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broken rubber mounting radius arm bolt


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Hi ,

Tonight, the strangest, scary thing happened 

While driving the esprit S2.2 in the neighbourhood, all at ones a big bang and the car went down in the rear.  The right rear wheel stood completely wrong an there was no way moving the car anymore.

After the first panic , i called a tow truck, and got home with the car (friendly guy and it was his second lotus today :blush:)

He helped me get the car in my garage above my work pit, so I could have a look an do the repair later on.

Apparantly the big bolt for the radius arm to the rubber mounting just clean snapped ! I dont understand what made this happen, because I wasnt driving wild or even quick ( luckily).... Any ideas ? Did this happen to other owners? This cant be just metalfatigue, can it? I have to take a better look, but its been enough for one evening. Any remarks are welcome.

To remove the rubber mounting and the remains of the broken bolt, do I just have to loosen the two bolts holding the plate reinforcing and rubber mounting?

 

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Edited by gvy
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  • Gold FFM

Lucky you weren't cornering at high speed,.....

I was told to use mild steel, never use stainless steel bolts in load bearing or stressed applications such as suspension components, stainless steel is brittle and will snap off rather than bend, I think you have just learned the hard way.

I would check all of the suspension, and replace any stainless steel bolts that may have been fitted, you may not be so lucky next time.

Steve

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Steve, that bolt aint stainless steel. I just tried that with a magnet.

And I have driven the car since 2011 uptil now , about 31000km with that bolt. I mean , I have recently worked on the suspension components changing the U/J s and loosenig the aluminium hubs, but I never had to loosen the radius arm. So in those 6 years I own the car , I did not touch this component. The bolt could even be a lot older.  So why does it fail now?

I was going to change the bolt with a 8.8 or higher grade bolt. I understand here that is a bad idea. What do you suggest. A 4.6 grade ?

Geert

Edited by gvy
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A few questions - What condition are the remaining rear suspension bushes in? I wonder if they're old and slack, that it's possible that movement has caused the bolt to fatigue, and shear, so maybe it's old age? When was the last time those bolts were were replaced? Have they been over-tightened?

In any case, I would replace them with whatever the factory specified, and to the correct torque, when fitting new ones.

Margate Exotics.

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Geert- bad news on your testing method. Some stainless steel is magnetic, it all depends on the manufacturing process. I'm not saying that bolt is stainless, just that you cannot prove it's not just by a magnet test.

 

That aside, what you want is at least 8.8, possibly higher tensile strength but whatever you use, make sure that the nut is compatible (8.8 bolt = 8 nut) because if you over-specify the nut you risk damaging the bolt when the nut would be the sacrificial part you'd hope to see.I'm with Ian, perhaps the bolt has been over-tightened in the past, perhaps it's too low spec, lots of possibilities but given it's one where the shaft of the bolt is critical (more critical than the nut) I'd be following his advice and replacing with new, after all a useful life of 35+ years on a throw-away part isn't bad.

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Geert,

Sorry for you dramas, but as said thankfully it did not happen while cornering at speed as could of had drastic complications :(  I have never heard of one of these radius arm bolts snapping on the forums, it would be down to the folks like Steve at sj to see if he has ever heard any stories etc,  but i would say it could well be stainless, or as Ian says overtightened as i we see sometimes on wheel bolts and engine mount bolts etc.  

Just make sure you change renew both sides and thank your lucky stars that you got of lighty imo with little damage to yourself, other people and the car thankfully :)

A

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Hi all,

 

Now since I have no history of the rubber mountings of the radius arm, I guess now is the time to remove them with new ones and also renew the bolts ans nuts.

As I said, after renewing the U-J 's  some time ago, every last bit of the rear suspension came out. But I didnt touch that bolt because I let the radius arms in place, andI loosened them on the other end with the two long bolts on the aluminium hub.

I may have played a bit to much forward and back with the radius arm and the bolt may have been brittle already?

I see that SJ's sell those bolts and the rubber mountings. I choose the rubber ones (not the red PU ones)

Edited by gvy
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Well I took the rubber mounting out. Easy enough and no rust there. That rubber mounting is in perfect shape. The two bolts to fix the mounting were perfectly clean, no rust and they had traces of copper paste on the tread, so I guess someone in the past must have worked there. I see no need to change those rubber mountings for now, as the rubber feels solid and flexible, not hardenend and in no way torn or ragged, infact it looks and feels like an almost new piece... So that leaves me with that bolt. Maybe it has been tightened the wrong way. Still strange it breaks on me after 6 years and more then 30000km.

