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Topic: Tensile strength of bolts... (Read 938 times) previous topic - next topic

Tensile strength of bolts...

Mentioned elsewhere that I'm finding the '7Zap' resource very useful.

Sizes and types of bolts / nuts etc. are often quoted, including their part numbers.

Like most things VW if you want the genuine article and can find it, it'll come at a premium price but armed with the dimensions I'm finding it relativelyt easy to source alternatives.

Where '7Zap' gets a little cloudy is on strengths, which it doesn't go into. I've been erring on the side of caution and getting 10.9 and even 12.9 items despite it being very possible VW used lesser 8.8.

Up to now trying to find 10.9 and 12.9 items hasn't been a problem, but now that I'm after the larger suspension / brake component bolts it's proving a bit less so. If I knew what the VW specs where it might save me wasting time tracking down higher tensile items when more readily available lesser ones are needed.

Is anyone aware of an alternative resource that quotes the tensile strength of MK2 bolts?

Re: Tensile strength of bolts...

Reply #1 –
https://www.whichcar.com.au/features/diy/guide-to-fasteners-for-automotive-applications    simple advice which actually matches 90% of whats on cars.  8.8 grade 5, is common.


https://www.google.com/search?q=N90517304&rlz=1C1CHBF_en-GBGB923GB923&sxsrf=ALeKk038KRnYjM9T6RT7u0kg8p2ai-yoTw:1624742315404&source=lnms&tbm=isch&sa=X&ved=2ahUKEwijnb7knLbxAhX7UxUIHe_BAkYQ_AUoAXoECAEQBA&biw=1536&bih=722&dpr=1.25#imgrc=qSW6DF9S8N29pM  shocker bolt, 10.9  so using info on the 7zap do part search and images see if some one has put picture with markings visible. 
Going high grade stainless and high tensile can be dangerous in certain applications,  bare in mind the tensile and sheering forces that affect the bolt. Grade 5 ,8.8 is the compromise, soft enough to flex and return to dimension, soft enough to drill out if becomes seized   and has has both high sheer and tensile properties.

Re: Tensile strength of bolts...

Reply #2 –
I have to say that I didn't know there were different grades of high tensile bolts until I replaced the rear brake backing plates.
I bought some high tensile bolts off a local bolt supplier probably 8.8 and torqued them up to find the bolt stretched as it exceeded it's operating limits, fotunately it didn't ruin the thead in the rear axle. If I recall correctly they are 12.9.
That was a lesson Iearned before causing an accident. I replaced them with genuine VW bolts. Yes I could have bought then elsewhere but once bitten..!
1991 Tornado Red BB 8v GTI Moredoor
2008 Skoda Octy Scout aka dirty diesel

Re: Tensile strength of bolts...

Reply #3 –
Had a look at the pinch bolt that came along with some new ball joints and it's rated 10.9.

Also cleaned up the original 2 x bottom bolts on the front shock mount last night. It's very faint, but I'm going to say they're also 10.9... so, so far that's the highest tensile rating I've found todate - Subframe bolts / rear beam fastenings may be off soon and if not too corroded should be able to say for certain their rating hopefully.

Are some of the bolts that are presumably under the greatest load, such as on the engine mounts / subframe and suspension single use?

Fortunately some replacement bushes and the like come with new fixings so presumably are correctly specced but I was also wondering was it because they're intended to replace 'stretched' originals?

I've this link bookmarked, found it expained things in a way I could understand!

VolksBolts

Like you, previously a bolt was a bolt, was a bolt to me - bit scary to think what someone might unwittingly have previously replaced on your car.

Maybe I picked up the adverts wrongly, I didn't read them closely enough but recall seeing full sets of stainless steel bolts being sold to replace all the existing ones on your MK2. They were being sold on the back of them not corroding like the originals, but as said above they're not strong enough for certain applications.

Re: Tensile strength of bolts...

Reply #4 –
I'll take a look at the markings on the rear axle bolts and post my findings here.
1991 Tornado Red BB 8v GTI Moredoor
2008 Skoda Octy Scout aka dirty diesel

Re: Tensile strength of bolts...

