Looking around for the reasons for the low mpg on my '84 SD, and the front brakes are definitly dragging. I can push the pads back, the push the brake pedal, they go back against the rotor, and the don't seem to release. Doing some searching of course, but anybody got any brake tips? Got approximate cost for new calipers and such? Probobly need new rotors too, there's a definite lip around the rim of the rotor....

__________________
'84 300SD veg-oil bliss
'83 300SD veg-oil beater

I think I paid around $38 a piece for the rotors. I bought rear calipers for around $30 3 years ago.
Try bleeding the hell out of them first. Maybe some dirt in there.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

This is common when the interior of the rubber brake hose colapses. If the rubber brake hose is old. Replace them, they will act like a one way valve.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Could also be the rubber hoses connecting the calipers to the steel lines. They can fail internaly causing difficult fluid backflow when the pedal is released. This will of course cause the pads to stay up against the rotors. Can you drive the car and allow it to stop without the use of the brakes, then check the rotors for relative temps? Stickers should be a lot hotter, and good ones should be barely warm..... heat transfer from hubs.

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

On many vehicles this could be caused by a lack of caliper lube. On the MB this is highly unlikely. I lubed mine anyway.

Matt,

This is the result of the caliper piston to caliper bore seal aging and losing its resiliency. The only thing that pulls the piston back when you release the brake pedal is this seal. It has a relatively high coefficient of friction against the piston and when the brake pedal is pressed, the hydraulic pressure created pushes the piston toward the disc a very slight distance. This seal deforms and stores a little energy. When you take your foot off the seal tries to return to its original shape. To do so it must pull the piston back slightly.

I repeat, this is the only mechanism in the system for pulling the piston back. When this seal ages, or gets worn from debris from corrosion or other souces of contamination, it slides along the piston instead of deforming and no energy is stored. The piston does not return.

I have a great deal of difficulty envisioning a failed hose acting like a perfect valve. For the hose to hold the pressure, it would have to truly be a zero leakage seal, as the volume of hydraulic oil that needs to be returned to the reservoir to reduce the pressure to its at rest pressure is next to nothing. It is this way on purpose. If a lot of fluid had to flow to apply pressure to the piston, it would result in each brake's performance being very sensitive to the flow path configuration. All brake lines, for example, would have to be precisely the same configuration or they would not activate at the same time.

So, remove the calipers from the wheel. Then push the brake pedal until the pistons pop out, and then clean the brakes until they are pristine. Examine the piston and bore, and if there is any significant scratching, corrosion or other signs of the plating coming off, the calipers are toast. The dimensions for the fit of the piston to the caliper bore are unbelievably tight and in my opinion they cannot be fixed by anyone who cannot remove the old plating and any signs of rusting, then replate and remachine/grind the parts to achieve the original dimensions. Anyone trying to do this themselves is looking for trouble with a major safety system in the car.

If the surfaces are in good condition, you can replace the rubber parts and put the pistons back in. Be very careful to keep things clean and well flushed with new brake fluid while you work. This will fix your dragging problem and likely return the original feel of the brakes. The kit of rubber parts for rebuilding is less than $25 for a set of two for most cars. I got mine at FastLane the last time I did them and it worked great.

Good luck, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Well, thanks for all the quick advice, at least now I have my beater running well so can afford the downtime to go over the brakes. Thanks again.... I'll let you all know what I find.

__________________
'84 300SD veg-oil bliss
'83 300SD veg-oil beater

Jim,

Brake hoses can and do collapse inside and stop the return of the piston. I had this problem on an '83 3/4 ton Diesel truck. I replaced the hoses and never had another problem. This may not be applicable to a MB but the problem does occur.

kip Foss,

There has to be a better explanation of the phenomenon than the brake hose collapsing. The internal pressure is higher than the external pressure (atmospheric) so I am at a loss to figure out how the hose collapses. Maybe the next time this happens to someone on the forum they can section the hose and take some photos.

I know of no mechanism other than the seal that would pull the pad back from the disc. Even if the pressure just relaxes to normal, the pad will stay in contact with the disc until it wears away enough to stop dragging. I find the role the hose could play in this, unless the hose is disintegrating and the particles are getting into the crevice between the piston and caliper bore, very hard to envision, regardless of manufacturer.

