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Author Topic: LHS trailing arm  (Read 947 times)
Matraman
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« on: January 03, 2020, 07:07:08 pm »

I know it's a long shot, but does anyone have a left hand side rear trailing arm they would sell? Mine has a hole on the outer surface where road grit hits it, I've cut it out to about 6cm x 1 cm in size to get to good metal. I also discovered a small 3cm x 1 cm hole near the hub carrier end. That, combined with a lot of dusty and rusty material I have got out of the trailing arm, suggests it's lost a lot of metal to corrosion.

One plan is to get it welded and maybe reinforced (not sure if there's enough clearance to add metal though), or maybe someone has one in decent condition which they would sell? Last resort is a new one from Polytecnic as I'm trying to avoid big spends where possible at this stage.

The RHS arm seems fine, no holes and not much sound of loose material inside it when I shake it. So not all bad news!
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Anders Dinsen
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« Reply #1 on: January 03, 2020, 08:27:27 pm »

Been there... http://www.matrasport.dk/forum/index.php/topic,3311.msg24428.html#msg24428

I ended up ordering two new ones from Politecnic as they tend to corrode from the inside. The LHS is fitted now and I'm now going to start on the RHS. I'll be sending the old hubs back to Politecnic so they can be used for new ones.

/Anders
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
Matraman
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« Reply #2 on: January 04, 2020, 09:25:14 am »

Hi Anders
Iíve read your thread with great interest over recent weeks since I bought my Murena 2.2 project. It has helped me to see what is possible with a single garage, which you and I both have. So while reading through it I saw your new trailing arms, very nice! Do they have to be ordered in pairs, or could I just buy one?

My trailing arms have been treated internally through some drlled holes at some point, the previous owner was very keen to tell me that it was done regularly. It seems to have been effective on the RHS but not on the LHS for some reason. I plan to give the RHS a good blast with Waxoyl inside, but Iím not confident about the strength left in the LHS. The consequences of it collapsing could be severe!

So if I could just get hold of a left one for now it would be another step towards getting it back onto the road after 20 years of sitting in a garage.
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Anders Dinsen
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« Reply #3 on: January 04, 2020, 11:29:21 am »

Glad to hear you've been finding inspiration in my posts Smiley

The "right thing to do" is to replace both with new ones remade from scratch. That said, they sell them one by one, as far as I know. Simon too. I have also heard of people welding them up successfully, as you're thinking about. It can probably be done so it won't be noticed, though it wouldn't be legal (at least not here). Suspension components should generally be replaced, not repaired.

That said, however, I think the arms are over-dimensioned, and especially the outer part is less critical part of it from a strength point of view. I haven't made any calculations (semi-trailing arm physics is hard...), but the upwards load is obviously on the spring/damper joint, and the lateral load on the inner joint. The outer joint is only there to control the suspension movement. You can see this by the fact that the inner joint has a face on which it's running against the chassis, whereas the outer is just a bolt running through the holes, so it's by the inner joint that the lateral forces on the outer wheel (which is carrying most of the weight of the car during cornering) are transmitted to the chassis. Also note the bar under the engine that connects these two points on the chassis to further strengthen that and ensure the lateral forces are transmitted through the chassis to the opposite front wheel to stabilize the car during cornering (the job of the roll stabilizer).

Matra knew what they were doing with the chassis. It's a pity they decided to save some money on the trailing arms... An aluminum design (as on the Bagheera) would have been much better for us now.

/Anders

« Last Edit: January 04, 2020, 11:47:58 am by Anders Dinsen » Logged

'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
roy4matra
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« Reply #4 on: January 06, 2020, 10:25:49 pm »

Hi Anders
Iíve read your thread with great interest over recent weeks since I bought my Murena 2.2 project. It has helped me to see what is possible with a single garage, which you and I both have. So while reading through it I saw your new trailing arms, very nice! Do they have to be ordered in pairs, or could I just buy one?
...
So if I could just get hold of a left one for now it would be another step towards getting it back onto the road after 20 years of sitting in a garage.

Hello Matraman,

You can certainly buy just one from any of the sellers, but the only accurate ones are from Politecnic as they have the angle on the bracket where the strut attaches.  The others have been welded on parallel to the arm which is incorrect, and I have not only told those suppliers, but sent photos, yet they don't seem to want to correct them.

So not only are the Politecnic ones made from better material but they are also accurate, which makes them worth the extra cost.  You have to send the old hub back as these would be too expensive to remanufacture, but normally the old ones are fine and can be reused.  If you buy the new ones first there will be a surcharge which you will get back on return of the old hub afterwards.

As Anders points out, welding suspension items is illegal in Denmark and here in the U.K. and maybe all the EU, so repairing old arms by patching them is not allowed and should cause an M.o.T. failure.

Trailing arms are such a critical part which is important for safety that fitting a pair of new arms is the best option in the long run.  As long as the RH one really is fine, then replacing the LH one now and the RH one when you have more funds should be the best way.

Also consider the state of the rear brake discs whilst replacing the trailing arms as the hub has to come off in both cases so it is best to do them at the same time.  The rear discs should be 11mm thick new, and 9mm is the minimum before replacement is needed.  2.2 rear discs are unique so are expensive unfortunately.

Roy
« Last Edit: January 06, 2020, 10:28:13 pm by roy4matra » Logged

Matraman
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« Reply #5 on: January 07, 2020, 12:07:01 am »

Thanks Roy, that's helped me make up my mind. I've emailed Politecnic in my best Google translate French (!). I may as well do the Silentblocs and bearing at the same time, I believe they can fit them. I'll keep filling the right hand one with Waxoyl through its specially drilled holes and monitor its condition while I'm there. As you say, I can change that later if required.

