Maybe a rear end noise in my 73?

[WH23G3G]

So I drove around my area in my 73 400 Charger and it does good. But at about 45-50mph it roars somewhere from the rear of the car and vibrates bad, making a sheetmetal vibration sound. So basically it sounds like it's vibrating the sheetmetal in the car but I can't pinpoint where exactly it's originating from. I was told by what it sounded like when someone else drove it was maybe the springs could be loose. So I went and tightened the u-bolts, shackles, and all the rear suspension pieces more. It still does it. I did install new leaf springs about 3 years ago when I was doing everything to the car. It has an 8.75 3.91 sure grip which I was told works good because I don't know how to tell, except I know the wheels turn hard by hand when you have the rear end raised up. The only thing I did to the rear end was remove the center section and have a pinion seal put in and was told everything looked new and tight. I also put new wheel seals on, of course a new carrier gasket, 80w-90, and a limited slip additve. I had two different sized cups on the u-joint so I had to swipe one from another u-joint so I could fit it on the pinion yoke. I had new u-joints pressed in by a machine shop just the rear had different cup sizes on it than the driveshaft. Any ideas what I need to check?

[74Rallye]

Different size cups? Do you mean the U-joint is the adapter type for when the yoke is a different size than the drive shaft? If not, that could be the problem.
Second question is why did you have to have a shop press the caps in? I'm asking this because I had a drive shaft on a Charger I had just built that was difficult to assemble the U-joint into and it tossed a cap when I shifted into 3rd around 95 mph. The cap retainers on the shaft did not look perfectly round. I don't know if that was the cause or the result from coming apart when I lost the cap. I replaced the drive shaft with a junk yard piece and never had that happen again.
It sounds like something may be out of balance. The first thing I would try, assuming the tires are balanced and everything else is in good condition, would be to rotate the rear U-joint 180 degrees on the yoke.

[WH23G3G]

I don't remember exactly what the circumstances were when I changed the u-joints when I was going through the car front to rear. I know I looked up the rear end numbers one time and it was a 8.75 3.91 sure grip with the small pinion. I remember when I bought new u-joints for a 73 Charger the front one fit fine and the rear fit fine but the u-joint cups that sat in the rear end pinion yoke were too big so I had ordered a "conversion joint" which had two of the smaller cups and two bigger cups. And since the u-joint was already in my driveshaft I just took the cups off of the conversion joint and put them on my already installed joint. Isn't there a pinion yoke I can order that will fit right up with the big u-joints? It's a pretty violent vibration it shakes the sheetmetal and the windows and it's definitely coming from the rear.

[firefighter3931]

The only thing I did to the rear end was remove the center section and have a pinion seal put in and was told everything looked new and tight.

Is this a 489 centersection ?

If so ; when removing the yoke to install a new seal it is very important to measure the torque required to remove the pinion nut and duplicate that tq value upon reassembly  The 489 housing uses a collapsible crush sleeve to set the preload and if you get that wrong pinion preload will be off resulting in a fubarred backlash setting. The result can be as you described...lots of whine & vibration. 

There are a few companies that sell solid spacers with shims to eliminate the collapsible crush sleeve and this is definitely a superior setup 

http://www.summitracing.com/int/parts/rat-4103/overview/



Ron

[WH23G3G]

Yeah 489 sounds right. I haven't got under it to check the fluid yet. The guy who did the pinion seal was an old mechanic not a parts changer so I didn't second guess him. Anyway if that is the case. Do I need to get the new pinion yoke to fit the big ujoints? Do you think it would be ok to drive it to the shop which is about 15 miles away without totally tearing up the rear end? That is if the Edelbrock cooperates and gets me there without a stall. I am working my way up to getting it back over the shop because after that it should be ready to go to the body shop for paint prep I hope. Still that stall out I had in the middle of one of the busiest intersections in my city at 5:30 on Friday wasn't a very enjoyable first ride, well second ride. 

[74Rallye]

I just took the cups off of the conversion joint and put them on my already installed joint.

That may be the problem. There could be a difference between the cups in regard to depth and diameter.

[firefighter3931]

If the vibration is as bad as described I would recommend not driving it until it is fixed. 


