Rubber A-arm bushing problem!!!
 

As many of you may know, I've had this problem for over 18 months now, asked it several times, in every Porsche board I know of, but this time I have a pic to go along with it.

OK, here we go:

Trying to figure out why EVERY single bushing I've tried, will deform, get cut through, etc. by the control arms, on my 84 944. Car is running modified brakes, and 245 section width tires. (seriously more braking power/traction).

Any ideas why this is happenning, or ways to stop it?

I'm thinking about putting large washers, between the control arm, and the subframe. (the steel control arms will eat through the subframe, which is why I'm replacing it).

I've attached a picture of what I'm talking about.

http://personal.rdu.bellsouth.net/rd...k/DSC00013.JPG

Any help would be appreciated,
Thanks.
Ahmet


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It's all the driver...

Just how much grip do I have?

http://personal.rdu.bellsouth.net/rd...k/DSC00002.JPG

http://personal.rdu.bellsouth.net/rd...k/DSC00003.JPG

I'm sure these tires grip a good bit better than ANYTHING you could've gotten in the original tire size of 215/60/15, or the optional 205/50?/15s, back in 85, which was the lastest year for the early suspension...

Ideas?
Thanks.
Ahmet

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It's all the driver...

NO REPLIES!!!

This has been the biggest mind boggler for me, EVER, and nobody has any ideas. (I've posted this before, here's the pic, say something!) http://www.pelicanparts.com/ultimate/wink.gif
Ahmet

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It's all the driver...

mabey your tires are too big resulting in to mouch force going to the suspension? it cant handle it?
---
by the way i was sitting in a geo metro today with a friend and absent mindly i pushed the clutch in and went to change gears - WOW not only is it definate but also SUCH a short throw its amazing - I have never been in a car that felt that good on the shifter... NOT EVEN A 944

The reason your bushings are getting cut up is simply because your driving the car in auto-xs, and probably mean spirited on the road from your burn out pics etc. i have seen ! http://www.pelicanparts.com/ultimate/wink.gif
Thats the hardest thing you can do to a road suspension wise, its made as a daily driver sport car!

[This message has been edited by AMCPorsche924Powerhaus! (edited 03-16-2001).]

Hi Ahmet,

That does look rough. Looks like you may need some work done on the A frames (control arms), too. What I think is happening is that heavy breaking and cornering forces are yoo much for the bushing material. It's about like a woman in high heels doing OK on the side walk but there is too much force per area for soft dirt (her weight on the small area of high heels) so she'll sink down if she steps into the flower bed. She would do alright stepping into the flower bed in tennis shoes with their wide flat bottom putting her weight over a large area. I think you need to try the snow shoe approach, weight, or braking force of 1.2 G, put over a larger area than the edges of holes in control arms on flanges of bushing material. A ss washer like you were talking about in earlier posts is like the side walk.

This would be big help if it didn't eat into stuff like the bolt. If the control arms are damaged, I suggest the "snow shoe", wide flanges on the ends of bushing holes. With the bushing ends, flanges cut off, some kind of thrust washer could be run between the the flange on control arm and sub frame.

This weekend, I'm putting up a fence but about Monday I'll look up bearing stress & safe operating temp of different common , easy to get materials and post them if you like.

drew1

Ahmet,
You're not going to like it, but still:
-The 944 came originally with 185/70 tires. The 215/60 were an option. I think the 185s never made it to the US.
-You put 245s on a car with a lot of miles, and you run over 1 G lateral, and you wonder why things break??
-The Cup cars (race ones) used to run 240s in the front, and they broke their front REINFORCED A-arms with alarming regularity. I own one, I got informed...
Ditto the power steering. Btw, I had a 1983 944 without power steering, and It felt MUCH better, with a lot more feedback during hard driving. I ran 225/60 tires in the front, and it went OK, but the bushings in the A-arms took a beating, too.
I guess you've reached the limits of the design.
GeorgeK

[This message has been edited by GeorgeK (edited 03-17-2001).]

Hmm, that's a little harsh...

