Rear end rebuild restores ride height, but I now have a rear end roaring noise
 

Today, the 1982 300sd got a new differential mount, new springs and spring pads, new shocks, and new sub frame bushings.

Coming home from the shop, I heard a distinct roaring noise that was not there before coming from the rear end. It sounds like metal on metal or a wheel bearring going bad but not quite the same.

It increases loudness with increase in speed. It decreases loudness with decrease in speed. It really starts about 30mph. Checked differential fluid, it is full. Mechanic put it back on rack and rechecked everything, even ran it in gear off ground, but it does not make noise off ground. He rode with me and heard it, but we cannot diagnose. Please help.

Ride height was restored. It was an inch and a half low. I measured before and after rebuild. The springs, spring pads, shocks, subframe bushings and differential mount brought the car up an inch and a half in the rear. And car does not lean in corners any more. I am going to crawl under right now and see if something is rubbing while car is on ground. Did all repairs change rear end geometry that much???

Problem found
 

Wolf Walker from the site here came by and helped me diagnose the problem. We went driving and when I applied the parking brake while my foot was still on the gas, the mystery noise became very loud.

I definitely am going to have to replace the parking brake shoes. Hope there was no damage to the drum. We loosened the parking brake cable which was maxed out to let the pressure off. Will test drive in a little bit and see if that temporary fix worked till I can get the parts.

Sounds like the parking brake shoes have been fried by improper adjustment -- you adjust them with a star wheel through a lug bolt hole, not with the cable! Using the cable will wear one end off the shoe, and the lining will come off. Also possible it's just old age, or the shoes are off the retainers.

Easy enough to check, just jack it up, pull the rear wheels, remove the calipers, and pull the rotors.

At least you don't have a fried rear end.....

peter

Check alignment too, if ride height changed I can bet the alignment is now off.

Where is the adjustment?
 

I am not sure where the adjustment is for the shoes. We got under the car and loosened the cable to get them to release. I guess I can fix that later when I do the shoes. Is there a picture in the factory service manual?

you adjust them through one of the lug bolt holes
I believe the adjustments are at the top and aproximately 10-14 degrees off of straight up on either side.
They are small, but if you take the wheel off and get a flashlight in there, you can see.
Also when you replace the shoes, you will see what I mean. Most likely though the adjusters are frozen from heat and dust and rust.
Mine were....some never cease and heat helped that problem :)

The star wheel is at about 1:30 on the left rear, 10:30 on the right if I remember correctly. Just jack up the rear wheel after removing one lug bolt, and slowly turn it while peering in with a flashlight. Works like any drum brake -- turn one way to tighten, the other to loosen (I don't remember which is which, it's opposite side to side, too!).

tighten shoes until they drag all the way around, then loosen 2-3 clicks. They may scrape a bit, but should not restrict wheel rotation.

Adjust cable to give brake application sufficient to prevent hand turning the wheels when the pedal has gone down three or four clicks. From that point, only adjust the shoes to restore correct application.

Peter

ordered parts
 

I ordered the new shoes this morning from the dealer. They give me a car club discount even though I am not a member. $57 for shoes.

I got on the service manual cd and looked it up and see the adjustment y'all are talking about. I will have to reset the cable and then let off the adjustment in the wheel.

Service manual says that pedal should hold at 2 detents. More than 4 needs adjustment. It said it should lock up at 4-6 detents.

It feels real nice when there adjusted correctly. w123 works the same way.
Actually more drum brakes are like that to one degree or another, but nobody remembers how to adjust them it seems. The cable adjustment is only for cable stretch, and will's were cinched up all the way. Lazy mechanics!! :(

letting off cable
 

Letting off the cable didn't stop the noise unfortunately. I think I will have to remove the rotors Monday morning when I am off. I hope removing the calipers isn't too complicated. I haven't done brake work in a while. Are there any special tools needed? I have plenty of metric wrenches.

I believe it's a 13mm if I remember correctly. If you have the lug wernech to remove the wheels and a 13mm to remove the rotor you're set. Oh yeah, don't forget the hex bolt that holds the rotor on.

Thanks
David

Thanks for the help
 

Thanks for the help. I was really scared the mechanic I had help me with the rear end had screwed up royally. It was just too wierd that as soon as I backed the car out of the garage bay that all this started. I still don't understand why it happened as soon as the other repairs were made unless the return spring broke inside the parking brake drum. Anything is possible.

It may have broken when he lowered the sub frame to get to the bushings. They did say they lowered the sub frame. Any thoughts??? I didn't think you had to lower it if you had the threaded rod tool.

Caliper screws (2) are 17 or 19 mm, very easy. Use some removable locktite on them going back in (blue, I think).

It's possible lowering the subframe caused something to come adrift, but is probably just coincidence.

Peter

rust loosened in park brake area
 

I asked one of the expert professional mechanics here what it may be and he said that doing the mounts can knock loose rust in rotor/park brake area and equal a really bad noise. He's had it happen before. He said remove rotor and inspect lining and dump out the rust and it is usually ok. It's 6:55am here. When it warms up a bit, will go to where my floor jack and tools are and remove the rear wheel and take a look and will take a picture and let you know.

Problem found
 

Finally found the resulting problems from the rear end rebuild. You fix one thing and it causes another problem to become apparent.

By reloading the wheels with new shocks and springs and replacing all the rubber under the rear end, the wheel bearings on one side that were already going bad but not making noise, became noisy and apparent. Very simple. It is not the rear end giving the noise. My other noise was listed in the factory repair manual for the sub frame bushings. If they vibrate, you add an additional 2.5mm washer under the bolt.

I removed the rotors and cleaned all the parts with brake cleaner and blew out the dust. Glad I did, because my rotors need replacing. I took apart the calipers and will order the seal kits for them too.

It does not look like I have rear wheel camber issues, but I am going to have a four wheel alignment done and change the rear end lube and put in the factory recommended 90 weight Lubrication Engineers brand lube. This is the best lube you can buy. They run LE lubricants in corvette racing cars and in coast to coast big diesel trucks. Many who have been running it since new have over 1,300,000 miles on the engines with no rebuild yet. That's amazing. The local sales rep said the Mercedes dealer won't tell people about their engine oil because they want to make money on oil changes. It can go up to 20,000mile intervals. Big truck tested with oil analysis. But Mercedes has been using their rear end lube for 30 years.