A subframe question (just the beginning ...) - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 09-02-2010, 01:52 AM

Today I bit the bullet and ordered all the rear subframe linkage for my 87 300D, which is pretty much just decrepit back there at this point. Other than the swaybar, sway links and shocks, everything is original, and it's time for the next round. I'm also planning on swapping out the subframe itself for one I got from an 88 300E ... mine has a crack under the diff (which can probably be welded, but I have this nice frame in my shed so might as well use it).
The only thing I didn't order was springs ... they don't look bad and I'm not sure how to assess whether they ought to be replaced, too. One thing I can tell you is my car lilts to the right in the rear ... perceivably. Is that likely because of the worn linkage, or should I consider it a sign the springs are in need of replacement as well? To be honest, I'm not entirely sure the physics or what holds what up, beyond the basics.
I don't want to finish the job and have it still lilt because I left worn springs in there, but I also don't want to throw out perfectly good springs. Thoughts would be appreciated.
I won't start this project for a couple weeks at least, so take your time. I also might wimp out and take it to my indy ...

layback40 · #2 09-02-2010, 04:49 AM

some one should be able to tell you the free length of the springs, as you look like you are going to have a complete disassemble/rebuild you will be able to check the lenght.

hanno · #3 09-02-2010, 08:25 AM

Spring replacement is relatatively minor

compared to the rest of the job. I'd do all else then see if the listing to the side is still there. Also, spring compressor is not absolutely required, but does make it easy.

TimFreeh · #4 09-02-2010, 08:34 AM

I agree with Hanno, dropping the subframe is a big, big job. By comparison spring replacement is about 2% of the total job - I'd keep your springs and see how things look. It's certainly possible a collapsed subframe bushing could cause the car to sag on one side a little bit.

One thing you want to check before you go too far with this plan is the bolts that hold the subframe to the unibody. They are usually very tight and 25 years of living in a fairly corrosive environment doesn't help. If you snap one of these bolts off you are going to have a much bigger job on your hands.

Here are some pictures from Dave's website that show various stages of the process.

http://www.w124performance.com/images/W124_subframe/

BodhiBenz1987 · #5 09-02-2010, 12:24 PM

Quote:

Originally Posted by TimFreeh

One thing you want to check before you go too far with this plan is the bolts that hold the subframe to the unibody. They are usually very tight and 25 years of living in a fairly corrosive environment doesn't help. If you snap one of these bolts off you are going to have a much bigger job on your hands.

Here are some pictures from Dave's website that show various stages of the process.

http://www.w124performance.com/images/W124_subframe/

Dave's website is a godsend!

Yes, my bolts do look pretty corroded. Are there steps I can take to make sure I don't snap one (aside from the obvious PB Blaster soaking)? Or is this a case of assuming it's going to snap no matter what. If it's a strong likelihood, I guess I may reconsider ... that could turn into disaster fast.

vstech · #6 09-02-2010, 12:27 PM

to prevent bolt breakage, after you have the car secured on stands, hit all bolts with a BFH I mean wail on them serious, then soak them down with aerokroil or PB blaster. try to get the spray on the bolt threads from inside the framerails if you can.

sjh · #7 11-08-2010, 08:23 PM

Quote:

Originally Posted by vstech

to prevent bolt breakage, after you have the car secured on stands, hit all bolts with a BFH I mean wail on them serious, then soak them down with aerokroil or PB blaster. try to get the spray on the bolt threads from inside the framerails if you can.

Is BFH a b.. f...ing hammer?

pawoSD · #8 09-02-2010, 01:11 PM

PB blaster is no comparison to AeroKroil. The runner-up is Liquid Wrench Penetrant. I use it with excellent results.

BodhiBenz1987 · #9 09-02-2010, 01:35 PM

Quote:

Originally Posted by pawoSD

PB blaster is no comparison to AeroKroil. The runner-up is Liquid Wrench Penetrant. I use it with excellent results.

