In trying to track down an annoying noise in the front end of my Miata, I found that the front upper control arm on the passenger side has something like 1/4" of play in it - it can be pried back and forth on the bushings fairly easily. I have poly bushings and am wondering if maybe the sleeves are a bit too long, allowing the control arm to be loose?
Is this a problem? I'm going to assume that it is, since ideally suspension parts should only move in their intended plane. Bent control arm or incorrect sleeves? Does anyone have a measurement for the distance between bearing cups on a stock control arm?
I don't think random dynamic caster adjustment is a feature so, I'd say that's a problem. I can't picture exactly where yours is moving or what's supposed to be preventing that. Could you post a photo?
Did you make sure the bolts are tight? The nb has one long ass bolt through both bushings and the k frame.....
Sounds like it's either incorrect sleeves or incorrect bushings, a bent arm seems unlikely to cause this. Poly bushings are a bit tricky in this sort of situation, because the washers need to be close enough to stop the arm from moving front-to-rear, but if you clamp it down too tightly then the washers rub on the sides of the bushing and create stiction.
Make sure there aren't any washers between the sleeves and the tube on the subframe that the long bolt goes through.
Yep, the long bolt is tight. I'll get a picture tonight. I don't think there are washers between the sleeve and the subframe tube but I will verify that as well. It seems like either the sleeves are too long, or the bushing cups are bent toward each other - the bolt is clamping the sleeves, but not the arm itself.
The poly upper control arm bushings are one piece, so I don't think it's likely that I installed the wrong ones. I'll try and check those too, if I can find the molded in part number on them.
The bushing cups being bent towards each other shouldn't make any difference, because to fit over the tube in the subframe they'd need to bend back outwards (unless that tube has been shortened with a grinder or something).
I just measured a spare upper A-arm. The sleeves in the bushings are 55 mm each, and the space between the two bushing sleeves is 157 mm. The bushings should be installed with the flanges outboard, next the two inch washers on the big bolt.
The sleeves check out. The tube in the subframe measures 6.125" on my car on both sides, which doesn't exactly match up with deadskunk's measurements. Something is screwy. Here are 2 pics of the driver's side:
Pushed to the back
Pushed to the front
May be wrong, but shouldn't there be a bushing flange of poly on both sides of the bushings?
I think that's a normal 'feature' of poly control arm bushings. That's been my personal experience anyway.
Tyler H said:
I think that's a normal 'feature' of poly control arm bushings. That's been my personal experience anyway.
It may be "normal" but it's not right. Most cars I've worked on have a bolt for each bushing that will clamp the bushing sleeve securely. When you have one long bolt thru both, I don't know how it's clamping the bushing sleeves unless it pulling the outboard ears against a solid center section in the K-frame. The upper control arm shouldn't be able to move fore and aft. If the two upper bushings are clamped with one long bolt, it may only need the poly "thrust flange" on the outboard side of each one. If the long bolt is tight against the bushing sleeves but the arm is still moving, the flange on the bushings is too thin. The total length of the bushing should be at least as long as the bushing sleeve (maybe a little longer to allow for pre-load on the bushing). If that's not the case, you can take up the slack with washers with an OD that fits over the bushing sleeve, between the bushing flange and the outboard mounting ears.
DeadSkunk said:
I just measured a spare upper A-arm. The sleeves in the bushings are 55 mm each, and the space between the two bushing sleeves is 157 mm. The bushings should be installed with the flanges outboard, next the two inch washers on the big bolt.
Did you measure the sleeves in stock bushings or poly? If that's the stock measurement, that would explain it. Energy suspension uses a 2.25" sleeve, which is about 57mm - so two of those would account for the ~4mm gap I'm seeing.
In reply to cmcgregor :
Mine is stock bushings. The rubber won't move on the stock sleeves. Will your poly bushing slide on their sleeves? It looks like the poly bushings aren't long enough.
Yes, the poly bushings will slide on their sleeves, which makes sizing the sleeves somewhat critical. It seems that Energy Suspension may have not done a great job of that - either the sleeve needs to be shorter or the flange on the bushing needs to be thicker.
