The other day, I was taking my 300SD to the store, and stopped in a gas station to fill up. After putting in $70 of diesel I shifted into drive and heard a little clunk. My immediate thought was that I left the fuel nozzle in the car so I jumped out and checked too see if I hit anything or of the nozzle was still in. Everything looked normal until...I shifted into drive and it went NOWHERE. Luckily, reverse still worked and I backed it into a parking spot while I figured out what to do with it.
Now, when this happened I knew exactly what was wrong. When I first got that engine and transmission (in the brown car) I replaced the B2 piston in the car, which is not a tough job at all. I had also replaced the seal and old style metal bushing with updated parts from Mercedes. Everything was working fine for about 30k and then this happened. Unfortunately, mine was a bit worse than I thought - I actually broke the band. Let me explain how the band works in the transmission.
When you shift into drive (or one of the lower gears), the valve body engages the B2 piston via hydraulic pressure. The B2 piston moves in and out, which pushes on a "pin", more commonly called a dog bone because of its shape, which seats in a receptacle on the B2 brake band that causes it to engage when pushed in. The B2 brake band piston is a common failure item because Mercedes originally used a steel bushing to seal the inner plunger of the piston. It doesn't take a rocket scientist to realize that this would wear down the aluminum bore and piston due to it being a harder metal--so Mercedes released a nylon bushing design along with a couple new redesigns for the piston itself. You also need the seal that holds the bushing in place (this is often overlooked) which went from a rounded shoulder to a square shoulder. The seal is just like a normal wheel seal or oil seal, but smaller (I could not find one at Napa, had to order through MB).
Mercedes-Benz Transmission terminology for dummies (722.XXX series transmissions)
I find that a lot of people immediately go to the internet and ask "why is my transmission not working" only to receive a number of seemingly cryptic answers filled with letters, numbers, and foreign terminology. Here is a quick crash-course on the most common terms and references when talking about these transmissions.
B1 - controls 2nd gear. A bad B1 band or piston will make the car shift from first to third.
B2 - most common failure in Mercedes transmissions for years, controls first gear, "shifting into drive"
B3 - reverse gear brake band. Some models of MB transmissions can be adjusted externally to reduce slipping and flaring when engaging reverse, others do not have this feature. If you have an older Mercedes with no reverse, the B3 is the most likely cause. I see this especially in the gas w124s and w201s for some reason, many many cars on the market with no reverse. This requires a trans rebuild to fix.
K1 spring - this is a spring in the valve body that controls the 2nd-to-3rd gear shift. Over time, both the K1 and K2 springs wear out and cause the transmission to flare a bit between shifts. There are "repair kits" available with new springs and seals for the DIYers, not a difficult fix. These springs actually control how the corresponding clutches (called K1 and K2 clutch packs) operate.
K2 spring - similar to K1 controls the 3rd-to-4th shift, along with reverse and overdrive.
"Flaring" - this refers to the RPMs spiking in between shifts under normal driving. This is usually caused by either overly-soft shifts (worn out springs and/or vacuum issues).
"slipping" - This means the car goes in and out of gear, typically creating a jerking motion under acceleration, sometimes also a bad jutter.
Vacuum tuning - The 722.xxx series transmission shifts are controlled by vacuum. A line comes off the engine and plugs into a part called the "vacuum shift modulator" on the passenger side, that will denote how firmly or how softly the car will shift between gears. If you completely disconnect the vacuum line, shifts will be extremely firm (neck-snapping in my diesel!). You can adjust the modulator by turning a plastic tee-connector on the outside of the transmission.
Bowden Cable - This adjusts the shift points. The Bowden cable is attached to the throttle linkage, and basically tells the transmission how far down you're pressing the accelerator...floor it and the shift points will be predictably higher. This typically cable stretches over the years and needs tightening, which can be done on top of the valve cover at a white cable-screw followed by a rubber accordion cover.
