Early shock tower clearance for IRS

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MegaManx
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Early shock tower clearance for IRS

Post by MegaManx » Sun Dec 17, 2017 8:39 pm

Hey all, so I have question regarding IRS conversion on an early (59) swing pan.

So I have a Manx over here in AUS that’s on a shortened early swing axle pan. A while back I decided to completely rebuild it including finally going to a proper IRS rear. So I sent the pan away to have some heavy duty IRS boxes professionally jiged up and welded in, and they did a great job. However now that I am starting to reassemble everything I have noticed that the trailing arm is going to hit the shock tower at the same time or before the bump stop and crush brake line. So I now I guess I have to notch the shock towers so they don’t hit.

So my question is how do I brace the towers after I notch them out? I was thinking welding some thick wall tubing from the top of the tower down to the torsion tube or welding a plate on the inside edge.

A few things to note, because this is a Manx in AUS I have to be very careful about what I do. I can’t just replace the pan or graft another IRS rear on as I have to keep the chassis stamps, so I have to work with what I have. Also this is going to be a street/ hill climb car not offroad.

Image

Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Sun Dec 17, 2017 10:37 pm

MM, I am probably one of the few glass buggy guys posting right now and maybe one of the few who ride off-road with them. There are a couple here like Dusty and Marc who have seemingly done it all and learned a lot of lessons from it. I ride the sand which might have some similarities to what you could be doing hill climbing; I more just cruise the sand not beat the heck out of my ride. Right now I am working on the rear suspension of my second glass buggy which has been a long drawn out process.

I have a ball joint (BJ) beam in front and IRS in the rear. The BJ beam has a limitation of somewhere around 6" of travel plus some other weaknesses. In the rear I run about 6" of travel based on how it is setup right now. I have a 1/4" (6.35mm) notch on the bottom of the spring plates allowing for the rear suspension to drop (hang) farther but I still use the stock IRS ('71 Bug) upper bump stop. I have converted the rear CV joints to Bus CVs by changing out the CV mounts on the transaxle and using stub axles that will mount the bus CVs plus different length half-shafts needed to match this setup. There are other CVs you can use to get more travel if you want but that also requires other mods.

I have also made some pan mods as the glass buggy is not capable of supporting the pan like the bug body is. I am also doing mods to the front suspension such as bump stops (hook and pin) and changing the torsion setup to soften the ride.

I have heard of people "boxing" (an old hot rod term") the shock mounts for added strength with both good and bad results. I'm not sure if the shock mount is cast or forged which can make a difference or so I am told. "C-notching" the mount I don't ever remember hearing about on a VW; I am not sure you would want to do that without the boxing of the shock towers. Also remember no sharp internal corners (a generous radius) to eliminate stress risers. One of the reasons is you will probably end up going to different valving of your "dampeners" because of the hill climbing bit which is going to change the loading/stress on this area.

For what it is worth I took some pictures tonight of what I am looking into which is why the rectangular tube on the shock tower.
Bugpack Truss Bar.jpg
It is replacing the after market Truss/Kaffer bar that is used to support the rear frame, aka "pickle fork" that the trans and engine mount to. The more I played with the commercial one (except maybe the Mendola "Stiffy" which is like this but has an extra contact to the trailing arm pivot) I bought that has a spreader bar that connects to the shock mount eye along with the shocks themselves. I don't like all that hanging off that eye especially with the longer bolt required.
IMG_0968 copy.jpg
This shows the later model ('71) shock tower (I am gather that you have taken the torsion bar out and cycled the trailing arm to see where is comes to the shock tower by the circles you have on the pix). I might assume that you could put a stop pad at that location but don't forget to allow for the rubber to squish some before the trailing arm is stopped. I am posting a couple of other pictures that I have taken to show some relationships.
IMG_0969 copy.jpg
A rear view of the way things are setup.
IMG_0970 copy.jpg
A little more detail. If you look to the left you can see the lower suspension stop. It is notched 6.35 mm but you can go more... up to a point. But the rear of the car will raise some your wanting or needing to add some additional preload from stock setting. The notching might be in the picture for you but don't go too far on that either.
IMG_0971 copy.jpg
This is some detail on the bump stop and its bracing used in the stock setup.

