|
Dr. Rob
Veteran
Date registered: Nov 2006
Location: Stockholm, Sweden
Vehicle(s): 280GE LWB, 280E Ambulance
Posts: 216
| Disc brake troubles
So, I sorta thought the front brakes sounded kinda funny.
You tell me...
One of the pads is GONE; not one grain of friction material left on it. The brake was going steel-on-cast iron. (helpful tip to mechanics and DIYers: if you ever open something up and see metal dust inside, close it as quickly as possible and run as far as you can)
As it happens, the run away option was not doable; I had to get it back together. So I machined up a temporary replacement brake pad, put all the bits and pieces back in there. Tried it out, and found that there was very little pressure available. Pedal goes almost to the floor. Hmm.
Questions and such:
Brake disc: Is this a Gwagen part only, or is it a common part to other models?
More brake disc: Where in Scandinavia? Tjaerand, I think you said Mekonomen was the place to go, for around 800 kr / each. Really? That's a lot for a brake disc. What about Biltema? Were they in stock, or special order?
More brake disc: I happen to own a machine shop. Is it considered okay to refurbish the disc on a lathe? Any idea of minimum wall thickness?
Brake pad: Same thing, where get and how much $ ? In pairs?
Brake pad: This is a piece of sheet metal with friction material bonded to it. Big deal. Why don't I make new ones and go the brake lining place and have them bond up a new lining? I have more than average knowledge of friction materials.
Part numbers: Anybody know?
--------------
Case specific questions:
Why is one brake pad worn out, while the other has like 8 mm of meat left on it? I thought they were supposed to be self-centering?
Why did I lose pressure in the system? I have no brake mech experience; only a sense of logic. Realizing full well that this is a closed hydraulic system, I made sure to clamp down the hoses before beginning and not open or loosen any brake line fittings. This in an attempt to ensure air not getting into system. Made sense to me. Assembled in reverse order.
The new temporary brake pad is thicker than the previous. (of course. Anything is more than zero.) But there is still a bit of a gap between the two pads and the disc in between. Say, about 0.5 mm. How can this be adjusted?
Do I need to bleed the system? How?
Brake detail questions:
The pad consists of a piece of 4mm sheet or flat bar in a circular segment. There are two 6 mm holes in the far corners. Why? They don't seem to fit anything.
There is also a protrusion along the far edge with a 6 mm slot cut into it, with an 8 mm counterbore. Why? This doesn't fit anything either. Although, there is a right / left difference. The two pads are not mirror images.
-----
Lot of questions, I know. Gotta start somewhere. Worth saying though, I might just leave the car with the mechanics. There is a lot of other funky stuff going on with it. Might be easier to just give them the keys and a billing adress....
Big thanks in advance to anyone who has any thoughts...
.
 (HPIM0365.JPG)
Attachments
----------------
 HPIM0365.JPG (162KB - 1 downloads)
|
|
| |
|
DesertStar
Expert
Date registered: Apr 2006
Location: San Diego, CA USA
Vehicle(s): 85-280GE/95-G320/08-G500
Posts: 2156
| RE: Disc brake troubles
I am not a lot of help in the disc brake department....but I will wonder if correcting this will get rid of the "perturbing smell". Ouch, you have your work cut out today.
Mike |
|
| |
|
4x4abc
Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
| Re: Disc brake troubles
looks like you took the caliper apart - that's a "No-No", unless you have detailed experience.
No brake pressure? You have your answer. Yes, of course you need to bleed the system after taking the caliper apart. |
|
| |
|
Dr. Rob
Veteran
Date registered: Nov 2006
Location: Stockholm, Sweden
Vehicle(s): 280GE LWB, 280E Ambulance
Posts: 216
| Re: Disc brake troubles
Ah, right... of course. Hydraulic circuit goes through the caliper. Too tired to see it last night.
Re smell, well maybe but the smell is old; this brake thing is new. |
|
| |
|
dai
Expert
Date registered: Apr 2006
Location: Oregon USA
Vehicle(s): 300GD 300TD BMW R100RS Landini 80F
Posts: 2110
| Re: Disc brake troubles
The reason that you have different wear on the pads is that one side of the caliper was probably not moving freely. That is, one or more of the pistons were sticking so the other side was doing more of the work. The caliper itself is not self centering, when the pistons in the bores are all moving freely they apply force equally to the center, pressing on the disk together. If one side is sticky that side will wear the pad less. The side that works well will do more of the work and wear more. When this symptom of a problem is found, rebuild both of the the front calipers or replace them with rebuilt or new ones.
