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.

pawoSD · #7 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 · #8 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 · #9 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.

layback40 · #10 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!!

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, 08:37 AM

X2 Jim on keeping front wheels on the ground. Many of these jack stands are not very stable. I use a couple of pieces of 18" diameter tree trunk. You can push as hard as you like on the car & they wont topple over. I have used a couple of wheels stacked on each other as a safety measure on the side of the road.
Bodhi,
Before you get under it, give it a good solid side ways shake to make sure its not going to move !! if you can make it wobble on the jack stands, its no good!!

BodhiBenz1987 · #13 09-25-2010, 07:35 PM

OK guys, I'm back from London, past jetlag, and ready to dig in on this. I got the "new" subframe from my parents' shed and have removed most of the linkage from it (one arm won't come off because the bolt is rusted to the inside of the bushing

). I also picked up my great big box of new parts from the dealer and ordered two cans of Kroil and pint of POR15 black. And I printed out most of the FSM pages regarding this job. Couple questions remain:
-Tools. Which ones do I need and where do I find them? I can't find any diff mount tools on eBay and I know I need that one. Do I need to use the subframe mount tool when removing installing the bushings with the frame off the car, or is there another legit way? Also, do I need a special pusher to remove the axle shaft from the wheel carrier? Do I even have to remove it from the wheel carrier, or can I remove it at the diff and just pull the carrier and axle off together to be reinstalled on the new frame? Any other tools I'll need that I haven't considered yet?
-The FSM says to remove the spring link, just unbolt it from the wheel carrier ... do I have to worry about the spring popping out when I unbolt the shock? I understand a spring compressor is not needed for the rears, but I have an underlying fear of spring beheadings.
-The FSM says to torque all linkage with the axle horizontal. I take this to mean with the wheels on the ground or supported. Am I correct?

Thanks. I'm off to organize my big box o' parts and unload the subframe out of my Jeep.

hanno · #14 09-25-2010, 08:29 PM

pm sent about compressor availability.

Fasteners for the links get tightened with wheels on ground or supported so that weight of car is loading the suspension in driving position.

The amount of force needed to free the subframe bolts could be enough to topple the jackstands, so as stated above I'd have the front wheels on the ground. Additional belt and suspenders approach is to use a long pipe as your breaker bar extender. You can really pull on it when it extends out from under the car (puts you out from under also

).

Can't help with the diff mounts, never did them.

Billybob · #15 09-25-2010, 09:20 PM

Quote:

Originally Posted by BodhiBenz1987

OK guys, I'm back from London, past jetlag, and ready to dig in on this. I got the "new" subframe from my parents' shed and have removed most of the linkage from it (one arm won't come off because the bolt is rusted to the inside of the bushing

). I also picked up my great big box of new parts from the dealer and ordered two cans of Kroil and pint of POR15 black. And I printed out most of the FSM pages regarding this job. Couple questions remain:
-Tools. Which ones do I need and where do I find them? I can't find any diff mount tools on eBay and I know I need that one. Do I need to use the subframe mount tool when removing installing the bushings with the frame off the car, or is there another legit way? Also, do I need a special pusher to remove the axle shaft from the wheel carrier? Do I even have to remove it from the wheel carrier, or can I remove it at the diff and just pull the carrier and axle off together to be reinstalled on the new frame? Any other tools I'll need that I haven't considered yet?
-The FSM says to remove the spring link, just unbolt it from the wheel carrier ... do I have to worry about the spring popping out when I unbolt the shock? I understand a spring compressor is not needed for the rears, but I have an underlying fear of spring beheadings.
-The FSM says to torque all linkage with the axle horizontal. I take this to mean with the wheels on the ground or supported. Am I correct?

Thanks. I'm off to organize my big box o' parts and unload the subframe out of my Jeep.

As you’re working on the subframe out from under the vehicle everything will be easier.

Diff mounts – first thing is to measure the distance from the rearmost part of the tapered opening for the mounts in the subframe to the rear edge of the mount’s outer steel tube. This dimension is what you want to replicate when your new mounts are eventually installed. The diff mounts can be R&R’d with the correct tool or with a large socket/bolt/washer facsimile if you don’t have a large socket a steel Female-Female pipe coupling for either black steel pipe or EMT can be had at most hardware stores or the Home Depot type’s for a couple dollars. With a coupling you’ll need some type of plate with a hole large enough for the bolt, if you make use of a large socket you’ll just need a thick washer or two after threading the bolt through the ½” drive hole. You can use this ad hoc tool to install the new mounts and by reversing it to remove the old ones.