Next I will remove the radius arm, to inspect that closer.

Edited by gvy
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I'm 99% certain that bolt was overtightened. It looks to be "necked" down slightly at the parting point. This is a sure indication of a yield failure. Use the right bolt for that application as specified on the parts book. It's probably 8.8 but replace it with the same. Never use SS on structural boltings! They do NOT have the same properties as alloy steel, such as yield and tensile strength.

 

Thanks to the motoring gods you are OK.

Jon - 1984 Esprit Turbo

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OK,

I invested a little further.

I have seen that the bore in the radius arm is an exact fit  for the 7/16unf bolt ( which is the diam of the used bolt according to the handbook), But the diameter of the bore in the rubber mounting is 12mm ( ment for a M12 bolt )

When I use an M12 bolt  it sits perfect in the rubber mounting, but it does not fit through the radias arm bore. ( 7/16unf is 11,1112mm). So the used 7/16 unf bolt has a little play in the rubber mounting.

 

radius arm.jpg

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A second thing that is occupying me is the picture below:

With a provisory bolt I bolted the parts in place as they would be on the car.

You can clearly see that the big round washer and the radius arm are touching, so if ther is a force (like I show in the picture) the bolt is getting a lot of stress, wher it broke:

If I look at the left side ( that did not brake) I see that 3 small washers are used between the big round washer and the radius arm. That allows enough play for them not to touch;

20170327_145536.jpg.e89392fd9736795bee163c432aebebef.jpg20170327_151418.jpg.ef469dded463c43b0ccaa660f72ad809.jpg

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Won't adding more washers affect the suspension castor setup? How does the arm sit when all the suspension is bolted back together and under load? I may be that on the bench it will not sit correctly.

Pete

Pete '79 S2

LEW Miss September 2009

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When you get it together have the rear toe checked, as Peter says more washers there = more toe in. If that washer was touching the end of the arm, then you'd see witness marks.I suspect that if it was touching it simply deformed the bush slightly.

I need to go and check the manual (it's been a few years since last I looked) but I think that there are two "correct" assembly methods, where you simply use the other method if the first one doesn't give sufficient adjustment of the toe-in, you may be better off using that other method.

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Andy there are witness marks visible

OK ,

I made my decision.

First thing that doesn't look OK is the fact that the bushing is M12 and the radius arm is 7/16 unf.

I decided to leave the 7/16 unf bolt route and go all the way with a bit heavier and easier to find over here M12 x 12cm 8.8 grade bolt with a new self locking hex nut. That fits precise in the bushing and using my tabledrill, I could position the radius arm precisely and ream from 7/16unf ( 11,1112mm ) to 12mm.

Next used an M12 washer 1.5mm, which is enough for the radius arm and the big round spacer not touch anymore. I'll check when installed.

20170327_175018.jpg.6a247fb534a2a7761fff00b3c45f0f80.jpg

Edited by gvy
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So,

I just did the first testdrive. It's a good thing I now my car very well, because she would not start. Apparently the shock yesterday, or the towing  did trigger the fuelpump inertia switch in the back, so I couldnt hear the fuelpump doing its "tick tick tick". The problem was solved in a second and off we went.

To be honest, I am still a little scared, because this was a thing I  couldnt  see coming. Yesterday that bolt snapped and bang...

But all went well,

I am planning to do the other side as well, just for the sake of having a brand new bolt torqued to spec on that side too , and because I want both sides converted to the same metric M12 . ( and not having one side 7/16UNF and the other side M12) .And I can check the state of the rubber bushing at the same time.

 

for info :

picture of the head of the old broken bolt and picture of the new slightly bigger metric bolt :

20170327_211126.jpg.3eadde98d47c625a99b1dbf21bb6de84.jpg20170327_213218.jpg.e46972fb9739b2a4ebdf26241513368c.jpg

Edited by gvy
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Thanks for your concern Ian,

 

However I have confidence in my new pgb M12x120 grade 8.8 bolts. For one thing , I now the marque, it is professionally used at work and by many other companies and is a ISO9001 certified company. So I don't think bying bolts from SJ or PNM will better that. Further more, the Metric M12 bolts are slightly thicker than the original 7/16UNF ( have higher specs ).

Based on the torque spec (40-45 lbs ft) in the lotus handbook of the original lotus 7/16UNF bolt, this must be an SAE grade 5 bolt. So when I use the equivalent M12 bolt I should use a  Metric 8.8 type bolt. Now the Metric bolt is slightly bigger and stronger.