Symptoms of a bad B2 piston - If your piston is scratched or scored, it will "catch" on the outer bore of the transmission housing, bushing or seal. This causes intermittent engaging of the forward drive gears. Basically, you can shift into drive, but the second you put any load on the transmission it slips. You won't be going anywhere fast. Many times a sticking B2 will turn into a broken B2 piston since the hydraulic pressure is extremely high, and scoring is only going to get worse (i.e. don't wait to fix it!).
Symptoms of a bad B2 band - this is what I'm dealing with at the moment. The piston itself is fine, no catching, marring, or scoring. However, there is no spring tension on the B2. I am able to push the piston in and it will not push out against my pressure - it should have quite a lot of pressure on it, so much that it is a difficult task to replace the outside cover without some sort of improvised "tool" jammed in between it and the transmission housing (I used a pipe the first time). There is NO drive, no forward motion whatsoever. To expand even more, you will not see a change in RPMs when shifting into drive, and not hear any hydraulic actuation under the car when you shift. Strangely, when mine went, there was no debris in the pan indicating it was a clean break or the debris is stuck somewhere (very possibly the valve body).
I am currently looking at a full trans rebuild (fully within my mechanical capabilities) but unfortunately I don't really have the space to do it since the car is in a friends' driveway and I am 250 miles away from home base where all my tools, stands, hoists, etc. are...although my trusty little socket set has gotten me pretty far before!
Sunday, June 19, 2011
Wednesday, June 15, 2011
w126 ignition tumbler, not something to mess with!
I realize I haven't posted in a while here so I'm playing catch-up! Here are some details about my ignition tumbler issues that I suffered about 2 years ago.
Here's what happened - my tumbler was "loose" but never had any trouble turning. I figured I'd be a little proactive and completely replace the tumbler before it started wearing out even more. Usually this is a super easy job, consisting of about 5 minutes of your time and an unbent paperclip. Somehow, when I inserted the paperclip and turned the tumbler, it got completely stuck! No movement either way. This would be the same problem and solution for all of you who actually have had a completely stuck ignition tumbler as well, not just my folly. Taking a look at the ignition face, there is no way to actually get the tumbler out without turning the key...unless you've got a good grinder and a drill!
1. Take out gauge cluster using the bent-coathanger method
2. Loosen bolts on the underside of the steering column and let it drop (gives about 1.5"). Taking off the steering wheel can help as well, but most of the time the retaining bolt is stuck on there with an ungodly amount of loctite and torque, I was unable to get mine to budge.
3. Here's where it gets fun. There's a little "pin" maybe 3/8" in diameter that holds the ignition assembly to the steering column. It is part of the steering lock mechanism. Some experienced folks on the internet have had success with punching this pin into the column with a drift, but I gave it everything and the damn thing did not budge. Time to take out the dremel! About 5 minutes with a tungsten carbide grinding bit and the pin was no more. This step is much easier said than done. There is almost NO room to work, and you need to get creative to find an angle that works. I was able to slip the dremel in between the plastic steering column sheath (you can take this off if you get the steering wheel off) and the dash...a large socket was used as a spacer since there is some flex in both materials. It was just enough to get the dremel bit in. After grinding down the pin, you should be able to rotate the entire ignition switch mechanism within the steering lock housing.
4. With the ignition switch assembly freely rotating, it should slide out with some coaxing. It isn't easy and still very tight in there, but I was able to get it out and have the igition switch dangling down below the column.
5. Grind off the heads of the screws that hold the back portion of the ignition switch on (i.e. all the wires and vacuum lines side). This will separate the actual ignition switch from the tumbler and steering lock areas. It will also allow you to work on the tumbler mechanism on the bench and outside of the car. Here is a picture of the stuck tumbler/lock assembly on the left and a new tumbler on the right.
