Front Suspension Bottomed Out

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steptoe

steptoe

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I have a problem with the front end of my '75 Dart bottoming out. I mean sitting on the bump stops. Looks like a car without any bars installed. I have new shocks and rebuilt the upper and lower control arms with new bushings and ball joints. Didn't help. I can adjust and set the ride height to a normal stance and bounce the car repeatedly. Everything is fine UNTIL the car moves forward 5 - 10 feet. The front end immediately drops until it bottoms out. Jack the car back up until the weight is unloaded and sit it back down - it looks fine again. Move the car 10 feet and it drops again. I have to suspect it's a torsion bar or mounting problem. The bars appear to be OK and the adjusters are working. I also looked under the car while it was bottomed out and the torsion bar adjusters are still lined up on the bars. I had suspected they were jumping off and allowing the suspension to unwind. I guess whatever it is requires the tires to move which allows the suspension to change. Remember the old Volkswagons? Jack up the rear end and the wheels tucked under. Sit it down and they stayed tucked under UNTIL you moved the car. Then the wheels would return to normal. This is what I have going on. I cannot find anyone local who is familiar with torsion bars but have read that the front or rear mounts could be rusted or damaged. I cannot find any rust or damage. Could the bars be slipping in their hex head mounts? If so, would they only slip when the car is moving?
 
steptoe said:
I have a problem with the front end of my '75 Dart bottoming out. I mean sitting on the bump stops. Looks like a car without any bars installed. I have new shocks and rebuilt the upper and lower control arms with new bushings and ball joints. Didn't help. I can adjust and set the ride height to a normal stance and bounce the car repeatedly. Everything is fine UNTIL the car moves forward 5 - 10 feet. The front end immediately drops until it bottoms out. Jack the car back up until the weight is unloaded and sit it back down - it looks fine again. Move the car 10 feet and it drops again. I have to suspect it's a torsion bar or mounting problem. The bars appear to be OK and the adjusters are working. I also looked under the car while it was bottomed out and the torsion bar adjusters are still lined up on the bars. I had suspected they were jumping off and allowing the suspension to unwind. I guess whatever it is requires the tires to move which allows the suspension to change. Remember the old Volkswagons? Jack up the rear end and the wheels tucked under. Sit it down and they stayed tucked under UNTIL you moved the car. Then the wheels would return to normal. This is what I have going on. I cannot find anyone local who is familiar with torsion bars but have read that the front or rear mounts could be rusted or damaged. I cannot find any rust or damage. Could the bars be slipping in their hex head mounts? If so, would they only slip when the car is moving?
Click to expand...

Do you have the upper control arms reversed (wrong sides)? This will cause the car to do what you are describing. And contrary to what some say, they can be put on the wrong sides. Another possible culprit is excessive toe-out and/or neg camber. Have you had the front end aligned?

Once it has dived after driving that 10 feet or so, back it up and see if the car returns to normal stance. Severely dragging brakes would cause something similiar to this.

Torsion bars would not cause the problems you are experiencing. If the bars were weak, you would have to keep adjusting them up each time it got low. The chances of the bar turning is the socket are about one in a million and if it turned, you would most definately hear it. If the t-bar cross-member is damaged or rotted you would be able to see it and know it was the cause.

Larry
 
Very unusual problem to say the least. :toothy10:

One other thing you can check is the area where the lower control arm pin goes thru the X-member. There is a sleeve welded to the backside of the X-member on both sides. Make sure the welds are not broken. If they are, the lower arm can move as the car goes forward or back.

Just another idea. Good luck.
 
6pk2godemon I like your reply about a bad weld but what is a lower control arm pin? Are you referring to the pin that goes thru the bushing on the lower control arm. It has a hex head on one end to attach the torsion bar. The other end goes thru the lower control arm bushing and has a bolt to attach it in place. I am going to remove the torsion bars again and get a 2nd pair of eyes under there. Something is broken, rusted, missing, etc. This is not an alignment problem. The car won't fall down because of toe-in, camber, and caster. It may not steer well but it will stand up.If I had a coil spring set-up then I would say the springs are missing or totally broken. Even a broken coil spring would hold some weight. The body is sitting on the top of the tires -literally. Bottomed out. What holds the car up - TORSION BARS. What is controlling the torsion bars - I don't know. Help.
 
Yes steptoe. The pin is pressed into the lower bushing, then slides into a sleeve in the X-member and attaches with a nut @ the front of the X-member. The sleeve I'm referring to is welded to the X-member @ the backside.

It's a longshot, but be sure the weld is not broken on either side in this area.
 
I have to wait until Monday to tear it apart again. I am certain now that I will find damage in the area where the sleeve goes thru. Thank goodness I have a friend who can weld. I am looking forward to finally getting this straightened out. I will keep you posted. Thanks again, David
 
That's probably the lower control arm "pivot shaft" you are referring to. Are you certain you torqued down the nuts properly on the ends of the shafts that go through your K-frame?