I hope this helps at least some.
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Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Sun Dec 17, 2017 11:38 pm

MM, based on your pictures and looking at my buggy the lower shape of the shock mount does look a bit different; maybe the lower side is raised up a bit plus there is some structure added inside of the outer shape of the casting/forging for additional strength.

The next question would be: would/could you extend the pad down for the bumper hits it sooner? The problem then is you reduce the travel unless you were allowed to notch the spring plate but that raises the rear of the car up when you preload the torsion bars.

'Tain't simple is it!
Lee

My opinion is worth slightly less than what you paid for it.

Bruce2
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Re: Early shock tower clearance for IRS

Post by Bruce2 » Tue Dec 19, 2017 9:37 pm

Lee, stay focused!
His problem is that the TA hits the shock tower. This is what happens when you convert a 67 and earlier car to IRS.
Notching spring plates isn't the answer, the spring plate isn't the limiter.

There are 3 ways to make the parts you have work.
1) Raise the suspension really high.
2) notch the shock tower
3) notch the TA.

Or do both 2 and 3.

A more extreme solution is to cut the shock towers off the torsion tubes and weld on 68 and later shock towers. Note: 68 and later swing axle cars have the same shock towers as IRS, so there should be no trouble finding donor parts down-under

Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Tue Dec 19, 2017 10:28 pm

Bruce again, learn to read w/o predudice.

I already covered the notching of any shape as not being a good idea as it weakens the shock tower considerably. I also covered the resetting of the preload which raises the rear end up and can cause the suspension to be stiffer if done too much. I covered the notching of the spring plate to get more hang travel. I covered the boxing of the shock tower and I covered the extension of the shock tower pad to lower it down but that limits trailing arm compression (see previous sentence for hang).

I also covered the supporting of the transaxle mount so they don't do the boogie-woogie when doing much other than restoration driving.

I didn't cover connverting to solid mounts and the straps to hold the trans in place on the mounts.

Lee

Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Thu Dec 21, 2017 10:24 am

I forgot to mention the reason that I posted the pictures of the later shock tower and that was to show the difference in the bracing inside of the later casting used to strengthing things up. To alter the stiffening features (ribs and flanges) by notching things out you considerably weaken the casting by quite a bit. When I got home I was going to copy your picture and post both pictures in the same post to show the differences easier but you have been "nasty photobucketed" so I couldn't do it.

I just remembered seeing was a rail with the rear bump stop, located on the trailing arm, having been raised rather than the bump stop pad on the casting being shimmed/lowered down. As I remember (this was back in the mid-90s) another pad mount was placed on top of the stock pad. I don't remember if it used the bolt holes in the stock pad or just how it was done but I remember seeing something different and wondered why but now I think I do. It still stopped the upward rotation of the trailing arm (suspension compression).

Lee

MegaManx
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Re: Early shock tower clearance for IRS

Post by MegaManx » Thu Dec 21, 2017 6:30 pm

Thanks for the info guys. I ended up getting a mate to weld on big 8mm plates to the towers to reinforce them before I notch them out. (yes I will be shaping and tiding them up a bit so they don’t look like elephant ears)
IMG_20171220_095758.jpg
Iv had a bit of a measure and that red line more than I will need to take out. I decided to go with the notch over spacing out the stops, mostly because this will be a low car and I don’t really want to limit my already small amount of travel, and in the end this is just as easy.
I will post some photos when I get it finished (probably after Christmas).
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Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Thu Dec 21, 2017 10:04 pm

An opinion:

If you look at the structure around where you propose to remove the structure there are two flanges that are 90 degree flanges you are going to remove most of one of them. You also have three holes 2 of the same size and one of a larger diameter in the face of the filler area which reduces the material there and they might weaken the filler area. You have added a large piece of aditional material of an unknown thickness of material but above the top flange. I think, but I am not positive, if you get any loading on the shock eye or shock mount stop you might get some twisting of the area and the twisting could cause failure in that local area without that bottom flange.

