Technical 51 Plymouth lowering question

I lowered my 51 Plymouth 3 inches in the front and back now I'm having these grinding and vibration in the floor. Do I need to shorten the drive shaft or what could it be I have lowered cars before and never had this problem

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On a modern set up you're supposed to have a inch of free play between the end of the shaft & the end of the receiving hole. If there's no evidence of interference in the tranny tunnel of lack of clearance.

 

All is clear there before I lowered it it was fine after the 3 inches in front and back sounds like its binding

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Push the rear axle back 1" on the springs & re-drill the locating hole in the lowering blocks. That should allow the driveshaft to "float".

You're jambing the driveshaft tight between the transmission and the axle, and it's grinding up the springs inside each end. You've possibly thrown the universal joint trunions out of alignment. If so the shaft will wobble until it's re-balanced.

 

maybe your drive shaft is hitting the hump, put it on a drive on hoist and look.

 

That's true. It could be rubbing the body/frame. I don't think so if it was only lowered 3" from stock.

BUT if it was lowered 3" from the original already sagging springs, then it could be 5" in reality, and that could be the limits of travel.

But I think if it was rubbing the body, it'd make a real noise, kinda like smacking the body grinder on a fender at 2AM, when you went over the slightest bump.

QUESTION: How much vibration accompanied the grinding noise? & at what speeds did you experience it?

 

Nope that's all clear

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The noise is coming more from the back of the motor not a rubbing noise a grinding noise it gets bad in 2nd and 3rd grinds the hole time. Was under the car today all looks good everything is tight . it wasn't doing it before I lowered it that has me puzzled the most. Out of gear it Push's and smooth no noise in gear its bad kinda sounds like the motor is shacking apart lol

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It's not the parking brake dragging is it? That would be the back of the trans, not the engine though.

Will the drive shaft "float" fore and aft when the car is siting still? There's a spring on each end, and it "floats" between them as it turns. You'll need the brake off and the trans in neutral to float it by hand.

 

while its on the hoist, put a stand under pass side axle housing, raise tire off hoist, have yer buddy start, put in gear, and let clutch out slowly and watch, problem solved.

 

We took the drive shaft off today because I thought the drive shaft had to be shorten while looking I found the 2 strings on each end I took one of the springs out to give less push forward it did free up some but the noise is still there

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So did it bind? Was there vibration or just noise?

(BTW, You kinda need both springs for that shaft to work right.)

I had difficulties with my own stock Detroit joint driveshaft, because the cross pin bore on one end was worn. It wouldn't stay in balance & vibrated badly.

I replaced the whole shaft with a custom-built one with modern Spicer joints & all that went away.

BUT, when I lowered the front of the car and raised the rear, the length changed, and I started to vibrate again, as the slip joint was not engaged enough. I made a 1/4" shim for each end of the shaft, to get more engagement.

So you see where I'm going with this: the shaft needs to be the correct length for how the car usually sits.

 

thats why i thought i would need to get the shaft shorten because you can see when you lower it the shaft pushing forward...that why i took out that back spring the shaft still has the back and forth movement but all the vibration is coming from the front and not the back

 

OK, so there is vibration.

I believe then that you've jambed the u-joint up and thrown the front one out of alignment. The driveshaft will be wobbling visibly by now & you're chewing up the internals of the u-joint.

 

I'll check to see if its wobbling but I checked it yesterday and it wasn't it was straight as a bell

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make sure all the driveshaft bolts are still tight too.

 

Have you checked your pinion angle?

 

Yep they are I took the drive shaft off and put it back on after ibtook the rear spring out I kept the spring I can put it back in if you think I should

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Yes that didn't move any if at all the only movement I seen was the drive shaft move forward

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Your pinion angle is probably going to be quite low, as member Chopped51 implies.

If you rotate the axle up with wedges to correct this, it'll shorten the driveshaft again, so get that set up before cutting anything.

 

OK I'll check that out

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Also if the pinion was off wouldn't I get shaking from the rear end? Because there's nothing at the rear

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Does your car have the original style Ball & Trunion joint? or has it a proper universal joint.....the ball & trunion will have a leather or possibly a rubber concertina cover over the "joint"........if you've lowered it that much and its a Ball & trunion type the driveshaft is located further forward with the cross shaft and balls further into the body of the joint and that maybe where the vibration/noise is coming from........if you have normal cross and roller type universal joints then disregard what I have just typed.....lol...........andyd

 

Yes has the og drive shaft with the springs ends

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Those originals are often called "Detroit" U-joints, where the modern ones are called "Spicer" U-joints.

And if the pinion angle is way off, it often presents itself by throwing the driveshaft out of balance. It does this by wedging the joint "sideways" until the cross-pin in it goes off center.

It could happen to one or either, but most commonly it's the front that goes off.

See, if the pinion angle is off, the angle at he trans will be off too. Just not quite as much, as the axle rotates up in the front as the body drops.

In fact, the pinion and trans tailshaft should be parallel in every view, but can't be all the time because of the rotation mentioned. Normally you set them up to be parallel at the body stance you intend to run normally.

If the driveshaft is out of wack now, that's causing the noise. If it's not the driveshaft I'd be surprised, because if it was the tailshaft bearings (the other thing right there) you'd be complaining about trans oil all over the floor by now.

 

I think andydodge has the answer...

 

Put it in a lift today everything is square the pinion is just a little low I mean little where the guy said it should bother anything

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Are you sure it's not the parking brake?

I'd stick jack stands under the rear axle, put the front tires up on blocks to the correct stance, and run it with the wheels off the ground so you can crawl under & see what's what while the suspension is compressed and it's running.

 

im gonna stop it by a transmission place tomorrow and let them check it out and as far as the ebrake i pull it whille going down the road and theres no nosie just alot of vibration from the motor its really bad around 25 to 40 mph

 

alos thanks for all the help Ulu....