Hey all, I need to make some new front suspension mount forks to get some more camber. I calculated they need to move the lower control arm out about 1/2" to get zero camber with no shims. 1. Anyone know what the stock ones are made of? there was a TSB I thought at one time 2. Welding the bolt in . .. you think I need to have the assembly stress relieved? 3. I'd like to just make them out of CRS, but If I make 'em out of chromoly, would I not worry about heat treating since that might mess up the heat treat of the bolt? 4. Was thinking of machining the fork piece out of billet . .. would keep a massive radius on the inside and perhaps even beef up the wall thickness if there's room . . . any thoughts on grain structure/weakness vs. forming the part out of one piece? Thanks, Sean
when I lowered it with the qa1's instead of gaining any camber seems like it lost some . .. I'm still +.5 degree with all the shim I can get before running out of thread . .. rear gained camber though.
The nicest solution is probably longer A-arms, but new mounts is probably easier. don't heat treat as it will mess up the bold strength. billet forks would be fine. If you have any doubt at all just make them thicker.
If you make new forks, I would not weld the bold, just a hole in the U and use 2 spanners or maybe a light tack-weld. I made new A-arms for my 308 to GTO conversion, out of mild steel. I stress relieved them in my kitchen oven hehe. First pizza afterwards tasted like fresh welded metal but what is wrong with that?
cool . . be nice to see some pics. what about just sourcing a longer bolt and making a thick spacer then shim final alignment as opposed to a new fork? don't think there's much room for a hex in there also so might need to tack 'em.
I have to pass giving advice. Standard suspension forks have failed in the past (I read about it here on Fchat) and modifying them wouldn't make them stronger. If you make a thick spacer, I would use a rectangle covering the whole supported area. My custom made rear arms, notice the gap the driveshaft has. Luckily driveshafts any length are available from the desert buggy guys, they often use Porsche 930 CV's and so does our 308/328. Image Unavailable, Please Login
Tacking th ehead of the bolt to keep it from turning would not scare me in the least....I 've done it many many times including the side shaft and crank pin nuts on my H-D crank and that lived 2 seasons at 9000 rpm Just don't go and try to full weld the thing so the whole head is glowing before you're done. Tack 3 sides and quench cool it after each tack and all the strength will still be there you're done. I agree the stock forks are not all that strong, but if yours are in good shape I wouldn't be scared to reuse them. You won't be making them any weaker that I can see, the new load will be in the spaces and bolt so as Bert said make the spacer as large as possible to add support.
My forks were brand new in '97 and the stock bolt is tacked in there just like you're describing . .. thanks
The rear forks have longer bolts because they go all the way through the chassis. They are a little bit different I think with the height but maybe you can use those.
thanks for the tip . . I'll check it out . . different height might change the camber curve in a good way.
Some pics of what I did and why. Pak ratted my old suspension forks from '97 . .. cut out the old bolt and tacked the spacer on in a way which "I hope" strengthens the piece . .. I think there was a TSB on these things and I think the fracture would of been around the bolt not on the two "legs" . . . . I let it cool then tacked in the new longer bolt after I machined the head down for clearance like the old ones . .. tacking is required . .. no way to get a wrench in there. I also rounded all the corners on the second one . . the square corners started bothering me . I just set it up with -1 degree of camber and holy cow what a difference . . obviously my tires are wasted so a lot of it could be I'm running on tread again but I don't recall 'er ever "pointing" liike this . . . gaining camber is the first mod the P guys do for autocross or track and people have complained about the understeer of the 308 . . . my right rear shock is shot and it still will not push even with the 375 springs and the front shocks on 9 . . . incredible turn in . The tire wear pattern was with pretty much 0 to just barely plus in front and the pic of the rear is -1.5 degree . .. aggressive driving style . I only ended up adding about 1/8" on each side so far to get -1 deg but will experiment all the way to -2 for autoX . . but I could've got the 1/8 with a standard nut and red loctite vs. nylock . .. thickness is 11 mm vs 14 mm. Cheers, Sean Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
A few more pics . .. I feel like a kid fiddling with my BMX bike Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
You know if you lowered the car that much you may solve the immediate problem with shimmed up fork. But what about bump steer in the front too? I think if you have gone that radical you may want to look at changing the pickup points because if your front rear A-arms are not fairly close to stock on their hortizontal position at rest you are going to get all kinds of toe changes as you hit bumps and heavy braking. You could have the front AND the back of the car steering all over the place.