I mean I'm running against guys in C-stock, with widest race rubber that'll fit under the fenders... My car doesn't even have slicks, how much of the 245s are sticking to the road?

So you guys think I reached the limit of the design, how dissapointing. On paper the later susp. looks a lot beefier, but I was planning to swap out all of the rear susp (eliminating torsion bars, etc.) with fabcar control arms, and spherical bearings anyway... I've been discussing this problem with a couple of very knowlegable 944 guys, and we're all trying to find a problem...

However, even if we can't find a problem, I still need a FIX .

OK, now for the interesting part, the bushing, as you can see is in good shape, it's the control arm that slides on it. I have no problem with changing these bushings every 5k miles (if that's what it takes), but this happens within a mile, not 5000!

Thanks for the replies, if you have any other ideas, don't hesistate to reply here, or e-mail me (over1g@hotmail.com).

GeorgeK, the "Cup" cars used the aluminum control arms, and the need to run springs that are stock, (or quite close to stock, but lowered) with free sway bars put a lot of stress on the control arms, between the strut mounting point (ball joint), and the sway bar mounting point. Besides, on lowered cars, the ball joint would operate near it's limit of movement=more stress. This is what I remember about the "TURBO CUP" cars, unless you're talking about something else.

Drew1, I'm always open to suggestions, if you come up with anything, as I mentioned I'd appreciate it if you let me know here, or by e-mail.

Now I got to go watch sebring...

Thanks everybody.
Ahmet

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It's all the driver...

Just found this at another message board, as a reply to the question "what are the widest tires I could use in the front of my 89 NA, without mods?"

Answer was posted as:

"at de's i have seen 275 front and rear with the car lowered and with noticable neg camber."

This is why I'd be dissapointed if I actually had reached the limit of this suspension.

I'm planning to inspect other 944s closely, and in person! Maybe I'm forgetting something. Is the caster setting bushing supposed to help with keeping the A-arm in it's correct position, in relation to the sub-frame perhaps?

Either way, I'll fix this, hopefully it won't mean that I can't run in stock class...

PS: Ahmet, who's never seen another early 944 at an auto-x, or a 924S... Maybe I should hurry up and by my next car!
Ahmet

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It's all the driver...

Ahmet,
Offhand, I'd recommend:
-get a non power steering rack
-put 225/50s in the front.
-Are you using the biggest anti-roll bars alowed, and the strongest shocks?
You're right that the Cup failures were at the balljoint. However, one car I know with a lot of power broke them at the bushing. The bottom line being that the stock geometry with stock parts has a load limit that you can't cross. Your '83 has lower quality componenets, meaning the limits are reached quicker.
Can you put aluminum A-arms and stay in the stock class?
BTW, seeing from your pics, when you load the suspension, you end up in a similar geometry to the lowered cars, with the same type of strain between the roll-bar mounting and the lower balljoint. That is the point to limit.
Some companies sell steel bushings for the 964s, maybe you can find some for your car.
GeorgeK

[This message has been edited by GeorgeK (edited 03-17-2001).]

GeorgeK, you got me thinking...

So many modified cars that are actually used for racing have SO many problems...

On my car, I've never had a problem with oil starvation (I know the #2 bearing will get messed up, but only if you're low on oil, taking a very hard right turn), fuel starvation, brake fade, caliper seals blowing, etc.

Never, anything. Actually with a cup clutch, and almost no engine mods, I can get about 7.3 secs to 60.

I don't think the steering rack is unsatisfactory, I've been racing my car for 55k or so, had it in a 24 hour race, etc. And I drive VERY hard. In 55k, the front bushings, and the numerous transaxles are the only things that ever broke on this car. I take care of it very well indeed, but I think the car, and it's design is up to the task. At the most, I need some washers for the front susp. Remember rear is doing fine, no abnormal wear, anything.

Also, since the car's been in a minor accident last year (which is about the time I started getting serious with the mods, about 40k ago), I replaced both control arms, and now I wonder if they're exactly the same geometry as Porsche (or if vw arms are any different). Just because parts are interchangable, doesn't mean they're identical.

Any other ideas/thoughts?

