Hi, I have just bought a Stilo JTD and I am slowly going through its multitude of problems (previous bodges galore). I have got new rear bushes to fit, they did not come with bolts. Would someone be kind enough to tell me the size, length, and grade of the bolt required. Thanks in anticipation. --- Bertie.

Two things:

1) Have you tried ePER (link above) for the part number of the bolts?
2) Have you checked the Guides section (link above) as I recall there's a 'how to' guide on the rear bushes that might help you.

Hi, Welcome to the FF.

It's unlikely that anyone would know the dimensions of the bolts without measuring them on their car, which of course, you could do yourself anyway.

From memory, they are 12 mm diameter. If you already have the bushes, measure the inner diameter to see the maximum size that's going to fit through it. Length will be about 3 - 4 cm longer than the bush.

Rather than hunt around for the correct size after market bolts, it would be better to get the correct bolts, with the correct threaded/unthreaded dimensions and grade from a Fiat dealer.

Bolts are part number 51795351 - about £7 each.
Nuts are part number 12578421 - about £2.50 each.

Get Fiat to check the part numbers with your VIN.
.

Ouch that's 19 quid for 2 nuts and 2 bolts. I have measured the required bolts ( I was just b eing lazy asking if anyone knew of the size) but that price got me measuring them at a fair old rate. Thanks anyway but I have found some suitable 10.9 grade bolts, with nuts Three pounds and 34 pence including vat for both sides.

bertiebumblebee said:

Ouch that's 19 quid for 2 nuts and 2 bolts. I have measured the required bolts ( I was just b eing lazy asking if anyone knew of the size) but that price got me measuring them at a fair old rate. Thanks anyway but I have found some suitable 10.9 grade bolts, with nuts Three pounds and 34 pence including vat for both sides.

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That'll do the job. I try to not get too hung up on bolts.. just measure the old ones and then try to find new ones the same size. There's plenty for sale on eBay for instance.

The tricky ones are engine mounts and shocks etc. since they support some weight and are fine pitch generally (to allow higher torques). They're probably higher tensile strength too.. but even here, a regular 10.9 bolt will be okay.

I'd attach a stainless nut though, even if the bolt is mild steel, since it's right in "Zone 1" for picking up salt and crud. If one of the fasteners is stainless, they won't rust together and it will be easier to dismantle next time.


Ralf S.

Ralf S. said:

That'll do the job. I try to not get too hung up on bolts.. just measure the old ones and then try to find new ones the same size. There's plenty for sale on eBay for instance.

The tricky ones are engine mounts and shocks etc. since they support some weight and are fine pitch generally (to allow higher torques). They're probably higher tensile strength too.. but even here, a regular 10.9 bolt will be okay.

I'd attach a stainless nut though, even if the bolt is mild steel, since it's right in "Zone 1" for picking up salt and crud. If one of the fasteners is stainless, they won't rust together and it will be easier to dismantle next time.


Ralf S.

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A few words of caution about suspension bolts.

Many are 10.9 grade, whereas the general grade of metric bolts is 8.8. There are lower grades available, so be sure any Ebay purchases are at least 8.8.

Stainless bolts and nuts are lower spec than 10.9. See the reference section of the guys in this link. They do a good selection of bolts, so may be able to supply what you need.
http://www.westfieldfasteners.co.uk/Ref_Strength_Spec.html

To avoid them seizing on, a smear of copper-based anti-seize on the threads will usually suffice.

Most stainless nuts will be austenitic and not remotely as strong as a grade 8 bolt shear strength is probably a third or less. Definitely wouldn't use on in suspension.

I think stainless is about 78% the strength of an new steel bolt... and a new stainless bolt can't be too much worse than a 10-15 year old steel one.

Ralf S.

Ralf S. said:

I think stainless is about 78% the strength of an new steel bolt... and a new stainless bolt can't be too much worse than a 10-15 year old steel one.

Ralf S.

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Tensile strength maybe. There are lots of different grades and *if* you could find one with 78% of the original tensile strength the shear strength would typically still be useless. If you really think a 10-15 year old suspension bolt is worse try and cut both with a hacksaw, try filing them, then try and bend them with a sledgehammer. Austenitic stainless is like butter compared to a 10.9 bolt.

Yeah but.... some perspective. An M10 stainless bolt needs a weight of getting on 5 tonnes to shear it... even more if it's mounted in a "sandwich" arrangement, where the load is supported at two places (as in a front suspension strut bolted either side of an intervening hub-carrier).