If you cut a bit higher/deeper (not good) then added some material that would connect to what is left of the existing flange and to the diagonal flange with no sharp corners then add some additional boxing (both sides if needed) of the whole area you might might get back some (but probably not all) of that lost strength.

Again, this is an opinion as there are too unknowns as to materials, the basic design and its perameters and without the math that would go along with it.
Lee

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Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Fri Dec 22, 2017 11:19 am

I also think I would put a rib in in the direction of any contact the trailing arm could make just to make sure the loads go the way you want them to. I'm not sure what the material you welded in place is but it (in the pictue) looks like there is a flaw just above the cut out pices is. Maybe it is only a "thing" in the picture but in case it isn't....

You are making a great try at something and I hope it works out. I hope even some of my 'put will help.

Lee

Bruce2
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Re: Early shock tower clearance for IRS

Post by Bruce2 » Fri Dec 22, 2017 6:13 pm

What you've done is plenty of overkill. Notch away!
Since you're doing hillclimbs, a low suspension is mandatory. I recommend taking that red bumper off and cutting it down shorter. Cut at least an inch off it's height. At the least, notch the shock tower to accommodate a shorter bumper.

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petew
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Re: Early shock tower clearance for IRS

Post by petew » Fri Dec 22, 2017 11:22 pm

Is that you Todd?

I did this years ago. I'll try and find the pics of mine, but basically I plated across the the curved "dogleg" where it hits and then cut the bump off the bottom.

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petew
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Re: Early shock tower clearance for IRS

Post by petew » Fri Dec 22, 2017 11:28 pm

Here it is...

DSCF0004.JPG

I plated back and front and added metal on the lower side too. It was strong enough for sure. Although I'd also suggest a kafer bar structure of some sort. They're super easy to build.
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69yellowbug
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Re: Early shock tower clearance for IRS

Post by 69yellowbug » Sat Dec 23, 2017 1:45 am

You could of just spaced up the bump stop mount off the trailing arm an inch thats what im doing.

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Bruce2
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Re: Early shock tower clearance for IRS

Post by Bruce2 » Sun Dec 24, 2017 3:19 am

It isn't the bump stop that's the problem. The TA inboard of the bump stop hits the early swing axle shock tower.

Ol'fogasaurus
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Re: Early shock tower clearance for IRS

Post by Ol'fogasaurus » Sun Dec 24, 2017 10:19 am

One of the confusing things is when he said street and "hill climbing" I was not sure just what he meant so I covered a milder form of off-road hill climbing than I might do on the sand. In a way the Pike's Peak yearly event here in the states could be considered as kind of a cross between an autocross, Gymkana, road race and an on-road hill climb. Hill climbing off-road is an other kind but requires more suspension travel than something like a Pike's peak style of hill climb.

I think he said that he wants the car to sit low hence the notching of the shock tower; so which of the several tradeoffs is going to be the best for him.

As I said, you could move the bump stop up enough to stop the suspension a bit sooner but you still have to allow for compression of the bump stop on a hard hit. The problem with that is the suspension is now limited as to a shorter travel on a compression hit. To compensate for the shorter travel you add some preload which raises the rear of the car a bit higher.

The shimming down of the bump stop pad is a way not to notch but not the best way either. You are still limiting potential suspension travel.

To add some more travel you notch the spring plate to get more hang but again, the additional preload needed raises the rear suspension so the car sit higher and the ride deteriorates some for the street.

Cutting some of the bumpstop away doesn't solve the problem of the trailing arm (TA) hitting the shock tower earlier than he wants.

He has been given several ideas of how to do the notch, some may be better than others, some required more work than other but still there is what he wants and what he doesn't want... but, in the end, the suspension trade-off problem is still there for him to decided on.
Lee

My opinion is worth slightly less than what you paid for it.

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