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Author Topic: Problem with left rear suspension mount  (Read 4810 times)
Jon Weywadt
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« on: July 16, 2009, 05:31:13 pm »

Before re-assembling the car I decided to clean the chassis and protect any rusty spots. In the process I discovered a problem with the mounting holes for the inside mount on the left rear suspension. It looks like someone enlarged the holes with a welding torch. As you can see on the picture, they are not round and do not appear to have been worn into that shape. There are some welding globs around the back where the hole is kind of square.

I wonder if this is due to a problem with the geometry of the, new style, left suspension arm. Perhaps the left axle is not tracking squarely with the original holes and it was necessary to enlarge them to get the tracking right.

I obviously want to repair the holes so they are round again and I don't risk the arm sliding back and forth. As I see it, there normally is no way to adjust the rear wheel setup. But, how do I measure if the wheel alignment is correct? Also, does anyone know, what is the correct angle between the line through the rear pivot point and the axle. I am trying to measure it on the suspension arms that I have and it looks to be close to 12 degrees. Does that sound right?

Update.
I did a trial mount of the arm and found that it cannot move back far enough, for the bolt to fit against the cut out hole. It looks like the only place there is room for it, is the original hole, so I will  try to find a way to fix the mess that was made. Perhaps the aluminum putty I used on the clutch cylinder will work. We shall see.
« Last Edit: July 17, 2009, 03:16:15 pm by Jon Weywadt » Logged

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Anders Dinsen
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« Reply #1 on: July 17, 2009, 04:58:50 pm »

It doesn't look good, Jon. The wheel alignment can indeed be checked - details are in the workshop manual. You are welcome to borrow mine and make copies/scans of the pages, or you can go to a workshop with a computerized alignment machine - most have the Murena in their systems.

But that won't help you now, where you need to fix the holes. I can measure the distance from chassis base to the centre of the fixing bolt on my car if you want?

But of course the question is whether the trailing arm is correct then... Was the left one the one that looked "repaired"? I'm going to remove my left one in a week or so to replace the differential seal - you are welcom to come by then and compare your trailing arm with mine when it's off the car.

/Anders
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Jon Weywadt
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« Reply #2 on: July 18, 2009, 07:06:21 pm »

But of course the question is whether the trailing arm is correct then... Was the left one the one that looked "repaired"? I'm going to remove my left one in a week or so to replace the differential seal - you are welcom to come by then and compare your trailing arm with mine when it's off the car.

/Anders
Hi Anders.

The left one is indeed the one that has been remanufactured. If I haven't figured out how to fix it I will take you up on your offer. But I hope to have the car put back together by next week, when my vacation ends. But here is what I have done.
I set up a jig to measure and compare the two trailing arms (photo). I put a rod through the pivot holes so the two arms were lined up. Then I lined the rod up parallel to the rear of the table and drew lines at right angle and along the outsides of the outer bushings. Next I held a plate flat against the bearing housing and drew lines parallel to the housing. I then measured where they intersected the first lines and as you can see the left arm intersects 4 cm closer to the pivot axis that the right arm does. (photo 2) I cannot be sure of course, because the axle may not run exactly at right angles to the housing face. But it probably means that the left wheel will track at a different angle than the right. I marked where the interception point would be if identical to the right. On the last photo I moved the inside pivot point back about 6 mm, as if the bolt had been pushed back in the enlarged holes. Drawing the line parallel to the housing face again (dashes) you can see that it intersects the same place as before, but more important, it now is parallel to the line matching the right trailing arm. I guess I will have to fix the holes so the center is moved back the 6 mm, before I remount the trailing arm. What a bummer.  Angry
I may try the measurements again with the axles and hubs mounted on the trailing arms and then check the angle in relation to the face of the hub.
« Last Edit: July 18, 2009, 07:13:37 pm by Jon Weywadt » Logged

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Matra_Hans
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« Reply #3 on: July 18, 2009, 07:48:06 pm »

To be honest: Don’t you think that the correct solution will be to get a new set of trailing arms (with correct measurements)? Instead of trying to make some crude adjustments to something that seems to be completely out of shape.

Hans
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Anders Dinsen
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« Reply #4 on: July 18, 2009, 11:17:53 pm »

That's a nice piece of measurement work you have done there, Jon.

You should remember that the pivot points on the trailing arms are angled on the chassis to add (negative) camber and toe out the rear wheels when the rear is loaded. This is very important. Static wheel alignment should be correct of course, but the dynamics are also very important for that cornering performance.

So I tend to agree with Hans. Your left hand trailing arm is incorrect. I know it's quite expensive to replace, and it may be possible to fix it by cutting it open and re-welding. Have you considered that? You have painted them nicely now, but why not get it right now that you have it all off the car?

I can't say how big the effect is, though. You can do some trigonometry calculations calculating camber and toe-out rates, but they won't tell you much about how it actually performs in the "live". Since you aren't racing the car, you'll probably not notice as you don't have a lap time or skid pan G-force to compare with.

So I'll surely understand if you refit it now the way it is... I just think you should give it a second thought. New (remanufactured) trailing arms are available and with a new one (and repaired holes in the chassis), you'll know it's correct.