Isn't bump steer tuneable by shimming/adjusting the height between the tie rod & spindle or something like that? This is what the P guys play with at least and actually dial different amounts of bump . .. I've always wondered what the stock 308 suspension geometry does with regards to bump steer. Looks like I'll be breaking out "Prepare to Win" to freshen up and dialing in bump .
bump is the easy thing to fix but best handlged by raising the rack but you can do the cheesy thing of adding a bump kit like the p-racers. when the A-arms have funny geometry from lowering such as looking like a letter "V" from behind or head on , or being outside the design range, all kinds of funny things happen as the suspension now moves in a new range due to the lowering. Sometimes you can lower a car and make it worse or unpredictable. That's why racers want to change the pick-up points and sanctioning bodies like SCCA in just about all classes forbids it. Remember tune chassis = gaining 100hp old school adage? Changing pick-up points is a radical way to up the suspension arms race by having a chssis that looks like something you expect but handles radically different that anyone elses due to an engineering of all new suspension geometry. The pickup point is the base position that determines the range which you can play in and if you have to go to the point you redesign the forks maybe you are outside the design range. I don't know enough about the math to comment anymore than that..but it is a math problem so you could probably figure it out with some research. Remember in engineering you can make anything it is the compromises that make it hard. You can make an airplane that no bullet can go through but it would be so heavy it would never fly.
I have the 308 a-arm geometry from Fchatter Steve Magxxxx and will lay it all out and see what's going on. I don't think I've moved the geometry that much . . . at max I'm only going to end up moving the bottom fork out an additional .25" beyond what the stock forks would allow with the bolt length . . original calc was based on spread on control arms not the ball joint seperation which is a better gestimate . .. . point taken about lowering though which I'll understand more after I graph the camber curve . .. this is all known info in the P world but not so for these cars. While it was disturbing I lost camber when lowering (as I think Lou did) it wasn't as extreme as I thought . .. . after the suspension settled seems like I was about neutral but the tire wear is why I got on this again due to the extra grip with the swaybars and spring/shock combo. Not sure cheesy is the right word for spacing the tie rods . .. do you think bump is dialed in properly from the factory to begin with? I've got the impression that all cars need bump dialing in when you're setting up for racing . . .. just like camber. The proof will be in lap times and what level of modded P car I can keep in the mirror . . . stockers a piece of cake now . Cheers.
Hi Fatbillybob, I did get a chance to fool around with the bump steer on my old P auto X car. Richie Ginther made some rack spacers, i think about 5/8 tall. Yes, you can do either the rack or the outer tie rod end. Prepare to win is good, but IIRC Tune to win had a good bit to say as well. hth, chris
I'll browse that one too . . . browsed Prepare to Win last night and the bump setup is just as I described.
Bump steer will be fine, seriously. Although the steering arms are now "uphill", the A-arms are too now. Bumpsteer comes from the relationship of the angles, not the angle of the tie rod itself. Ferrari has done an above average job in this area, and luckydynes will be fine. Jay Morris
If you measure it you will fine significant deflection and that is bad at high speed on bumps. I guarantee you will be outside the desing range with significant lowering. You have to be do the math.
Well yes the factory does its compromises for street driving. You and I change th geom for racing and that include bump, ackerman etc.... You need to start with an analysis like this to see what your suspension geom is. Then do the math to create what you want. Image Unavailable, Please Login
I really wanted to "start" by not destroying the outer shoulders of my Hoosiers in 1 hour . I'll do those layouts and post 'em . . pretty simple once you have the geometry which Steve Mxxxxxx gave me. I initially wanted to do them to get an idea of what was going on with wheel rate 'cause I still get so much front end dive under hard braking.
