Posted: 5/20/2026 5:37:57 PM EDT
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Son is chasing a drivetrain vibration in an LS swapped ‘96 Mustang. He’s got all driveline angles correct compared to his stock Mustang. But around 40-50 MPH, gets a bad vibration. He’s already replaced all the rear axle housing bushings. Driveshaft was balanced when he had it cut down recently and had it rechecked. Although I’m not sure if he ran it at these speeds on the lift with the wheels off yet. Coworker is bringing in a dial indicator tomorrow. Today he just did a quick screwdriver against the hub check and it appears slightly warped. His other thought is something is bad in the 6 speed automatic transmission. He’s already swapped the tail shaft bushing. |
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Get going at 50 mph, shift to neutral, does the vibration go away? If it does, its in the driveline somewhere. Its possible that an axle/hub/rotor is out of balance. Put it up on a lift and run it, holding at 50 mph and look to see what is shaking. Before driving it, note engine RPM at 50 mph, park it, run the engine at that rpm and see what shakes. If it is only affected at road speed, it's in the rear axle, or driveline. I've had a truck that had an out of balance brake drum and shook itself half to pieces at 50 - 55 mph. (I'm that old, i drove something with drum brakes) Put it on a lift and run it up to 50 mph. You should be able to locate it. If it seems to be in the trans, drop the drive shaft, strap a plastic bag over the tail shaft so it doesn't blow trans fluid everywhere, and run it up again... I've never seen a transmission cause a road vibration, but it is possible.. |
Another old guy
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Does the Mustang have a center driveshaft bearing? Been 15+ years since I was under one, I don't recall and am too lazy to Google. If it does, that can also be the culprit. Bent axle flange should cause issues at a wider range of speeds. Check all engine, transmission, and axle mounts too for damage. A torn mount can cause it. Like others, I have never heard of transmission issues causing vibrations at speed. I assume it is purely speed-dependent and not rpm-dependent? If the latter, can also be the harmonic balancer. |
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The last time I saw a actual bent axle, it wasn't vibrating. It had a weird side to side wobble in the rear. Of course the boss didn't believe me that the axle was bent. If you're going to spin the axles in the air do it on jack stands so the axle is carring the weight of the car rather than hanging by the shocks. |
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A torque converter slipping could be confused with a vibration. Is the vibration in the seat / floor or steering wheel. Bad u-joints or loose straps can cause vibrations as well as a center bearing on a two piece driveshaft. If the u-joints have grease fittings, grease them. Do all 4 caps produce grease? Thats one way to tell if u-joint is bad. Lifetime u-joints will show major signs of rust around the cap to joint connection when they are bad. Just some suggestions. Also, dont overlook tires. Slipped belts will make a hell of a vibration that will get worse before it blows. Worth looking those over too. After rereading the op, it sounds like he is testing the build off the ground before running it? If so, those driveline angles must be taken with the vehicle level and with its load on the suspension and settled. To answer the question, with out the tires on and to feel a vibration and not really seeing the axle wobble while in the air, I would think either axle isn't the culprit. I think the axle being bent to cause a vibration would be easily seen. Is this a vibration that happens while driving with tires on the ground and at those speeds? |
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Check the transmission mount and motor mounts. I chased a vibration for a long time (new wheels, u joints, balanced driveshaft, even did new axles). Recently found that my damn transmission mount was shot. Seems much better now. Im due for motor mounts too, but they're a pain in the ass to get to. |
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Originally Posted By jake03: Did it get mustang'ed into a curb and bend the axle flange? Not a curb, but hooked up hard running slicks and launched and went sideways landing on the one axle. This was back when he was running twin turbos. He switched to one turbo. But axles are Moser Streets, 31 spline. As far as other questions, brand new K member with all new urethane mounts, brand new transmission crossmember from the same company with new urethane mount. Just replaced the rubber mounts in the rearend housing and new control arms. Driveshaft is a one piece unit, no center bearing. I was mistaken, he was testing everything with it sitting on stands, under the axle to load the chassis. Just called