Driveline Hitting underside of floor (at rear)

-
Tjhoward84

Tjhoward84

1969 Barracuda Convertible
Joined
Mar 19, 2014
Messages
171
Reaction score
10
Location
Bothell
Finally found out what the clunking (techincal term) was making all the noise when shifting from 1st to 2nd (Torqueflite 727). Where the driveline and 3rd member meet at the U-joint appear to be hitting the underside of floor just above teh rear axle. This happens during shifting or when I hit an uneven section in the road that cycles the rear suspension. The car ('69 Barracuda Convertible) has a Dana 60 for a rear axle and is lowered about an 1" using the Hotchkis rear leaf springs from their TVS kit. As I see it, I only have a few options:

1) create clearance in the body so the U-joint/driveline/3rd member don't hit anymore
2) somehow rotate the 3rd member so it points more towards the road and not the car. This would require some angled shims on teh axles
3) Airshocks to lift the body away from the axle. I really don't want to do this as I love the stance of the car as it sits right now.

Anyone got any other ideas I'm not thinking about?

Thanks for the help.
 
Check your pinion angle, should have a few degrees towards the ground, around 5*......

Pinion snubber? That will keep it from hitting
 
Possibly option #1, definitely not #2 if the pinion angle is currently correct, and never #3 on a car that you care about.

I'm assuming that your Dana is originally a truck housing without a pinion snubber. Check your current pinion angle. Check your axle housing u-bolts to make sure they are properly torqued. Consider welding a pinion snubber to the floor so that the differtial hits it instead of your drive line; you'll probably have to reinforce the floor before attempting this option.
 
twayne24365 said:
Check your pinion angle, should have a few degrees towards the ground, around 5*......

Pinion snubber? That will keep it from hitting
Click to expand...

The pinion angle should be 2 to 3 degrees lower (toward the ground) relative to the transmission output shaft angle. Of course it depends on what type of suspension you have...leaf spring, 4 link, etc. The "ground" has nothing to do with pinion angle, it's a relationship between the trans/engine and the pinion angle.:

http://www.moparts.org/Tech/Archive/axle/8.html

When you accelerate the pinion yoke rises. When the drive line is under "load" (acceleration) the pinion rises. If the pinion is too high in the static position (no load) it will rise even higher under load causing a vibration. If the pinion angle is too low it will never rise high enough (under load) to properly align under acceleration. The trick is to get the drive line to properly align under acceleration.

treblig
 
twayne24365 said:
Check your pinion angle, should have a few degrees towards the ground, around 5*......

Pinion snubber? That will keep it from hitting
Click to expand...

The rear axle is a Dana 60 posi from Strang Engineering. It was brand new when my buddy put it in a few years ago. It came with (and I still have) a pinion snubber but with the weight on the wheels there is not enough room to put it on. If I install it with the car in the air when I lower it onto it's wheels, the snubber will bottom out on the body of the car. I don't think this would be a good idea.
 
The problem came when you lowered the car. Sometimes there are adverse affects when deviating from stock that need to be worked out...

You need to raise the rear for more clearance. :violent1:

Run a pinion snubber, but it will be hitting the floor board constantly while driving. :banghead:

Leave it the way it is and put up with it... Grin and bear it... :D


I know you like it lowered, but that is making things too tight under there... :???:
 
krazykuda said:
The problem came when you lowered the car. Sometimes there are adverse affects when deviating from stock that need to be worked out...

You need to raise the rear for more clearance. :violent1:

Run a pinion snubber, but it will be hitting the floor board constantly while driving. :banghead:

Leave it the way it is and put up with it... Grin and bear it... :D


I know you like it lowered, but that is making things too tight under there... :???:
Click to expand...

Agreed. The other issue is the Dana 60 rear axle. That thing is huge compared to the stock axel setup that came with the car.

The pinion snubber will go back on for sure.

We will either deal with it or I'll make for room for it to live with a hammer and torch. A little modification is alway necessary. This after verifiying the pinion angle is correct.
 
Treblig said:
The pinion angle should be 2 to 3 degrees lower (toward the ground) relative to the transmission output shaft angle. Of course it depends on what type of suspension you have...leaf spring, 4 link, etc. The "ground" has nothing to do with pinion angle, it's a relationship between the trans/engine and the pinion angle.:

http://www.moparts.org/Tech/Archive/axle/8.html

When you accelerate the pinion yoke rises. When the drive line is under "load" (acceleration) the pinion rises. If the pinion is too high in the static position (no load) it will rise even higher under load causing a vibration. If the pinion angle is too low it will never rise high enough (under load) to properly align under acceleration. The trick is to get the drive line to properly align under acceleration.

treblig
Click to expand...