Reply #5 –
That's spot on thanks... had a look at the rear stub axle to beam bolts, of the eight only one was rust free enough to see what looks like 10.9.

On the otherhand the drive shaft bolts at the gearbox end are spotless, likely all the oil over the years but they're unmarked.

I've seen non-VW replacements for those advertised that are rated 12.9,

An odd one is the bolt holding the distributor clamp, it's marked 10.9... wouldn't have thought it'd need to be so strong?
 

Re: Tensile strength of bolts...

Reply #6 –
Few bits'n'pieces arrived today, some of which came with various items of hardware.

Might just be that certain manufacturers are more complete in what they offer or perhaps it's an indication that you're also expected to routinely change certain items if replaced?

Front ball joints and the drive shaft bearings ( 2 x different purchases) both came with new 10.9 pinch bolts and nuts.

The ball joint also had the 3 x bolts (10.9) and triple plate with captive nuts to attach it to the control arm and the bearing had a new hubnut, pinch bolt / nut (10.9), plus 2 x nuts (10.9) for the shock absorber bottom bolts, but not the bolts themselves and a nut for the anti-roll bar retaining bracket (10.9) ... so basically all new nuts (and pinch bolt) for the items that are dismantletd when taking off the bearing carrier.  Also seems to suggest the shock absorber bolts aren't single use or would've een included?

New driveshafts came with bolts and they're 8.8 (original VW's where unmarked) ... I'd have thought there'd be more stress there than most other places but have to assume not!



Re: Tensile strength of bolts...

Reply #8 –
Quote from: L90E on
Few bits'n'pieces arrived today, some of which came with various items of hardware.

Might just be that certain manufacturers are more complete in what they offer or perhaps it's an indication that you're also expected to routinely change certain items if replaced?

Front ball joints and the drive shaft bearings ( 2 x different purchases) both came with new 10.9 pinch bolts and nuts.

The ball joint also had the 3 x bolts (10.9) and triple plate with captive nuts to attach it to the control arm and the bearing had a new hubnut, pinch bolt / nut (10.9), plus 2 x nuts (10.9) for the shock absorber bottom bolts, but not the bolts themselves and a nut for the anti-roll bar retaining bracket (10.9) ... so basically all new nuts (and pinch bolt) for the items that are dismantletd when taking off the bearing carrier.  Also seems to suggest the shock absorber bolts aren't single use or would've een included?

New driveshafts came with bolts and they're 8.8 (original VW's where unmarked) ... I'd have thought there'd be more stress there than most other places but have to assume not!




its the shear stress or torsion rather than tensile strength .  on the driver shaft.  the distributer clamp bolt maybe a higher grade due to standing water and temperature deviations. again if you change them regularly or dont use car then you would be unlikey to suffer stuck bolts or excessive rust.   Ive come across a few loose drive shaft bolts recently, all on cars with polybushes and coilover, not sure if increase in vibration/low resonance   is having affect on daily drivers

Re: Tensile strength of bolts...

Reply #9 –
One of those subjects you really need to be sure you understand properly... and I don't, hence wanting to err on the side of getting the original spec. items, specially for safety critical components like suspension / brakes and steering.

Just speculating here - maybe talking b***ocks, but was wondering could you go the other way and cause unintended issues by over speccing a bolt... ie. using a 12.9 when 8.8 is needed?

Like you say it's more than just about sheer strength, the ability to flex or withstand changes in temperature / humidity will probably also come into it?

Re: Tensile strength of bolts...

Reply #10 –
I didn't post an update re the rear stub axle bolts.... that's 'cos I realised the discs will now be hiding them!
Just found this post which suggests they are 10.9
Stub Axle Bolts
1991 Tornado Red BB 8v GTI Moredoor
2008 Skoda Octy Scout aka dirty diesel

Re: Tensile strength of bolts...

Reply #11 –
Thanks - does make sense considering the load they're probably under.

I think when I was looking into the VW belleville washers, they were an odd size and expensive, though found a supplier a while back that does them to the same spec... should still have the details if needed.