With that much metal to metal contact it is more than likely you will need a new rotor(s). The minimum thickness of the rotor should be stamped into the outer edge of the rotor. If there is rust so you can't see it take some emery cloth and clean it off to find the specs.
The brakes on the G share some part numbers with Mercedes Vans in Europe. The pads come in sets of four, two for each side and they should be installed that way all at the same time. You probably have a sticky caliper that needs to be rebuilt and it would be a good idea to rebuild both sides. Given what you have said and showed in the photo I would buy pads, two new rotors and rebuild the calipers. Carefully inspect the flex hoses for age cracking. This is the time to replace those as well if there is any evidence of damage.
Get ahold of a manual like Harald's brake service guide or some other service manual for the G. Those pads come out of there without taking the caliper apart. To bleed the system of air it is almost impossible to do a decent job without a pressure bleeder. They are available inexpensively. The pads have a slot and a drilling into the friction material for G models that have wear sensors that fit in that spot.
Consider trying to get the brakes that Amzimmy found down where he lives in South Africa. He thinks they have made a dramatic improvement in his braking. This is your opportunity to improve things on yours. The front brakes on a vehicle do something like 80% of the work of slowing down the big heavy metal thing.
Check out the tech articles on clubgwagen. Dave G has a great article he posted about the pressure bleeder he has and how to use it. He offers details that are important when servicing that system in a clear way with great photos.
-Dai |
|
| |
|
Tjærand
Extreme Veteran
Date registered: Oct 2006
Location: Nøtterøy, Norway
Vehicle(s): 1996 G320
Posts: 403
| RE: Disc brake troubles
Dr. Rob, Mekonomen has everything you need to rebuild your entire brake system if need be. Disks are just above 700 SEK per disk. Those are Brembo mind you so I don't think the price is steep at all. They are dimensioned for your G...
They also sell claiper rebuild sets and new calipers for around 3000 SEK if all else fails.
Pads from Mekonomen are Mintex or ATE, the latter costing more. 600 SEK ++ for a complete set. Buy new mounting hardware too. The pads also fit the old vans like 601D, but they'll cost you the same no matter what car you buy them for...
Note that Mekonomen sells bearing sets and drivknutar too ;-) A very cost effective alternative to the Mercedes dealers. |
|
| |
|
roughneck
Expert
Date registered: Apr 2006
Location: UK, Germany & USA
Vehicle(s): 270 cdi.300 GD 300 GE.lwb 300 GE.swb. Disco 2
Posts: 4398
| RE: Disc brake troubles
Dr Rob, this is just my opinion, take your G to a competent mechanic and don't mess with things that could kill someone.  |
|
| |
|
amzimmy
Elite Veteran
Date registered: Apr 2006
Location: South Africa/Italy
Vehicle(s): GD300 1981, Alfa GT 3,2 V6, Alfa Brera Q4 3,2 V6.
Posts: 850
| RE: Disc brake troubles
Dr Rob, I fully agree and support the comments of Dai and Roughneck! Don't fool around with brakes, let the specialists handle the matter! If you would be interested on the "Powerbrake" rotors and pads send me a PM and I see if I can organize something for you.
amzimmy |
|
| |
|
Tjærand
Extreme Veteran
Date registered: Oct 2006
Location: Nøtterøy, Norway
Vehicle(s): 1996 G320
Posts: 403
| RE: Disc brake troubles
Dr. Rob, if you have time to wait for the discs amzimmy mentions they will cost you the same as a full set of rotors and pads from Mekonomen. And thats a bargain for vented disks and matched pads! I would have taken the Powerbrake ones but I had 2 days to pass inspection. |
|
| |
|
Dr. Rob
Veteran
Date registered: Nov 2006
Location: Stockholm, Sweden
Vehicle(s): 280GE LWB, 280E Ambulance
Posts: 216
| Re: Disc brake troubles
Thanks for the thoughts, guys.
Thanks for the offer amzimmy, but I think I'll decline. Any new rotors and pads will be a drastic improvement over what was, what with the existent surface quality and minimal contact surface that is in place now. And if I want to improve upon that, I have an array of friction materials and resources. Right now I just want to get it done.
