Snapping the Rear Trailing Arm on a Manta

calvin · 10-19-2003

Snapping a trailer arm

Somewhere between breaking in the 22 miles of new pavement on rural route 94 and home I snapped part of my suspension. One of the trailer bars. I am not quite sure how as I wasn’t driving too too overly extremely. I noticed the car seemed to have a kick when dropping it into gear like the rails shifting as the right rear tire bit (no posi here). Seems that the bars are hollow!!! I was going to put in a solid bar shaft and weld it up.

Anything wrong with this fix idea?

It the thick looking bar on the top there. It broke about an inch behind where you see the bushing on the smaller bars.

What would make that snap?

calvin · 10-19-2003

second maybe clearer view, both prior to the snap.

Travis · 10-19-2003

Calvin,

Those pictures are a bit rough. In the first picture it looks like I'm seeing a sway bar in an odd place and in the second picture there are parts that just don't look familiar to me. Though it's been a number of years since I've looked under the rear of a Manta. Are we looking at a non stock suspension?

-Travis

RallyBob · 10-19-2003

That's definitely not a stock Manta sway bar. It appears that the attachment point of the sway bar created a lever-effect on the trailing arm, causing the break. While the stock trailing arms are definitely not the strongest (I've broken a few), I don't think the solution is to weld in a piece of solid bar stock....it will weigh a ton. Use something like 1" x .095" DOM steel tubing, and weld 360 degrees at the front and rear bushing housing. Opel only welds a few degrees around the bushing housings top and bottom (common breakage point).

I would then relocate the sway bar to a better spot, the trailing arms were not designed to deal with those loads.

Bob

calvin · 10-20-2003

I will try to get some better shots.

No the sway bars are not stock actually nothing much on the suspention is. There are three bars in the back and two in the front, Orange koni's, much heavier, shorter springs in front. The front ones are almost twice as thick as stock.The ones in back which have been cut down , I am assuming are from a sportwgon.

A guy in California named Bob Holden (sp?) set it up or had it done as he was listed as the first owner. The car was marked with DSP on the side when I got it so someone wanted it to go around corners. It came without a motor, glass or tranny but the suspention was in place.

I just don't know how it broke when it did as it was not under extreme duress at the time. I think because it is the power side it gets more pressure. I will take Bob's instructions to the welding shop.

thanks,
Calvin

Travis · 10-20-2003

Calvin,

On a normal Opel rear suspension those bars are never really under much duress. The forces during cornering are minimal. The only load they see is during braking and acceleration. Very little ~30% of the braking force is created in the rear and our cars certainly don't accelerate that well. Lets say you could accelerate at 1g, which in reality you can't even come close to. At 1g you're only looking at ~1100lbs of force on each of those bars. This is well within what those bars can handle.

In your case with that extra sway bar you are trying to bend that trailing arm every time you go over a bump or around a corner. The arms just weren't specified for those loads. Rather than a one time occurance which caused the bar to break it was likely a lifetime of bending abuse that led up to it's failure.

One thing to keep in mind with that sway bar it that with the way it's mounted its effective length is no longer measured from the center of rotation to the rubber bushing but rather from the center of rotation to the far end of the trailing arm. If you move this bar back to a more conventional position the rear end is going to stiffen up considerably...

-Travis

calvin · 10-20-2003

I would move it back but there already is another bar there at the back. One behind the rear axle, one above the rear axle and then the two pictured in front of the axle. I think you are right with the accumulated stress it just wore out.

Travis · 10-20-2003

Calvin,

If you want to keep the sway bar where it is you should reinforce the trailing arms. I'd suggest doing it the same way I've seen it done with non-straight panhard bars. I just did a quick search and here's the best pic i could find PN 46-1120

http://www.ubmachine.com/page20.html

Basicly a piece of steel plate is stood up on end and welded in place. This should really help to stiffen the bar up.

I'd try to find a better pic but I'm off to the airport in 4 minutes. See you all in a few days...

-Travis

calvin · 10-20-2003

as usual thanks Travis!!

Travis · 10-26-2003

Calvin,

How'd things work out with the trailing arm?