6. The plot thickens. Since the metal ring around the tumbler was not moving, more grinding is in store. Putting the new tumbler next to the old, I was able to figure out where the detent was in the ring and tumbler. I cut the ring's detent lock around that area to free the old tumbler:
7. More grinding. I needed to grind the old tumbler's detent down so that I could more easily unscrew that hardened steel ring. That was a pain, by the way--that steel is TOUGH and it takes a lot of cutting and patience. You can see how the tumbler appears to have completely imploded and fallen apart.
8. Finally, after much grinding and fitting, the old tumbler can come out. Small victory:
The new tumbler went in easily!
9. Reassemble, pretty much the reverse (minus grinding) of disassembly. To get the ignition switch back together, I just tightly wrapped electrical tape around the two portions. It lasted 30k miles until the car was parked with no fuss at all. Even the steering lock still works somehow, the pin that I ground down was still slightly large enough to catch just a bit in the hole and secure the mechanism. I imagine it could be removed with a punch now.
Moral of the whole story is: don't wait too late to replace that sticking ignition tumbler!!
Here's what happened - my tumbler was "loose" but never had any trouble turning. I figured I'd be a little proactive and completely replace the tumbler before it started wearing out even more. Usually this is a super easy job, consisting of about 5 minutes of your time and an unbent paperclip. Somehow, when I inserted the paperclip and turned the tumbler, it got completely stuck! No movement either way. This would be the same problem and solution for all of you who actually have had a completely stuck ignition tumbler as well, not just my folly. Taking a look at the ignition face, there is no way to actually get the tumbler out without turning the key...unless you've got a good grinder and a drill!
1. Take out gauge cluster using the bent-coathanger method
2. Loosen bolts on the underside of the steering column and let it drop (gives about 1.5"). Taking off the steering wheel can help as well, but most of the time the retaining bolt is stuck on there with an ungodly amount of loctite and torque, I was unable to get mine to budge.
3. Here's where it gets fun. There's a little "pin" maybe 3/8" in diameter that holds the ignition assembly to the steering column. It is part of the steering lock mechanism. Some experienced folks on the internet have had success with punching this pin into the column with a drift, but I gave it everything and the damn thing did not budge. Time to take out the dremel! About 5 minutes with a tungsten carbide grinding bit and the pin was no more. This step is much easier said than done. There is almost NO room to work, and you need to get creative to find an angle that works. I was able to slip the dremel in between the plastic steering column sheath (you can take this off if you get the steering wheel off) and the dash...a large socket was used as a spacer since there is some flex in both materials. It was just enough to get the dremel bit in. After grinding down the pin, you should be able to rotate the entire ignition switch mechanism within the steering lock housing.
4. With the ignition switch assembly freely rotating, it should slide out with some coaxing. It isn't easy and still very tight in there, but I was able to get it out and have the igition switch dangling down below the column.
5. Grind off the heads of the screws that hold the back portion of the ignition switch on (i.e. all the wires and vacuum lines side). This will separate the actual ignition switch from the tumbler and steering lock areas. It will also allow you to work on the tumbler mechanism on the bench and outside of the car. Here is a picture of the stuck tumbler/lock assembly on the left and a new tumbler on the right.
6. The plot thickens. Since the metal ring around the tumbler was not moving, more grinding is in store. Putting the new tumbler next to the old, I was able to figure out where the detent was in the ring and tumbler. I cut the ring's detent lock around that area to free the old tumbler:
7. More grinding. I needed to grind the old tumbler's detent down so that I could more easily unscrew that hardened steel ring. That was a pain, by the way--that steel is TOUGH and it takes a lot of cutting and patience. You can see how the tumbler appears to have completely imploded and fallen apart.
The new tumbler went in easily!
9. Reassemble, pretty much the reverse (minus grinding) of disassembly. To get the ignition switch back together, I just tightly wrapped electrical tape around the two portions. It lasted 30k miles until the car was parked with no fuss at all. Even the steering lock still works somehow, the pin that I ground down was still slightly large enough to catch just a bit in the hole and secure the mechanism. I imagine it could be removed with a punch now.
Moral of the whole story is: don't wait too late to replace that sticking ignition tumbler!!
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