I'm heading over to the mechanics later on, mostly as a matter of convenience. Working with critical components doesn't bother me; I do that regularly anyway. But they have plenty of experience, do it all the time, have all the tools, have deals with suppliers and can fix all the other stuff while they're at it. I have other things to think about.
Although I am kind of interested though...
We'll see what they say.
Doc.
|
|
| |
|
BusBar
Extreme Veteran
Date registered: Apr 2006
Location: UK. North West / Wales
Vehicle(s): 463 300GDL, 460 280GEL
Posts: 382
| RE: Disc brake troubles
My local parts supplier has provided me with disc's and calipers form these people in the past. http://www.brakesint.co.uk/
Disc's around 400kr and calipers around 1000kr including our purchase tax @17.5%.
I know they are UK based but at least it gives you some idea of prices. |
|
| |
|
Dr. Rob
Veteran
Date registered: Nov 2006
Location: Stockholm, Sweden
Vehicle(s): 280GE LWB, 280E Ambulance
Posts: 216
| Re: Disc brake troubles
I gave it to the mechanics to deal with. No problem and thank you; there's enough work left on the car for me anyway.
They had an alternative source for parts though, with slightly lower prices on pads. Discs were the same Brembos. Meca.se, a pro supplier. Mekonomen is for privateers; Meca is for pros.
Well, got that done... Now what? |
|
| |
|
Iver460
Veteran
Date registered: Apr 2006
Location: Norway
Vehicle(s): '82 300 GD STT Cab (two other Gs in family)
Posts: 291
| Re: Disc brake troubles
Dr. Rob - 3/25/2007 4:33 PM
Meca.se, a pro supplier. Mekonomen is for privateers; Meca is for pros.
They're about equal competitors here, and prices are about the same.
Oh, and manual says discs should not be turned when thinner than 13mm and calls for change when under 12mm.
www.vtp.no has good prices on calipers. |
|
| |
|
Dr. Rob
Veteran
Date registered: Nov 2006
Location: Stockholm, Sweden
Vehicle(s): 280GE LWB, 280E Ambulance
Posts: 216
| Re: Disc brake troubles
FOLLOW-UP POST, A COUPLE DAYS LATER:
So anyways, the mechanics did the job quick and easy. Life must be a lot easier when you have lifts, lighting, all the tools and 40 years of experience.
And they only charged me for the parts; we'll trade work favors sometime in the future. Jeez life is easy when you enlist others to work.
The brakes? Oooh that's nice... sooo smoooooth.... visions of velvet slippers sliding across a polished hardwood floor. No pulsating, no jerking. Niiiice.
FUNNY ADDENDUM:
Took a look at my old disc... it was shot. No way worth the effort of trying to fix, and even if so it would've been way under minimum thickness. "Oh yeah?" says my mechanic. "You gotta see THIS !"
And pulls out a disc they changed on a Discovery last week.... It was worn so thin it was unbelievable.... absolutely flat and parallell, and I measured it-- 1.7 mm thick!! That's like 1/16" ! Thinner than an LP record!
.
|
|
| |
|
GwagenLover
Extreme Veteran
Date registered: Apr 2006
Location: Winston Salem, NC USA 27104
Vehicle(s): 2016 G550 & 2016 GLE350
Posts: 473
| RE: Disc brake troubles
I did not read the responses that the other guys added, but I had a similar problem on an older Mercedes.
The caliper piston was sticking.
The result was just what you have experienced.
I took the caliper apart.
I placed one half of the caliper inside of a large vise, leaving the jaws open about one inch larger than the caliper.
I put some shop towels over the jaws to soften the force of the exiting piston.
I then took the air hose and blew the piston out of the cylinder.
KEEPING IN MIND THAT THE FORCE OF THE PISTON COMING OUT OF THE CYLINDER WILL BE GREAT!
Once I had the piston out of the cylinder, I honed the inside with a small barke cylinder hone and my electric drill.
I replaced the "O" rings and there was no more stuck piston.
"O" rings are easily avaliable in a kit from Harbor Freight.com Very inexpensive.
I saved myself the cost of a new brake caliper. |
|
| |
|
roughneck
Expert
Date registered: Apr 2006
Location: UK, Germany & USA
Vehicle(s): 270 cdi.300 GD 300 GE.lwb 300 GE.swb. Disco 2
Posts: 4398
| RE: Disc brake troubles
Dr Rob. There is a lot to be said for being able to stop when you want, the experience is often under rated  |
|
| |