/Anders

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Jon Weywadt
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« Reply #5 on: July 19, 2009, 01:11:32 am »

I installed the hub in the left trailing arm and did the measurements again. The result was only marginally better than when measuring off the bearing housing.  Sad

So, the question is now what solution to pursue. I did find out that John in Aabenraa is the one who had trailing arms manufactured here in Denmark. But if the left one is one of those, then that may not be the way to go. I am of course assuming that the original right trailing arm is aligned correctly.  Huh

If I get one of the ones that are available from i.e. Simons, then they will probably be like the original, with the dual layer steel plates that cause the interior rust problems (my right trailing arm sounds like a childrens rattle, due to rust flakes inside it).
On the other hand I have been toying with the idea of having the arms made from stainless steel. I am not too sure about it though, after seing how the bearing housing is made. Still, a stainless steel version does not have to be identical, as long as the measurements and angles are the same. I will find out how expensive that is.  Grin

But, for now I have repaired the holes in the chassis to original placement and I will have the alignment checked out. If the tracking is not too bad I will go ahead and drive the car until I can afford new trailing arms.
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Matra_Hans
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« Reply #6 on: July 20, 2009, 08:14:39 am »

Hi
I doubt very much that your repaired and "out of shape" left trailing arm is from the Danish reproduction of trailing arms. This reproduction of trailing arms have been done at a highly qualified machine shop, parts are laser cut with high precision and they have made a jig for the production so measurements will be correct. Several set of tailing arms have been manufactured without any complaints, and I got one set myself and the shape was spot on.

It is my understanding the tailing arms from Simon are also rebuilt units as original are no longe available.

Hans
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Jon Weywadt
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« Reply #7 on: July 20, 2009, 11:11:38 am »

Hi
I doubt very much that your repaired and "out of shape" left trailing arm is from the Danish reproduction of trailing arms. This reproduction of trailing arms have been done at a highly qualified machine shop, parts are laser cut with high precision and they have made a jig for the production so measurements will be correct. Several set of tailing arms have been manufactured without any complaints, and I got one set myself and the shape was spot on.

It is my understanding the tailing arms from Simon are also rebuilt units as original are no longe available.

Hans
Hi Hans.

I hope you are right about my trailing arm not being from the Danish reproduced ones. I would like to talk to the machine shop about how they make them. I am assuming that they at least re-use the bearing housing. But if they can make those, then perhaps they can make the whole arm in stainless steel instead. That would be really nice.  Grin
However, I tried to write Johnny Hansen in ┼benrň (who you mentioned in another post as being the contact person), at the email adress from the membership list, but that adress is no longer valid. Do you have a current adress for him?

In the meantime I have fixed the holes and will mount the trailing arm. Then I will have the alignment checked to see how bad it is off.

/Jon
« Last Edit: July 20, 2009, 12:59:28 pm by Jon Weywadt » Logged

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Matra_Hans
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« Reply #8 on: July 20, 2009, 04:43:24 pm »

Hi I have send you a PM with the contact details.

The machin shop is reusing  wheel hub or  bearing housing.

Hans
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lewisman
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« Reply #9 on: July 21, 2009, 01:43:51 am »

Hi Jon

I would doubt the need to use stainless steel.  Decent quality mild steel - ideally galvanised - would be fine as long as it was properly protected.  I think the main problem with the originals was the multiple layers and the lack of any significant rustproofing.  Waxoyl type products are good but they need to be re-applied every year.

Good luck finding a solution.

David
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Jon Weywadt
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« Reply #10 on: July 21, 2009, 09:46:56 pm »

Hi Jon

I would doubt the need to use stainless steel.  Decent quality mild steel - ideally galvanised - would be fine as long as it was properly protected.  I think the main problem with the originals was the multiple layers and the lack of any significant rustproofing.  Waxoyl type products are good but they need to be re-applied every year.

Good luck finding a solution.

David

Hi David.
Much as I would like to make them of stainless steel, it will be a significant problem to make a new housing for the wheel bearings. It will remain a wish for the time being, but maybe a solution will present itself.  Cheesy

In the meantime I am now communicating with Johnny, who has a contact to a Danish machine shop, that has made a few remanufactured swing arms. They re-use the bearing housing of course, so you have to send in you old arms. But the design is much improved and looks like my left swing arm. They use a single layer, but 1 mm heavier guage and high tensile steel. The shock absorber bracket is open at the bottom, so water and gravel won't collect like on the originals. The new design is lighter, thus offering lower suspended mass. This should keep the wheels more firmly on the road.

I have gotten som rust protection wax from my friend Jan, that I will pour into the swing arms. But I may wait until I find out about the wheel alignment, especially with the left swing arm. If it is off, I will probably opt to have both arms remanufactured. We shall see.

I should have it back on the road before the week is over. Grin
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Oetker
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« Reply #11 on: July 22, 2009, 11:54:16 am »

I picked up a revised one last week.

It is filled with oil, so no rust is possible from the inside anymore.(see the red filling hole)
When the left one goes off, I wil fill it to.
« Last Edit: July 22, 2009, 11:56:33 am by Oetker » Logged

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Murena 2.2 Red 1982. Murena 1.6 black on places.
Jon Weywadt
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« Reply #12 on: July 23, 2009, 09:30:20 am »

I picked up a revised one last week.
It is filled with oil, so no rust is possible from the inside anymore.(see the red filling hole)
When the left one goes off, I wil fill it to.

That looks nice. Smiley I can see that they welded a plate across the shock absorber bracket instead of leaving it open at the bottom. I hope water and gravel won't collect there.
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« Reply #13 on: July 23, 2009, 09:34:31 am »

It is plastificated, this wil last the next 100 years Grin
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I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
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