Don't cut a hole in your body just take it off the pan. It will only take an hour or so to remove the body and then you will have easy acces to the suspension parts. If you can get at the suspension easier you will actually spend less time modifying the suspension...

Mod to rear IRS arms
 

Here is an idea I had been thinking about.......
Firstly cut off the end of the IRS arm...right behind the bush.
Fabricate a plate 4-5mm with a beefy threaded tube on one side,weld this on to the IRS arm..this would give you a threaded hole in the end of the arm.
Now you could run a rose joint or rod end here,this would eliminate all movement as does the uniball system.Toe settings would now be very easy.

Second...the rod end wouldn't be as wide as the original bush so a new box section could be fabricated with a series of vertical holes...this could be fabricated inside the original inner mount.

It wouldn't give you fine camber adjustments but some adjustment.

I think toe settings are more a priorety than camber for a good handling car,though both are very important.

Your thoughts would be appreciated here.

regards Brent Marquart.New Zealand.

Just to cover the IRS camber post...
I ran IRS arms swapped over side to side and found I could only just get 0 camber on the rear wheels with the car being absolutley on the floor! Otherwise you ended up with positive camber (not good ).

You can adjust the camber on the rear suspension by simply loosening the 3 bolts which connect the spring plate to the rear arm and move the arm up and down. Up will give you move negative camber and down will give you more positive camber. Remember just the 3 bolts which hold the spring plate to the arm.

I'm sure you've all covered this.. just saying it in different ways :)

Re - adjustable inner mounts for IRS arms. It's only worth doing with coil overs and you must move both inner and outer suspension points up as one or you'll end up with the most horrible suspension geomtery imaginable.
You can see this on the spring plates of Porsche works race 911s.

MG

You've got it backwards Mike. Tilting the rear of the trailing arm up gives positive camber. Down gives negative.

Bruce,
Are you sure? Think about it as simply jacking the car up and down. If you jack the car up (the suspension arm goes down) you get positive camber and if you lower the car down (the suspension arm goes up) you get negative camber....

Mike

Positive Mike (pun intended)

As the stock suspension articulates, the pivot point is not the TA's inner pivot. It is also not the center of the torsion bar at the spring plate. It is along a line drawn between these two points. Because this line is not parallel to the torsion bar but tilted back as it extends from the spring plate's axis to the center of the car, the TA goes negative camber when the TA goes up.

Now loosen the 3 bolts between the TA and SP. The new axis is along a line from where the 3 bolts are to the TA's inner pivot. This line is tilted opposite of the one above, so therefore camber changes are opposite.

Bruce,
Point taken... for some reason I was thinking that it was the inner leg which the bolts were on :rolleyes:
Going from the outer TA being longer to being shorter ... as in pivot point... yes it reverses the action.

:D

Chers

Mike

AWESOME information in this thread. I'm foregoing the camber boxes for now ... no time to complete it but will perform the TA/SP alignment mentioned.

I will reort back with my findings in about 2 weeks :D

Sandeep

Bruce you da man
 

Bruce, reading your posts I realize that you’re a lot smarter than I. So, I’d like to bounce a couple of things off of you to see if they make sense. First of all, the way I see it, the reason that camber changes as the TA moves up and down is the angle of the pivot axis relative to the center line of the car. That axis runs thru the center of the inner pivot bolt to the intersection of the spring plate with the center line of the torsion bar. If the pivot axis was perpendicular with the center line on the car, there would be no change in camber. If it were parallel, there would be extreme changes in camber. I think this agrees with what you have said.

As far as moving the inner pivot up, I like this idea because it would provide anti-squat for lowered cars. But it seems to me that in doing so you would be increasing positive camber unless you also moved up the outer pivot. Since my car is lowered I’m thinking of raising the pivot points (inner and outer). I’m using narrowed TA’s and spring-over-coils so this shouldn’t be too hard to do. What do you think?

Also, looking at the picture above of the “BugPerformance red tube chassis beetle” where the outer pivot is not on the same axis as the inner pivot, doesn’t this setup cause unnecessary stress in the suspension components?

