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Modifying a-arms, caster?

i'm about to lengthen a pair of a-arms for more camber, If I just lengthen it I also lose caster, maybe not a big problem in it self, but I have a clearance issue with the tires and tub at large steering angles. So I cant let the wheel move rearwards, I would rather make it move a little forward.

Do you see any issues with me angling the a-arm so the ball joint would move forward ~1/4 inch from stock?

Would more or less caster be benifical?

For background, the car is a track and auto-x focused 911 with rsr-ish fenders 9 and 11 by 15 inch wheels. I have big brakes so on front I have relatively high offset and spacers, cant remember exactly what.


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911 Silver Targa -77, 3.2 -84 with custom ITBs and EFI
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Last edited by safe; 03-25-2018 at 04:04 AM..
Old 03-25-2018, 03:56 AM
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When you say you'll lose caster with this modification, is that because you also plan to move the strut bottom mount forward by .25", or some other reason? By a quick back of the napkin calculation, that will cause you to lose about 1 degree of caster. That's not insignificant, but honestly you might have a hard time noticing the difference.

How much are you planning to lengthen the A arms? Don't forget that this will widen the front track - make sure you have fender clearance to account for this (or plan to buy new wheels). I'm sure you know this, but another option is to de-camber the spindles to get more negative camber.

Scott
Old 03-25-2018, 04:38 AM
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Quote:
Originally Posted by stownsen914 View Post
When you say you'll lose caster with this modification, is that because you also plan to move the strut bottom mount forward by .25", or some other reason? By a quick back of the napkin calculation, that will cause you to lose about 1 degree of caster. That's not insignificant, but honestly you might have a hard time noticing the difference.

How much are you planning to lengthen the A arms? Don't forget that this will widen the front track - make sure you have fender clearance to account for this (or plan to buy new wheels). I'm sure you know this, but another option is to de-camber the spindles to get more negative camber.

Scott
I have lengthend aarms today, that modification moved rhe ball joint slightly rearward (because on the angle of the arm).

I want to redo this and in the process create more clearance by moving the ball joint forward. That will increase caster, or am i unlucky in my thinking?
If . 25" only equates to 1 degree it can't be that significant. Maybe I could move it a bit more...
Old 03-25-2018, 07:14 AM
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i would keep the at least the current caster or better yet add more.. car turns in better, gives you a better camber curve and adds stability though the efforts will go up. i believe elephant sell an offset 911 ball joint that may be easier to help you fabricate something up.

old un- assist steered cars like the 911 ran with little caster with mild camber curve unlike the moderns with stiffer chassis and pwd steering.
Old 03-28-2018, 11:18 AM
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Stay away from that offset ball joint......
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Old 03-28-2018, 01:56 PM
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Ok, so nothing bad, except heavier steering, to add 1-2 extra degrees of caster in the a-arms?

I really should be welding in camber boxes, but that is a bit to much engineering right now. I'm gonna extend the a-arms by 15-18 mm that is the maximum I think I can get away with, I'm really close fender-to-tire today.
In the same time move the ball joint mount 10 mm forward to increase caster and clearance.

I have the offset ball joint in my Targa, its worked there for a couple of years, but it gives to little camber to be meaningful i think, at least in this case.
Scott heard anything bad happen to them?
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Old 03-28-2018, 09:50 PM
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Scott heard anything bad happen to them?
Yep.....
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Old 03-28-2018, 11:48 PM
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Quote:
Originally Posted by safe View Post
Ok, so nothing bad, except heavier steering, to add 1-2 extra degrees of caster in the a-arms?
The only other thing to keep in mind is you also get less camber change when steering. Typical caster settings also yield some additional negative camber on the outside front wheel when turning. You'd get a little less of that.

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Originally Posted by safe View Post
I'm gonna extend the a-arms by 15-18 mm that is the maximum I think I can get away with, I'm really close fender-to-tire today.
In the same time move the ball joint mount 10 mm forward to increase caster and clearance.
Careful on the tire/fender clearance if you're already close. Remember that moving the lower strut mount outboard by 15-18mm will also move the top of your wheel/tire outboard by a few mm (i.e. closer to the fender), since the pivot point (the top of the strut) is above the top of the tire.

Scott
Old 03-29-2018, 11:18 AM
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safe,

I don't have much to add to this conversation other than I'd really like to do something similar with my '87 turbo. Basically I'd like to lengthen the arms ~21mm, then do away with the built-in 21mm front wheel spacers with an end result of reduced scrub radius while the wheels sit in basically the same position within the fenders as they do now.

I hadn't thought about the caster reducing effect of this, so yeah I'd want to also factor in adding back the lost caster (or slightly increasing caster) when modifying the arms.