Jerry
 
Jerry. Well, I tightened everything to whatever torque values the book called for. I don't understand what you are asking? This problem was there when I bought the car. I took it apart, rebuilt both upper and both lower control arms. I also replaced the calipers and brake pads and all new wheel bearings. David
 
what holds the torsion bars and keeps the front end up is the mounts next to the trans, crossmember. i would think it might be those recievers broke free or you might have somehow indexed the front at the pivot wrong. check if the front adjuster bolts are seated in that cam ok or did they miss. did you feel tension when you tighten those adjusters?
 
take pics of the rear anchors in the trans xmember and the torsion bar adjuster bolts.
 
I don't understand. You described exactly what's happening when talking about the Volkswagen. The tires do move inward when the car is in the air, and hold it up until it rolls forward. Adjust the ride height on the ground, or crank them up farther while in the air and check height after rolling the car several feet.
 
375instroke. We found out what it is. The "sleeves" in the rear of the K-frame have broken their welds and cannot support the torsion bars properly. This allows the lower control arms to shift outwards ONLY WHEN THE CAR MOVES. The reason the arms do not shift when lowering it down off the jack is because of friction. You don't lose the friction until the tires move. (the VW theory) As the control arms shift outwards, the upper part of the tire cannot shift because the upper control arm is holding it's position. This makes the camber change drastically resulting in the suspension pushing up. This gives the illusion of the car dropping down on the tires. I hope I explained this right. We are going to weld the "sleeves" this weekend. I sure hope this works. David
 
You don't even need to roll the car just turn the wheels lock to lock in both directions and the tires will scrub back to their static position.

If continual cranking of the adjuster always winds up with the control arm on the stops something is giving that shouldn't. The most likely candidate is the rear torsion bar mounts. Another posibility is stripped threads in the adjuster bolts. Unload the car and there is enough bite to allow you to crank them but put the weight on them and they slip back.

Looks like I was typing when you posted, glad you found the issue. I had a broken weld once. Didn't change the ride height but the car wouldn't hold the camber adjustment and it banged as the suspesnion loaded and unloaded.
 
David, You shouldn't have any problem once the sleeves are welded back into place. Just be sure they're centered....:thumblef:
 
Well was I wrong. Jumped that gun too soon. Thought the K-frame "sleeves" was the problem. NOT! Front end still falling and the K-frame sleeves are just fine. The pins (or whatever you call them) that go thru the sleeves have a tiny bit of play in them, but it seems to get tight when the nut on the front is tightened. Three people worked on this today and no one can find the problem. We all agree that the problem is NOT the torsion bars or upper control arm assembly. The bars were totally removed and all of us inspected them. They are installed correctly and have V8 part #'s. We found nothing missing, broken, rusted, etc., at the rear and front bar mounts. The bars also fit the sockets. We have concluded that the problem has to be with the lower control arms. We just don't know what is wrong with them. Could it be possible that they are the WRONG control arms for this car? Are there different versions for the various bodies?
We do know that something is not supporting the weight of the car after the car moves. The car drops about 6-7 inches. The upper control arm may allow a change in camber but it does not support the weight of the car. Only the lower control arm does this thru the torsion bars and mounts. I certainly could use an old school Mopar mechanic about now. Thanks everyone, David
 
When the suspension collapses does it make a noise or does it just quietly settle? I'm leaning towards stripped/worn out adjusters or the spring pockets in the torsion bar crossmember are loose.
 
Did the torsion bars slip out or did you have to drive them out? The torsion bars are not a slip fit in the pockets. If it is you have a torsion bar pocket that is worn out and needs to be replaced.
 
i would mark the adjuster bolts and make a line from the torsion bars across the pivot then the lower arm. this should tell you what piece is the problem. im still leaning towards the adjusters or the recievers in the crossmember.
 
You say you adjust it and it's fine, then you drive it and it collapses. How do you adjust it? Are you out of adjustment? Set the car on the ground and crank the adjuster until it is at the height you want. Drive the car and see what happens.
 
had something similar happen to my dart years ago. turns out the upper control arm cams woud feel tight when tightening them but wern't actually tight. don't remember how i figurd that one out beause it was so long ago. put new cams in and all was fine. it was really pissing me off because everything up there was new. it has to be something stupid.
 
The front end "settles" or drops very quietly when moving the car. Set and adjust the ride height before moving and everything looks good. Put the car in gear and move forward about 10 feet at 2 mph and the front end settles as though the front tires just went flat. It just goes down smoothly and quietly. If we jack it back up, it will return to normal. We also had to drive the torsion bars out of their sockets also. Everything looks good to the untrained eye. We cannot find anything to cause this problem. It has to be something to do with the lower control arms, but WHAT? Where have all the old Mopar mechanics of the 60's and 70's gone? This doesn't make sense. I can't see the forest for the trees in the way. Or, maybe I have this problem ---:bootysha: Thanks everyone, David
 
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