Suspension Repair Question

WildHair · 10-20-2009, 06:04 PM

I have a 91 MR2 that has had some sort of damage to the driver’s side front suspension. I'm in the process of repairing the repair work performed by a previous owner. From the damage, it appears the Lower Control Arm (LCA) was forced backwards at the wheel end (towards the rear of the vehicle), which forced the LCA mount on the car frame to spread apart. It appears that this also striped the treads from the bolt/hole of the bolt that mounts the LCA to the frame. Rather than get a new bolt and re-tap the hole in the frame, a previous owner/repairman simply welded the bolt to the frame with the LCA trapped in place. Needless to say, the rubber bushing in the lower control arm didn't fare well and the bolt diameter has been reduced due to wear/corrosion, which allowed significant play in the LCA. I have removed the bolt (after allot of cursing, grinding, welding, and blood) and removed the LCA.

Now that the LCA is off, I can see that a previous owner/repairman has welded an approximately 1/8" wide plate to the inside of the frame mount for the LCA (the side the bolt threads engage). Even with this plate the frame mount is spread too wide for the LCA and washer to fit without play. The spreading of the frame mount appears to have taken place completely on the bolt head side (toward the front of the car). I could probably use an air hammer to push the forward mount flange back (toward the rear of the car) and take up the play, but I am worried about the 1/8" plate welded to the mount. Despite the damage to the mount, I cannot see any additional damage to the rest of the unibody (the seams and structure look identical to the other side of the car). However, I do not have access to a frame straightening machine to check the alignment of the car overall. I don't know if the plate was welded in place to move the LCA mount back into the correct position (relative to the other side), or if it was just a half-arsed way to quick-fix the front end. The plate does add a little meat to the aft side of the mount and allowed me to tap the hole in preparation for a new bolt (one that is not striped beyond use).

Ok, so that was allot of explanation and background and here is my question. If the plate is incorrectly locating the LCA car-side mount forward an 1/8", what are your opinions’ about how it would affect handling?

I'm not sure how this suspension is designed and I really know nothing about car suspension geometry, but just thinking through things logically, here are my thoughts. If the car can be aligned (with the condition above), I don't see straight-line travel being affected. However, as the front suspension is side-loaded (while in a turn), the wheel will either shift aft or forward based on how the geometry was designed and the direction of the side-load. I say it will shift either aft or forward because the rod-link mounted to the LCA and running to the forward portion of the car (forward brace) is connected to the frame via bushings, which will give slightly. Therefore, wouldn't the wheel shift forward (slightly) if the side-load is aimed between the LCA and the forward brace (placing the forward brace in compression) and aft slightly if the side-load is aimed aft of the LCA (placing the forward brace in tension). If the LCA mounts to the car slightly forward of where it is supposed to, then the geometry of that triangle changes and the wheel will shift aft sooner than designed. Right? Perhaps it is too small to even matter, or all this is crazy talk, I'm not sure. But I'm hoping there is a suspension expert out there that can provide some insight or someone with front suspension repair experience.

I really don't want to grind that plate off, because then I would need to weld the bolt hole closed so there will be enough meat for me to re-tap the hole so the threads of the bolt will engage. I could do it, it's just in a pain-in-the-neck location for that sort of work and the plate may be there to get the suspension back into alignment in the first place.

Help and thanks,

Mike.

kbrew8991 · 10-21-2009, 03:44 PM

some pictures of the damage would help, I'm having trouble picturing what all is going on...

10-20-2009, 06:04 PM	#1 (permalink)
WildHair No Skills Join Date: Oct 2009 Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	Suspension Repair Question I have a 91 MR2 that has had some sort of damage to the driver’s side front suspension. I'm in the process of repairing the repair work performed by a previous owner. From the damage, it appears the Lower Control Arm (LCA) was forced backwards at the wheel end (towards the rear of the vehicle), which forced the LCA mount on the car frame to spread apart. It appears that this also striped the treads from the bolt/hole of the bolt that mounts the LCA to the frame. Rather than get a new bolt and re-tap the hole in the frame, a previous owner/repairman simply welded the bolt to the frame with the LCA trapped in place. Needless to say, the rubber bushing in the lower control arm didn't fare well and the bolt diameter has been reduced due to wear/corrosion, which allowed significant play in the LCA. I have removed the bolt (after allot of cursing, grinding, welding, and blood) and removed the LCA. Now that the LCA is off, I can see that a previous owner/repairman has welded an approximately 1/8" wide plate to the inside of the frame mount for the LCA (the side the bolt threads engage). Even with this plate the frame mount is spread too wide for the LCA and washer to fit without play. The spreading of the frame mount appears to have taken place completely on the bolt head side (toward the front of the car). I could probably use an air hammer to push the forward mount flange back (toward the rear of the car) and take up the play, but I am worried about the 1/8" plate welded to the mount. Despite the damage to the mount, I cannot see any additional damage to the rest of the unibody (the seams and structure look identical to the other side of the car). However, I do not have access to a frame straightening machine to check the alignment of the car overall. I don't know if the plate was welded in place to move the LCA mount back into the correct position (relative to the other side), or if it was just a half-arsed way to quick-fix the front end. The plate does add a little meat to the aft side of the mount and allowed me to tap the hole in preparation for a new bolt (one that is not striped beyond use). Ok, so that was allot of explanation and background and here is my question. If the plate is incorrectly locating the LCA car-side mount forward an 1/8", what are your opinions’ about how it would affect handling? I'm not sure how this suspension is designed and I really know nothing about car suspension geometry, but just thinking through things logically, here are my thoughts. If the car can be aligned (with the condition above), I don't see straight-line travel being affected. However, as the front suspension is side-loaded (while in a turn), the wheel will either shift aft or forward based on how the geometry was designed and the direction of the side-load. I say it will shift either aft or forward because the rod-link mounted to the LCA and running to the forward portion of the car (forward brace) is connected to the frame via bushings, which will give slightly. Therefore, wouldn't the wheel shift forward (slightly) if the side-load is aimed between the LCA and the forward brace (placing the forward brace in compression) and aft slightly if the side-load is aimed aft of the LCA (placing the forward brace in tension). If the LCA mounts to the car slightly forward of where it is supposed to, then the geometry of that triangle changes and the wheel will shift aft sooner than designed. Right? Perhaps it is too small to even matter, or all this is crazy talk, I'm not sure. But I'm hoping there is a suspension expert out there that can provide some insight or someone with front suspension repair experience. I really don't want to grind that plate off, because then I would need to weld the bolt hole closed so there will be enough meat for me to re-tap the hole so the threads of the bolt will engage. I could do it, it's just in a pain-in-the-neck location for that sort of work and the plate may be there to get the suspension back into alignment in the first place. Help and thanks, Mike.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

10-21-2009, 03:44 PM	#2 (permalink)
kbrew8991 gimme some turns Join Date: Apr 2006 Location: Houston, TX Posts: 1,415 Thanks: 60 Thanked 73 Times in 63 Posts My Google Map iTrader Rating: (4/100% )	some pictures of the damage would help, I'm having trouble picturing what all is going on...