I am planning on adding a bit of caster into my Mark IV. My intial setup has 3 degrees caster and 1/16 toe with the Factory Five manual rack. The car has 17" rims with 22-24 psi pressure. I run down the highway great, however I am looking for a bit more high speed stability. I was thinking about taking my caster to 4 or 4.5 degrees. My question is...How much caster can I add while still having enough thread engagement with the Factory Five upper control arms and not having to replace the stock adjusters with longer ones? Thanks.
Not sure about your front end set up but have you considered the SAI mod? Whitby has it(forum vendor) and works well with the 17 inch wheels. It is the best change I made to my Coupe for handling stability, easy bolt in well worth the $$. FYI for more info on the SAI mod do the following: go to google and enter site:ffcars.com SAI mod or anything else you wish to find related to steering setup like caster/camber , ackerman etc. I found this as great source of info during my build.
HTH
CB
HTH
CB
I'v tried a variety of caster settings - from 1-6*. For track use, I'v settled on 2.5*, and for the street 3*. The car definatly starts to feel heavy at 3*. More than that and it's becomes a work out to drive, but doesn't seem to add anything to the handeling.
If your car is unstable at less than 3* of caster, look somewhere else for the problem.
__________________
.boB
Dart 427W, Momar 8 Stack EFI, 600'ish hp, TKO, 3.55 TruTrac, Red with Ghost Flames. More fun than should legally be allowed. http://home.comcast.net/~bobcowan035/site/
Ok thanks for the input. I have a few miles on the car now so I need to recheck ride height and might consider a little more caster. I am used to my 5.0 mustang at speed. The Factory Five is definitely more responsive to small steering inputs. Originally my tire presssures were 35psi and it was all over at those pressures. Reset tire pressure to 24/26 and the car is much better behaved. I might try 4 degrees caster to see what that does to the handling.
I have a couple of thoughts for you.
1- tires down to 20f and 20-24 rear. The front being the most important.
2- what is the rack in turns lock to lock? I assume 3.0 for a manual rack but just want to double check.
3- What is your toein setting? About 1/16 inch total toe should be good but another 1/32 could help some.
4- Agree that SAI is a good thing and not sure if built into your MkIV or not. As i understand it the complete kit got it, but the base kit may not have. Search for help on what this is and how your can determine if you have it.
5- If all the above doesn't get you where you want to be, now you know why a lot of us like power steering. It will allow much more caster ( I run 8.5 degrees).
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FFR 5353K,351/400hp,TKO 500, 3-link w/3.08 and Truetrac, Koni DA coilovers front and rear,APE hardtop,Forte front and VPM rear swaybars
Thanks for the thoughts. I checked my tire pressures tonight. F 22 R 24. Might try 20 in the fronts. I do have 1/16 toe in so I might try a bit more. I purchased the donor kit but opted for the new manual rack which is 3 turns. I thought the Mark IV with their rack was supposed to fix the bump steer issues but I might have to give Factory Five a call. My car runs straight under heavy acceleration but fights a bit when settling down from a well over the speed limit run. Part of my issues might be the Ohio roads that are built with a slight crown to allow for drainage. I have the caster at 3 now and it is not too difficult to streer around town so I think I will recheck my ride height since I have a few miles on the car now and then go to the alignment shop for a few tweaks.
What front spindles and lower control arms do you have? You say you bought the donor kit (base kit?) which doesn't include either. The donor LCA's should work OK, but they do need to be installed properly. But if you are using donor Mustang spindles, which ones? Definitely some are better than others. I'm assuming you don't have the newer FFR 2-piece front spindles. Those are supposed to have vastly improved bump steer and the SAI mod is built it.
Assuming the tire pressures are right (sounds like you're in the ballpark now) and alignment OK, how many miles have you driven the car? It does take a little getting used to. Short wheelbase and quick steering is always going to take a little more attention than your daily driver. If you're still not happy with it, get an actual bump steer measurement. There are specific ways to check it to see how much your wheels toe in/out throughout the full suspension range. Obviously, less is good.
I have the Factory Five tubular lower control arms with the 87-93 fox mustang spindles. I have put about 500 miles on it to date. I do agree that you definitely need to pay attention when driving, but there is nothing like driving one of these cars!
I have the Factory Five tubular lower control arms with the 87-93 fox mustang spindles. I have put about 500 miles on it to date. I do agree that you definitely need to pay attention when driving, but there is nothing like driving one of these cars!
The Fox spindles likely would benefit from a bump steer kit, if that's what you're feeling.
Put away the check book, and pick up the measuring tools. You're taking wild guesses about what might be wrong, and planning on parts purchases that might fix this nebulous problem.
Don't guess - Know!
I use FFR's lower tubular arms, a manual rack, and Fox spindles. I run 3* of caster, 1* camber, and 1/6" toe out. This week end I was running up to 140mph lap after lap, with no stability issues.
This is not a snap-tite model. You can't just bolt things together and expect them to work properly. Things have to be very carefully adjusted and set properly. 1/8" in the wrong direction can make a big difference.
The first thing to do is carefully recheck your alignment settings. Are they really what you think they are?
Second, check your rear alignment. If you have a solid axle, make sure it's perfectly square in the chassis.
How's your corner weights? You probably don't have access to scales. But you can get the corner weights really close without scales. A search here will help you.
Actually measure your bump steer. It may not be nearly as bad as you think it is. Even if you do buy a kit, you'll have to measure the bump steer to make sure you installed it correctly. Otherwise, you could make it worse. Again, a search here will help you.
Don't worry about Ackerman too much. It's pretty well set with the chassis design, and doesn't effect street driving that much.
You've done all the hard work. Now it's time to do all the tedious and meticulous work.
__________________
.boB
Dart 427W, Momar 8 Stack EFI, 600'ish hp, TKO, 3.55 TruTrac, Red with Ghost Flames. More fun than should legally be allowed. http://home.comcast.net/~bobcowan035/site/
Actually measure your bump steer. It may not be nearly as bad as you think it is. Even if you do buy a kit, you'll have to measure the bump steer to make sure you installed it correctly. Otherwise, you could make it worse. Again, a search here will help you.
THANK YOU BOB! Probably my biggest pet peeve is people who want to throw a bump steer kit on the car without even knowing if they HAVE bump steer. It is akin to one of your patients coming to you asking for a kidney transplant "Just in case mine might be bad"!
Bob and Jeff -- Of course you are right. For the record, in post #9 I also pointed out the need to confirm alignment settings and actually measure bump steer before doing anything (e.g. get out the checkbook). As I understand Fox spindles do often benefit from a bump steer kit, but actually measure first is exactly right.
The SN95 spindles in my Mk3 actually measure a little bit of bump steer, but for the driving I do it's barely noticeable and completely acceptable. My new Mk4 build has the new FFR spindles. I will be very interested to see how they measure and drive in comparison.
...I run 3* of caster, 1* camber, and 1/6" toe out. This week end I was running up to 140mph lap after lap, with no stability issues...
I'm sure that Bob means 1/16" toe out.
When you run negative camber, toe out (not toe in) in needed to compensate for the dynamics of the rotating wheels. Many people (except for those who set up race cars) don't know this and use normal street settings because normal street cars do not have negative camber.
My have run my car as high as 170 (on track) and have had no stability issues.
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