Ah AeroKroil ... I knew there was one on the market that had a really god rep but couldn't remember that name. Thanks. I'll order some.

Billybob · #10 09-02-2010, 01:51 PM

Quote:

Originally Posted by BodhiBenz1987

Dave's website is a godsend!

Yes, my bolts do look pretty corroded. Are there steps I can take to make sure I don't snap one (aside from the obvious PB Blaster soaking)? Or is this a case of assuming it's going to snap no matter what. If it's a strong likelihood, I guess I may reconsider ... that could turn into disaster fast.

The only part you can see from underneath is the bolt head, so that is not much of an indicator. The subframe bolts are very fine thread which screw into internally threaded tubes extending downward from the chassis. Spray penetrants may help somewhat with any corrosion between the bolt head and the washer/plate above it but not much more I’d suspect.

The subframe bolts use blue threadlock so as with any blue threadlocked fastener a very useful tactic is to use a propane torch to heat the fastener for a minute or two perhaps. The fastener doesn’t need much heat, blue threadlock softens at about 150 F so if you get the head of the bolt a little too hot to touch with your finger that’s about right. In the case of the subframe bolts heating the head will by convection heat the treaded shaft so you shouldn’t have any problem.

I have done complete subframe rehabs on 4 or 5 of my personal 124 cars and on a pair of my 201 cars and have never had a problem with a subframe mount bolt, I’ve done another dozen or so on other cars and the only problem was one car that had been hit in the rear, the subframe tweaked and as a result the bolt and its receptacle where bent some which put some lateral friction on the bolt as it was being removed.

The bolts and nuts securing the various multi links will deserve some attention where a penetrant like Kroil is well worth the $15 a can costs.

With regard to the rear springs, try to get a look at the ends of the springs, there is a tendency for the first coil or a portion of it to break off with age and mileage. It’s kind of hard to see it because it’s down inside the rear LCA.

I haven’t priced springs of late but they used to be about $100 for the pair, it would seem a relatively small additional investment to have a new rear suspension! New rubber spacers would be in order also but you’ll really need to get everything installed and rode in before you can determine the actual ride height and what thickness spacer will be appropriate.

TimFreeh · #11 09-03-2010, 08:06 AM

Quote:

Originally Posted by Billybob

I have done complete subframe rehabs on 4 or 5 of my personal 124 cars and on a pair of my 201 cars and have never had a problem with a subframe mount bolt, I’ve done another dozen or so on other cars and the only problem was one car that had been hit in the rear, the subframe tweaked and as a result the bolt and its receptacle where bent some which put some lateral friction on the bolt as it was being removed

Lots of great info from Billlybob, my success rate on subframe bolts is more like 50/50 but I have to admit that on all the cars I've had problems with they were shall we say??...... I bit crusty underneath to begin with so maybe I'm a bit more pessimistic than I should be.

The heat trick sounds like a good play but I'm always a little leery of using heat in the immediate vicinity of rubber (like subframe bushings) once that kind of rubber starts to burn it can be non-trivial to put out the fire, and boy does it generate a lot of black acrid smoke!!! Maybe heating the whole assembly with an electric heat gun would be a good way to go?

One other thing worth noting in Dave's pictures is that he jacked up the rear of the car but left the front wheels on the ground - even if you have access to a lift I'd recommend this approach because sometimes if a car is on a lift and you remove a very heavy component (like a subframe) it can actually upset the balance to the point where the car can become unstable on the lift. With the front wheels on the ground (and properly secured) this would not be an issue.

layback40 · #12 09-03-2010, 01:10 AM

Bodhi,
The ASME did tests s few years ago on various anti seize products. The best result by far was a 50/50 mix of acetone (nail polish remover) & atf. I guess you have both of these!!

Give it a try, it works for me. I get into trouble for "borrowing" nail polish remover, but what the heck!!

sjh · #13 11-08-2010, 08:25 PM

Quote:

Originally Posted by layback40

Bodhi,
The ASME did tests s few years ago on various anti seize products. The best result by far was a 50/50 mix of acetone (nail polish remover) & atf. I guess you have both of these!!

