A few questions about my new 300TD - PeachParts Mercedes-Benz Forum

robbsclassics · #1 04-18-2011, 08:34 PM

I just got an 85 300TD about a month ago. It was a good deal, and not too much rust. I have fixed a few things but, just don't know about a few others. I have to research more on the tranny, tach, cruise, vacuum leaks, running hot, AC, among other little things.

My main question is fuel milage. I am getting 22mpg, which I think is low. I would like to get 30mpg, is that possible? Also, what would the original gear ratio be? I know I'm off on my speedo, so maybe a taller rear affecting my mpg? My car seems to love heating oil more than diesel also (less nailing, smoother idle), anyone know why this is...sulfur content? (Same mpg with either.) I know it needs to have the valves adjusted, a compression test, and new injectors (I'm pretty sure the originals are still in @ 290k.) It idles a little rough, but is relatively smooth on the road. I will look into the tranny slamming into gears as soon as I get the engine smoothed out.

Besides these problems, I love the ride, options, space, and looks I get. I took it out on a dirt road, and my LSD rear and ABS works great. Now if only I could do a cheap 5 speed conversion....

aaa · #2 04-18-2011, 09:00 PM

LSD? ABS?

Anyways, I got 27mpg. Look into the vacuum system for the transmission thing.

layback40 · #3 04-18-2011, 09:08 PM

Valve adjustment & air filter replacement would come first. Driving style & the sort of driving have a big influence on mpg.

kerry · #4 04-18-2011, 09:10 PM

LSD? ABS?

30mpg when hell freezes over. 24-25 mpg.

vstech · #5 04-18-2011, 09:30 PM

the 85 with the 2.88 rear ratio and the slightly more advanced cam profile/fuel map in a sedan is capable of 30, but it requires extreme driving conservation. more likely is 25-28 if you have a wagon, (as your TD notes) then it's less likely to reach 30 due to weight and aerodynamics... what makes you think you have LSD? how far off and in which direction is your speedo/odo to reality?

robbsclassics · #6 04-18-2011, 10:46 PM

aaa and kerry: LSD is limited slip differential. Basicly when one rear wheel slips, they both lock and turn the same. ABS is anti lock braking system.

vstech: I know I have it because with the rear jacked up and in park, it is hard to turn one wheel. I also can do a burnout on gravel and not do a one-wheel-peel. I tried 3 times and same result. The speedo is off about 2-3mph fast at 40mph. What would that mean? I'll have to count the wheel to driveshaft ratio when I get the chance.

babyjames · #7 04-18-2011, 11:32 PM

How about a slip-limiting rear brake? Sure you don't have a stuck piston?

Jay

bamba · #8 04-19-2011, 12:10 AM

Congrats on your new wagon. There are many advantages to the 85, not least of which is the 2.88 rear diff. It definitely helps with fuel economy. I have consistently gotten 28-30 on the highway if I keep it under 65. If you inch above 65, your mpg falls precipitously.

w123s did not ship with a limited-slip rear differential. I'm not one to hypothesize on why you're experiencing LSD-like symptoms. I suppose it's possible the previous owner did a conversion to a LSD. Perhaps you can take a photo of the diff part # for us?

vstech · #9 04-19-2011, 12:52 AM

2-3 fast readout at 40mph (meaning you are actually going 37...) hmm. it's not a very accurate way to figure out loss. best is to travel 100 miles on the highway, and see how far off the odometer is. 10 miles is ok, if your trip is working, and the tenths shows well.
then a percentage is figurable. (is that a word?) I'd guess your diff is changed from the stock 2.88 and your original odometer is in place still. (post the part number for your speedometer) but I'd expect a larger difference from a 3.07 rear... perhaps your tires are smaller than stock, or severely bald? or both...
with both wheels off the ground, and the trans in park, turning one wheel, forward should turn the other wheel forward as well. if the other wheel spins rearward, then it's not LSD... sometimes. hard to turn is not a sign of any LSD I'm familiar with.
only way to know for sure is to pull the cover and look for the clutches.

aaa · #10 04-19-2011, 06:04 AM

Quote:

Originally Posted by vstech

only way to know for sure is to pull the cover and look for the clutches.

Actually there's a pretty obvious metal tag on the back cover, some german saying "Special Oil Only" or something.

ABS will have the box in the engine bay with all the brake lines going to it.

MTUpower · #11 04-19-2011, 08:43 AM

Congratulations on your new wagon. The 85 year like most MB's in the last couple years of a chassis's run will have a few differences than earlier years. The 85 diesel wagon has a slightly different tranny set up, rear end gear ratio, oil pressure reading at the gauges and more. LSD was never an option with the chassis, and is exceedingly difficult to install on the w123 chassis so it is very highly improbable that you have that. ABS was an option, but also exceedingly rare- again highly doubtful you have ABS. You'll have a black ABS box in the engine compartment if you have it. The wagons actually got better mileage due to better drag co-efficiency by perhaps 5%. Your mileage and quest for a better running machine needs to start with the basics: you need to replace all filters and fluids, check your tires and front end alignment/suspension, and slowly work you way thru the engine's systems and parts to make sure it's running in tip top shape. The best place to learn is right here at the Diesel discussion at Peach Parts.

kerry · #12 04-19-2011, 09:21 AM

Quote:

Originally Posted by robbsclassics

aaa and kerry: LSD is limited slip differential. Basicly when one rear wheel slips, they both lock and turn the same. ABS is anti lock braking system.

We knew that. We put the question marks because no US model 85TD's came from the factory with LSD or ABS to our knowledge. That's why we were questioning. If you have ABS and LSD on an 85 300 TD(wagon) then you're the only one on the forum with such a set up as far as I know.

robbsclassics · #13 04-19-2011, 11:09 AM

Quote:

Originally Posted by kerry

We knew that. We put the question marks because no US model 85TD's came from the factory with LSD or ABS to our knowledge. That's why we were questioning. If you have ABS and LSD on an 85 300 TD(wagon) then you're the only one on the forum with such a set up as far as I know.

Interesting, I thought I read somewhere that 85s had the option of ABS. I'm pretty sure I have it. I went down a straight gravel road, then locked the brakes, then I put my head out the window and looked at the front tires. The tires would lock and release very regularly untill I was almost stopped, then locked up completely. I checked the car, and I don't have a box that the lines go to, but I do have speed sensors at all tires. Is this a normal MB thing?

As far as the LSD, I'll have to look more into that. It would be cool to have a rare car. A hung caliper would make sense though. I have low mpg, the car was sitting for a while before I got it, and the brakes are spongy. There are a lot of problems with this car, but for $600, I can't complain too much.

kerry · #14 04-19-2011, 01:20 PM

Quote:

Originally Posted by robbsclassics

, but I do have speed sensors at all tires. Is this a normal MB thing?
.

What do the speed sensors look like?

vstech · #15 04-19-2011, 05:32 PM

are you sure you have speed sensors and they are at all wheels? the front wheels will have a wire going to the caliper that is meant to alert you to worn brake pads. a speed sensor would be on the hub, and a magnetic hookup would read the pulses from it.

if you have abs, your master cylinder lines will connect to a large box with ABS on the box, and several lines will exit the box.