Hi, I am going to replace my rear suspension buffer (?)

 

I am looking for the correct torque setting for the marked bolts and nuts.

 

 

Some websites specify the following:

A: 30 Nm + 90°

B: 25 Nm

C: 40 Nm + 90°

 

Does that sound correct? What does the +90°? Is it just 30 Nm and a quarter turn?

 

Best regards
Mathias

Yep, you have all the right info and understanding. The 25Nm isn't easily done with a torque wrench since you have to counterhold the (flattened) top of the shock rod and use an angled ring spanner on the nut, but I don't think 'guessing' that one will be a problem.  It's usually a nyloc or other type of self-gripping nut.

 

Bottom nut and bolt are supposed to be replaced with new ones, as are the top bolts but I think if they aren't too corroded you'll be OK re-using.   

 

Thank you.

I've gotten new nuts, and i will see if the bolts can be re-used.

Preferably replace the bolts as they are "one time use only" as the "+90 degrees" is taking the bolts into their yield/stretch zone - and you don't want to do that more than once.

 

Possibly debatable if the 40Nm +90 degrees on the bottom bolt will be giving it much stretch - but as you asked, replacing them will be the better plan.

 

I'm guessing that your buffer/bump stop has biodegraded as that material does seem to do very quickly,  I've always replaced both sides doing that means you don't need to revisit this bump stop breaking issue again.

Hi Rum4mo

I have purchased replacement bolts and nuts just to be sure they don't fail. I am going to replace the buffer on both sides as you propose.

Thank you

2 hours ago, rum4mo said:

Preferably replace the bolts as they are "one time use only" as the "+90 degrees" is taking the bolts into their yield/stretch zone - and you don't want to do that more than once.

 

Never in a million years on fasteners of that diameter, they are well within the elastic limit even with any service load, when I was a jig & tool designer the fastener manufacturers like Umbrako called it the "torque tension" method and it was to prevent loosening under cyclical loads.

 

The manufacturers would have you believe that a sump plug with 20mm threads screwed into an aluminium sump will stretch when tightened with a 13mm A/F spanner & has to be replaced each time, yes they will stretch microscopically but they will return because they are within their elastic limit.

 

No designer is ever going to specify a fastener that is taken beyond its yeild point by the recommended torque plus the service load.

 

I found the Unbrako information but its a PDF that I can neither copy/paste from nor give a link to but the various methods will never take a fastener to more than 80% of yield and its derated where the service load acts in tension.

As you can probably guess I have yet to throw away perfectly serviceable stretch bolts & that includes on cylinder heads.

 

When I was racing some fellow competitors were mechanics, often main dealer ones sponsored by their employers and with an endless supply of free parts, they could dismantle & rebuild and engine, gearbox, diff etc so quickly that they would always attract a crowd, they never bothered replacing stretch fasteners and like me they greased all their gaskets & would usually reuse them, head gaskets aside but we would grease them nonetheless so they released without needing a clean up or scraping the surfaces.

 

It was all about speed and when you have ignored the recieved wisdom many times & reused the same fasteners or gaskets you know what matters & what has bitten you back.

 

At work of course they would be signing the job sheet for all these parts & the customer being billed, rarely fitted because they would sell them to people who bought the whole deception, if a mate asked if they could get him some stretch bolts cheap he would say "you dont need them"