Have the 9inch out of my hatch at the moment so tossing up weather to upgrade the trailing arms or just box in the stocky ones.
Whats other peoples thoughts and previous experiences with this.
After market suppliers and prices?
Pics would be good too.
cheers
Trailing arms
Started by
TORLX8
, Aug 15 2006 10:24 AM
14 replies to this topic
#1
TORLX8
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Posted 15 August 2006 - 10:24 AM
#2
_MAWLER_
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Posted 15 August 2006 - 10:35 AM
Mc Donald Bros have both adjustable upper and tubular lower trailing arms. I've got the lower tubular and I reckon they are a good thing. A lot stronger than the originals and of course new bushes. Think they cost about $250? I'll have a search for pics, I'm sure I took a couple before I stuck em on.
Have a look on their site, they will have pics I'm sure.
Peace,
Have a look on their site, they will have pics I'm sure.
Peace,
#3
_lxhatch_jim_
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Posted 15 August 2006 - 11:18 AM
I have recently fitted a 9 inch and been through the same process. I opted to put steel straps on the trail arms rather than box them in entirely. You can box the upper arm completely but the lower may need gaps depending on how your rear sway bar fits up (for the mounting bolts).
I purchased a metre of 40 x 3mm flat mild steel for $3 and welded 3-4 straps on both the upper and lower. One thing to be careful of is how close you bring it to the ends of the arms as the mounting points need a fair bit of clearance. They already had plastic bushes fitted so after a couple of coats of paint in they went - all for $3 and some welding wire.
I'm not saying that the tubular ones aren't worth it but it just depends on your applications. I'm not going to be track/drag racing every weekend so I thought that the strapping option was a good compromise. I've also heard reports that mega-stiff trailing arms can stress the mount point on the floorpan, causing them to crack/come off. I've never seen it so it may well be rumours. To be sure I seam welded both the floorpan and diff mounting points.
If you'd like photos I'll take some after work and put them up.
Cheers
Jim
I purchased a metre of 40 x 3mm flat mild steel for $3 and welded 3-4 straps on both the upper and lower. One thing to be careful of is how close you bring it to the ends of the arms as the mounting points need a fair bit of clearance. They already had plastic bushes fitted so after a couple of coats of paint in they went - all for $3 and some welding wire.
I'm not saying that the tubular ones aren't worth it but it just depends on your applications. I'm not going to be track/drag racing every weekend so I thought that the strapping option was a good compromise. I've also heard reports that mega-stiff trailing arms can stress the mount point on the floorpan, causing them to crack/come off. I've never seen it so it may well be rumours. To be sure I seam welded both the floorpan and diff mounting points.
If you'd like photos I'll take some after work and put them up.
Cheers
Jim
#4
TORLX8
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Posted 16 August 2006 - 02:59 PM
Thanks for the responses Liam & Jim.
Liam, I did have a look at the McDonald Bros racing ones, but they seem expensive seeings I probably won't ever use the adjustment feature once they're set up.
Probably leave a bit more room for exhausts though which is a good thing.
Any reason you only bought the lower ones?
Jim, that sounds good the way you have strengthened your trailing arms.
Good idea to put those extra strengthening welds on the floor pan and mounting points too.
Would be great if you could post some pics.
Does anyone else other than McDonald Bros do aftermarket ones?
Liam, I did have a look at the McDonald Bros racing ones, but they seem expensive seeings I probably won't ever use the adjustment feature once they're set up.
Probably leave a bit more room for exhausts though which is a good thing.
Any reason you only bought the lower ones?
Jim, that sounds good the way you have strengthened your trailing arms.
Good idea to put those extra strengthening welds on the floor pan and mounting points too.
Would be great if you could post some pics.
Does anyone else other than McDonald Bros do aftermarket ones?
#5
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Posted 16 August 2006 - 03:08 PM
Exactly the same reason as you, I wouldn't be needing the adjustable uppers 
.
The lower ones are a straight non adjustable replacement for the original trailing arms. The upper ones are adjustable and are used for adjusting the pinion angle and all that stuff, and yeah, I didn't think I was getting serious enough to justify needing them. So I bought the lower tubular and just boxed the upper ones in the same fashion most ppl do.