Please keep us updated while you work through this modification!
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Old 03-29-2018, 11:23 AM
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Yep.....
I though about getting them...Are they failing?
Old 03-29-2018, 02:16 PM
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What kind of caster numbers are you looking to achieve?

A few years ago I spent quite a few hours studying methods to get a bunch more negative camber up front in my '75 911-based race car. It is similar to Winder's car.

As part of this, I considered having my factory arms lengthened, and I did a bunch of research. That included conversations with a bunch or known experts with racing experience, including the gentleman that built my car. He extended the arms on a friend's car a few years ago for the same purposes.

In the end, I decided on the Eisenlohr Racing Products 935-style set up. I found a like-new set in the PP forums after posting a WTB ad. In addition to that set up, I bought a set of Tarett camber plates, which are really nice.

I did not consider the Elephant Racing Products offset ball joints since I have a contact that got them to fail IMMEDIATELY on 1-2 different cars. This contact has a LOT of experience and runs a well-known business that does a lot of racing and street car work. The main technical expert there was IMSA Mechanic of the year in 1977 and has a lot of extensive pro racing experience.

I do have other friends with extensive pro experience that have run those joints and/or installed them in customer's cars-- they keep a close watch on them.

For me, the extra ~0.6-0.7 degrees of negative camber you get from them is just not worth the risk. I had ball joint issues in 944 series cars, including one on track that was very scary. So this is not an area where I want to add risk with my 911.

As for caster, I think it factors into the overall approach to lengthening factory arms. I have not heard of anyone lengthening factory arms and trying to change the geometry to get caster back. That doesn't mean that folks don't do it-- I have just never seen it. There are some threads with pics in these forums.

In the end, I like the flexibility of the 935-style parts. When I did my analysis, there was a ~$3-500 difference between having my arms lengthened and a lightly used set of the ERP parts. I like the flexibility that the $3-500 additional investment provided.
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Old 03-29-2018, 02:52 PM
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I think this is a torsion bar car so the ERP a-arms are a no go....
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Old 03-29-2018, 06:14 PM
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Quote:
Originally Posted by Kaefer View Post
safe,

I don't have much to add to this conversation other than I'd really like to do something similar with my '87 turbo. Basically I'd like to lengthen the arms ~21mm, then do away with the built-in 21mm front wheel spacers with an end result of reduced scrub radius while the wheels sit in basically the same position within the fenders as they do now.

I hadn't thought about the caster reducing effect of this, so yeah I'd want to also factor in adding back the lost caster (or slightly increasing caster) when modifying the arms.

Please keep us updated while you work through this modification!
That is a cool mod, you have to compensate for the camber by decambering the struts with this I think.
Been thinking about that, but I like some depth to the rims for looks and I need spacers to clear the front calipers.
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Old 03-29-2018, 11:37 PM
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Quote:
Originally Posted by Mahler9th View Post
What kind of caster numbers are you looking to achieve?

A few years ago I spent quite a few hours studying methods to get a bunch more negative camber up front in my '75 911-based race car. It is similar to Winder's car.

As part of this, I considered having my factory arms lengthened, and I did a bunch of research. That included conversations with a bunch or known experts with racing experience, including the gentleman that built my car. He extended the arms on a friend's car a few years ago for the same purposes.

In the end, I decided on the Eisenlohr Racing Products 935-style set up. I found a like-new set in the PP forums after posting a WTB ad. In addition to that set up, I bought a set of Tarett camber plates, which are really nice.

I did not consider the Elephant Racing Products offset ball joints since I have a contact that got them to fail IMMEDIATELY on 1-2 different cars. This contact has a LOT of experience and runs a well-known business that does a lot of racing and street car work. The main technical expert there was IMSA Mechanic of the year in 1977 and has a lot of extensive pro racing experience.

I do have other friends with extensive pro experience that have run those joints and/or installed them in customer's cars-- they keep a close watch on them.

For me, the extra ~0.6-0.7 degrees of negative camber you get from them is just not worth the risk. I had ball joint issues in 944 series cars, including one on track that was very scary. So this is not an area where I want to add risk with my 911.

As for caster, I think it factors into the overall approach to lengthening factory arms. I have not heard of anyone lengthening factory arms and trying to change the geometry to get caster back. That doesn't mean that folks don't do it-- I have just never seen it. There are some threads with pics in these forums.