A Stilo weighs 1250kg empty... so even if you load the car up to its maximum weight...let's call it "2000kg" / fully loaded .... and if we assume a 60:40 weight distribution, then it's putting 1.2 tonnes through the front suspension (which is 600kg on each strut). Throw in some age/hardening/vibration and what have you... it's still not too much drama for a 5-tonne capable bolt.


Ralf S.

Ralf S. said:

Yeah but.... some perspective. An M10 stainless bolt needs a weight of getting on 5 tonnes to shear it... even more if it's mounted in a "sandwich" arrangement, where the load is supported at two places (as in a front suspension strut bolted either side of an intervening hub-carrier).

A Stilo weighs 1250kg empty... so even if you load the car up to its maximum weight...let's call it "2000kg" / fully loaded .... and if we assume a 60:40 weight distribution, then it's putting 1.2 tonnes through the front suspension (which is 600kg on each strut). Throw in some age/hardening/vibration and what have you... it's still not too much drama for a 5-tonne capable bolt.


Ralf S.

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This is irresponsible.
The link I posted shows strengths of various bolt grades, and clearly shows stainless to be lower than 10.9 steel. I have seen in various places that stainless should not be used where high stress is encountered. The vehicle manufacturer is trying to do everything as cheaply as possible, so when they use 10.9 bolts, there is a good safety reason. Unless you can show with evidence from a qualified stress engineer that stainless would be ok, we should always replace 10.9 with the same. Let's not create risks.

Ralf S. said:

An M10 stainless bolt needs a weight of getting on 5 tonnes to shear it...

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'An' M10 bolt can have all sorts of shear strengths an A1-50 M10 bolt could be as little as 800kg, and thats just one of the bolt parameters.

Its clear from your 'weight' calculation you know little about the forces and loads in a suspension. A piddly 5cm bump at 70km/h on a test track exerts 5g on a car. Now imagine a 15inch wheel dropping into a 10cm deep pothole at 100km/h etc. etc.

I thought we were done with this topic but it looks like you still want to argue about it.

It's true I did not pay all that much attention at skool... but as I understand it you do also need to include the duration of the bump in your calculations and you didn't... (although admittedly I know little about it).

If our bump is 2" high and has a duration of 6" then the theoretical (if it was a uniform bump) angle of the bump would have a radius of arctan (2/6) = 0.32 rad, or 18.4 degrees).

Now our car travelling at 50kmh:

Our Horizontal speed over the 5cm bump (as I'm sure you know) is 50 x cos18.4 = 47.44 km/h (It's also 1318cm/sec We'll need this later).

Vertical speed of the wheel over the bump will be 50 x sin18.4 or 15.78 km/h


Now then... The time it takes to travel 6" (or 15cm) at 47.44km/h = (15 / 1318cm) or 0.011s

Our wheel's vertical speed over the bump is 15.78 km/h or 4.38m/s.

Upward acceleration of the wheel is therefore 4.38 / 0.11 or 39.8m/s2 ... which comes out at 4.06g. You can see that a longer duration bump reduces the G loading through the wheel... so your 5g was a pretty good estimate.

Anyhoo.. if the unsprung weight of the wheel, tyre, hub and brake caliper etc. weighs in even at a portly 25 kilos then (ignoring any dissipation of force by the tyre).. hitting that ^ 5cm bump at 31mph (50km/h in the old money) means it would exert a force of 995Nm (or Kg/m2).

I still can't see why that would be a problem for a bolt with a shear-limit of circa 5 tonnes, even if we add half of 60% of the weight of the car (I offered a generous 600kg) to it.


I don't know enough about it to work out the force through the suspension if the wheel hit a 10cm deep pothole at 100km/h... (and I though UK roads were bad.. ) but;

a) I doubt it would be as much as hitting the 5cm bump at the same speed, since the suspension is in extension, not compression. The wheel speed (G) is reduced to the force exerted by the springs.
b) Hitting the edge of the pothole (coming out of it) might be a different story
c) If I dropped an 11" radius wheel (7.5" plus 3.5" of sidewall) into a 4" deep pot-hole at 100km/h, then suspension bolts is not going to be the biggest problem..

Ralf S.

Ralf S. said:

I thought we were done with this topic

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We have now.
bertiebumblebee Probably better to start a new thread if you need any more advice.

THREAD CLOSED.