Ron, I appeared to have you fooled. It took me a long time to figure that out. I first saw how the relationship works about 5 years ago. A guy I know didn't install the 3rd bolt attaching the TA to the SP, and the rear of his TAs tilted up causing lots of +ve camber. I tilted it down and got -ve camber. At that time I didn't understand why this happened, I just knew the relationship.

Then when Mike posted the opposite a couple of nights ago, I again thought of why and it finally came to me.

In your first paragraph, you have it exactly right. When the pivot axis is parallel to the torsion bar there is no camber change. A perfect example is the front suspension on a torsion bar Bug. This design exhibits absolutely no camber changes of the susp relative to the car's chassis. Unfortunately body roll causes the tire to be positive camber relative to the ground.

If you move the inner pivot up, how does this give you "anti-squat"? Squat as I know it is caused when there is weight transfer, like when you dump the clutch. How can moving the pivot up prevent weight transfer?
If you do move it up you get radical positive camber. I have a friend who converted his 54 swing axle pan to IRS by welding in the pivot points. By mistake they got the pivots in too low. Its not much, but it caused horrible negative camber. Even after flipping the TAs left to right, he still had negative camber. If your chassis is an original IRS one, raising the inner pivot would be difficult. Raising both inner and outer would be even more difficult. I don't see the point. The geometry change wouldn't be any different from stock.

In looking at the red tube chassis suspension, I think the long link (that replaces the spring plates) is that long for convenience. It had to be that long to reach the chassis. Just a guess. Being so long is bad for camber change. Small changes in ride height will cause massive camber changes. It doesn't look like the car is finished, so he probably doesn't know what's going to happen. I think you are right. Its going to be hell on the inner rubber pivots. Worse if he's got urethane. If you look at the stock pivot bolt, its axis, if extended, would probably intersect with the center of the torsion bar at the spring plate. Thus there is no binding. But move that outer pivot that far forward, you're in trouble.

Anti-squat
 

Bruce, if the TA pivot axis is higher than the center of the rear wheels, the force transferred from the wheels to the TA tends to cause the TA to rotate about the pivot axis in a clockwise direction on the driver’s side and counter-clockwise on the passenger side. The result is a lifting force at the pivot points, which works to reduce squat. If the pivot axis is lower than the center of the wheel, the opposite is true and the car will have more of a tendency to squat excessively under acceleration. Have you noticed at the drag races how the entire car is “lifted” under acceleration? This is caused by the lift bars. If you crawled under one of those cars you would see that the rear of the lift bars are lower that the front. Therefore, under acceleration, the wheels are causing the lift bars to rotate such that the entire chassis is lifted upward. The Bug’s TA can act like a lift bar.

With the stock Bug chassis, the rear of the TA is lower than the front as it should be -- no problem. However, if you lower the rear of the car much, the rear of the TA will be higher than the front, and handling will suffer. I have seen some people argue that squat isn’t all bad since it helps with weight transfer. I think they are getting confused, thinking that squat some how aids weight transfer. The amount of weight transfer is dependent on the height of the cars center of gravity, the higher the better. When a chassis squats, the center of gravity is lowered. Anyway I hope this all makes sense to you, if not please let me know.

I see what you are saying Ron. But you are making a fundamental error. The reactive torque is not absorbed by the TA, but by the engine/transmission unit. This is why the nose of the trans wants to rise on acceleration. There is no rotational torque applied to the TAs. They just support the bearings.

The phenomenon you describe occurs in solid axle rear ends like 60s and 70s American cars have. When they install ladder bars (which look like the spring plate substitute on that red chassis car 2 pages back), the ladder bars are fixed to the axle housing, which is fixed to the diff housing. When they launch, the front of the rear end wants to rotate up. By installing ladder bars, the counter rotational force causes the whole rear end to be forced down, creating more traction. In a VW swing axle, some guys do install links that look exactly like the ladder bars on an American car's rear end. But they don't have any function except as a trailing arm. This is because the VW's axle tube is not rigidly connected to the rear end housing (trans case).