In the end, I like the flexibility of the 935-style parts. When I did my analysis, there was a ~$3-500 difference between having my arms lengthened and a lightly used set of the ERP parts. I like the flexibility that the $3-500 additional investment provided.
I have no goal for the caster, its mostly to move the wheel forward, but if more caster is beneficial then why not try to optimize.
Tried to fix the clearance with a hammer (why not), but its where the inner fender meets the sill so it doesn't move.

I'm really annoyed, because I have lost my alignment paper, so I can't find my current caster. It's at maximum I guess, that's what I usually want to have.

I have coil overs so I could go the 935 way, but it is expensive, lengthening the a-arms is basically free as I would do it myself and a pair of extra a-arms was inexpensive to. They are from an old E so they are open on the underside and have splines for torsion bars.
I also inquired Elephant Racing (basically the whole suspension is ER) about the space requirement between the ball joint and rim, I think the 935 took a little more space than the original set up. I'm very, very tight between the rim and ball joint today. I had to grind of the safety cotter pin and shorten the ball joint nut to fit the wheel....
Had to shave of the calipers (928 S4) a little too....
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Old 03-29-2018, 11:56 PM
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Magnus,

I'm curious to see what you're proposing to modify in order to angle the A-arm forward. As you know, the lengthening of the A-arm pushes the wheel rearward since the A-arm main lateral member is skewed rearward.

I know exactly what you're speaking of with the chassis clearance. My racecar has lengthened A-arms and the tire clearance in the inner rear tub area is tight with wide tires. This is not necessarily due to just the added width, but also due to the rearward shift of the wheel. You're also correct that there's not much opportunity to clearance that part of the chassis wall because it's curved and pounding it is like hitting a brick wall. It's rock solid and doesn't want to take a dent.
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Old 04-16-2018, 02:25 PM
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Magnus,

I'm curious to see what you're proposing to modify in order to angle the A-arm forward. As you know, the lengthening of the A-arm pushes the wheel rearward since the A-arm main lateral member is skewed rearward.

I know exactly what you're speaking of with the chassis clearance. My racecar has lengthened A-arms and the tire clearance in the inner rear tub area is tight with wide tires. This is not necessarily due to just the added width, but also due to the rearward shift of the wheel. You're also correct that there's not much opportunity to clearance that part of the chassis wall because it's curved and pounding it is like hitting a brick wall. It's rock solid and doesn't want to take a dent.
I cut up a pair of E-arms, made a sort of jig so I could have some sort of reference. I don't recon I got it absolutely perfect.
I lengthened the arms about 18 mm from stock ant tried to move it forward by 10 mm, but I think I only got 7-8 mm. Somehow it moved on me....
The welding isn't the prettiest, I'm confident it will hold.







I've also fitted them with Elephant Spherical bushings and installed Elephants Quick change camber plates. There I hit a brick wall, the camber plates isn't compatible with mt Elephant coil overs. Which I missed when I read the installation manual before I bought them. So new spring perches are on the way from Elephant.
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Old 04-17-2018, 11:53 AM
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Magnus, looks like you are making progress. And let us know what caster and camber you are able to achieve.

Please be careful to make sure that your welds and reinforcement are robust--- I would hate to see you have a failure. I had a failure of a ball joint in a high bhp 951 track car, and it was very scary. I was lucky.

I know that you have done this kind of thing before, so hopefully your experience with that set of modified arms was good.

When I was considering having my arms modified, I consulted two different people with extensive IMSA and WEC, et cetera, experience with air-cooled 911s. I never went as far as asking them exactly where they'd cut and how they'd reinforce, or what materials they'd use. One of them did an extension on a friend's car and as far as I know it has held up very well.

In my case, I struggled with the decision for quite a while. My situation was different since I cannot weld. As I stated above, my WTB ad in the classifieds yielded a nice newish set of the Eisenlohr parts. Price was nearly half of a new set.

I still think that is the ideal solution, but it is not inexpensive.
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Old 04-17-2018, 03:43 PM
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Thanks for sharing your method of modifying them. Looks like you have a nice way of jigging them for reasonable consistency. I'd still consider adding some plate steel to beef up the area that was chopped and welded.

Typically the extension is done further inboard. We've shared info. with Magnus before on this and he's well aware of the potential pitfalls.

How much camber...

That said i'm in agreement with Mike that messing with the ball joint area is not one to be taken lightly.
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Old 04-18-2018, 07:47 AM
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Yeah, on the last set of a-arms I cut them further in.
This is a coil over car, so the loads isn't that great. With torsion bars I would be much more careful.

The bottom piece is 3 mm thick, fully welded.

Last edited by safe; 04-18-2018 at 12:03 PM..
Old 04-18-2018, 07:59 AM
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How do you align the steering wheel up after having all part?
Old 04-18-2018, 11:51 AM
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