slngsht Posted October 7, 2007 Share Posted October 7, 2007 Some of you may remember my car suffers from a condition where under hard (and sudden) breaking, the front wheels go to a hop rather than a slide - not all the time, but sometimes. With my high unsprung weight, I've upgraded to stiffer springs, and cranked up the shocks (both rebound and compression). I *think* it has helped, but not eliminated the problem. I'm already running heims, so i doubt joint flex is causing this. Any other ideas? Link to comment Share on other sites More sharing options...
Mandurath Posted October 7, 2007 Share Posted October 7, 2007 I had a 65 mustand that did it. Was due to weak front springs combined with old shocks. Link to comment Share on other sites More sharing options...
xflow7 Posted October 7, 2007 Share Posted October 7, 2007 This may be a long shot, but have you played with tire pressure at all? Link to comment Share on other sites More sharing options...
slngsht Posted October 7, 2007 Author Share Posted October 7, 2007 I had a 65 mustand that did it. Was due to weak front springs combined with old shocks. Heh, that's where I've been playing... But my QA1 shocks are 20 out of 24 clicks on rebound and compression. If I jump up and down on the front of the frame, it doesn't even move anymore :lol: My springs are 425 lb/in now... was running 375 until today. I forget my lever ratio, but it is approx. 1.7:1... so my real spring rate in the front is 250 lbs/in now. Link to comment Share on other sites More sharing options...
slngsht Posted October 7, 2007 Author Share Posted October 7, 2007 This may be a long shot, but have you played with tire pressure at all? I've been running 24 psi. Do you suggest I go lower or higher? I really don't want to go higher, because I think I'll lose some grip. Link to comment Share on other sites More sharing options...
xflow7 Posted October 7, 2007 Share Posted October 7, 2007 I've been running 24 psi. Do you suggest I go lower or higher? I really don't want to go higher, because I think I'll lose some grip. I don't really know. I did seem to find that wheel hop under acceleration on my Audi (totally different kettle of fish, I realize) improved when I increased air pressure. But, I'm not sure if that's applicable in this case. Link to comment Share on other sites More sharing options...
Arya Ebrahimi Posted October 7, 2007 Share Posted October 7, 2007 Any chance of tracking down a high speed video camera? Would be relatively easy to mount it up and film it, then slow it down to diagnose it. Link to comment Share on other sites More sharing options...
JBH Posted October 8, 2007 Share Posted October 8, 2007 The first reaction is bad shocks, but it sounds like these are new. So....You may be running too much compression. Too stiff and you take out the function of the shock in absorbing the bumps. If the front starts jumping, it doesn't matter how much rebound you have dialed in. What is the condition of your rotors - any chance they are warped or have brake compound built up? Link to comment Share on other sites More sharing options...
slngsht Posted October 8, 2007 Author Share Posted October 8, 2007 The first reaction is bad shocks, but it sounds like these are new. So....You may be running too much compression. Too stiff and you take out the function of the shock in absorbing the bumps. If the front starts jumping, it doesn't matter how much rebound you have dialed in. What is the condition of your rotors - any chance they are warped or have brake compound built up? Front rotors and pads are new... put on before the dragon. To make one thing clear... The brakes are fantastic. Smooth, no fade, and plenty of stopping power. The problem occures when the front wheel traction is exceeded - instead of going into a slide, they sometimes go into a shake. Otherwise, everything is as smooth as silk. I think based on your note here, I will experiment with keeping high rebound, and backing off on compression. Link to comment Share on other sites More sharing options...
locostv8 Posted October 9, 2007 Share Posted October 9, 2007 I remember a discussion on C-C about the geometry of the rear unloading the front. IIRC the 4 link should never be paralell with the ground but should angle down toward the front. Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Author Share Posted October 9, 2007 I remember a discussion on C-C about the geometry of the rear unloading the front. IIRC the 4 link should never be paralell with the ground but should angle down toward the front. During braking? I thought the links angle down towards the rear, to provide anti-squat. I'm in Boston at the moment, so can't check the car. 100% sure they're not parallel to the ground. Link to comment Share on other sites More sharing options...