Ron

[WH23G3G]

It only happens around 50-60mph. I did some more research on what I did when I was changing the u-joints. I have the 741 8.75 with the 10 spline 1 3/8 stem. I checked my warranty of the u-joints I bought and had installed, it was the 2-1175DG from Autozone. My driveshaft has the 7290 u-joints installed in them. Ok they fit the driveshaft fine and it was fine. But when I installed the driveshaft to the rear yoke flange the cups were too big. So I ordered a conversion u-joint that had 7290 cups on one side and 7260 cups on the other side. Instead of changing the whole u-joint out I just swapped the cups to the one I needed since I didn't know how to install a u-joint. If I have to replace that crush sleeve with a solid one isn't there a pinion flange that's already made to fit the 7290 u-joints in a 10 spline? This is where I found my information on the 8.75 http://www.mymopar.com/Mopar8_75RearEndGuide.htm

[WH23G3G]

I jacked up the rear end on my 73 and checked the fluid. It is full. I took a look at the u-joint to pinion because I knew that was the weak link in all I did when redoing my 73 Charger drivetrain. You can see the gap between the u-joint cup and the u-bolt. It is tight. Those straps were hard to tighten I think they had threadlocker on them. I don't know if I got the right straps but they were cheap ones from Dorman. Those cups in the picture are the ones I took off of the conversion u-joint. According to the specs on the u-joint I bought from Autozone 2-1175 these are the 7290 joints. So I still have those original cups but maybe I need the right straps. Does anyone make them or maybe I still need a new pinion flange? Anyway I figured out the problem for sure or a very major part of it. I can grasp those u-joint caps on either side and the driveshaft will flop significantly with a lot of play. But if you grasp the ones that came originally on that u-joint which are the ones pressed into the driveshaft they have almost no play. So those cups I swapped are too small and the driveshaft is probably vibrating at higher speeds. What do I need to do? Is this a quick safe fix at home on the ground or do I need to take it somewhere?

[firefighter3931]

The loose caps are a definite problem ! 

You need to find out what u-joint fits into that pinion yolk and size the caps accordingly. 

The 7260 u joint is 2 1/8 measured on the inside of the yolk

The 7290 u joint is 2 5/8 measured on the inside of the yolk

The cap diameter on a 7290 u joint is 1 1/8



Ron

[WH23G3G]

Yeah I think I know what I did now. The straps I got were for a 7260 joint and the u-joint I had installed was a 7290 so I couldn't tighten the straps. So I ordered a conversion joint and took the caps off and installed them only they're too small apparently. I don't think I could find the 7290 straps back when I did this but I've found them and I'm going to try and swap the straps and put the original caps back on.

[WH23G3G]

This has definitely got to be the problem or a large part of the problem. I swapped out one of the caps to the correct 7290 caps and the correct u-joint straps and now there is almost no play. That one was easy to access and the snap ring was easy to get off. Now I'm trying to get the other one off and it's proving to be a pain. Is there any trick to getting the snap rings off? I'm trying to change it out without removing the whole driveshaft. The one I'm changing now is up in a high position and it's hard to get the snap ring out because there's no where to grasp it to pull it out. I was lucky on the other side because it had enough play to get a tiny flat head in there and pry it up. I've got it up on 4 jackstands, is it ok to put it in neutral and turn the back wheels to reposition the driveshaft? So is there anyway to get these snap rings out easy? If I can get this other side swapped out I should be able to test drive it again.

[c00nhunterjoe]

By that last picture, its time for a new yoke. There should be no play at all, even without the straps. It should be a snug fit into the yoke.

[WH23G3G]

Yeah there is no play now. But I still have to swap out the other small cap. Then tighten it and there will be no play. If I can just pry out the c-clip to pull the other u-joint cup off. I already broke a find blade screwdriver trying to get it off. I'll mess with it more this week.

[c00nhunterjoe]

Use a hammer and small screwdriver.

[WH23G3G]

Hey I just did it. That's exactly what I had to do. I've got the correct 7290 caps back on. So my u-joint is correct now, 7290 all the way around. Is it suppose to have any play at all when you tighten up the u-joint straps, because it doesn't at all. Whereas before you could just push back and forth on the driveshaft and it would move all over the place. Now there's none whatsoever. Is that good or bad? The caps fit snuggly in the pinion flange and the straps fit good. I still don't know exactly how the u-joint works. I know it's got the needle bearings in all the caps so it must roll. Is there anything I need to do before I call this done? While I've got it up I need to inspect the oil leakage up front. Shouldn't be leaking on a rebuilt motor but I'm pretty sure it's still from that crappy power steering pump resevoir.

[c00nhunterjoe]

no play is what you are going for.

[WH23G3G]

Then this should be good to go because there definitely isn't. Hopefully get it out and drive it this week and see if the vibration slowed or even better stopped.

[firefighter3931]

Having the caps tight in the saddle is definitely a step in the right direction....good job ! 

Let us know how it's working 


Ron