Vacuum fail- on the road
 

Here we go!

Last night at about 9:50 PM I got a call from my daughter. Her description led me to believe there was some sort of vacuum system failure on her 1980 300TD. Shifting problems, then nearly all brakes lost. She was on her way to work. She made it, but now that the shift has ended her car will remain until I can find a way to get into town and have a look.
We had replaced the glow plugs and fuel return lines on Thursday; there is a chance that the main vacuum line was damaged then. Don't know. I am hoping the worst case is only a matter of a torn diaphragm on the pump. I can handle a pump rebuild, but I'm not quite ready to pull the engine if the pump grenaded.
She has Monday and Tuesday off, so if I can manage to get out there, diagnose the problem, get the rebuild kit and rebuild/ install it before Wednesday noon we will be OK. She really doesn't want to miss work!
She apparently drove over 10 miles (highway) with the trans acting up, but she did manage to get it back into 4th and get to town. While in town, the shifting problems were intermittent. The brake booster stooped boosting in the parking lot at work; fortunately it is a big parking lot and she got to her parking spot without further incident.
It's nice to have some excitement in your life! But not this type.
When things calm down I will repeat my instructions to her- If the car starts acting up, stop, and call me before driving any further!
If there are any forum members in our area (Bellingham) that are bored today, we could sure use some help!


snapped_bolt

Could be a failed diaphragm. Could also be a failed main vacuum line. I'm tending towards the latter.

x2 the "latter"
 

at least for simplicity's sake! If so, the pump will be rebuilt, it was in the offing, but now has become forefront. I probably will not have too much difficulty in convincing my daughter to spend money on the car now!


snapped_bolt

Do you have A Vacuum Pump With a Diaphragm? In you info you show an 81 240D; and I thought buy that time they had Piston type Vacuum Pumps.

If it turns out you have a Piston Type Vacuum Pump check the Check Vlave on the Vacuum Pump and also as you said inspect the Main Vacuum Line.

On the firs Oil Change I did I lean on the Main Vacuum Line and cracked off one of the Nipples; I suppose worse could happen.

240D on jackstands....
 

the car in question is my daughter's 1980 300TD. She has had it a little over a month. We have been working on it as we go, it is her daily driver.
I am thinking that the vacuum line may have been cracked, perhaps that is why my daughter reported intermittent failures. The only fast bandage I know of for that is gap-filling ACC (super glue) over the joint while it is held closed; then toss baking soda on the glue to turn it into a "weld bead"- the baking soda instantly freezes the ACC. Once a small bead is built up around the break, wrap with duct tape to keep the joint from vibrating apart. Beats towing the car, and the main vac line to the booster will have to be replaced in any case.
I believe we both have the same type of vacuum pump. Her car was built 10/79, mine was 01/81- but neither one may have the original engine. Lots of years and miles between then and now!
I first did a repair with the ACC/ baking soda about 20 years ago- to a broken vacuum connector. It actually holds up really well. But since this is a Mercedes, the proper repair is appropriate, and the ACC is only a temporary measure.

Silicon 'rescue' tape might work, as might epoxy putty.

Looks like the pump...
 

Booster line looks fine. Vacuum tested branch lines, booster holds vacuum, cannot find an excuse for loss of vacuum other than the pump itself. Have to rebuild. Also had to leave it there, I had everything I needed but the correct length 3/8 extension.
Since I wasn't there, and my daughter's description leaves much to be desired, I can't risk starting the car until I get the pump off and have a look and either rebuild the pump or toss it.
Take it from one with experience- it must be better to go ahead and repair the pump at home with the car in the garage rather than 27 miles away!!! Repair those pumps!

-sigh-

snapped_bolt

If it's a diaphragm pump, I'm pretty sure they don't have a reputation for grenading and taking out the timing chain, that's only the piston pump (I think).

Vacuum pump rebuilt; car is home
 

Got a diaphragm-type rebuild kit with step-by step instructions from the Source in Bellingham, WA today, rebuilt the pump, and now it really sucks!
This was my first W123 "roadside" repair (in the parking lot, actually). Another daughter of mine stood by as I worked and commented on the ease of doing the job- everything went smooth.
Having step-by-step instructions (with photographs) for this job made it go quickly- and I realized while driving it home the reliability confidence factor got quite a boost. Since the car had fewer than 5,000 miles logged since 2003, I was worried about any rubber parts that had been in the "deferred maintenance" category before that time. Well, with a good 1" tear in the diaphragm, the pump is now off the "deferred maintenance" list after the rebuild.
The diaphragm was torn nearly straight along the reinforcing cord near the washer.
Now that I have done it, I am going to rebuild the pump on the 240D. The peace of mind factor is important! You can't be driving around with a failed pump! Fix it at home, where the coffee's always hot and there's someone asking you "Are you done yet?" every six minutes!

snapped_bolt

Congratulations!

Good to hear you got it fixed so easily!

PE