Or, do as djsilver suggested and put washers that have an ID greater than the sleeve diameter. You just have to be sure not to put force on the A-arm itself.
Yep, that would work too. Thanks to djsilver for his coherent explanation of what's going on here too - I'm not always great at that.
I think it will be easier to take some length off the sleeves than to find a washer that's just right, so I'm going to do that.
Turn one of them the other way. You have both end thrust surfaces on the same side.
Edit- I see that's two pictures of the same pivot. My statement may still stand, though.
It looks to me like the design relies on the strength of the control arm given the lack of retention on the inside face, but the control arm bushing to bushing distance got shorter because it's not strong enough. Only way to be sure is to compare against a known good one.
In reply to Knurled. :
He should be able to crank that 12" bolt to failure and not put any stress on the A-arm. There's no metal to metal contact between the bolt/sleeves/washers and the arm, or there shouldn't be.
In reply to DeadSkunk :
The A-arm probably got deformed from braking loads. Given that the bushings slide easily in the arm, the longitudinal forces all resolve on the one bushing that has a "stop", the front one. This will bend the arm over time, until it is so pinched that the rear leg of the control arm starts beating on the crossmember.
If you want a nice SWAG, if the ball joints' center-center distance is half the tire diameter, and the front brakes do 70% of the work, and the car weighs 2000lb, then braking at one gee will put 1400lb of force on that leg. This assumes smooth braking, not stuttering into bumps or whatnot.
This of course is imperfect math (the upper ball joint is further from the torquing axis than the lower, for starters) but I hope it's sufficient to illustrate my point.
Knurled. said:
In reply to DeadSkunk :
If you want a nice SWAG, if the ball joints' center-center distance is half the tire diameter, and the front brakes do 70% of the work, and the car weighs 2000lb, then braking at one gee will put 1400lb of force on that leg. This assumes smooth braking, not stuttering into bumps or whatnot.
Definitely SWAG 
... but if it was correct, then it would 700lbf as there are two of those, on on each side of the car.
In reply to Slippery :
Yes, but the braking torque should result in roughly doubled forces due to the ball joints being close together.
SWAG compounded on guesstimation, of course, but should be within an order of magnitude, We're talking the kind of forces that you make with a hydraulic press, not with a prybar.
Should be noted that 2000lb with driver is closer to Exocet territory than Miata, too. And bumps may introduce momentary 5g+ shocks.
In reply to cmcgregor :
Measure the distance from the front edge of the bushing tube (not the sleeves) to the same point at the trailing edge. My stock parts are 10 3/32" (257 mm). If you arm is bent it should be measurable.
Thanks for that measurement. That's the next thing I'll check.
These arms aren't super well known for bending and this car has always been on street tires, so I doubt it's bent from braking force. I know that it's been crashed at least twice, so bent bits are very possible but the slop is the same on both sides and I have aftermarket parts in there. Generally that's where I look first.
I'm out of town for a few days but I'll report back.
IMHO this particular problem is much more likely to be caused by a having a steel bushing sleeve that's too long by a couple mm, or a poly bushing that was cut short by the same then it is by a damaged control arm. My front upper control arms are bent enough so that when you hold it up to the tube with the sleeves in teh right place, the tube looks like it's 2mm too short and needs a washer in there. Putting in that washer is exactly the wrong thing to do, it causes exactly this problem. Instead, the fix it on my car is to install it without the washer and when I torque the nut on the long bolt it bends the "cups" on the arms back in to close up that 2mm gap and the arm works fine.
I'm not sure what caused the bends in my arms. The car's got a LOT of track days and autocrosses with sticky tires on it, so it's possible it's that. It's also possible that I've bent them in the process of swapping bushings around using threaded rod (the car is only its 3rd or 4th set of bushings at this point, and I didn't always have a press to do them with.
I think the right fix is to shorten up the sleeves so that they're just barely longer than the bushings they go in. A few minutes with a grinder will probably do it.
