There are several things to check, and most of them are vacuum related. Any part of the vacuum system that is failing can and will cause disruption to the transmissions ability to shift properly
SYMPTOMS:
Transmission quickly progresses through gears (1-4) from a stop and does so a bit sloppily. Or perhaps there is flaring between particular shifts. Or perhaps, the transmission is not wanting to shift at all or shifts very late.
These symptoms should be checked at once to avoid potential damage to the transmission. The following check list will help determine what might be going wrong.
CHECK LIST:
Transmission Fluid: Drive car for at least 15 min. to make sure engine and transmission are at full operating temperature. Check fluid level with gear selector in "N". Do not use "P" as you will not get an accurate reading. NEVER OVER FILL the transmission.
Vacuum System: Must be in perfect working order. Even the smallest leak can cause havoc on how the transmission shifts. If need be, isolate the leaking sections by disconnecting them and capping off at the location. Remember, if the vacuum is to high the transmission will want to shift to quickly, if the vacuum is to low, the transmission will not want to shift at all. The transmission vacuum system for the Mercedes 240D is as follows:
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Main Vacuum Circuit Components
Change over valve (located on top of valve cover) This part breaks regularly!
Vacuum control valve (VCV)
Vacuum modulator (located at side of transmission)
Vacuum Dashpot (check valve) green in color
ADJUSTMENTS:
If your transmission fluid is at a proper level the next step is to ensure your vacuum system is in perfect working order along with the throttle linkage being properly adjusted
Once you are sure the fluid, vacuum and linkage are in good working order, the next step is to adjust the VCV valve.
HOW TO ADJUST THE VAVLE:
1. Loosen the VCV valve retaining bolts (no need to remove)
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| When bolt has been loosened, screws and hose removed, gently remove cover. |
2. Remove side cover
3. Using a wrench, turn the nut on the end of the spring counter clockwise if your transmission is shifting early and clockwise if shifting late. NOTE: To make this adjustment you MUST hold the throttle linkage in the closed position while turning the nut. It is also important NOT turn the the adjusting nut more than a few millimeters at a time. If you over adjust, your transmission will not shift out of first gear.
Leave the cover off while test-driving the car to make it easier to make adjustments while you are on the road.
If this adjustment still leaves your transmission shifting a bit late or early the next step is to adjust the transmission vacuum modulator which we will cover in a subsequent article.
Hello, what does loosening the VCV mounting bolts do?
ReplyDeleteI just went out and adjusted mine. The reason you loosen it is to make sure you can clear that screw in front of the plate that comes off (the one connected to the injector pump) And to make it work, you have to loosen the one in the back as well.
DeleteWhere can I find the tranny mod valve n the other parts pictured below the vacuum chart to buy?
ReplyDeleteThis comment has been removed by a blog administrator.
ReplyDeleteI have an 81 240D as well but my modulator vacuum line comes off the brake booster T just before the vacuum changeover valve. The car ran fine when I bought it but after driving it in the rain it now won't shift above 2nd gear (except on rare occasions or downhill past 45 mph). Would it be worth it to re-orient my vacuum lines to match the diagram?
ReplyDeleteI get vacuum to the modulator but I didn't measure any vacuum from or to the VCV top line, and no change to modulator vacuum under throttle. Any ideas on what's going on? Also disconnecting the vacuum line to the modulator completely definitely changed driving behavior (would only shift into 2nd hard at max speed), but it still wouldn't shift into 3rd.
Thanks i have a w123 230 petrol carburator engine .. the car dont shift .. i have to shift it in L to move or if i stand skew the car wont shift at all .. the reverse only moves a few seconds after putting it in reverse i checked all the oil everything please help
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