Mysterious force holding the car back: slower acceleration, lower mileage. brake???? - PeachParts Mercedes-Benz Forum

wawago · #1 05-05-2007, 03:19 AM

Hi, I have an 87 560SEL. Recently (1month) I feel the car accelerates noticeable slower than before. Another person feels it too without me telling her the problem in the first place. It feels like when you press on the gas paddle and you wonder why the car is (about 20%) slower. But he engine feels as strong as before. In other words, it feels like something like the brakes are holding the car back. In addition the gas mileage is lower too. Everything else feels normal: brake power, engine power, fluid level, parking brake, etc. This problem seemed to first start after I put in a new front parking brake cable. But I am not quiet sure because during that time I also changed the brake fluid, A/T fuid, P/S fluid and Diff. oil all with MB spec.

I have checked and readjusted my parking brake according to MB manual: release parking brake, loosen parking brake adjuster, tighten parking brake until the wheel can't spin freely, then back off 4-5 clicks, tighten the adjuster until no cable slack, press/release parking brake several times, and retighten the adjuster until 120N (don't quite remember) is required to press the parking brake 1 click. Both front wheels spin freely about 2 rotations per spin by hand. Where as both the rear wheels spin only about 1 rotation per spin. I have compared them to my 88 300ce they seem to be about the same.

I really don't know what to look for to solve this problem. You help will be greatly appreciated.

Thanks

Rick

Falsapartenza85 · #2 05-05-2007, 09:27 AM

Does the car have any kind of whine or noise to her when driving or accellerating? You could have a rear differential/ bearing problem. I had a similar issue with a 1990 Volvo 780....

-Just a thought....

P.S. After driving for a while, do you smell anything burning? That would be a sign of a binded parking brake. Your cable may seem ok, but the brake shoes might not be releasing from behind the rotor. Best thing to do at that point is nock one of your rear rotors off and investigate. By no means does it sound mechanical.

wawago · #3 05-06-2007, 04:26 AM

The car does not have any kind of whine or noise to her. I just drove it just to make sure. I also just checked all the hoses in the engine bay and underneath the car everything seems to be connected properly.

Thanks
Rick

wawago · #4 05-07-2007, 12:59 AM

update: no one wheel is particular hot that I can tell the difference. So I begin to suspect that over tighten brake is not the cause. Any suggestion as where I should look for next?? THanks

Rick

G-Benz · #5 05-07-2007, 09:25 AM

Don't know if your model has a MAS (mass air sensor) or not, but on the ML, a bad one seriously degrades acceleration and gas mileage.

My indie discovered a cracked intake manifold when doing the head gasket on my W124...while it didn't hamper gas mileage, but it did diminish acceleration ability.

Bad ignition coils will also create the same symptoms.

Just some other things to check out...

DarkOneSK · #6 05-07-2007, 01:12 PM

Quote:

Originally Posted by wawago

Hi, I have an 87 560SEL. Recently (1month) I feel the car accelerates noticeable slower than before. Another person feels it too without me telling her the problem in the first place. It feels like when you press on the gas paddle and you wonder why the car is (about 20%) slower. But he engine feels as strong as before. In other words, it feels like something like the brakes are holding the car back. In addition the gas mileage is lower too. Everything else feels normal: brake power, engine power, fluid level, parking brake, etc. This problem seemed to first start after I put in a new front parking brake cable. But I am not quiet sure because during that time I also changed the brake fluid, A/T fuid, P/S fluid and Diff. oil all with MB spec.

I have checked and readjusted my parking brake according to MB manual: release parking brake, loosen parking brake adjuster, tighten parking brake until the wheel can't spin freely, then back off 4-5 clicks, tighten the adjuster until no cable slack, press/release parking brake several times, and retighten the adjuster until 120N (don't quite remember) is required to press the parking brake 1 click. Both front wheels spin freely about 2 rotations per spin by hand. Where as both the rear wheels spin only about 1 rotation per spin. I have compared them to my 88 300ce they seem to be about the same.

I really don't know what to look for to solve this problem. You help will be greatly appreciated.

Thanks

Rick

My money is on a clogged front cat. very common

Spook74 · #7 05-07-2007, 09:11 PM

The other thing that can make it feel like that is an accessory like the power steering pump, a/c compressor, or alternator with a failing bearing or such. Try pulling the belt and turning them by hand and feel for loose bearings, tightness, etc.

What kind of power steering fluid did you use? The MB stuff is supposed to have special viscosity improvers, (but I think they are just for cold weather.)

Spook

wawago · #8 05-08-2007, 02:22 PM

Thanks for the replies.
I'll check to see if I have a MAS in my car.
what is a clogged "cat"?
I'll check the accessory bearings. This could be the cause as I remember hearing some noise from on the the bearing for awhile before the slow acceleration started to appear.
I used MB steering fluid.

thanks
Rick

manny · #9 05-08-2007, 04:30 PM

I'm with DarkOneSK.

Sounds like a typical plugged Catalytic Converter.

Hirnbeiss · #10 05-08-2007, 06:26 PM

I don't think it's the cat. That problem plagued later models, and it doesn't give the impression that your engine is "as strong as before".
I think your rolling resistance sounds OK - the rear wheels have more drag from the axle & diff.
Did you check tire pressure?

Also just a thought: is it possible the brakes are engaging somewhat only when the engine is running, which would point to a booster/vacuum issue that happened after you bled the brakes? You could test by spinning the wheels with & without the engine running.

wawago · #11 05-08-2007, 07:12 PM

I couldn't find MAS on my car.
The Alternator makes some squeaking noise when start the car. The noise is gone after it has been driven a little and warmed up.
If it is the plugged Cat how can I clean it? Or do I need to replace it?
I'll spin the wheels with the engine running.
I think it has something to do with the booster/vacuum issue because I think it happened after I bled the brakes. What can I do in this case?

Thanks

Rick

just-n-time · #12 05-09-2007, 05:55 PM

I think you need to have your Indy look into the o2 sensor and the potentiometer,readings. then perhaps the EHA reading. you may wish your Indy to look into the throttle position switch. The cat. is costly and I would look to make sure that all the other items where in proper parameters. JNT

wawago · #13 05-14-2007, 10:32 AM

k, I spun the wheels with the engine running but no noticeable difference in number rotations compare to engine off.
Now I really don't think it is the brake because the tires rotate normally with engine on and off. In addition when I let off the gas and let the car cruise the car doesn't feel and the speedometer doesn't show faster deceleration.
So now I think the sluggish acceleration is due to the engine.
thanks

Rick

wawago · #14 05-15-2007, 02:59 AM

no more mystery......it is the parking brake!!!!
I released the parking brake tension from the driver seat and underneath the car. The I drove the car. The car moved like before... free of burden. So I readjust the parking brake this time with less tension ... just enough to take away any slack.
thanks for all who have tried to help.

Rick

I think posting resolution is just as important as posting question. So others will know the resolution not just suggestions/opinions.