86 560SEL Trans. Modulator Leak - PeachParts Mercedes-Benz Forum

GradyService · #1 12-01-2006, 10:52 AM

Sorry for being away for so long, haven't had time to post. Anyway, the tranny modulator is leaking on the 560 (It looks like I'm going to have to keep her for a while

). From what I can gather, there is a o-ring on the modulator to keep it from leaking fluid out of the case and that is dryrotted on mine. Local MB shop is saying ,"no, you can't just replace the o-ring, you must replace the modulator, o-ring, and any vac hose, just like when you change trans fluid and filter, you have to replace fluid, filter, gasket, and PAN." Basically, I feel like every time I pull up to a shop with this car, a 20 dollar repair becomes a 200 dollar repair because its a Mercedes-Benz

. Honestly guys, do any of you feel like that repair shops jack up their prices because it is a MB, or am I just having a bad day

. Anyway, is replacing the modulator o-ring acceptable or do I need to replace everything like the shop I called (they haven't looked at it, that cost $65.00 extra) said. Also, is it an involved (i.e. complicated) proceedure that would be best left to a shop, or is it something that a fairly competent D-I-Yer can do?
Thanks, Dave.

ATLD · #2 12-01-2006, 11:05 AM

If the modulator holds vacuum, then replacing the o-ring itself will correct the fluid leak. It is rather cheap to replace the rubber vacuum lines, so I'd agree with that. If you are doing this yourself, buy more than one o-ring from the dealer. It is rather tricky to install and you are likely to cut a few o-rings before installing it right.

I'd only repalce the whole modulator (which the new one are more easily adjustable) if you have poor shift modulation.

ATLD.

GradyService · #3 12-01-2006, 11:12 AM

Well, I don't seem to feel but 2 shifts with the car (I haven't ever felt but 2 shifts since I bought it), but one of the mechanic's who looked at it said that it was designed to start off in 2ND gear

. I don't know, but I think that I will try just a o-ring replacement first. However, do you think that I have to get the o-ring from the dealer (50 miles away) or that an aftermarket o-ring, i.e. carquest, will work?
Thanks, Dave.

david s poole · #4 12-01-2006, 11:25 AM

there is a plastic piston behind the modulator.buy a new one when you buy the o ring.75% chance it is broken.you need 5mm allen socket to remove the bolts neither of which you can see easily.good luck.

ATLD · #5 12-01-2006, 12:14 PM

No reason to get the o-ring from the dealer. For their price for a handful or rings, you can buy a full metrix set of o-rings from a reputable auto-store and have o-rings for life. Just have the current o-ring with you so you can find an exact match. I've found that my local dealer (who knows me well) will just give me small ticket items like this if you ask politely (not worth the trouble to write up the reciept) but if your dealer is 50 mi away, it's not worth it in fuel.

This is an easy job that a DIYer is more than capable of doing, but the trick is getting comfortable under the car so you can access the side of the transmission between the case and the car's subframe. This is tight and you can't see much (this is where a lift really helps) but you can do this by feel. It's really important that you clean this area up first before you do the job, any dirt that gets into the tranny here goes thru NO filters before it goes to the valve body.

Getting the modulator with the o-ring back into the tranny is about as difficult as setting a piston back into a brake caliper bore. If done carelessly you will damage the seal-ring. Since you can't see the modulator o-ring well when you install it, this is a little harder, so have pleanty of spares so you don't have to run out to the store again mid-operation.

Another thing, if you replace the modulator, you will probably have to jack the car up to access the modulator several more times to get the spring preload properly adjusted right.