Using a higher SAE grade 8 bolt or equivalent Metric 10.9 bolt would not make it safer, because their tensional strenght may be higher, but they are also more brittle, so no go on this suspension part.

And about the rubber mounting, I know they can be changed, but if you had them in your hands, as I did , you would agree that they are in perfect condition. They did not cause this problem.

Edited by gvy
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Geert, as I just replied to your 'other' forum posting. The bolt has been installed the wrong way around. Bolt head should be towards the engine and the nyloc nut against the radius arm. This allows you to remove the radius arm for wheel alignment fairly easily.  I expect some stress was applied to the original bolt that caused it to fracture - possibly as a result of its incorrect orientation.  Also, as Pete correctly pointed out, by adding washers between the arm and the bush you are altering the rear wheel alignment. Doing so will give you more toe-out.

Sorry its all back together, but my recommendation is to disassemble and refit in the manner shown in the workshop manual. Then do a rear wheel alignment to ensure your fitment of the small washers has not upset the rear tracking.

 

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46 minutes ago, jonroberts said:

Geert, as I just replied to your 'other' forum posting. The bolt has been installed the wrong way around. Bolt head should be towards the engine and the nyloc nut against the radius arm. This allows you to remove the radius arm for wheel alignment fairly easily.  I expect some stress was applied to the original bolt that caused it to fracture - possibly as a result of its incorrect orientation.  Also, as Pete correctly pointed out, by adding washers between the arm and the bush you are altering the rear wheel alignment. Doing so will give you more toe-out.

Sorry its all back together, but my recommendation is to disassemble and refit in the manner shown in the workshop manual. Then do a rear wheel alignment to ensure your fitment of the small washers has not upset the rear tracking.

 

Jon,

I did reply on the other forumB-)


in the picture you are refering to, i used a smaller long bolt, I had lying around  just to keep things together and show the situation and make my point.
You are right that in that picture the bolt is sitting the wrong way around (it isn t even the right bolt)
But the bolt that snapped and my new M12 bolt I is installed as in the manual.
Good perception though emo1.gif

 

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Geert,

Do you know if your car was ever involved in any kind of shunt? I had the exact same failure on my first 95 S4s not long after I acquired it in 2003. I was aware that the first owner had been in some kind of fairly minor traffic incident which involved replacing the right rear hub carrier. I assumed at the time that my bolt failure was probably due to suffering some damage during that incident but was not replaced during the initial repair...

  

1995 S4s

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3 hours ago, lotus4s said:

Geert,

Do you know if your car was ever involved in any kind of shunt? I had the exact same failure on my first 95 S4s not long after I acquired it in 2003. I was aware that the first owner had been in some kind of fairly minor traffic incident which involved replacing the right rear hub carrier. I assumed at the time that my bolt failure was probably due to suffering some damage during that incident but was not replaced during the initial repair...

  

Not that I know. I own the car since 2010, but I have not much history of it before that date. I know it's an RHD english car that first came to the netherlands before I imported it into Belgium. I have ones spoken to a former dutch owner, that recognized his car on a meeting somewhere.

It got a respray in the past and all chassis and suspension parts are in a very good condition when I bought it. There are no rusty parts. The S2.2 has a galvanised chassis that is also painted black . There is no visible mark of past damages under the car.

I drive it a lot, and all things considered ( 37 year old handmade english sportscar ) it only left me twice on the side of the road. ( one time with an ignition problem , and now this severe suspension failure )

Since 2010 I keep a very detailed maintenance file and I must have touched 80% of all nuts and bolts, suspension parts  and engine parts. pity the one bolt I didnt touch breaks:(

 

for the record : This is the new M12 bolt and locknut  I installed yesterday.

20170328_081404.jpg.36873c1811389c0ba028a6de307b3b8d.jpg

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It would not have to be serious damage Geert,  Could of well been tail end happy in the past at some point and just side swiped the kirb with the back wheel, The only damage may of been an alloy wheel etc at the time if something like this had happened you would never know,   It is just one of those things, once the bolts are replaced the worry is over :)

A

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So today , I took the time to change the bolt on the left side. Just to be sure.

I noticed that on this side , the rubber mount was also in a very good condition and it also had a M12 bore. So I took out the radius arm and roamed it to M12, and mounted all back on the car with a new M12 bolt and locknut.

I noticed that the old bolt was not tensioned at the right torque. I guess the side that broke wasnt either ?

Job done on both sides now.

 

Geert

 

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