I meant 5* pointing to the ground simply as a reference,
 
Larger rearend, in a smaller area and lowered. If you have no vibes now, fudging with the pinion angle may get some vibrations.

Raising the rear would probably be the solution, and not with air shocks.
 
unfortunately the problem is the car is too low. (is that possible) these cars would wind up it that situation even when everything was stock due to the springs sagging. they just weren't built with any margin for ride height modification. You my find that the pinion angle is too shallow because of the change in height and find some help in returning it to oem spec. lots of luck in getting where you want to be, My grandfather used to say: "there's more that one way to skin a cat" I think that applies here?
 
I'd check the pinion angle like the others recommended and if it's higher than it should be correcting it will give you some clearance. Other than that all you can do is raise the car until it clears.
 
The rear axle is a Dana 60 from Strang Engineering. What are people's thoughts about adding ladders bars to my setup to stop the axle wrap?
 
I can't see ladder bars helping with it bottoming out when hitting a bump, as you described in the OP.

Raise the rear up a bit.
 
Bad Sport said:
I can't see ladder bars helping with it bottoming out when hitting a bump, as you described in the OP.

Raise the rear up a bit.
Click to expand...

I love the stance of the car and don't really want to raise the rear up at all.

Here is what I am considering. Tell me if I am being stupid.

1) Sell the Dana 60 less my SSBC disk brakes(less than 1,000 miles on it and it looks brand new). Purchased from Strang Engineering for $2,300 plus shipping.
2) Purchase a used 8 3/4 and completely go thru it - new axles, new 2.76:1 gears, posi, powder coat the housing
3) Reinstall SSBC disk brakes
4) Probably have to lengthen driveline.

This swap will get me the clearance I need and also get me the taller gear set so I can run at 60 mph at 2,200 rpm.

Thoughts????

Stupid??
Smart???

The car is not going to be drag raced and autocrossed. It is just a cruiser for the weekends with an occasional "jack rabbit" start from a stop light.

I am worried about the low end if we put 2.76:1 gears in it.
 
2.76 is way too high, IMHO. I'd put very some easy to find 3.23s in it, which are a good all-around gear.
 
69_340_GTS said:
2.76 is way too high, IMHO. I'd put very some easy to find 3.23s in it, which are a good all-around gear.
Click to expand...

All the rear end ratio calculators I've used say with a 25.7" tall tire (which is what I have: 245/45-18) that is the ratio I need to run at 2,200 RPM at 60 mph.
 
Check the pinion angle, something is not right.
What brand springs do you have under it.
There was a manufacture a while back that their springs lost their arc and temper after a few hundred miles, resulting in the same issue you are describing.
 
I just re-read your first post, the manufacture was the same as the springs you have under the car now.
Buy a new set of springs, I bet your problem is solved.
 
sireland67 said:
I just re-read your first post, the manufacture was the same as the springs you have under the car now.
Buy a new set of springs, I bet your problem is solved.
Click to expand...

He has it lowered to begin with because that's the way he wants it. New springs will probably raise it, which he doesn't want.

Raising it an inch or two seems like the rational thing to do, in the grand scheme of things, would and inch higher even be noticeable?
 
Bad Sport said:
He has it lowered to begin with because that's the way he wants it. New springs will probably raise it, which he doesn't want.

Raising it an inch or two seems like the rational thing to do, in the grand scheme of things, would and inch higher even be noticeable?
Click to expand...


Its the spring rate, of the junk springs, other company's sell a spring that actually work.
Unfortunately the ones under his car happen to be from the company that had major issues with mopar springs / torsion bars.
Search this site, there are plenty of complaints.
Yes this same company got my hard earned money (once) for their garbage, never again.
 
Tjhoward84 said:
All the rear end ratio calculators I've used say with a 25.7" tall tire (which is what I have: 245/45-18) that is the ratio I need to run at 2,200 RPM at 60 mph.
Click to expand...

That's about right, I get 2165 RPM at 60 MPH. But you did say this: "I am worried about the low end if we put 2.76:1 gears in it." You should be. It's going be be slow taking off from a stop. Why is "2200RPM @ 60 MPH" so important? With 3.23 gears it'll be turning 2533 RPM. What's wrong with that? Heck, I have 3.55s in my Dart (340 engine) and it runs great at 2800 RPM at 60 MPH.
 
You must log in or register to reply here.
-

Back
Top