The discs are 10 mm at the back and 10.5 mm at the front. Just a light coating of rust and no scoring. The car won't be doing big mileage so I think they will be fine for several years yet.
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Morne
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« Reply #6 on: January 25, 2020, 11:41:27 pm »

Initially when I took off my arms, they looked to be in a fairly good condition. After a bit of hammering to remove the silentblocks, some small holes appeared on the righthand side one. Which means this needs to be replaced.

I have been looking around for sources to buy the arms from, as they are costly but I will buy both sides. I was thinking about buying from Carjoy:
http://carjoy.nl/matra-shop/index.php?route=product/product&path=62_131&product_id=368

Now Roy has me worried that these might not be correct. Roy I did not 100% understand where the differences are which you mentioned. Can you please clarify.

I am also intrigued how the "incorrect arms" get fitted, or what fitment issues this will cause?
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roy4matra
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« Reply #7 on: January 26, 2020, 05:04:23 pm »

Initially when I took off my arms, they looked to be in a fairly good condition. After a bit of hammering to remove the silentblocks, some small holes appeared on the righthand side one. Which means this needs to be replaced.

I have been looking around for sources to buy the arms from, as they are costly but I will buy both sides. I was thinking about buying from Carjoy:
http://carjoy.nl/matra-shop/index.php?route=product/product&path=62_131&product_id=368

Now Roy has me worried that these might not be correct. Roy I did not 100% understand where the differences are which you mentioned. Can you please clarify.

I am also intrigued how the "incorrect arms" get fitted, or what fitment issues this will cause?

The suspension strut is mounted to the chassis at the top further inboard than the connection at the semi-trailing arm, so it comes down at an angle of around 9 degrees from vertical.  Therefore the bracket on the trailing arm where the strut fits, should also be at that angle so the bolt holes align for the bolt to pass through the arm and metallastic bush which is fitted in the bottom of the strut.  The original arms made by Matra and now by Politecnic have the bracket welded on to the semi-trailing arm at the correct angle.

Those from Simon & Carjoy do not.  They have been welded on square with the arm such that the bolt holes are horizontal and parallel with the ground.  This means that when you push the bush at the bottom of the strut into the bracket to fit the bolt, the holes will not line up.  If you get the bolt into one hole and start it in the tube in the centre of the bush, since the bush is at an angle it will not line up with the hole in the other side of the arm.  The only way you could get it through is to twist the bolt at an angle but that means twisting the tube in the bush, to get it through and secure it.  It is possible although difficult, but then you have a bush that will be compressed on one side and expanded on the other as it will be perminently distorted to fit the incorrectly mounted bracket on the arm.  This stresses the bush and the arm as they try to mate with one another and over time will lead to additional wear and/or failure.

(if either of those two suppliers have corrected their arms very recently, then they could now be correct, but the last one obtained within a year from this posting, was still incorrect even after I have sent many photos some years ago showing the mistake)

If your arms are original Matra designed ones, look at the bracket where it is welded to the side of the semi-trailing arm and you will see that there is a wide gap at the top and it is much narrower at the bottom because of the angle.  With the incorrectly welded arms, the bracket is parallel down the side of the arm.

Here are two photos of a genuine Matra 2.2 semi-trailing arm, clearly showing the correct bracket angle.  I have had these LH and RH genuine arms for years and were two of the very last original stock. (and they are spares for me so they are not for sale! Smiley ... and they match the original arms on my Murena 2.2 which I've had from new so I know these are correct.)

Now the 1.6 Murena has a sligthly narrower rear track but it is only 10mm per side, and I have never measured the positioning of the brackets on a 1.6 arm to know if they moved it relative to the chassis so the angle is the same or if it was slightly inboard compared to a 2.2 in which case the angle would be fractionally less, but I do know from seeing original 1.6 cars that the brackets were also at an angle, not parallel to the side of their arms.

I hope this is now clear.

Roy
« Last Edit: January 26, 2020, 09:03:43 pm by roy4matra » Logged

Morne
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« Reply #8 on: February 02, 2020, 08:31:23 pm »

Thank you Roy for the very clear explanation.

I got a round to take some photos of my arms. Indeed the angle on the 1600 is less.

Taking these photo, I noted the left arm also seems to be bent. The left rear quarter panel on my car was replaced somewhere in the past. It could be that the arm also go damaged during the damage.
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roy4matra
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« Reply #9 on: February 04, 2020, 08:43:56 pm »

Thank you Roy for the very clear explanation.

I got a round to take some photos of my arms. Indeed the angle on the 1600 is less.

Taking these photo, I noted the left arm also seems to be bent. The left rear quarter panel on my car was replaced somewhere in the past. It could be that the arm also go damaged during the damage.

Yes that LH semi-trailing arm is definitely bent!  That wheel would have been running a positive camber (unless the chassis was also bent to compensate!)  That definitely needs replacing because if it is bent and giving the incorrect camber, there is a good chance the rear castor and tracking are also incorrect.

As for the angle of the bracket - you say it is less but have you measured it?  Because just from the photos I would say there is little difference to the 2.2 arms.  It would have been better to have taken suspension geometry measurements before the suspension was disturbed and the arms were removed.

Once you get it back together you definitely need take a set of rear suspension geometry readings to make sure they are all in tolerance; because to bend the arm as badly as that it must have taken quite a thump, and you cannot be sure the chassis and mountings are still exactly correct.

Roy
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