Cheers,
.The lower ones are a straight non adjustable replacement for the original trailing arms. The upper ones are adjustable and are used for adjusting the pinion angle and all that stuff, and yeah, I didn't think I was getting serious enough to justify needing them. So I bought the lower tubular and just boxed the upper ones in the same fashion most ppl do.
Cheers,
#6
_lxhatch_jim_
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Posted 17 August 2006 - 08:41 PM
Pictures late, but delievered as promised.
1. Lower trailing arm showing the four plates strapped across.
2. Upper arm - note the thickened area at the top need the rear mounting point. I welded one too close to the end allowing no travel - had to cut it out. TRap fpr young players.
3. Upper arm strap at the far end. I'm going to pull it out and put another one in at the close end, but not too close this time.
4. Lower control arm - note the gaps in the braces allowing the bolts for the rear sway bar to be fitted. It does depend on the mounting point of the sway bar as to if this is necessary.
5. Seam welding of the mount point to the differential housing. I couldn't get far enough under to show the floorplan mounting points but you get the idea.
So as I said, inexpensive exercise with reasonable results. Hope it helps
Cheers
Jim
1. Lower trailing arm showing the four plates strapped across.
2. Upper arm - note the thickened area at the top need the rear mounting point. I welded one too close to the end allowing no travel - had to cut it out. TRap fpr young players.
3. Upper arm strap at the far end. I'm going to pull it out and put another one in at the close end, but not too close this time.
4. Lower control arm - note the gaps in the braces allowing the bolts for the rear sway bar to be fitted. It does depend on the mounting point of the sway bar as to if this is necessary.
5. Seam welding of the mount point to the differential housing. I couldn't get far enough under to show the floorplan mounting points but you get the idea.
So as I said, inexpensive exercise with reasonable results. Hope it helps
Cheers
Jim
#7
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Posted 18 August 2006 - 07:35 PM
I used 2mm X 50mm X long enough (I think) and stitch welds. Have a spare set of uppers that I still have to get done and fit.
Dirty and bent lower arm is what was in the car when I bought it (other side was similar but not as bad) and stored for hsysterical value.
Dirty and bent lower arm is what was in the car when I bought it (other side was similar but not as bad) and stored for hsysterical value.
#8
_355lxss_
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Posted 21 August 2006 - 09:13 PM
i just pick up my lower arms which have been boxed up like EXLXSL has shown in his pic. This will be more than enough for steet and strip! tubular are a little expensive, but very strong! Rod tech in Adelaide sell lower tubular and adjustable uppers. He also boxes up your original ones.
Boxing the upper arms is a wast of time as the load from the diff pulls on the upper arms so it wont bend/flex them.
Boxing the upper arms is a wast of time as the load from the diff pulls on the upper arms so it wont bend/flex them.
#9
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Posted 22 August 2006 - 08:00 PM
It was explained to me that the reason for boxing/strapping of control arms was to increase torsional rigidity. Given the U shape (looking at the arm in transverse section) the lateral rigidity is quite reasonable. As the car accelerates, the "twisting" of the arms is a more significant force given that the rotation of the engine is perpendicular to the rotation of the axles? This is all just first principles though - please shoot me down. I'm just interested in the physics of it all.Boxing the upper arms is a wast of time as the load from the diff pulls on the upper arms so it wont bend/flex them.
Perhaps a mechanical engineer could help? Matt?
I really would like to understand this in more depth.
#10
TORLX8
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Posted 28 August 2006 - 10:57 AM
355lxss, My diff guy also recommended Rod Techs own tubular lowers and adjustable uppers. So I went and saw him and they do a really good price on the kit rather than just buying the lowers separately. As you said they also box in the standard type trailing arms, but don't think I can go past the price of his tubular ones though. 
#11
gtrboyy
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Posted 28 August 2006 - 03:33 PM
Fit std bushes in the top arms & housing,no real need to box top arms.
For the bottoms get a plate welded in like EXLSL has & run std bushes or medium grade urethane bushes.
The guy that mini-tubbed my car had only boxed in lower arms with std bushes,he used to run low 9's,didn't want to rip the brackets out of the floor.Another mate boxed his lower t/arms,std bushes & ran 12's no problems.
I would have done the same thing had I known.Read too many magazines lol.
For the bottoms get a plate welded in like EXLSL has & run std bushes or medium grade urethane bushes.