-Travis

calvin · 10-26-2003

I got it welded up, a temp fix till I figure out something better. However today I lost first third and reverse so i think the syncro gears are gone...

Limped it home in second... Peeked under the car at the garage and everything looks ok from the outside so I guess I will be pulling the trany.

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10-19-2003	#3 (permalink)
Travis Senior Contributor Join Date: Apr 2002 Location: Temple, NH Posts: 781	Calvin, Those pictures are a bit rough. In the first picture it looks like I'm seeing a sway bar in an odd place and in the second picture there are parts that just don't look familiar to me. Though it's been a number of years since I've looked under the rear of a Manta. Are we looking at a non stock suspension? -Travis

10-20-2003	#5 (permalink)
calvin Senior Contributor Join Date: Mar 2002 Location: St Louis, Mo Posts: 653	I will try to get some better shots. No the sway bars are not stock actually nothing much on the suspention is. There are three bars in the back and two in the front, Orange koni's, much heavier, shorter springs in front. The front ones are almost twice as thick as stock.The ones in back which have been cut down , I am assuming are from a sportwgon. A guy in California named Bob Holden (sp?) set it up or had it done as he was listed as the first owner. The car was marked with DSP on the side when I got it so someone wanted it to go around corners. It came without a motor, glass or tranny but the suspention was in place. I just don't know how it broke when it did as it was not under extreme duress at the time. I think because it is the power side it gets more pressure. I will take Bob's instructions to the welding shop. thanks, Calvin

10-20-2003	#6 (permalink)
Travis Senior Contributor Join Date: Apr 2002 Location: Temple, NH Posts: 781	Calvin, On a normal Opel rear suspension those bars are never really under much duress. The forces during cornering are minimal. The only load they see is during braking and acceleration. Very little ~30% of the braking force is created in the rear and our cars certainly don't accelerate that well. Lets say you could accelerate at 1g, which in reality you can't even come close to. At 1g you're only looking at ~1100lbs of force on each of those bars. This is well within what those bars can handle. In your case with that extra sway bar you are trying to bend that trailing arm every time you go over a bump or around a corner. The arms just weren't specified for those loads. Rather than a one time occurance which caused the bar to break it was likely a lifetime of bending abuse that led up to it's failure. One thing to keep in mind with that sway bar it that with the way it's mounted its effective length is no longer measured from the center of rotation to the rubber bushing but rather from the center of rotation to the far end of the trailing arm. If you move this bar back to a more conventional position the rear end is going to stiffen up considerably... -Travis

10-20-2003	#7 (permalink)
calvin Senior Contributor Join Date: Mar 2002 Location: St Louis, Mo Posts: 653	I would move it back but there already is another bar there at the back. One behind the rear axle, one above the rear axle and then the two pictured in front of the axle. I think you are right with the accumulated stress it just wore out.

10-20-2003	#8 (permalink)
Travis Senior Contributor Join Date: Apr 2002 Location: Temple, NH Posts: 781	Calvin, If you want to keep the sway bar where it is you should reinforce the trailing arms. I'd suggest doing it the same way I've seen it done with non-straight panhard bars. I just did a quick search and here's the best pic i could find PN 46-1120 http://www.ubmachine.com/page20.html Basicly a piece of steel plate is stood up on end and welded in place. This should really help to stiffen the bar up. I'd try to find a better pic but I'm off to the airport in 4 minutes. See you all in a few days... -Travis

10-20-2003	#9 (permalink)
calvin Senior Contributor Join Date: Mar 2002 Location: St Louis, Mo Posts: 653	as usual thanks Travis!!

10-26-2003	#10 (permalink)
Travis Senior Contributor Join Date: Apr 2002 Location: Temple, NH Posts: 781	Calvin, How'd things work out with the trailing arm? -Travis

10-26-2003	#11 (permalink)
calvin Senior Contributor Join Date: Mar 2002 Location: St Louis, Mo Posts: 653	I got it welded up, a temp fix till I figure out something better. However today I lost first third and reverse so i think the syncro gears are gone... Limped it home in second... Peeked under the car at the garage and everything looks ok from the outside so I guess I will be pulling the trany.

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