KENLUDE97 Posted October 9, 2007 Share Posted October 9, 2007 Any thought to chassis flex? With the big/powerful engine are you running any additional tubes for stiffness? Link to comment Share on other sites More sharing options...
gjslutz Posted October 9, 2007 Share Posted October 9, 2007 Mazda likely you have thought of this: Existing condition or new? What has changed if new condition? I would think it would be: Loose or deflecting in suspension or in steering, ball joints? Loose wheel bearings, brake pads chatter. Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Author Share Posted October 9, 2007 Any thought to chassis flex? With the big/powerful engine are you running any additional tubes for stiffness? Only occures under pure braking... also did not happen with my old upright/wheel/brake combo. At that time I already had the LS1 engine. Link to comment Share on other sites More sharing options...
Davemk1 Posted October 9, 2007 Share Posted October 9, 2007 Sounds like a geometry issue (caster?) or a damping issue. Dave Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Author Share Posted October 9, 2007 Mazda likely you have thought of this: Existing condition or new? What has changed if new condition? I would think it would be: Loose or deflecting in suspension or in steering, ball joints? Loose wheel bearings, brake pads chatter. It is a new condition, after new uprights, wheels, brakes, Aarms. There is only one suspect part of the suspension, and that would be the inner upper Aarm mount, which I will redo this winter. All the joints are new 1/2" heims. Aarms are .12" wall 1"D DOM tubing. I'm sure they're more than strong enough. I will double check my rack mounts. Everything is tight all the time. I'm pretty sure wheels just go into an up/down bounce during lockup. Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Author Share Posted October 9, 2007 Sounds like a geometry issue (caster?) or a damping issue. Dave Can you please explain about caster? Link to comment Share on other sites More sharing options...
JBH Posted October 9, 2007 Share Posted October 9, 2007 Dave raises an important point...do you know the settings on your alignment? Under heaving braking weight shifts forward and the front end begins to move downward. The wheel geometry is changing at the same time, so the first thing to do is to make sure you are in correct alignment. Setting the dampers to the highest setting can induce excessive anti-dive. This can hinder performance by causing the front suspension to stiffen while braking for a corner, which can cause understeer. In extreme amounts, anti-dive geometry will cause wheel hop and caster changes under braking. The place to start is with your alignment - make certain that is correct. Then you tune the dampers starting with settings somewhere in the middle. Link to comment Share on other sites More sharing options...
slngsht Posted October 9, 2007 Author Share Posted October 9, 2007 well, I don't know what's "correct" since it's all home made I'm running -1 degree camber, 5 degrees caster (need to verify this). I cannot recall how much toe-in I'm running... maybe 1/32" or 1/16". Under other situations, I'm happy with the response of the car. It tracks straight, has excellent grip in corners, etc... I'm sure alot of trial and error is ahead, but this is the only really BIG problem I have not been able to overcome. Link to comment Share on other sites More sharing options...
Davemk1 Posted October 10, 2007 Share Posted October 10, 2007 If I understand this right it started after you changed the uprights and some brake components. Is that right? If that is the case then we can rule out things like weight distribution and the like since it didn't do it before and you haven't appreciably changed that with your front end work. I assume you've got adjustable shocks and that they have a dial for adjustment. If that's the case then take it out to an empty lot and lock them up and make sure it happens with the current set up and then make a huge change to the damping and see what it does. You might not want to run the car full soft but try it and see if it goes away and you'll learn something. If you don't have the luxury or spinning a knob to make the adjustments things just got less convenient but it's still worth trying anyway. You'll also want to play with rear shock settings. Not enough rebound damping can cause too much weight shift and funny things to happen. You also need to verify your suspension settings. Make sure that your camber is set with your weight in the car. It changes a lot once you drop you butt in the seat. Check the caster too and make use both sides are close to the same and make sure there is enough caster overall. Too little caster can have negative effects under braking. Is your brake bias adjustable? If so you'll want to confirm that you haven't given the front end such good braking that the tires are overwhelmed. That's all I've got. Dave Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now