Not Counter Rotational Torque
 

I’m not talking about torque causing the lifting action but rather the force transmitted to the TA from the wheels which push the car forward. Physics would say that the force exerted by the wheels to the chassis through the TA has two components, a horizontal force and a vertical force. The horizontal force pushes the car forward and the vertical force pushes the car either up or down depending on the angle of the TA. The amount of the vertical force is dependent on the angle of the TA relative to the horizontal.

Or, a another way of explaining it --- looking at the passenger side for example, if the TA angles down to the rear, the force exerted by the wheel will try to cause the TA to move in a counter clockwise rotation. In order to do so it must lift the car.

It would be easier to explain this with a drawing but I don’t know how to do it on my PC.

Not that it matters, but don’t ladder bars lift the car? I don’t believe I have ever seen a ladder bar design that could push the rear of the car down. Maybe if excessively long, push the front end up and thereby helping weight transfer to cause the rear of the car to squat from the additional load. Also, it seems to me that the counter rotational torque is absorbed by the ring gear in either case (fixed axle or IRS). But then I have been wrong before.

The bottom line is, I think that among other handling problems created when lowering a Bug, anti-squat should also be given serious consideration.

Oh yes, of course! There will be a force pushing the TA down due to the forward force on the TA. And the higher the front pivot, the greater the force. When you break it down to the horiz and vertical components its clear.

Ladder bars on American cars do lift the rear of the car. They do it by planting the rear end down harder. Have you ever noticed how some of them don't squat at the line?

I think we're in ageement
 

Bruce, that is what I was trying to say when I said the thing about drag cars being lifted as they come off the line. So, I guess you agree that the angle of the TA can have an anti-squat effect? I have personally observed this on the previous cars that I have built. The benefits were very noticeable and very positive not only for straight-line acceleration but also for overall handling.

The only problem I see is that when you raise the inner pivot, you will get positive camber. Raising both will require you to raise the whole torsion housing (a big job). Then it also raises the engine/transmission.

Still In the Planning Stage
 

The plan would be to raise both the same amount. I'm not using the torsion bars so it will be less complicated. I'll let ytou know how it goes, but don't hold your breath, I move pretty slow these days.

Well, I've completed Bruce2's method of alignment to get +ve camber and I am happy to report that it works ! :clap:

I've only completed the mod on the passengers side rear and went from -2.93 deg to -1.38 deg measured using a bubble level and some trig. I filed the two rear bolt holes from slots into what looks like a "D" rotated 90 deg CCW. I could get more +ve camber if I wanted but my arms got tired from all the filing work ! :laugh:

So thanks again Bruce2 for the suggestion and direction as you've probably saved me atleast $1000 in rear tires. :bowdown: :haveadrin

Sandeep

Camber Adjustment
 

Hello SAndeep, I'm new here. Did you ever get this adjustment to work for you? I am going to try it on my 69 bug. Can you tell me for sure if the TA goes up or down for more + Camber?

I have / \ and want | |

Thanks

Yes the mod did work. You have to rotate the rear of the trailing arm up in relation to the springplate.

Sandeep

Spring Plate Mods
 

Thanks for the reply Sandeep. I took my rear suspension apart last night and fond that I have 4 bolt on the spring plate. The previous posts only mention 3.
The bolt closest to the torsion housing is threaded into the trialing arm and the bolt does not stick through the inboard spring plate. The other three bolts go in trough the inboard spring plate, through the trailing arm and out past the outboard spring plate where there is a spring washer and a nut.

This brings up two questions:

Which bolt do you want to use as the pivot point for the TA to rotate about?
Why can't you slot the TA holes vertically instead of over sizing the holes in the spring plates so you have movement in two axis? (There's not much meat around the rear spring plate slots.)

I think that only the 1969 beetle had double sided spring plates while every year after that had an easier to work with single spring plate. The single spring plates only use three while the double spring plates use 4 bolts.