I have an MB paper manual for my 240D from 1975 that goes into this issue in detail and it only mentions the seal failing. They have an elaborate test set up, of course, to measure how much the caliper relaxes when the pedal is released, and they have a specification for it.

I do not know a hose cannot cause these problems, I just do not understand how it would accomplish this task. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Jim, I have to back kip Foss (and Dave and lycoming) on this one. Brake hose deterioration to the point that it acts as a one way valve is a common failure mechanism for any car. It's been well documented. I just don't understand that after being such an active senior member on this web site, you haven't run across this phenomenon.

Think of the problem hose as acting like a clogged artery. The high pressure from brake application forces fluid through the restricted hose to apply the brakes, but the hose chokes off flow at a lower pressure, but still trapping enough pressure to fight the resiliency of the seal. This is my guess.

I'm familiar with the anelasticity of piston seals and how they retract the brakes off the rotor. You gave a good explanation of it. Also, knockback from the slight wobble in a rotor will push the pads back away from the rotor.

I too am curious to understand the exact mechanism of hose deterioration and how it makes the hose act as a one way valve, but the fact remains that it does happen, and replacement of the brake hose is the cure.

Matt, I recommend you start with brake hose replacement. It's probably cheaper than the calipers, plus it's a good bet the hoses are your problem.

__________________
95 E320 Cabriolet, 159K

I don't think it's "Soydriver's" problem, but I've also seen the "one way valve" brake hose failure phenomenon. One front wheel caliper on a Chevy Van...new caliper did nothing, new hose fixed it. I recall the parts person I dealt with at the time telling me he'd seen this type of failure before.

__________________
Diesel-guy

Guys,

I did a Google search on brake hose failures and found a write up that says using different brake fluid types and brands can cause the rubber to swell so much it seals the pressure inside the caliper. First time I heard of that, but, if it is true it would explain why I have never expererienced it. I use Castrol GTX LMA fluid, exclusively and have never had a brake hose problem. I have had seal aging issues though. The write ups also suggest there should be visible signs of distress, including some weeping of fluid at the metal end connections (edit).

I still find the concept that the hose can swell so much that it forms a perfect seal in one direction but not the other (edit) hard to understand. In any case, it is probably not a bad idea to change the hoses at the same time if you use a variety of brake fluids. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Jim, I do not know about your use of " perfect seal" in your statement but I do know this can happen. Perhaps thinking about the tiny amount of pressure the piston seal can exert one direction compared with the pressure from the brake master cylinder would help the picture.... the brake pad is forced into position one direction....and all that is required by the messed up brake line is to overcome that tiny piston seal capability to ' retract' the piston... thus it stays in contact.
It was 25 years ago... but it happened to me ...and drove me crazy till an old mechanic suggested what might have happened.... Presto! fixed in a flash...

Here are some links to help.....
http://www3.bc.sympatico.ca/Volvo_Books/brake6.html

http://www.alldata.com/techtips/2002/20020517d.html


Very simple documents. RE: brake hoses.
http://64.233.161.104/search?q=cache:3goANTGoq7kJ:www.parker.com/hpd/literature/pdf/SAEJ1273.pdf+automotive+hydraulic+hose+failure&hl=en

http://64.233.161.104/search?q=cache:4u4t3OqBkmoJ:www.truefog.com/TrueFlex%2520Fog%2520Line%2520Specifications.pdf+automotive+hydraulic+hose+failure&hl=en


Unrelated but interesting link:
http://forensicmechanic.com/sys-tmpl/pictures/

__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

Jim:

Brake hoses are multilayer, and what happens is the innermost layer starts to come off. If a flap forms, it's very easy to see how applying and releasing pressure can cause a flap to obscure the hole in the liner, holding pressure. I've had this happen on at least four different manufacturer's lines (Ford, MB, Chrysler, GM) and in no case was it visible on the outside.

However, it doesn't cause the brakes to drag, it causes them to stay applied all the time in the cases I've seen. Smoking brakes, violent brake pull, etc.

Soydriver:

You need to rebuild the calipers, the piston seal is shot. Plan on doing all four, it's not all that hard, and if the fronts are bad, the rears aren't far behind. Pretty normal for that age car, I've done all fourn on all the older MBs we have.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!