds the rear bushing. Bolt is part #90008202003.

Anyone know what grade this is? I found it locally in 8.8, but thought it might be 10.9.

I surprised I didn't notice it handling funky or anything, should I have?

[winders]

I would get it in a 12.9 if I didn't buy it from Porsche....

Scott

[Nickshu]

If we're talking about the same bolt the OEM bolt is 8.8 M12 x1.5. Front suspension cross member to body. Not sure if its different on a 71.

I just ordered one bc I found mine was stripped when doing some suspension work. Ordered an OEM Porsche bolt and was surprised it was only 8.8

[RD911T]

Thanks Nick, I had an order coming from PP, so I called to see if the bolt could be added. It's a special order part, but the sales rep told me he had just done his suspension and all the bolts with a few exceptions were 8.8

Tom

[Nickshu]

Originally Posted by TomViers

Thanks Nick, I had an order coming from PP, so I called to see if the bolt could be added. It's a special order part, but the sales rep told me he had just done his suspension and all the bolts with a few exceptions were 8.8

Tom

Yes I had to special order from Porsche as well. I usually get hardware from McMaster-Carr but this one was a wierd length, something like 85mm and McMaster only had 80mm and 90mm in their catalog.

Best,
Nick.

[RWebb]

critical fasteners should always be checked against the PET for your particular model year

[RD911T]

Originally Posted by RWebb

critical fasteners should always be checked against the PET for your particular model year

I'm not sure what you mean. I looked up the part on the PET, which is how I discovered it was a 12m x 1.5 x 80 bolt with a spring washer, but I couldn't see anything on the PET that mentioned grade.

Tom

[frankc]

I found this thread while searching for some answers.

I was ordering some new fasteners while working on the rear suspension, and noticed that the M12x1.5x35 fasteners that clamp the spring plate to the trailing arm are grade 10.9, but the same size bolts for the rear calipers are grade 8.8.

I then opened up PET to see if the grade is listed anywhere. The description for both bolts is simply M12x1.5x35 - however they have different part numbers. I guess this means that if you want to ensure you have the correct fastener grade for a given application, it is safest to order them by part number - but it seems a bit unsafe for PET to not list the grade in the description.

So I have some extra grade 10.9 M12x1.5x35 bolts, but as I mentioned, the original caliper bolts were grade 8.8. Any harm in moving up a grade on these fasteners instead of purchasing new 8.8s?

[chris_seven]

Originally Posted by frankc

So I have some extra grade 10.9 M12x15.x35 bolts, but as I mentioned, the original caliper bolts were grade 8.8. Any harm in moving up a grade on these fasteners instead of purchasing new 8.8s?

No but don't torque them any more than that recommended for the 8.8.

[javadog]

Wouldn't that give an inadequate amount of preload on the 10.9 fasteners? More likely to loosen over time?

JR

[bpu699]

Originally Posted by Nickshu

Yes I had to special order from Porsche as well. I usually get hardware from McMaster-Carr but this one was a wierd length, something like 85mm and McMaster only had 80mm and 90mm in their catalog.

Best,
Nick.

Should a lenght difference matter? If it were 5mm too long, I don't think it would hit anything going in due to the extra lenght?

I bought the porsche bolts too as mine were stripped, and I am not convinced the thread pitch was correct. They screw in, but go in 5 threads or so and I have to shim about 1mm with a washer.

I mention this because I bought the drop link kit for the rear a-arms, and it came with the bolts. For the life of me I couldn't get them to screw into the a-arms. Went in 2-3 threads and jammed. I got a pitch guage and the pitch was wrong!!! The pitch didn't match what the WSM said it was supposed to be, nor the original bolt pitch...

Plan to check the pitch on the bolts in the spring...

[Flieger]

Originally Posted by javadog

Wouldn't that give an inadequate amount of preload on the 10.9 fasteners? More likely to loosen over time?

JR

No, the modulus of the material doesn't change with the grade, and as long as the plating is the same the friction properties should also be the same, meaning the same torque-preload relationship.

[javadog]

It ain't the modulus I'm thinking about...

JR

[Flieger]

Originally Posted by javadog

It ain't the modulus I'm thinking about...

JR

Preload is dependent on modulus and stretch. (Modulus also affects the distribution of the stress between the engaged threads- lower modulus means more load sharing). Stretch is dependent on thread pitch and tightening angle. Angle is dependent on torque. Torque is dependent on the preload, thread pitch, and friction. Friction also keeps it from backing out. Use the same plating on the bolt and washer and everything should be fine.

[frankc]

Thanks for the responses. I was placing a fastener order this morning anyway, and just went ahead and added the 8.8 caliper bolts to the order since I didn't know how this would play out here at the time. Good info for the future, though.

While we are on this topic, I was trying to find information on when a hardened washer is required vs. a standard washer, but I was not able to find too much. Are standard washers only for grade 8.8, and hardened washers must be used for 10.9? What about 12.9 grade?

Thanks.

[chris_seven]

Originally Posted by javadog

It ain't the modulus I'm thinking about...

JR

Where else does the preload come from?

15 lbsft of torque on a Grade 12.9 fastener will be identical preload to that on an 8.8 fastener providing the friction is the same, so plating and finish are important.

As Max says the Young's Modulus is what creates the preload and the pitch angles and other features of the screw thread stop if from loosening.

As all threads are identical regardless of grade the only change is the load at which the bolt will permanently deform.

It is , however, unwise to consider bolts in isolation they are used to clamp components together and this needs to be taken into account.

Overtightening bolts as a strategy may be OK in terms of the bolt but may damage the components being bolted together.

In the same way if you increase the strength of the fastener and tighten to the new maximum preload it is possible you could damage the component's being clamped together, hence the reason for my comment.

[proffighter]

Originally Posted by frankc

I found this thread while searching for some answers.

I was ordering some new fasteners while working on the rear suspension, and noticed that the M12x1.5x35 fasteners that clamp the spring plate to the trailing arm are grade 10.9, but the same size bolts for the rear calipers are grade 8.8.

I then opened up PET to see if the grade is listed anywhere. The description for both bolts is simply M12x1.5x35 - however they have different part numbers. I guess this means that if you want to ensure you have the correct fastener grade for a given application, it is safest to order them by part number - but it seems a bit unsafe for PET to not list the grade in the description.

So I have some extra grade 10.9 M12x1.5x35 bolts, but as I mentioned, the original caliper bolts were grade 8.8. Any harm in moving up a grade on these fasteners instead of purchasing new 8.8s?

I can speak for a 930:

The bolts of the spring plate changed about 1984 to 10.9 with increased torque

The ones for the tranny beam where always 8.8

Higher grade does not any harm, only the price does

[Harpo]

The nut & bolt are designed as a set. Upgrading to a stronger bolt and applying more torque puts the nut at risk for stripping out. More torque is not always better as Chris_seven as alluded to. My suggestion is to replace with the exact same thing that the Porsche engineer designed for in the first place.