low mpg's and grinding noise from rear wheel's - PeachParts Mercedes-Benz Forum

benzdude42 · #1 01-15-2015, 05:49 AM

I was given my 1984 300sd about 6 months ago and was getting about 27 mpg, but after about 3 months my mpg went down hill and im now geting 18.75. ive done everything i can think of; new injections, valve adjustment, new fuel lines, and new filters twice! so i jacked up the car to check for dragging brakes and the rear feel's way tighter than my 300d did. it sounds like a girding noise from both wheel's even with the rotor off. the calipers are fine and i've got new rotors on order. but even with the brakes off its still really tight. no wheel play that i can tell either. is it possible that the bearings are bad? would this cause my massive lost in mpg's?

Stretch · #2 01-15-2015, 06:37 AM

Quote:

Originally Posted by benzdude42

I was given my 1984 300sd about 6 months ago and was getting about 27 mpg, but after about 3 months my mpg went down hill and im now geting 18.75. ive done everything i can think of; new injections, valve adjustment, new fuel lines, and new filters twice! so i jacked up the car to check for dragging brakes and the rear feel's way tighter than my 300d did. it sounds like a girding noise from both wheel's even with the rotor off. the calipers are fine and i've got new rotors on order. but even with the brakes off its still really tight. no wheel play that i can tell either. is it possible that the bearings are bad? would this cause my massive lost in mpg's?

Yep quite possible that poor rolling resistance will cause poor fuel economy. I can't say for sure that it would mean a loss of 8 mpg though - even so seems like a reasonable explanation...

Increased rolling friction in the bearings would normally mean an increase in running temperature (of the bearings) - do you have a temperature probe and a digital voltmeter that can measure temperature or better still a non contact IR thermometer?

Mxfrank · #3 01-15-2015, 11:01 AM

It could be that your emergency brakes are jammed. The cables and adjusting link need to be inspected along with the shoes.

leathermang · #4 01-15-2015, 11:12 AM

To produce 8 mpg difference ( that is A LOT ) one would think if it were stuck parking brakes it would smell a LOT.... look and feel hot.... and destruct at some point not too many miles into the situation..
same with rear end... could be... but that would mean a lot of friction inside that gear box.... and an total failure relatively soon...
so this is a real mystery.....
and yes, could be the wheel bearings.... and you did not say how long this decreased mpg situation has been developing... to have the bearings cause that much drop in mpg.... they should be glowing hot...and about to seize up in ten miles of driving....
would have been nice before you took things apart... to aim one of those laser infrared thermometers at each of these parts for comparison.....right after a nice drive...

rob300SD · #5 01-15-2015, 11:14 AM

Yeah check those emergency brakes. If those are free and the hubs are still hard to turn, then you'll have to check the bearings and the differential. It should rotate pretty smoothly.

rob300SD · #6 01-15-2015, 11:16 AM

Also, what is "girding"? Do you mean grinding? Grinding is bad.

benzdude42 · #7 01-15-2015, 04:40 PM

AutoCorrect is supper dumb on my iPhone. Sorry about that. Yes I don't have any idea what's going on but I'm getting mad. You can turn the wheel about 1/8 a turn before the diff kicks in maybe its time to rebuild the rear and put a new 2.47 diff in. The motor is the strongest 617 I've seen in person. Almost no blow buy. Starts as fast as my parents 2014 tdi when the glow plugs work. No smoke unless it's cold out and only for a mile. I guess nothing is free right. Haha.

rob300SD · #8 01-15-2015, 04:55 PM

Yeah all these old cars need some kind of work. I've put at least 80 hours into mine in the last 6 months. Well, if the bearing on one side is tight, then when you rotate the opposite wheel it will turn the drive shaft. So it may just be the bearings.

Zacharias · #9 01-15-2015, 05:25 PM

Just want to mention that depending on when you saw the mpg drop, it might be due in part to the transition to winter diesel at the pumps.

Last year my car had a humungus drop with the winter diesel stock, I estimate 4 mpg easy.

This year is much better, and even more so since I threw in kerosene to deal with the really cold weather.

ah-kay · #10 01-15-2015, 07:13 PM

NOTHING mechanical will drag down the mpg by 29-30%. If there was you would have smelled something burning, or worse still, something locked up already. It is not winter diesel either. I suspect the original reading was not right to begin with or you are leaking diesel somewhere.

Zacharias · #11 01-15-2015, 08:25 PM

Quote:

Originally Posted by ah-kay

It is not winter diesel either.

And living in California qualifies you to comment on the effects of winter diesel how, exactly?

Diesel911 · #12 01-15-2015, 09:33 PM

Check the Rear Wheel Bearing End Play with a Dial Indicator.

Prop and block (the Wheels) the Car safely up on Jack Stands so the Rear Wheels can hang free.

Start the Engine and put the Car in Gear see if you can locate specifically where the grinding sound is coming from by listening with a Mechanics Stethoscope or a piece of Wooden Broom Stick with your Ear on one end of the Stick.
Beware of moving parts.

When I did the above on My Volvo Diesel I found the Driveshaft Support Bearing was grinding as well as a U-joint.

Diesel911 · #13 01-15-2015, 09:37 PM

Quote:

Originally Posted by Zacharias

And living in California qualifies you to comment on the effects of winter diesel how, exactly?

I am from CA and it used to be common for People to post complaints about poor milaged about the time Winter Fuel comes out. However, in this case the milage drop is way too much for it to be Winter Fuel by itself.

The Place I buy My Fuel is a Truck Stop. I am sure here in CA they also have Winter Fuel because you never know where a Truck is going to go. I mean in a matter of Hours the Truck could be in another State.

In short you can learn about Winter Fuel from readin the Posts and Threads.

ah-kay · #14 01-15-2015, 09:49 PM

Quote:

Originally Posted by Zacharias

And living in California qualifies you to comment on the effects of winter diesel how, exactly?

You notice San Diego is in CA? I do not need to live in frigid weather to know that. It is common sense, I have something between my ears.

Zacharias · #15 01-16-2015, 10:48 AM

Perhaps before showing off your immense brain, you might consider using it to read what I actually wrote:

"it might be due in part to the transition to winter diesel at the pumps."

Just let me know if you want it a bit larger.

Roy Hunter has posted mulitiple warnings about the quality of winter diesel in the US northeast, for several years. I have had tankfuls myself where my 300d ran like a *****bucket and the exhaust smelled like something had died.

Common sense would also make me question an assertion that California gets the same winter diesel formulation as the northeast.