Erratic steering

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TheDude

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Hey Guys, I've had this car mostly parked for most of the time I've owned it as I've been going through different parts of the car so don't really have a good feel for how the car drives normally and hardly ever had it up to speed for more than a few times. Now I'm finally getting this thing more driveable and on different wheels and tires and now I'm finding that the steering is pretty terrible. The steering basically won't center and anything over 45-50MPH and this thing is all over the place. It seems to grab any contour in the road and darts off that way. It's genuinely not safe to drive like this even around town. 

While I didn't drive it much before changing the wheels and tires, I don't think I noticed it being this bad. A little while back I had a local Mustang shop give it the once over and they told me the suspension is fine. Ball joints, wheel bearings etc. everything looks solid. Could use new strut rod bushings at some point, but not bad. 

Right now I am running on very low profile tires, too low actually, but it's what came with the wheels and not ready to replace them just yet. It's on 235 X 30 X 20's. The wheels are 20 X 8.5 and there is a 1" spacer.  

So any thoughts on if this is just alignment, tires, strut rod bushing or is something genuinely messed up in the suspension?

Thanks for any advice. 

 

Don C

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You didn't say what your tire pressures are. Stiff sidewalls and too much pressure will cause even radials to track every ridge and groove. I'm guessing your alignment is also messed up and/or aligned for bias ply tires. Caster and camber are probably both wrong for those tires.

 

TheDude

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Hi Don and thanks for the reply. Good point, air pressure is 32PSI. I've never had it aligned. I'll drop the pressure down to 24-26 and see how that goes. Didn't even occur to me to try that. 

 

TheDude

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So it was actually higher than I thought at about 35. Lowered it to 25 and drove it. It's better but still all over the place. And just to correct the tire size, they are 255 35 20's. 

 

Bentworker

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I’m curious what you find when checking alignment.  Reminds me of my GMC pickup when I had toe out.

 

droptop73

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I have the same issue on asphalt roads with deep "18 wheeler" ruts. A little extra toe in seems to help with the short sidewall tires. Mine are 245-40-18. Part of it may also be issues with scrub radius due to the offset of the wheels. On smooth asphalt or concrete roads the car drives like a dream. I plan to add more caster and toe in to try to correct it.

 

TheDude

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OK thanks. Going to try and get it in and have it aligned this week by someone who know's these cars. This thing isn't a dream ever right now. I have a hard time just staying in a lane unless the road is perfectly smooth. 

 

droptop73

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If a shop told you the strut rod bushings were marginal, I'd replace them beforehand. Whatever you do, don't let the shop align the car to stock specs. Radial tires need more caster. 

https://opentrackerracing.com/technical/
+1 - Caster is the steering angle that provides directional stability.

From what I've found even late model cars with wide low profile tires can have this issue. I try to drive on the "ridges" rather than the valleys. It can be a handful to catch the car when it twitches. Bad strut rod bushings will definitely add to the loose feel especially under braking.

 

droptop73

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Just an update. I'm getting ready for a road trip with my convertible and wanted to try a couple things before I leave. I increased the tire pressure from 32 to 40 on the front and increased toe from 1/8" to 3/16" and it made a significant improvement. I suspect it was more the tire pressure since I have a 245 tire on a 9" rim and the lower pressure would place more "weight" toward the edges of the tire. At this time there is very little wander due to the ruts and a bunch more relaxing to drive.

I felt some pressure to improve this since my son and I will be sharing driving duties and I want to relax when he's behind the wheel. LOL!!

 

B229218

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Dial in as much positive caster as you can, at least 3.5 degrees, sounds like toe is out, not in.

 

SteveO_71

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What condition is the steering box, rag joint and pitman arm in? Maybe rebuilds or replacements are needed.

 

TheDude

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Thanks for the follow up. 

Digging into this more it was pretty clear that the local control arm bushings are in really bad shape, in particular the one on the left. I've ordered new arms for both sides and will get those installed this weekend if it's not too hot then add a bunch of caster as well before aligning it. 

It has a new rag point and idler arm. The pitman arm looks good. The box seems loose but not crazy. Seeing how much those control arms are moving around I'm thinking that getting fixed will go a long way to getting this to drive like a regular old car and not complete death trap. 

 
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