PS: If I decide to race the car on track (competitively), then I'd consider strengthenning the control arms, first I need to attend to the problem at hand.
Ahmet

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It's all the driver...

I'm running the optional sport sway bars, with some sport shocks, that are admittedly not at full blast.

Steel bushings are not allowed in the stock class, and even with washers, I'd be cheating. However technically, this is a mod that doesn't make the car handle any better.

My car's an 84, which has the steel arms, that don't break like the aluminum ones, instead they flex...
Ahmet

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It's all the driver...

Ahmet,
You're absolutely right that considering what you do with the car, it's a real tank.
Still, if it was my money, I really wouldn't like the shot bushings, the leaking power steering, and the broken transaxle (s?).
The thing that bugs me most is the wide front tires. Even the factory, with all its mighty power, decided on NOT going so wide in the front, fully knowing that the same width in the front and the rear is the best setup on that particular chassis, given its engine (up to 310HP from the factory)
Maybe pushing a little, but wouldn't you be better off bringing the car to a better reliability level first, even if it means losing some performance edge, and working on your driving skills, using the car as a constant value to gauge your progress?
All the money spared by NOT upgrading or repairing the car could then go to a 968 CS or an elusive 968 Turbo...
GeorgeK

[This message has been edited by GeorgeK (edited 03-17-2001).]

George, the car was tuned considerably more agressive a few thousand miles ago, with 350lbs progressive springs, 17 inch (heavy!) wheels, more agressive alignment, polygraphite bushings, etc.

I wanted to return to stock class, and decided to keep this car for a long time to come, as a race/daily driver, or race/back-up car.

I'll be picking up a 968, and turbo that, or a 951, and modify the living crap out of that car. That's going to happen, regardless of what I do to my current car. So I'll have two Porsches. The sad thing is, my next car will likely have a lot more potential, than the current one, but I'm not planning on racing it, maybe track days now and then, but nothing like my current car has been. Ofcourse that may change, but I doubt it will, not before I can afford two turbo/fast Porsches.

To the best of my knowledge, the turbo cup cars used the "updated" factory alloy control arms, "normal", factory stock gearboxes, torque tubes, etc. including the turbo cup cars, and the 300+hp 968 Turbo RS. I'm going to (likely) switch to a completely different rear susp, eliminating torsion bars, fabcar front control arms, with about 450-500lbs springs, etc, etc. With about 400+hp at the wheels would be what I'll go for. However I think the 968, OR 951S chasis/drivetrain is a much better point to start with, than the 924 turbo delivered early 944 drivetrain.

Now only if I knew this two years ago!

Feel free to post anything else you can think of or suggestions.

Thanks again for the replies, I'll post updates as to what I do with this car here.
Ahmet



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It's all the driver...

just about finished that fence, with a lot of help from wife & kids. still have to do gates. plan to check wife's car, A-frame & bolt up on 924 is same as 84 944 I think.

what kind of restrainsts are we dealing with in rules? bushing material - can be substituted but no more metal than with stock. components can be worked as for accident repair. are these right?

when it's too dark for me outside I'll hunt some data on materials.

drew1

Ahmet-

I assume you already tried replacing the a-arms again. If you haven't, it sounds like the bushing bores might have been manufactured out of tolerance, and the bushings didn't fit as tightly as they should. Now, over time with the bushings slipping the holes have probably worn, and the bushings are loose, which is why the a-arms slide on the OD of the bushing.

Here's a possible solution to the problem that would not require replacing the a-arms. Try using some Loctite 290 on the outside of the bushings next time you replace them. If you do that, you have to clean and etch everything like i'm going to describe, or it won't work.

When you get the new bushings, clean all the paint off the outside of them, and clean the bushing holes on the inside of the a-arm with fine sandpaper. Use some phosphoric acid (metal prep etch, normally used before painting) on the outside of the bushing, and the inside of the a-arm to get them chemically clean, or the Loctite won't really stick at all. Keep them wet with the phosphoric acid for 10-15 minutes, and rinse it off with hot water, and dry it quickly. put the loctite on, and let it cure for 24 hours (longer if it's cold)

I know that's really more of a band-aid than a solution, butit should work for you, that stuff is very strong.