A similar tool can be assembled from a large 4” dia. pipe coupling some steel plate or a pipe end cap with a hole for the bolt drilled in its center as a puller for the sub frame mounts.

The subframe mounts can be very difficult to get out without some type of puller, but if you're going to be repainting the subframe anyway prying them or even using a torch to burn the rubber free is an option. Of course you’ll need to clean that area afterwards and repaint it to prevent rust. When installing the subframe mounts, set up your ad hoc screw type puller and squeeze them into place. That install is made easier if you coat the mount and the cup into which it will install with a liberal slathering of personal lubricant, i.e. KY or its generic equivalent. You don’t want to use a petroleum product for two reasons it will degrade the mount’s outside rubber surface and it will remain slippery, the remaining slippery thing is the same reason you don’t use rubber friendly lubes like silicon based lube. The personal lube is slippery as heck when it’s wet but after it dries it isn’t because it’s really gelatin based and it won’t impact the rubber material.

The axles will come free of the wheel carrier using a brass drift, usually quite easily. The axle nut is a 30 mm 12 point, the interface section is rather shallow, so a good socket is best but a cheaper socket can have it’s initial 1/8” radius ground off to allow a better fit on the nut. A small cold chisel can bend or break the crimped collar out of the securing cut in the axle’s end. The nut comes from the factory treated with micro-encapsulated blue thread lock, with the collar unbent set up a counter brace using a couple lug bolts and a piece of pipe on the wheel hub, then heat the nut and when it’s too hot for your finger put the socket/breaker bar to it. It’s usually a little hard to crack it free but it comes off easily once it does. If you’ve got a decent impact gun and a good socket you can often blast that nut off without even worrying about the crimped collar!

You’ll want the axles off and out of the wheel carriers just because they will be ungainly when trying to move things that last mm to get a bolt to slide into place!

When you get to the point of removing what is on the car now. This is the way I do it. Jack and support the car, disconnect the rear flex disk and swing the driveshaft over a bit and hang it with a wire or bungee cord, disconnect the ABS sensor inside the car behind the rear seat, the screw holding the clip holding the wire and push the connector and the rubber grommet out through the hole in the chassis, pull the wheels of and then remove and hang the rear calipers, unfasten the rear sway bar either at its end or the wheel carrier (alternatively you can unfasten the rear sway bar from it’s mounts to the chassis, these are usually rusted and a little hard to get to so I just disconnect and remove it after the subframe is out of the way), then using your breaker bar and a 19 mm 6-point socket break the sub frame mount bolts loose, on the passenger side there is the fuel fill overflow/drain hose that threads down through holes in the subframe, work that free if you can or at least loose so it can come free. Then put the wheels back on with a couple lug bolts, I lower the car down to the ground, unfasten the shocks at the top, and remove the four subframe bolts. Then you can use a pair of jacks to lift the car up off the sub frame nice and slow and controlled! Once the rear of the car is high enough the springs will be free, and you will be able to roll the entire sub frame out from under the elevated rear of the car on its two wheels!

If you are thoughtful and methodical you can carefully chock the front wheels and use a pair of Mercedes standard screw type jacks to lift and lower the rear of the vehicle going from side to side raising each a couple inches each time, of course that depends on good jack holes! For controlled lifting and lowering a screw type jack offers more control than hydraulic jacks particularly when lowering when you’re doing stuff like this. Over time I’ve accumulated an assortment of pairs of GM bottle type screw jacks, scissor type screw jacks, hydraulic bottle jacks, and other weird configurations just to have for jobs like this.

P. S. when doing stuff like I have a pile of 4" X 4" and 6" X 6" sections of landscape type timbers 1-2' long and a couple 3-4' long. When I'm doing something where I might be applying serious force to big fasteners where you could shift the car, instead of jack stands with a small surface area contact to the underside of the car, I use these timbers to in a criss-cross fashion in the manner that is used for cribbing under boats in dry dock. It's like building a temporary platform under the vehicle. Once you jack the car up, set the cribbing and lower the car onto it, there's no way to shake the car off it.

I almost forgot you will also need to unbolt the exhaust, it's easiest to do that at the joint between the down pipe section and the resonator, then either free the exhaust from the hanger at the subframe or unbolt that mount from the subframe, and lift the muffler off the hangers at the rear. Then you can just slide that part of the exhaust out from under the car. The joint between the muffler and resonator is a slip joint and usually is quite difficult to seperate particularly when you're under the car! The rubber exhaust mount at the subframe will likely be stretched and cracking, replacing it will never be easier and if you do your exhaust will not hang as low.