Questions on rear end of 90lx

logonhappy

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May 28, 2021
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Well I am back, with another question. I started looking into why the rear end on my 90 mustang lx 2.3 converted carbbed 5.0 hatchback is sagging. I already replaced springs, started looking and saw atleast the drivers upper torque box is ripped. I haven't checked the others quite yet. So first can ripped torque boxes cause my rear end to sag? Second if they are just slightly torn am I good to weld the seams and weld in reinforcements? I'm just trying to figure out if I should buy replacement boxes if I go ahead doing the repairs, otherwise I might just sell the car. Thanks in advance
 
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JasonRP

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May 25, 2018
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what would make the torque boxes rip? I'm assuming the 2.3 and 5.0 used the same torque box metal/thickness/reinforcements? Is your 5.0 motor making a LOT of power? Did you replace the upper rear control arms with poly instead of rubber? Not being snarky, I'm genuinely curious, I knew the torque boxes could get beat up, but I thought that was from dudes running stroked/power adder mills? (Maybe that's what you've got?)
 

90sickfox

Wasn't a pretty sight...and I've got big hands
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Mar 2, 2015
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what would make the torque boxes rip? I'm assuming the 2.3 and 5.0 used the same torque box metal/thickness/reinforcements? Is your 5.0 motor making a LOT of power? Did you replace the upper rear control arms with poly instead of rubber? Not being snarky, I'm genuinely curious, I knew the torque boxes could get beat up, but I thought that was from dudes running stroked/power adder mills? (Maybe that's what you've got?)

Rear torque boxes can rip on any fox that's driven hard. Street tires and hard launches can tear torque boxes. The metal gets fatigued over time. I've had cars with stock bushings that destroyed torque boxes.
 

90sickfox

Wasn't a pretty sight...and I've got big hands
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If you have cracks they can be straightened, welded up, and reinforcements installed. The proper way is to find the end of the crack and drill a hole in it first so it won't spread.
 

logonhappy

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May 28, 2021
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I'm not making alot of power maybe around 260hp max but that would still be pushing it. Maybe after my new cam. But the car has been driven hard not much by me but the couple previous owners. Glad I shouldn't have to replace the boxes, but can the bad boxes cause my rear end to sag?
 

90sickfox

Wasn't a pretty sight...and I've got big hands
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Bad boxes and / or bushings can cause the rear to sag. Do the hatch and door gaps line up ?
 

logonhappy

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May 28, 2021
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Doors and hatch appear to be fine. Hatch didn't close nicely when I got it. I got a bushing for the striker for the hatch and closed just fine then. Drivers door does sit a lil low all together but the hinges are bad or the pin bushings
 

revhead347

Apparently my ex-husband made that mistake.
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It's probably the bushings in the control arms. Notorious for causing sagging issues. Time for some better lower control arms.

Kurt
 

KRUISR

5 Year Member
Apr 16, 2015
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Pictures of torque boxes and lower control arms/rear suspension can help others with that answer.

You don't have a mechanic fix your car without looking at it. Same thing helps here.