Evening all,

 

So I have been working through TeflonTom's excellent guide on replacing the arb (http://www.briskoda.net/forums/topic/66187-guide-how-to-change-fabia-front-arb/).  Having gotten everything apart and a new arb in the right place, I tried to get things back together but there were a couple of mishaps the highlight of which is ballsing up the thread for a couple of the main sub-frame mounting bolts.

 

The main problem though is that when I referred back to my Haynes for torque specs I noted the dreaded asterisk informing me that I should renew:

• the main bolts for mounting the subframe
• the bolts for fixing the steering rack to the subframe.

Firstly - is this even true (or is it referring to other bolts - or have I missed any?) but mainly is this actually necessary and what would happen if I didn't renew them?

 

Many thanks,

 

Neil

VW group seem to be very conservative when it comes to recommending bolt/nut replacement, lately.  In some case it's an excellent idea, e.g. where a steel bolt goes in to a thread in a cast aluminium part, where the slightest corrosion on the bolt's thread could cause galling and destruction of the alloy thread. Also where a bolt goes into a thread, and out the other side to a place where it can get wet/rusty like caliper slider bolts, it's a great idea to replace them before that rustiness builds up to the point it starts to tear up the female threads on the way out. 

 

Another factor is that pre-load (tension) versus torque is strongly affected by the surface condition of threads and mating faces of bolt-heads etc. because of the huge influence of friction.

So starting with a new bolt instead of one in 'other' condition gives you a much better chance of loading it correctly, for minimum risk of later problems.

 

As a summary, I'd say it's nice to fit new, but rarely really essential. If it's something that you may need to remove again in future, think about that too.

A lot of bolts they recommend replacing they say it due to the fact they have pre applied thread lock, so once its been used once that threadlock is no good to use again.

So unless your removing stretch bolts in the engine the bolts are reusable if as above not rusty etc, just add your own thread lock

^ Yeah, good point, I forgot about that.

One thing that might be making Haynes issue warnings is, you will find a lot of VAG bolts have a greenish coating, a techie on here, years ago, explained that that coating (barrier) was to avoid any interaction between the steel and any aluminium that it was being screwed into. So, it seems that VAG have done the correct thing and used these coated bolts in places where they screw into aluminium and where they screw into steel - to cut down on variations of bolts and wrong selection. This might have lead Haynes to advice replacing all greenish coated bolts on removal.

 

As said already, any steel bolt that is getting screwed into aluminium must get treated to a lot of respect for the sake of the aluminium threads, also when removing the calliper mounting bolts or any bolts where there are exposed "through threads" you need to try to clean up first, apply release fluid (something stronger than WD-40) and work them in/out gradually - or the threads could get destroyed. I even bought a very usual tap/die set from Screwfix for this very purpose, ie to clean up exposed threads before removing the bolts.

 

From a VW Polo owner's use of dealer experience, none of these coated bolts were ever replaced when the car was worked on in the local VW dealer, and I am referring to the task of replacing the ARB specifically.  I did order in and replace they all later though - as well as painting and coating with wax, any exposed thread that might cause trouble in the future.

 

Note that most if not all of these bolts needed to be ordered in, I hope that they are held in the workshop stores, but it seems that they are not held in parts department stock.

Edited 23 July, 201510 yr by rum4mo

Thanks for all your input guys.

 

I'm off to my nan's this weekend and so I couldn't wait long for some not-off-the-shelf bolts to come in, so as the bolts are in pretty good condition I'll get some threadlocker and then keep an eye on things from there.

 

I did notice there was a coloured tinge to the bolts (blue to my eyes) when they came out, which I assumed was a threadlock coating.  I've already ordered an extra tap for the larger holes specifically (M12x1.5) that wasn't in the kit I got from Halford's (happy to lend it to anyone!) to clean up the threads.

 

Cheers,

 

Neil