When you enlarge the the spring plate hole you allow the TA to rotate either counter-clockwise or clockwise which changes the camber of the rear suspension.

Am I correct???

Camber Adjustment
 

Thanks for the info on the spring plates. I thought that because the slots in the spring plates are elongated horizontally already for toe adjustment that I could elongate the holes in the TA vertically and that way I would have adjustment both up and down and front to rear without over sizing the spring plate holes.

But I still need to know if I use the middle bolt for the rotation center or the forward one closest to the torsion housing.

Good to hear that. Beer's on you if we ever meet!

I´ll better go trough what I`ve learned from the earlier posts:
-When you lower rear IRS suspension, tires get negative camber.
-For even tire wear and good handling performance, you want to get rear tires near zero camber.
-When you put those two statements together you get:

After lowering your IRS rear suspension you need de-cambering, right?

-One way of de-cambering is to move the inner pivots of trailing arms upwards.
-This can be done with a camber-box familiar from Porsches, or maybe by fabricating a DIY mounting, higher than the original one.
-Again we couple the two earlier statements and get a question that I`m interested of:

If you move the inner IRS mount upwards the same amount that you have lowered your rear suspension, do you get stock camber???

Justin

My bus has bolt on IRS pivots, so I was able to loosen and turn them to get the negative camber out... but, the amount I rotated them did not seem consisitent with the amount the bus was lowered. Several inches on lowering but it took a lot less than that to correct the camber. Sorry I didn't take exact measurments at the time but I would say it was less than half the amount. No way to gaurantee that this would translate the same to your project but maybe it helps?

Jeff.

My project is a `63 pan and a ´61 body. A mixture by coincidence, nothing special.
But I would like to get The IRS conversion welded into it before getting it sandblasted and painted.
Has anybody else any thoughts or experiences on this, "rear-lowering to pivot-lifting ratio"?
Justin

I too would like to see a beetle with adjustable inner pivots done to a stock IRS pan. I would do this in the future when my car is a weekend/warrior only as currently it is a daily driver in the summer :D

My rear is lowered to the point that if I had the stock snubbers for a '74, I would be riding on them :eek: I've cut mine down to about half the height and I have acceptable travel. I have -1.15 deg on the drivers side and -1.28 on the passengers side and it corners beautifully.

Sandeep

Panelfanstic: your setup might not be directly comparable to a bug, but close. Thanks for your opinion.
Sandeep: so you made an adjustment similar to Porsche 924/944. OK, but I want zero camber, and I dont need an adjustment...hopefully.
But has anyone done an adjustable or fixed camber-box into a beetle???
Justin

Justin,
You don't want zero camber, it'll handle like a pig!
I spent a lot of time on my Oval swapping the rear IRS arms over side to side (relocating the shocker mount on the other side of each arm etc) to get zero (or close to) camber. I achieved it too... but it would not handle. I tried different tracking settings, but as I had swapped the arms over I was limited to about 0.3 negative camber and the car simply would not go around corners, apart from sideways (:D) which is great for fun but not when you want to go fast.

If you look at factory settings for the Beetle, they are listed as -1o + or - '40.
So negative camber does not always equal tire wear.. but mis-alignment and over the top settings will.
The factory setting for the 944 are similar at -1o + or - '20.

MG

OK. So -1 degree would be ideal?
Somekind of chart of lowering factors would be useful. For example: if you lower stock IRS rear suspension 10mm you get 1.5 negative camber and so on.
Has anyone taken such measurements?
I`m planning to weld my IRS-jig this weekend, and all hints concerning of repositioning the inner pivot for decambering are welcomed.
Justin

Camber
 

Justin,
As the camber alters as you move the arm in relation to the spring plate, the camber could be anything as you have to disturb the bolts between the 2 items mentioned above.
Basically you should be able to choose your camber setting at most suspension heights... that is not including the extremes... very high and very low.

MG

eh? I'm having a bit of trouble understanding this, where is the axis of rotation? I thought michael ghia was right, but if he's not...

