OK,

So I searched around before I asked, but I think I may be stumped. My car has a cruise control issue, when my car has the cruise set above 72MPH it disengages almost right away. I replaced the brake switch, no help. I have on stock tires on 16 in stock rims. Before this problem happened I had a blowout, and my two rear tires, while the same size and pressure, are mismatched. I don't think that would cause the issue, but I am not sure. Should I be buying an amplifier next?

Thanks,

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98 E300 white/tan 220K miles

i'll be paying close attention. my 99 E320 just started doing this...at 61 mph
which is even more annoying than your 72 mph. i swapped out 16s for 18s
but the rotational measure is within 2% so should not be a factor. argh...

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-- raymond~
47º 34'N 122º 18'W

Tire SIZE is the most likely cause ON both cars.

Measure the circumference of all 4 tires & make sure the "shorter" tires are on the FRONT!

Even a 1/4" difference will cause that problem!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

OK, so in theory, if I am running stock tires all the way around, and this is the case, I can let say, 5 lbs out of each front tire, and jack the back tires +5, so run 25 in the front and 37 in the back, and my cruise will work?

Let me know if this is a valid test, and if so, I will try it today!

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98 E300 white/tan 220K miles

The term "stock tires" means nothing in todays world.

Between tire brands there can be 1/2" difference in circumference!

Take the time to measure correctly.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Thanks for explaining this. If I was to upgrade my rims and tires in the future, how would I go about getting the cruise to work again? I have looked and can get the new tires within 2% size of the old (circumference). Is there a computer reset that needs to be done, or will it never work?

Thanks again,

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98 E300 white/tan 220K miles

Due to electronics...you need to keep circumference with-in 2-3% of original.
And remember that even 1/2" on a 100" circumference is 0.5%.

Traction systems go crazy as well as the transmission.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Remember , the computer sees Rolling Circumference/1 rev....simply meaning two tires with different wear OR air pressures will have different rolling circumferences.

So, a postive measure I use is to mark the tire at the ground and roll the car for a 5 revolution tire distance. Then devide that ground covered distance by 5..that will give you an accurate RC per Rev measure to compare each/all 4 tires. [ As DOC states, ASR systems have to be all the same b/c there are WSS on all 4 corners]

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A Dalton

These cars are too smart for their own good. I just came back from a used tire shop, where I found the same make/model of tire that was flat, that had a similar wear amount to what was on the car. I had them mount the tire up, we put the none brand match (but size match) tire in the trunk. I drove home and the cruise worked.


This is INSANE that the car is so sensitive.

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98 E300 white/tan 220K miles