him up. He’s going to pull the driveshaft and cap the tail shaft and try running it up as suggested. He did just get his torque converter rebuilt by a reputable shop. I think it’s a 2500-2800 stall. He also replaced the flex plate with a high performance heavier duty unit since OEM crack all the time. He said he’s about to pull the plug on this project and strip it all down and start over down the road after he buys a house with a garage or shop. His current employment in the shop he’s got now comes to an end at the end of June. Owner sold the building because his boss was iffy with keeping the shop open with another lease and was doing month to month. He’s just trying to knock this vibration issue out before the shop is gone, or the car is done with. |
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Latest update. Axles are perfect. But, I told him to take a closer look at his “new” driveshaft and U joints. Told him I don’t care how new it is, examine it. Total mess. With the new K member/cross member it’s too short and driving it around with all the wrong angles, he destroyed the U joints in short order. Also, he was running a cheap Amazon/Temu yoke. Completely wrong one for his transmission. He was hoping to avoid spending $350 on new axles. He did. But now he is getting a new DS made to the tune of $500 with a correct yoke. Attached File |
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Originally Posted By Borngrumpy34: Feels good to finally find a problem! Well, he hasn’t bought the DS yet. He’s skeptical about everything since he’s fired the parts cannon at the issue. I told him it was an old, well used car and parts. Everything replaced was necessary even if it didn’t fix the actual problem. He’s going to pause because someone (him) left an ink pen in the washer and it ruined $500 of his wife’s nicer, high end clothes she has to wear to work.  She’s in retail at a high end clothing store in Charleston. Cannot show up wearing Target or Walmart clothing to work. |
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Originally Posted By ScottsGT: Latest update. Axles are perfect. But, I told him to take a closer look at his "new" driveshaft and U joints. Told him I don't care how new it is, examine it. Total mess. With the new K member/cross member it's too short and driving it around with all the wrong angles, he destroyed the U joints in short order. Also, he was running a cheap Amazon/Temu yoke. Completely wrong one for his transmission. He was hoping to avoid spending $350 on new axles. He did. But now he is getting a new DS made to the tune of $500 with a correct yoke. https://www.ar15.com/media/mediaFiles/32016/IMG_2719_jpeg-3765872.JPG When I ls swapped my camaro, Holley shifted the engine/trans forward .625" and I had a nasty vibration until I got a longer driveshaft. I used Denny's driveshaft, did it all over the phone. |
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Originally Posted By Spaceboy: Wow, I was going to suggest that, had it all typed out even and deleted it because I thought it was too fringe of a case. When I ls swapped my camaro, Holley shifted the engine/trans forward .625" and I had a nasty vibration until I got a longer driveshaft. I used Denny's driveshaft, did it all over the phone. There’s a really good DS shop in Charleston he’s working with. The guy actually handed him the correct yoke, told him to take it back to the shop and give him the measurements. I threw the idea at him to run a DS spacer at the pinion. They make a 1” for the Fords. And have the shop install the correct yoke. But he would still be a 1/2” too short. |
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Originally Posted By Ops: Get going at 50 mph, shift to neutral, does the vibration go away? If it does, its in the driveline somewhere. Its possible that an axle/hub/rotor is out of balance. Put it up on a lift and run it, holding at 50 mph and look to see what is shaking. Before driving it, note engine RPM at 50 mph, park it, run the engine at that rpm and see what shakes. If it is only affected at road speed, it's in the rear axle, or driveline. I've had a truck that had an out of balance brake drum and shook itself half to pieces at 50 - 55 mph. (I'm that old, i drove something with drum brakes) Put it on a lift and run it up to 50 mph. You should be able to locate it. If it seems to be in the trans, drop the drive shaft, strap a plastic bag over the tail shaft so it doesn't blow trans fluid everywhere, and run it up again... I've never seen a transmission cause a road vibration, but it is possible.. You are more than 3 years old then. Tacoma had rear drums until the introduction of the current generation in 2023. Everyone else had rear disk for a long time. Though a solution has been found I wanted to add to look for an out of center wheel installation. I had a hell of a time getting the right centering rings for my Audi wheels and it would shake the car like crazy above 50MPH. |