See I thought that because the trailing arm was well rigid I thought the motion was with in it's path thus as the arm moved up the arc of the path pulled the end of the arm towards the center of the car.

I fail to see how the arms motion could be along an axis other than this, unless there was binding, and okay I see that there could be some binding but not a lot. but to move away from this axis to provide positive camber is hard to see.

and all though I havn't lowered my car yet, even with irs should you get a little bit of the neg camber.

The way I'm picturing this is; where ever the axis of rotation is to draw a mental perpendicular radius or moment arm to the point in question, then to following the arm as it rotations under a constant distance.

help please

Sandeep - I have SAW adjustable spring plates to install and want to correct for excessive negative camber as you did.

My trailing arm has 4 holes (1 threaded in front, 3 through in rear) -- its a 70 standard with the double plate spring plates. The SAW spring plates have only the rear 3 slots. Do I need to drill a hole in the SAW spring plate for the front (threaded) mount in the trailing arm? Or, just use the three rear mounts?

When enlarging the spring plate slots, how much material did you remove along the top of the slot? 0.05", 0.10" ?

Only enlarge the rear TWO slots so the trailing arm can pivot up about the unmodified front bolt #3 (not bolt#4, the threaded one in the trailing arm, '69-70 only)?

Thanks for the help,
Bill

Hey Bruce!

You should make an article about how to adjust the rear camber, like in your previous posts here, and have it posted in Germanlook.com technical section!! I think it would be a great addition because when the rest of us (me) get our wide rear wheels, we can just point and click in the Tech Articles instead of searching through the forums!

Thanks for the great info everybody!!
Clint :cool:

This has been a good read and helpful.I am in the middle of this dilema at the moment.I have done an IRS conversion on my pan using jigs I made years back,and have used on 2 previous conversions with no issues.This time I have also done a major mod on the pan-cut the frame horns off and moved them out 50mm each side,to fit in an auto trans from a Type3.When I got it all back together,I had serious neg camber issues,so pulled it all apart and rechecked everything to see if there was distortion of anything because of all the welding.I suspected the outer ends of the torsion bar tubes may have pulled up,but using a straight edge across the outer body attaching spots and measuring the difference between the 2 pans at the centre of the tube-the auto pan was 0.5mm different-so that's not the problem.I put it all back together and tried moving the adjustment of the 3 bolts,and got it slightly better,so it looks like the small die grinder is going to get a work out.I did spend some serious time thinking about making the inner pivots adjustable,a bit of work,but would be easier on this one because the inner threaded bits are now exposed on my pan.

IRS camber adjustment is made simple by installing the Kerscher rear anti-roll bar bolts.

A spanner (open ended wrench) is used on a hex bolt to make the adjustment.

I can't find a picture of the bolt so I will try to discribe it..

The forwardmost springplate bolt is substituted. The hole in the springplate is enlarged to a circle that is the same diameter as the first shoulder. The new bolt then rotates in the sprigplate. The 2nd shoulder is eccentric and 12mm, threaded to take a lock-nut to secure the TA from the outside. The head of the bolt is in the middle :) The other side of the same bolt is shouldered 10mm and locates the anti-roll bar drop-link. Offers +ve to -ve camber adjustment. Has zero effect on toe adjustment. Very trick.



Matt

That bolt sounds like the ones on my '87 944 springplate setup. I can take a picture on and off the car if someone needs to see it.

hello i need help , i have dropped my irs back end by 1 spline and fitted a set of 1.5" lowered spring plates , the camber was -ve3" i followed the instructions and ovaled the holes in the rear of the spring plates using this method i have -ve 1.5 degree's of camber ,i would like -ve 1.0 degrees as am running 255 rear tires , because i have rotated the rear of the arms up in relation to the springplates the the a arms are catching the top of the spring plate just behind the top hole , this has left me with 1mm of toe in 1\2 mm each side i would like another couple of mm , i do not want to cut anymore material behind this top hole as there is not a lot there to start with and with filing the holes oval there is even less , any help or advice will be welcome or am i making a fundamental error with the method of changing the camber ,
cheers jon