Wobbly props?

Anonymous · Post by **Anonymous** » Sat Mar 26, 05 5:03 pm

I was looking around on the old message board and found the topic below;

http://www.mopartalk.co.uk/discus/messages/6/2327.html

I know Dave had a fright when he came face to face with the propshaft on the charger (almost literally) and there is now a new prop with UJs on my car. But I still have a vibration on the car which I guess has been there since ages ago. I dont see it as a problem but as im sorting some stuff out on the car this is one of the jobs thats on the list.

Now Im not sure but I dont think that the prop has been balanced unless it was before Dave took delivery. Ive had all the wheels balanced and, I do think its worth getting the prop balanced. Is there a way to check if a prop is out of balance? The vibration happens at about 80mph, Ive rechekced that all wheel nuts are tight and no weights have fell off.

Anyway, does anyone know where and how much to pay for prop balancing?

Pete · Post by **Pete** » Sat Mar 26, 05 6:38 pm

Mark the position of the UJ's on the Rear Axle; unbolt them and turn them around 108 degrees and test - it may improve it or make it worse but it may help isolate the prop as the problem. Some of my cars hve had vibration from the rear - some were tyres (despite being balanced - Rob Tyrell re-balanced them PROPERLY and it was then OK); some I think are rear axle Bearings. Do not assume anything.....

Dave-R · Post by **Dave-R** » Sat Mar 26, 05 6:58 pm

If that don't work it could be the pinion angle. Measure the angle of the engine/trans to the ground with an angle finder. Use the edge of the sump or edge of the head or something that is parallel to the crank centerline.

Then remove the pinion snubber on the diff and use the machined flat surfaces there to find the angle of the pinion. You need the weight of the car on the wheels while you do all this.

You want the pinion close to or slightly nose down to the engine angle.

Anonymous · Post by **Anonymous** » Sun Mar 27, 05 10:04 am

Cheers guys Im going to take a look at this tomorrow. But first, some silly questions (as ever

).
1.How does rotating the prop 180deg isolate that it could be prop balancing?
2.What are the pinion snubbers (duh!)?
3.If I pull out the prop I guess I'll have to drain my trans fluid?
4.Where exactly do I unbolt the prop? Is it where its highlighted (see piccies below)
5.What the recommended torque settings for these bolts?

Rich · Post by **Rich** » Sun Mar 27, 05 10:25 am

Those are the 4 to undo,
You dont need to take the prop out of the box to turn it 180,if you need to take it out the box,jack up the rear of the car to minimise fluid loss.

Pete · Post by **Pete** » Sun Mar 27, 05 10:53 am

Looks to me like the Prop has been balanced at some point.

The Snubber bolts on top of the Centre Section carrier with 2 bolts - it holds the rubber "bump stop" bit. it prevents the axle rotating under load by hitting the floor - very sophisticated but it works.

Anonymous · Post by **Anonymous** » Tue Mar 29, 05 8:20 am

Ok, so I rotated the prop yesterday and the vibration seems a little better although that could just be me. Its still there though, its almost like a resonating vibration rather than a full on wobble if you know what I mean. I could make the sound for you but its hard to describe it in text but i'll have a go...

You get to about 90mph and there a lot of noise as you would expect from the road, the engine and everything else! But this vibration seems to run through the whole car and its like a "mmmMMMmmm" then "mmmMMMmmm" and so on.

Sorry about that but thats the best I can do

Plus im not sure about thos little u-caps that bolt the UJ into the diff coupling, they dont look very substantial when compared to everything else, the bolts are only teeny (1/2"?) also, is this a normal stock setup, what does everyone else have?

Jon · Post by **Jon** » Tue Mar 29, 05 8:58 am

Those little caps and bolts are the normal stock setup, but you're right they aren't that substantial, Ive had some let go before and it threw the prop and wrecked the gearbox, not that I want to scare you or anything
I've got an aftermarket one with big u bolts now

Dave-R · Post by **Dave-R** » Tue Mar 29, 05 9:01 am

And your pinion angle compared to your crank centerline angle is...?

Anonymous · Post by **Anonymous** » Tue Mar 29, 05 2:07 pm

Oh sorry Dave, I didnt get to do that yesterday. I wanted to ask you what an angle finder is

im a bit dim you'll have to forgive me! Can I removed the pinion snubber when the car is jacked up and then lower it down for the weight and then measure?

I took advantage of the nice weather yesterday and gave the car a good old polish and stuck on my new sticker (thanks to hugh for that).

Jon, where did you get those aftermarket ubolts? Can you show me a picture? I have a prop loop but its right by the gearbox. If the prop snapped at the rear it could still cause a lot of damage and even flip the car over couldnt it? That does worry me as I do take the kids out in the old girl sometimes, my little boy loves it even though its a bit noisy for him at the moment -im trying to train him

I'll see if I can get under the car and find out tonight or tomorrow. I'll keep you all posted. Thanks so far guys

Jon · Post by **Jon** » Tue Mar 29, 05 2:48 pm

I havent got any pics but its basically a heavy duty yoke with u bolts through it instead of the bolts and straps, its probably overkill for a street car and you shouldn't need them if everything is in balance, but having said that mine did shear off the stock bolts so I bought the biggest strongest thing I could find
any of the drag race shops would be able to sort you out

Dave-R · Post by **Dave-R** » Tue Mar 29, 05 6:10 pm

Markie. Put all 4 wheels on blocks. Then you have the weight on the wheels and can still work under the car.

No angle finder and you don't know what one is.

Ok. Well take a school protractor and drill a very small hole through it so you can hang a weighted length of cotton from the center of the baseline. Now you can measure the angle of things.

Measure the angle of the engine. Then measure the angle of the diff. If you use a protractor it might be easier to rotate the prop so that one of the UJ cups is at the bottom. Then place your tool on that to get an idea of the angle of the diff. A washer put into the recess for the cup will make a level surface.
You want the diff to be just a couple of degrees nose down from the angle of the engine.

To adjust the angle you can buy wedge shaped plates to fit between the axle and the spring mounts.

Pete · Post by **Pete** » Tue Mar 29, 05 8:52 pm

The Prop loop is in the correct postion, if the Front UJ fails then you are in deep twouble.

If the Rear fails then the prop slip yoke drops out of the transmission and you have to walk back down the road to collect it and hope an Artic has not run over it.....

Anonymous · Post by **Anonymous** » Tue Mar 29, 05 9:34 pm

Thanks for that tip, im sure my local tescos will have a school protractor.

The previous owner did as you can see from the thread above, had a very close encouter with his propshaft when the front joint failed and came through the floor!

Kev · Post by **Kev** » Tue Mar 29, 05 9:38 pm

Yeah, Dave had a prop loop when the 'shaft let go. Only thing was, it was hanging on his workshop wall waiting for fitting

I welded up the resultant hole and put in extra metal as he was catching up with the 'Cab!

He never found the prop.....