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Top Bolt - Rear Shock Absorber

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Charlie Dog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Topic: Top Bolt - Rear Shock Absorber
    Posted: 22 Oct 19 at 14:28
Haynes says to fit a new top bolt
every time you take one out.

Torque it to 80nm
Then turn it 180 deg.

Please would someone tell me
where I can get a couple of top bolts
at a sensible price.

Working on an 05 Caravelle
Is the bolt likely to be rusted in please?
If so, what's the solution please?

Does anyone actually fit new bolts?

Or do you stick the old one back,
as in the Autodoc video please?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 22 Oct 19 at 20:27
I've never heard of a stretch bolt on a shockabsorber.  Stretch bolts are normally reserved for critical  parts that mustn't loosen at all over time, like crank/cam pulleys, head bolts etc.  Unless it's something new I think it's a mistake.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 23 Oct 19 at 22:18
Thanks T5 TDi.

Like you, I don't see any reason
to use stretch bolts on shocks.

Coupled with the fact Google 
can't find me any new bolts, 
I wonder if Haynes made it up.

However, it's written in 2 places.

10*2 
Shock absorber lower mounting bolt 
and nut,
Stage 1 - 120nm
Stage 2 - Angle tighten a further 180 deg.

Shock absorber upper mounting bolt
Stage 1 - 80nm
Stage 2 - Angle tighten a further 189 deg.

10*10 
Tighten all new nuts and bolts 
to the specified torque
and, where applicable, 
through the specified angle.

Google found this guff
most of which is beyond me.

Can anyone put it simply please?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 19 at 10:09
 I've never seen that type of rear shocker bolt come loose unless someone didn't tighten it up properly in the first place.  I reckon using the wrong type of bolt (like standard mild steel) on suspension components is a far more dangerous thing.  Usually stretch bolts are used where even a slight loosening can mean a disaster of one kind or another. 

At the end of the day the main thing is that a bolt/nut doesn't come undone with time or vibration or temperature changes.  On stretch bolts the last part of the tightening process (whichever method is used) lengthens the bolt very slightly in a controlled way, which puts a pre-load on the bolt and makes it less likely to come undone.  Critical suspension bolts are usually made of high tensile steel anyway but stretch bolts are specifically made for that purpose.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 19 at 10:30
Thanks T5 TDI :o)

I just Googled "Stretch bolts"

"In order for a stretch bolt 
to be cost effective, 
it is often made from 
low grade steel 
with a class rating of 10.9 
and a typical tensile strength of 150,000 PSI. 
A metric class 10.9 rated bolt
has about the same tensile strength 
as an SAE grade 8 bolt available from 
your local hardware store.."

A bit off-putting innit.
Especially at the price 
VW charge for bolts.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 19 at 11:28
Aha!  The VW bean counter at work again?  It is important understand the application though.  For example if you re-use a stretch bolt on a crank pulley that doesn't have a woodruff key expensive things are likely to happen if it loosens even slightly.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 19 at 13:23
Very true Sir.

Until someone shows me otherwise,
I think it unwise to re-use shock bolts.
Any takers please?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 19 at 13:57
Thank you for your advice T5 TDI.

I've scratted around the Internet
a fair bit and decided to buy
2 shouldered M14x1.5x95 10.9s
2 shouldered M12x1.5x65 10.9s

That I will tighten to
210Nm & 135 Nm.

I got those torques from sites 
as correct for those bolts.

As far as I see see there's no point
in tightening by angle, since: -
The whole point about 
tightening by angle
appears to be to get
all bolts on, say a head,
as tight as each other.

With shocks, it matters little 
if one bolt is a little tighter 
than the one on the other
side of the van.

Please will you tell me if you
think I've got it wrong,
and why?

Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 19 at 20:33
Originally posted by Charlie Dog Charlie Dog wrote:


Please will you tell me if you
think I've got it wrong,
and why?

Thanks

Torque angle is not so much for even tightening, you can do that using standard bolts and a torque wrench.  It's to stop it coming loose.  The stretching of the bolt as you put the last bit of force on it keeps some extra tension on it which would have to be released before it could come loose.

As long as the bolt shoulders are a good fit in the shocker bushes and the right length I can't see why there should be a problem.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 19 at 21:07
As long as the bolt shoulders are a good fit in the shocker bushes and the right length I can't see why there should be a problem. 

Thanks T5 TDI.

From my point of view,
there's a lot of bullshine
lighting up stretch-bolts.

When you torque a bolt
not all the force goes into
stretching the bolt.

Some of your strength 
is wasted fighting friction.

I went along with the idea
that friction get less predictable
as torque increases.
That, if you torque to say 75% 
of the torque need to stretch 
the bolt, and then turn the bolts
say 3 flats, you get more equal results.

How do you find that idea please?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 26 Oct 19 at 21:46
Here's a more technical view: -

Torque-angle Method 

In the first step, the bolt is snugged down to the cylinder head by means of a pretorque. 

With the second step, the so-called torque or tightening angle, the bolt is tightened into the plasticregion, i.e. beyond its elastic range. 

Using the torque-angle method, the variations in bolt clamping force lie in a range of ±10%

Using the simple torquing method with several steps, the variations will be within ±30% of the calculated bolt clamping force. 

The reasons for this lie in the dispersion range of torque values and the overall coefficient of friction, i.e. the friction occurring under the bolt head and in the threads

I snitched it from Praxis who make stretch bolts: -

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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 19 at 08:48
Can't say I know that much about the science of it.  I certainly wouldn't ever replace a stretch bolt with a standard bolt on any critical part but if both shocks fell off, apart from an unpleasant bouncy ride and terrible handling nothing much would happen.  The suspension wouldn't sink or collapse or anything because that type of rear shocker isn't load bearing, it just damps the natural oscillation of the spring.    
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 19 at 09:05
Thanks T5 TDI

What you say about shock bolts
coming loose seems spot on to me.

If we are picky, shock bolts
aren't proper "Stretch bolts".
Haynes led us up the garden path
by telling us to tighten by 3 flats.

I Googled "Stretch bolts" this morning,
stretch bolts have a narrow shaft.

T5 shock bolts look like normal bolts.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote T5 TDI Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 19 at 09:17
Head bolts often look like that but often the wasted part may be more to stop them corroding to the head.  This is a stretch bolt for a con rod.  Not how fat it is.  Crank stretch bolts are much the same.  https://www.turnerengineering.co.uk/PBSCProduct.asp?ItmID=20634864&AccID=122596&PGFLngID=1&gclid=Cj0KCQjwgNXtBRC6ARIsAIPP7RvdVeCmXk-24fhJ2se_2qJzsG64qCsdNbHXXq_YEq3wkcdFblB82iMaAuo8EALw_wcB

It would be interesting to know what the elswin manual says about it all.  Smile


Edited by T5 TDI - 27 Oct 19 at 09:18
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 19 at 09:59
True :o)

A little bit narrower between
where the shank ends and 
the thread begins.

Unless my eyes deceive me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stryne Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 19 at 11:55
Elsawin says replace bolt (surprise, surprise) 80 Nm plus 90 deg further. 

One coud do what DIYers, RAG backyard repairers, bush mechanics (I'm one),  have done for centuries,
no discussion, no intellectualising, no forum lookups, just tighten the old bolt and forget about it, and they
don't come loose. LOL
2005 T5 2.5L 128Kw 6SpA LWB med. roof
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charlie Dog Quote  Post ReplyReply Direct Link To This Post Posted: 27 Oct 19 at 15:39
Very true Stryne, thanks :o)
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