Driveline Hitting underside of floor (at rear)

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The car has the Hotchkis TVS front suspension system and the matching rear Hotchkis springs. I contacted Hotchkis and they gave me the dimension from the center of the wheel to the underside of the wheel lip opening (12.5 inches) for the rear tires so I could check if the leaf springs were saggin. I measured it and they are dead nuts on 12.5". The Hotchkis leaf springs lower the car 1" from stock and that appears to be where it's at. The issue still is the Dana 60 is a much larger (physical size) rear end compare to what the car came with. Before swapping out the rear ends, I will have the pinion angle checked and make any adjustments necessary. If that checks out, I really only have the swap out option which I'm OK with. It fixes several issues with one action.
 
Did you use the Hotchkis front hangers that come with the springs? If so, put the stock ones back on. If it is a Dart, 111" WB, it is to low. I wouldn't ditch the Dana for anything. I do know the Hotchkis springs suck with wrap, they will say they're fine but they are not. I made some Assassin bar knock offs for mine, I have probably 5" of clearance between the driveshaft and tunnel at rest but without some kind of traction bar, it will hit under acceleration.
 
72BBSwinger said:
Did you use the Hotchkis front hangers that come with the springs? If so, put the stock ones back on. If it is a Dart, 111" WB, it is to low. I wouldn't ditch the Dana for anything. I do know the Hotchkis springs suck with wrap, they will say they're fine but they are not. I made some Assassin bar knock offs for mine, I have probably 5" of clearance between the driveshaft and tunnel at rest but without some kind of traction bar, it will hit under acceleration.
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It's a1969 Barracuda convertible. Don't know if the Hotchkis front hangers were used or not but would assume so. I got the car after my best friend passed away from a motorcycle accident 2 years ago. Not sure what he used. They look fairy new so I'm going to assume they came with the kit. Again, the stance is prefect - don't really want to change it and also don't want to get rid of the Dana. I've nothing but glowing remarks about that rear end. However, I do think it is overkill for the car as it will never be raced or driven really hard. Do you have pictures of your "Assasin Bar Knock Offs"?
 
72BBSwinger said:
Did you use the Hotchkis front hangers that come with the springs? If so, put the stock ones back on. If it is a Dart, 111" WB, it is to low. I wouldn't ditch the Dana for anything. I do know the Hotchkis springs suck with wrap, they will say they're fine but they are not. I made some Assassin bar knock offs for mine, I have probably 5" of clearance between the driveshaft and tunnel at rest but without some kind of traction bar, it will hit under acceleration.
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If I was to replace the leaf springs, what would you suggest? Just weighing all my options.
 
If I were you I would locate 2 semi-long leafs and add those the existing springpacks to firm them up a bit. Then maybe install a 0.5" or 1" lowering block to bring the stance back to your liking.

As an even more cheaper solution you could also try and add sturdy spring clamps to the leafsprings to limit springaction and axle windup.
 
Just get some Caltracs and call it a day. Then you can leave everything else as is.
 
Tjhoward84 said:
If I was to replace the leaf springs, what would you suggest? Just weighing all my options.
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Replacing the leaf springs probably won't help if puts the rear end in the same place (vertically). I would think that if you put the car on a lift you could look underneath and see where (exactly) the rear end is hitting the body. If it's hitting where the u-joint is located then it's your pinion rising too far "up" (pinion angle). If it's hitting on the top of the center section then you simply don't have enough clearance for that differential with the body as low as you have it. You need to determine "where" the differential is hitting before you spend any money attempting to fix the problem. It should be obvious where the rear end is contacting the body. I've had similar problems and I always put the car on a lift to see where the rear end is hitting the body. You need to identify the exact origin of the problem before you start drawing conclusions.
PS - If I remember correctly you've already looked under the car and you said that the yoke/u-joints are rising up and hitting the body. If this is correct then you need to verify your pinion angle to see if (maybe) the pinion angle is set too high?? Even if you replace the springs it won't change the pinion angle?

treblig
 
I made my suggestions based on having the same springs. I have 1" longer rear shackles, raised/lowered the front eye, added 2 half leafs to the bottom of the spring packs and STILL needed to add an anti-wrap device.

 
Theres lots of really good suggestions here.
If the pinion angle turns out to be ok, and the front spring segment is ok and you really really don't want to change the stance, then I think you only have two options, which have already been mentioned;
1) swap out that Dana for a smaller rear, or
2) modify the floor.
Thing is; if you are running big power,or dragging it,the Dana could be justified(since its already in there).
And modding the floor on a convertible, may take some resale out of it.

So I vote to slip a smaller rear under there, with the correct pinion angle and a set of nice street springs, possible re-arched to set the stance. A bit of work, to be sure, but hey, winter is coming
 
Treblig said:
Replacing the leaf springs probably won't help if puts the rear end in the same place (vertically). I would think that if you put the car on a lift you could look underneath and see where (exactly) the rear end is hitting the body. If it's hitting where the u-joint is located then it's your pinion rising too far "up" (pinion angle). If it's hitting on the top of the center section then you simply don't have enough clearance for that differential with the body as low as you have it. You need to determine "where" the differential is hitting before you spend any money attempting to fix the problem. It should be obvious where the rear end is contacting the body. I've had similar problems and I always put the car on a lift to see where the rear end is hitting the body. You need to identify the exact origin of the problem before you start drawing conclusions.
PS - If I remember correctly you've already looked under the car and you said that the yoke/u-joints are rising up and hitting the body. If this is correct then you need to verify your pinion angle to see if (maybe) the pinion angle is set too high?? Even if you replace the springs it won't change the pinion angle?

treblig
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Treblig - You are correct. We've already put the car on a lift and verified the U-joint/pinion is hitting the underside of the body. My next step will be to check the pinion angle, make any necessary adjustments before buying parts.

