Planning on doing a wishbone replacement soon. The Haynes manual says that the bolts must be renewed once removed.

Do these need to come from a dealer? Anywhere else to get them from? In general, how do you know which bolts need to be renewed and which can be refitted? Is it just a general thing that suspension bolts need to be renewed?

Thanks,

Martin

Edited 13 March, 201016 yr by 2SkodaFamily

I recently changed the bumptops on the rear suspension and I got a set of bolts from the dealer, hey had to order them in but that only took a day or so. The full set of bolts and nuts came to less than a tenner.

Oh and they get covered in a fair amount of crud and the ones on the bottom of the shockers looked quite manky compared to the new ones.

Edited 13 March, 201016 yr by trundlenut

Most of the bolts are stretch bolts so must be replaced.

Most of the bolts are stretch bolts so must be replaced.

I think you are getting mistaken !

Stretch Bolts as you call them are used for engine cylinder heads, not for suspension parts, they are

High tensile bolts.

The only think that could be changed is the nuts, and fit "nyloc nuts"

Radiotwo

All bolts stretch to some degree when tightened. " Stretch Bolt" is the term normally given to bolts that are stretched to some desired dimension by angular turning of the bolt/nut.Stretch bolts are normally initially tightened to a fairly low torque figure and then further tightened by specified angle of rotation to "stretch" the bolt further . This may be done in stages to achieve the desired clamp load. .Unless this method of tightening is specified the bolt is probably just a normal high tensile bolt . If bolt is corroded then is it good practice to renew with new one and its associated nut .

Prior to the angle rotation tightening method being widely used, high torque figures were used which in theory stretched the bolt to the same limit . However the angle method is much more accurate.The torque figs. were significantly influenced by surface finish of the threads , accuracy of torque wrench , oil on threads etc. Stretch bolts can be used for any critical area where the clamp load between two components needs to be accurately controlled but less critical areas may use high torqued bolts that may be stretched that should be replaced..

Edited 14 March, 201016 yr by vwcabriolet1971

I think you are getting mistaken !

Stretch Bolts as you call them are used for engine cylinder heads, not for suspension parts, they are

High tensile bolts.

The only think that could be changed is the nuts, and fit "nyloc nuts"

Radiotwo

Sorry, it is you that is mistaken my friend. There are a number of suspension bolts that are "stretch" type. If the torque specification includes a stage which turns the bolt through an angle rather than just tightening to a torque setting, then they are stretch bolts and should technically be replaced.

I think you are getting mistaken !

Stretch Bolts as you call them are used for engine cylinder heads, not for suspension parts, they are

High tensile bolts.

The only think that could be changed is the nuts, and fit "nyloc nuts"

Radiotwo

In that case the official Skoda Workshop manual is wrong (which it isn't) Any bolt used that has angle tighten after torque setting is a stretch bolt. :p

In that case the official Skoda Workshop manual is wrong (which it isn't) Any bolt used that has angle tighten after torque setting is a stretch bolt. :p

Moggytech is right. Stretch bolts are used all over the place including the suspension. You can easily spot them as the thread stops before the head and the bolt is waisted between the head and the thread. At one time they all had a cone-shaped end but I'm not sure that is always the case.

Suspension example - the three balljoint/lower arm bolts are stretch bolts

The Haynes Skoda Octavia Manual actually has a picture showing the two types of bolt (2C.10 - Fig 7.24)

On the subject; does anyone know if the bolts that hold the suspension units (shocks/springs) in place at the turrets are stretch bolts? Cheers.

On the subject; does anyone know if the bolts that hold the suspension units (shocks/springs) in place at the turrets are stretch bolts? Cheers.

Yes they are: Screw, 15 Nm + torque a further 90° (1/4 turn) replace after every use.

Just in case anyone is interested in why stretch blots need to be replaced after each use. Steel has a certain elasticity and can be stretched to provide a tension between bolt head and fixing. Stretch bolts are designed so that when tightened, the 'waste' of the bolt stretches and the steel is tensioned to a point on a break graph, to roughly the top of the elasticity curve. This gives a pulling force on the bolt, and thus prevents the bolt from coming loose.

When you remove the bolt, the structure of the steel molecules changes (it gets weakened) and will either break under load when refitted, or more likely fail to stretch to the correct tension, and thus be prone to working loose.

I still remember the graphs from metal work at secondary school (good memory ) A straight line at about 30 degrees, then it changes to a curve that rises then dips, then there is a slight recovery up gain, then the breaking point is reached.

Olds bolts can be annealed in an emergency, heat them up till cherry red and drop them in cold water. Usually done on classics when a new bolt would have to be machined to order.

The bolts (technically 'screws') on the suspension are for the most part NOT stretch bolts.

A stretch bolt has an unthreaded portion which stretches (goes into plastic deformation) once it is tightened beyond a certain point. These are used to ensure consistency of clamping force (particularly with power tools used during assembly) and they also allow the manufacturer to use a cheaper quality steel for the bolt.

Torque+angle does not necessarily indicate the use of a stretch bolt. On setscrews it is normally specified to ensure reasonable consistency of clamping force - but the screw is not actually stretched (no plastic deformation). The reason that torque+angle is often used is that once a relatively low tightening torque is exceeded, the relationship between torque and bolt tension tends to break down. This is because more than 75% of the torque is being used to overcome frictional forces (thread friction and bolt head face friction). By specifying a low torque and then an angle, the bolt tension tends to end up being more consistent because frictional scatter between bolts is reduced. Also a thread prep coating is also often used to reduce friction.

Because of the greater consistency of bolt tension the manfr can also get away with a cheaper bolt material and for this reason its best to replace after each use.