Give it a try, it works for me. I get into trouble for "borrowing" nail polish remover, but what the heck!!

I'll give it a try. Thanks.

BodhiBenz1987 · #14 11-09-2010, 01:02 PM

These are not going to come off. For anything. I am never going to finish this stupid project. Should I try firing the torch up bthe bottom of the mounts? I am prying with a huge prybar, and have also tried a chisel and a wood splitter with a big hammer. They don't break because the rubber gives and can't possibly exert enough force. And I can't seem to get anything onto the metal part of the bushing to avoid that.

Billybob · #15 11-09-2010, 05:06 PM

Quote:

Originally Posted by BodhiBenz1987

These are not going to come off. For anything. I am never going to finish this stupid project. Should I try firing the torch up bthe bottom of the mounts? I am prying with a huge prybar, and have also tried a chisel and a wood splitter with a big hammer. They don't break because the rubber gives and can't possibly exert enough force. And I can't seem to get anything onto the metal part of the bushing to avoid that.

Man! Wind is gusting to 50 here and its raining hard, but I went out and crawled under my tractor trailer box to get a first hand look at a nice clean South Carolina sub frame I've got there to refresh and get an idea of what things look like! Took a couple pics, sorry the one from below is a little blurry.

The one from above shows why that approach won't work; until you stretch the rubber enough you’ll never reach the mounts metal bushing. So forget that for now, although some penetrant in and onto the stud could only have helped.

From below does your view match this picture?

If so that is where your efforts should be directed! It looks like the entire metal bushing is exposed. What you need to accomplish is to hit that hard with a decent hammer and punch/drift/chisel. You want to hit it so that you are rotating it around the tubular stud at its center. Give it a hard whack on one side and then the other, you just need it to break free and move a little. You want to direct your blows in the direction of the poorly drawn Chartreuse arrow points and attempt to get the mount to move in that rotation.

Before doing that if you're worried about the subframe falling just reinstall a couple of the mount bolts, the other rear one and the diagonally opposite front one, that way it can't come crashing down. You don't need them turned all the way home just a couple rotations, clean any residual thread lock off before you do and it will make it a little easier, just be careful and make sure the bolts are straight and square you don't want any cross threading.

With everything secured try and hit the metal bushing to turn it, if you don’t get some results after the first ten or twenty hits, you could try heating the metal bushing with a torch, just have some water or an air blowgun at hand to keep things from getting out of hand and of course a fire extinguisher so you don't burn the place down. Get it hot, it doesn't need to be red or anything like that, just too hot to touch. Then give it the heavy hammer treatment again.

If by some chance you still are unsuccessful, you can destroy the metal bushing itself, hopefully you've got a decent drill and a cobalt bit or two. Depending in the size of the bit you have drill a hole or holes straight upwards in parallel with the tubular stud. I put a couple blue spots in the general place which appears to be the weakest part of the metal bushing where you would drill! That alone might do the trick, especially is you carefully wobble the spinning drill gouging the sided of the hole/holes some. If not after you've removed as much material as possible with the drill, it's time for a cold chisel and a hammer. Put the chisel across where you drilled and there are only webs of material holding it together and use the chisel to destroy the remaining webs.

If you have shop air a pneumatic impact hammer might well work in substitute for a swung hammer and chisel n both these methods, trying to turn/loosen the mount and later if need be splitting the mount off the stud. Usually Harbor Freight has them for around $10-15. I'd try it old school first, but your size and strength might not be enough and the air tool will allow you to use its power and your brain to get it done easier perhaps. Good Luck, don't get discouraged, this stuff is the real deal, anyone can change oil and brake pads! You’re doing great! When it gets time to install your nice pretty new rehabbed sub frame , are we going to slather the inside of those metal bushing and the outside of those tubular studs with Permatex Never-Seize? Your damn right we are!!!!