Mike

you can reinforce the control arms by welding a strip down the sides of the control arm between the "lips", if you will.

Thanks for the replies, I don't mind changing the a-arms one more time, they're not expensive. They're deformed slightly.

Anyway, thanks for all the posts.

Drew1, I need to look at the rulebook, but I think any other bushing besides stock is illegal, as well as accident damage (fixing), if performed in a way to enhance performance, or alter mounting points by more than "X" mm, etc, etc.

Mike944, I'm putting off some of these repairs for a little while, as I concentrate on others. I will be (or am planning on) pulling the oil pan, changing bearings, seals, etc, and want to swap the subframe, control arms then. Since I have an auto-x every 2-3 weeks, I cannot leave the car apart. (specially since I need to have an alignment done right after this). I'd appreciate it if you could keep in touch for specific questions, and thanks.

Hoff, reinforcing is NOT allowed in stock class. Depending on the future of the car, I may go out of stock class, but only because I may want to upgrade a part of the car that's not permitted. (then the car won't be competitive at all, with reinforced control arms, running against cars that have full custom susp. no interior, higher compression, etc.) Right now, I'm concentrating on a daily driven (or drivable since I don't have a valid driver's license!) 944, pushed to the limits of mods in stock class. (which isn't much, but it adds up). I think I'm gonna attack exaust in the next few weeks.

Thanks again everybody, I'll post updates.
Ahmet



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It's all the driver...

Ahmet,
Used following specs to figure weight transfer to get max load on front wheel.
wheel base 96"
CG height 20"
weight 2800 lbs
track 58"
brake decel & lateral acel 1.2 G or 1.2 gees ( you had to get it somewhere)

With the specs the front has all weight during braking and the inside has about all the weight in corning. That is 1300 - 1400 lbs. Did not consider that force carried by spindle & take sum of moments to see how much carried by strut bearing and bushings separately. The bushings will carry the load if made from Delrin or UHMWP, with metal inside sleeves and metal flange on rear bushing as they are in stock rubber. The bushings should be a running fit on the sleeve. I recommend UHMWP as it is real tough, self lub (a little vaseline doesn't hurt in break in), wear resistant, & real kind to mateing materials. Reprocessed is better than virgin susposedly because polymer chains are randomly arranged.

You can check out materials at Tstar.com. Will post formulas I used if you wish.


drew1

Also see if seam welding the control arms is OK.

drew1

drew, didn't see your last reply...

I'm going with delrin, which looks like it will solve the problem. I'm also going with original 944 control arms, I'm buying used, I will strengthen them. (as long as they're rust free, I should be OK). It seems that when VW shifted manufacturing to Brazil, from Germany, the control arms were not built to the same standards as the old one. Tolerences are lower, and welds aren't the same quality. And as suspected, the bushing contact area is smaller with the newer brazil made control arms.

Anyway, what's the deal with UHMWP?
At Tstar.com, how do I know which one to go with?

PS: The weltmeisters that I messed up are discontinued, I wonder why!!! Maybe I should try a refund, I paid lots more than $100, as I used more than 3 full sets of this stuff, not to mention the alignments!

Thanks for the help so far, I need your opinions the most now though, as I need to come to a conclusion soon, as the new subframe is going in friday night! (I'm getting custom Delrin, but wanna go with the ultimate bushing there is).
Ahmet

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It's all the driver...

Ahmet,

UHMWP is ultra high molecular weight polyethelyne. It is used in wear & impact parts in textiles, agriculture, mining, etc. Delrin & Acetron are trade names for an acetate polymer. With Delrin close machining tolerances are easier to hold, since it's modulus of elasticity is higher. The drawbacks as compared to uhmwp are moisture absorsion (don't think it's enough to hurt), impact resistance (uhmwp is what you would call unbreakable from about 20 to 200 degrees F), it's not as wear resistant, wears mating parts more. The higher modulus of elasticity or less give may mean holding your alignment better.

At tstar.com, I found it during a yahoo search to compare properties. Check out the mechanical properties for bearing plastics.

