So it wasn't the OVP. I replaced that with a brand new unit and the problem persists. To refresh, here's what has been plaguing my 300e.
Very intermittently my car loses RPMs and stalls, but ONLY under load. This first happened once in a parking lot after warming up, then again in the driveway. Not too long afterwards, I parked the 300e for a bit since I didn't have a place for it, and it now does it about 40% of starts. It is fine when cold, but after it warms up, the idle becomes rougher and as soon as you step on the gas a bit (still in park) it misfires and shakes badly up until about 2500 RPMs. However, shift it into drive or reverse and it does the same misfiring but the RPMs drop until it stalls. I thought it was the OVP since that is a very common replacement item, but no luck. Also, during this time I found that my EHA valve (stands for electrohydraulic actuator) began to leak massively. Again there was a glimmer of hope, but even after replacing it with a known good part, the problem persists. Actually, I might as well just list all the stuff I've checked
- replaced ovp with new unit
- replaced cap and rotor, just inspected them again today to see if there was anything wacky there...cap had some usual corrosion on contact points but nothing out of the ordinary
- replaced wires, checked again for arcing today and nothing
- replaced EHA (was leaking wildly, had to be done anyways)
- checked engine temp sensor, appears to be fine
- checked the flywheel crank sensor (which goes to EZL), came out to 880 ohms, which is well within spec
- replaced O2 sensor
- fuel pump is always on during this so that rules out FPR
- replaced spark plugs (proper style - ordered from here)
- checked vacuum connections, seems fine
- duty cycle (checked via X11 diagnostic port) remained within 47-51%, which is very good--Lambda tower does not need adjustment.
Really not sure where I am heading from here. I think I am going to replace all of the vacuum lines that I can find and hopefully fix any leak that might exist. Stay tuned....
Showing posts with label DIY. Show all posts
Showing posts with label DIY. Show all posts
Thursday, March 8, 2012
Sunday, June 19, 2011
More B2 transmission woes
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!
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!
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