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#1
10-17-2010, 07:38 PM
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Why would someone cut the brake pad wear sensor wires...
Had a previous post that stated I was changing out the upper control arms, lower ball joints, rotors and brake pads on the front of a 1985 300SD. I managed to shuffle the bearings while cleaning them and for a while, lost track of where they came from. IE: left or right side of car.... I was able to retrace my tracks by some identification on both the bearings and races.... BUT decided to order new bearings and races anyway.... They didn't look all that great and figured if I am doing all this other work, might as well change out the bearings as well...
While waiting for the new bearings, I installed the new upper control arms. Bushings were not quite right. Had to ream them out in order for the bolt to pass through them without resistance... Was tempted to use the old bushings and rubber surrounds but found the right size drill bit to open up the holes. Can't believe they were so far off. Lower ball joints were knocked out and replaced at an independent shop. I got everything back in place and cleaned up the calipers. The calipers had no wear sensors when I dismantled things the other day. While looking around I noticed some severed wires hanging down from the wheel wells. Light gauge wire, I suspect that they were to go to the pad sensors. Do I need wear pad sensors? Been driving the car for 2+ years without them... A whole different topic. What is the cylindrical part that gets pushed through the knuckle and is held by a 5mm socket cap screw. It has a small "slotted head" that faces the backside of the hub? It has a wire attached to it and has a secondary fastening point at about 10 o'clock on the rotor guard... passenger side, that is.
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1985 300SD 
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#2
10-17-2010, 07:47 PM
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I think the sensors are needed on the car. other cars brake pads have a metal part that will scrape the rotor when the pads get thin, ours do not have that, so the sensor is very important, unless you inspect the pads every oil change or something...
and, I find it VERY hard to believe new subframe bushings arrived with the need to bore out the sleeve! if they are tight, they likely are supposed to be!
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 560SL convertible 1987 190D 2.5-5SPEED!!!  1987 300TD 2005 Dodge Sprinter 2500 158"WB 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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#3
10-17-2010, 07:48 PM
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You don't really need the sensors. They're pretty darn convenient though, nice to know when you need new pads immediately. As for why, looks like someone got their pads from the local McParts and forgot to/couldn't get the sensors.
As for the thing in the knuckle, only other thing I can think of with a wire hanging out are the ABS sensors.
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#4
10-17-2010, 07:49 PM
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Answer
Quote:
The sensor you are asking about is wheel speed... .
__________________
ASE Master Mechanic https://whunter.carrd.co/ 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 2003 Volvo V70 https://www.boldegoist.com/
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#5
10-17-2010, 08:41 PM
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Hey bud, you just keep typing and bashing your brains in...
Regarding the sleeve being tight. this is what i did before installing the new upper control arms. I took the old bolt and pushed it through the old upper control arm, while it was dismantled from the car. It had no resistance, was free floating. I took the new arm out of the box and took the old bolt. I tried pushing the bolt through the bushings and found that it had some interference. I could not make it pass through the new part. Tried from the other side and had a similar problem. Looked through the hole and saw something that did not look like a lined up thru hole. If it was a tunnel that was being constructed from both sides of a mountain, they missed the center point by "that much" Pulled one rubber end out with the bushing inside of it and tried passing the bolt through just one piece of the assembly. The bolt got stuck. Next I measured the outer opening as well as the inner opening, the diameters of the ID. They were very different. If my memory serves me correctly the bolt was .470". The outer dia was a little more than that and the inner dia was .462, therefore the bolt would enter the bushing but it would get jammed in the "taper".... I was actually going to swap out the old bushing/rubber sets but decided to ream out the new ones thinking that the new rubber was more important than the hole size, not that I was actually altering the hole size, I was just correcting a manufacturing problem... Next problem that I have it that the inner piston on the right side caliper was really hard to press in with a c-clamp. I have noticed in the past that the right front tire was harder to turn when the car was up off the ground, so I guess that the inner piston has been stuck for some time. Should I try rebuilding the caliper or get new front calipers, plural.... ***** NOTE: Front Pads were paper thin, I mean they were probably .030" thin on both sides of the front of the car... Perhaps the projection of the piston, that far, has something to do with the sticking of one piston in the right side caliper.
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1985 300SD
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#6
10-17-2010, 08:45 PM
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Hi Roy,
Thanks for the info. Bought sensors, but I guess I won't be needing them for this car! How does the speed sensor work, and why are there 2 of them, (one one each front wheel)...? Any advice on the caliper problem. The inner piston being stuck or restricted.
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1985 300SD
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#7
10-17-2010, 09:00 PM
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Quote:
Unless the Caliper has come out too far what most often causes sticking is rusty muck keeping the Piston from returning. Pulling out the Caliper/s cleaning it out and Replacing the Seals and Boot/s is most often the Cure. Ounce in a while the Caliper or the Piston is in such a bad condition due to rust they cannot be reused and expected to function or last long.
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84 300D, 82 Volvo 244Gl Diesel
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#8
10-17-2010, 09:28 PM
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I noticed that the heat shields are also deteriorated on both sides of the front ends calipers. Where can I get new ones from? I did not see them at peachparts.com. Only as part of a new caliper purchase... Was going to call a local Mercedes Dealer tomorrow, unless someone has another source.
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1985 300SD
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#9
10-18-2010, 12:43 AM
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With regards to the caliper issue, often times, calipers are fairly cheap to replace. It is best to get a new caliper than to rebuild the old one. make the call on your own.
Note for the future, this is exactly why it is SO important to flush and bleed your brake system as regular maintenance. Every two years at a minimum. Even if the pads are still fine, the system needs fresh fluid. best of luck.
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85 300D 3 pedal. Current project. 83 300TD (need rear wiper assembly dead or alive) 84 300SD Daily driver 85 300TD almost 400k miles and driven daily. 98 E300D *sold 86 300SDL *sold and made flawless 10 hour journey to new home. 
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