I'm not a polymer chemist scientist, but what I say is based on my experience and published properties.

Got to go, in the middle of helping wife do research for grad school paper.

drew1

Drew, thanks for staying with me on this one.

I'm specifically wondering, how do I go from no bushing to bushing in my 944 control arms, in less than 8-9 days max. I'm not going through all this work, to have my new subframe messed up too. Subframe should be in, along with new con-rod bearings, and oil pan gasket by saturday morning (that's when I return the engine hoist). Control arm bushings can wait, but not much longer, as I would still need to get an alignment. Lets say my deadline is April 9th or 10th, 11th at the very latest.

I like the tstar, but don't know how to go along picking up the right dimention? and right material? in the right shape???

Lacking the practical thinking here...
Ahmet

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It's all the driver...

Hey Ahmet, send me the dimensions of the bushing you need and Ill turn them out for you. Have had these thoughts myself, about taking the squish out of the bushings. Grab some dial calipers and just measure the a-arm for what you need. I've got just what you need to use (nylatron). Used it on a guys dirt track car, works great!

that's an interesting idea, i don't know why the thought of making my own bushings never crossed my mind. Mine need replacement soon, and i certainly have the equipment, and know-how. After all, i used to work for a bearing company that made plain sleeve bushings.

It looks like i've got a new project on my hands! I guess i'll have to order some UHMW

If you think we have a good shot at doing these bushings, I'll be glad to take measurements and send them to you.

I'll keep in touch, and as I'm sure you know by now, my e-mail is "over1g@hotmail.com".

As long as you've got the right tools, and material I don't see why one wouldn't make his own tools...
Ahmet

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It's all the driver...

Ahmet,

If the rules say "... no more metal than stock", I suggest a steel sleeve inside the same diameter as the stock bushing's sleeve.
One of the rubber flanges can be forced through on the stock bushing but you'll need a two peice plastic bushing because the flange won't go.

I would make the back bushings too. The rubber in the flange giving on them puts more stress on the flanges of the front during braking.

If I had known a week or two ago, I could have got some material a week or two ago & took it to work and fixed you some. Now it's really a short notice unless KC can't fix you up.

drew1

They'd be illegal in stock classes, per the rules. They WOULD however be permitted in street prepared classes, whereas straight out bearings would go in the modified class. I may set up the car for street prepared, which is still this side of having to tow the car to the track for EVERY race (but only barely, if you take racing seriously).

Anyway, I still don't know how to go along with this???

Let's say I'm using UHMW, and got the dimentions, how would I order this part? And machine (trim?) it to shape? There's no problem with a two piece bushing, most aftermarkets are like this anyway.

PS: Haven't heard from KC!

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It's all the driver...

Ahmet,

I would use round stock material & cut to size on a lathe. If using 'as extruded' plastic, getting one size bigger than the flange diameter is best because of material out of roundness.

For your flange diameter, go as big as you can can without rubbing the frame. The OD of the bushing should be a press fit in the control arm. I'm remembering about 1 1/4" on the bushing part. With UHMWP, this should be .001" + .005" or .006". Since UHMWP is a real ductile material, for the ID "running fit" use .002" + .006" (squeeze of press).

I'll tell the steps I would use if you're doing it yourself.
1. Put stock in chuck of lathe, leaving enough sticking out the part & cutting off.
2. Face the stock or cut the end flat & true.
3. Center drill the stock.
4. Drill the stock (under ID size).
5. Bore to ID.
6. turn bushing OD.
7. I wound cut a small pilot (same diameter as arm hole ID) about 1/4" back to help in starting bushing installation.
8. Turn flange OD.
9. Cut off with parting tool.

For deburring, a leather working tool works good.

The Carolinas are a big textile machine area, so you may be able to find a local machine shop with material and equipment to fab these if you can give them a sketch of what you need.

drew1

edit: to order stock, order by OD then get enough to make bushings & chuck up on in making then. 1 ft may be enough but if 5 ft is standard lgt, you may come out about same by not having to pay a sawing charge.

[This message has been edited by drew1 (edited 04-04-2001).]