The guy that mini-tubbed my car had only boxed in lower arms with std bushes,he used to run low 9's,didn't want to rip the brackets out of the floor.Another mate boxed his lower t/arms,std bushes & ran 12's no problems.
I would have done the same thing had I known.Read too many magazines lol.
#12
makka
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Posted 28 August 2006 - 04:44 PM
I agree that there is no real need to box the uppers, they are pretty short and stumpy. although I would do it anyway as its only gonna take 10 min to do.
I would definatley box the lowers though. and run rubber bushes on the uppers, it helps reduce the bind.
and I am on my way to being a mechanical engineer, only a coulpe of years to go!
I would definatley box the lowers though. and run rubber bushes on the uppers, it helps reduce the bind.
and I am on my way to being a mechanical engineer, only a coulpe of years to go!
#13
Toranamat69
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Posted 30 August 2006 - 09:47 PM
I agree I would not box the upper arms and I would use rubber bushes in at least one end of the upper arms. These upper control arms are designed to flex as the suspension rolls as you go through a corner.
The upper control arms see forces in tension under power, twisting forces as you corner and compressive force under braking. If you stiffen it all right up with polyurethane bushes and boxed upper arms, all you achieve is the car will lift weight off the inside rear tire on a corner until the stage you get the pics below.
I used the softest grade polyurethane in the front of upper control arms and the medium grade in the diff housing end and after approx 10,000 km of street / fun driving both the front upper bushes split badly where they bind and compress.
These arms are boxed as well.
See the pics below.
Regarding the lower control arms, I would definately recommend boxing those.
Does anyone have any pics of the Rodtech ones?
M@
The upper control arms see forces in tension under power, twisting forces as you corner and compressive force under braking. If you stiffen it all right up with polyurethane bushes and boxed upper arms, all you achieve is the car will lift weight off the inside rear tire on a corner until the stage you get the pics below.
I used the softest grade polyurethane in the front of upper control arms and the medium grade in the diff housing end and after approx 10,000 km of street / fun driving both the front upper bushes split badly where they bind and compress.
These arms are boxed as well.
See the pics below.
Regarding the lower control arms, I would definately recommend boxing those.
Does anyone have any pics of the Rodtech ones?
M@
Edited by Toranamat69, 30 August 2006 - 09:50 PM.
#14
TORLX8
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Posted 31 August 2006 - 04:55 AM
The rod tech trailing arms look pretty much the same as the McDonald Bros ones.
So Mat, would you just recommend getting the tubular lowers and not the adjustable uppers? Do you think the uppers would be too stiff, and have all the same effects you previously mentioned with boxed uppers?
Thanks everyone for the excellent info.
So Mat, would you just recommend getting the tubular lowers and not the adjustable uppers? Do you think the uppers would be too stiff, and have all the same effects you previously mentioned with boxed uppers?
Thanks everyone for the excellent info.
#15
Toranamat69
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Posted 31 August 2006 - 06:00 PM
Adjustable uppers are a great idea as you can adjust you pinion to get the best traction at the drags.
You can still use rubber bush in the diff housing end though.
I actually now use the Edelbrock adjustable upper trailing arms as I wanted something with a spherical bearing in the front so it wouldn't break like the polyurethane ones.
It is certainly not the ideal solution as the suspension binds differently - with my setup, the bind is 3 of the trailing arms are all trying to stretch the 4th one lengthwise so it still pays to have compliant bushes on the diff housing end.
End result is it still tries to unload weight from the inside rear wheel on a turn...not really that much different.
That is still a far better drag setup than it is for corner work.
Unfortunatley a converging arm 4 link is always going to be a compromise - at least the setup I use now doesn't damage and spit out parts, it just doesn't corner as nice as I would like.
M@
You can still use rubber bush in the diff housing end though.
I actually now use the Edelbrock adjustable upper trailing arms as I wanted something with a spherical bearing in the front so it wouldn't break like the polyurethane ones.
It is certainly not the ideal solution as the suspension binds differently - with my setup, the bind is 3 of the trailing arms are all trying to stretch the 4th one lengthwise so it still pays to have compliant bushes on the diff housing end.
End result is it still tries to unload weight from the inside rear wheel on a turn...not really that much different.
That is still a far better drag setup than it is for corner work.
Unfortunatley a converging arm 4 link is always going to be a compromise - at least the setup I use now doesn't damage and spit out parts, it just doesn't corner as nice as I would like.
M@
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