Thanks for the advice.
 
Pinion angle is checked against the driveshaft. The front u joint angle is the transmission output shaft checked against the driveshaft also. Both can be adjusted. Rear angle with leafs should be 5-7° nose down against the driveshaft. Will not make any difference with your clearance issue. That 5-7° is for drag racing. For cruising down to 2-3° is okay. Do not run 0°!
 
hangn0ut said:
Pinion angle is checked against the driveshaft. The front u joint angle is the transmission output shaft checked against the driveshaft also. Both can be adjusted. Rear angle with leafs should be 5-7° nose down against the driveshaft. Will not make any difference with your clearance issue. That 5-7° is for drag racing. For cruising down to 2-3° is okay. Do not run 0°!
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this is wrong.pinion angle the dirrerence between transmission angle and dirrerential angle,driveshaft has nothing to do with it
 
The ideal is to have the front and rear crosses at some non-zero angle relative to the driveshaft(for jdsduster;that puts them relative to eachother),but in opposite directions. This would cancel out the vibration. However, since the rear joint is captive to the rear suspension which is constantly moving and changing, a compensating factor needs to be included for worst case situations. Worst case situations are when load is applied from the engine and during braking. Another compensation factor is needed for the springs. If they are soft, they will wrap up under power and yank the cross way up. If they are stiff, less yank will be experienced.Another compensation factor would be for use. A drag car might/will require a different factor than a cruiser.
-So then the rear compensation factor could be from zero to several degrees. That is to say; If the front angle is 2*, then the rear would be 2*(in the opposite direction) plus the compensation factor, which could be from zero to about 5*; always in the opposite direction, from the front.See, at the front, the shaft usually, almost always, travels downwards from the tranny. Therefor when it gets to the back, the driveshaft needs to travel back up to the diff yoke. When viewed or compared to the diff, this is called nose-down cuz the pinion is down compared to the shaft.Now with your extremely lowered convertible,and the big Dana back there, I have no way of knowing in which direction your d-shaft is traveling as it leaves the tranny. It may even be traveling up! If thats the case, you are in trouble. This cannot be compensated for, and major changes are in your future.
Guys have already mentioned some nose-down numbers, which are valid.With soft springs, 7* down is typical.
I would add that the best number for you,might be illusive. This is mostly cuz of the soft springs.
If you change springs, you will likely be able to tighten up the compensating factor.

Also, like mentioned, an anti-wrap device might cure your problem, especially if combined with stiffer shocks.But then, stiffer shocks kinda kills the cruiser aspect.Unless the car is full of passengers, in which case stiffer springs is a better option. So you can see that your situation is somewhat unique, and some compromising may be necessary.
All the best to you.
 
The best way that I've found to set the correct pinion angle is to remove the drive shaft and put an angle finder on the back surface of the trans tail shaft (where the seal is). This will tell you how many degrees the drive line is pointed down (typically). Then you put the angle finder on the flat (front) surface of the pinion yoke. Sometimes you have to get a piece of flat metal to hold on the pinion yoke face so you have a nice flat surface for the angle finder. This will tell you how many degrees your pinion is pointed down (or up). The pinion should be 3-4 degrees "down" with respect to the trans angle BUT it depends on your type rear suspension of course.
The whole purpose of setting the pinion angle is so that when you accelerate the pinion will rise and get aligned with the drive line (the pinion and the engine/trans drive line should be parallel during acceleration). A pinion will typically rise 3-4 degrees under acceleration "depending on your rear suspension". 3 to 4 degrees is a relative measurement, in the end you set the pinion to an angle that gives you the best results!! Go HERE:
http://www.moparts.org/Tech/Archive/axle/8.html

Remember your pinion WILL rise when you accelerate the trick is to find out "how much" it rises.

Treblig
 
Under hard acceleration the u joints and attachments (d/s&pinion) are forced into a straight line,dependent on power. This is why more pinion angle will make a car hook better. But it will mph slower as it takes hp to straighten these angles.
 
If the trans is 3* degrees tailshaft down then you want the pinion 3* nose up under power. This usually means the pinion needs to be from 1* degree nose up to 3* nose down at rest to compensate for wrap. With the Hotchkis springs its a crap shoot because of the amount of wrap is ridiculous. If you are to far nose down at the pinion you end up with vibration at cruise and decel.
 
I just read the moparts tech article. Interesting. The first section "setting pinion angle" appears to me to be for everyday driver type cars. It makes sense for production cars,not high performance modified cars. The second section is taken word for word and picture for picture from the mopar performance chassis book. Its interesting that a picture there shows a driveshaft angle being measured. Third section seems to draw information from both previous sections and as such is rather confusing. For myself its obvious. I use the performance chassis book as the base for mods. Of course its highly biased towards drag racing but then so am I.
 
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