All new 230SL front Girling brakes

[Tomnistuff]

My restoration reassembly is progressing and a concern has arisen.

With new fluidless Girling rebuilt calipers, new rotors, new pads, new caliper hardware and Permatex Ultra Slick Ceramic Extreme Brake Lubricant, my brakes were a little difficult to install due to tightness.   I put a light coat of the brake lubricant between the shims and the pistons and another light coat between the back of the pads and the shims.  When I installed them on the rotors, it was necessary to wedge open the pads to get them over the rotors (both front wheels).  When rotating the rotors by hand, the pads drag but are not really, really tight.  I can still rotate the rotor by hand.  When I add the two spring clips on the pads of each caliper, the piece of wire that goes between the pad back plate and the shim makes the system even tighter.  See the photo.  I can still rotate them by hand but they are really tight.

Here`s my opinion, but I would like the opinions of you experts.  Since there is not yet any fluid in the calipers, I can`t pump the brakes to squeeze the lubricant down to it`s working thickness.  As assembled, I have four thin layers of lubricant  on each caliper (pad to shim and shim to piston, twice).  I think that accounts for about 1 mm of pad tightness on each wheel.  Additionally, I don`t think the wire spring clips are necessary to stabilize the pads on the pins.  The wire spring clips look like they were desinged to work with Teves shims but not with Girling shims.  I think I must either notch the shims to provide clearance for the wire spring clips between the shim and pad plate or toss out the spring clips.  That will reduce the tightness by another millimeter.  Opinions?

The parts all measure to be correct to the MB specs.

Tom Kizer

[Tomnistuff]

I`m curious as to why this post was moved to R&D.  My car came with Girling brakes.  I`m just restoring it with some rebuilt parts instead of new Mercedes parts.  There is nothing R&D about this post that I can see.  Does using rebuilt parts in a restoration constitute R&D?

Tom Kizer

[Cees Klumper]

Are you sure the pistons are all the way back in the calipers? I don't think the pads should drag the disks at all. But I would hold judgment until the system has fluid in it and is at 'operating readiness'. Perhaps the pads are the wrong kind? The lubricant you added seems like it would squeeze out to much less than a mm when some, even light, pressure would be applied, so I would not expect that would be the cause. Anyway, just one shade-tree mechanic's 2 cents.

[Tomnistuff]

The lubricant that I used is about the consistency of "creamy peanut butter".  It's quite a heavy high temperature grease, and there are four light layers in each caliper.

I spread the pads by inserting wood blocks that are 0.25 mm thicker than the rotors.  As I push the calipers onto the rotors, the wood blocks are pushed out the front of the caliper, so installation is quite easy.

I do notice, however, that the pistons move back when I insert the wood blocks, but spring forward again when the wood blocks are pushed out by the slightly thinner rotors as I push the calipers onto the rotors.  It seems as if the piston seals are preventing the pistons from bottoming comfortably.

My calipers are Girling type 17/3, three-piston calipers.  I suppose that it's possible that I just need to finish the job and pump the brakes a few times to seat the pads with high pressure.  Everything is at maximum tightness with new calipers (new tight piston seals), new pads (maximum no-wear thickness), new rotors ( maximum no-wear thickness), old CAD replated shims (possible slight deformation from previous use) and new stiff brake lubricant on all the recommended contact surfaces (un-thinned by brake pressure and heat).

Maybe I worry too much.  I"ll finish the restoration and see how things work when I get the car up and running.  After all, even my shoes and shorts are tight when they are new.

Tom Kizer

[Cees Klumper]

Quote: "I do notice, however, that the pistons move back when I insert the wood blocks, but spring forward again when the wood blocks are pushed out by the slightly thinner rotors as I push the calipers onto the rotors.  It seems as if the piston seals are preventing the pistons from bottoming comfortably."

I think there lies your answer somehow. I'm not used to the pistons moving as if under pressure from a spring, by themselves, as far as I know they need pedal pressure to move, and then somehow when the pressure is removed, they let up just enough for there to be no drag. In our garage, there is an ever-so-slight incline and I'm always surprised how my cars will start moving by themselves if not put in gear or on handbrake.

[UJJ]

You may have trapped air in the system. If all the hoses and lines are connected (closed system) and you then push the calipers open you compress the air in the system, Since air is compressable it acts like a spring. Perhaps that is what you did.
What happens when you open the bleeder? If the pistons still extend with the bleeders open, I think there maybe something wrong with the calipers.
I do not have the Girling but the ATE Calipers. The gap between the rotors and new pads is surely 1mm on each side of the rotors.
Perhaps this helps, Urban

[Neil Thompson]

Tom, looking at the photos I think  the shim plates should face the other way, ie the flat face you see should face inwards so the spring clips cover this face and allow the shim to fit tight to the pad at all times. The way it is currently is making the shim not fit flush and jammin the aperture. The easy way to also check if the brakes are binding is to remove the shims completely and connect the hydraulics and pump up the system.

Neil

[garymand]

Sorry, I'm not a 230 guy but just looking at the picture, something is really wrong with how those bright metal things are arranged.  They align the wrong way, they are interferring with the jaws of the calipers.  I'm sure that is what is pushing the pads into the disc. 

The later calipers I've workled with have a heat shield pressed zround the pistons.  This heat shield has tabs like the shiney metal faces but they are deap down at the bottom of the jaws that stop the pads from going too deap (I assume) into the jaws. 

It looks to me like the metal 'shims' are in upsidedown and reversed, but then the pins don't have holes to go through?  so just reversed?  turn them around. But then do the clips still fit?  Do you don't remember how you took the old ones out?  What were they like?

[Tomnistuff]

Thanks for all the comments.  I`ll try to address them in turn.

Cees wrote (reply #4):  "I think there lies your answer somehow. I'm not used to the pistons moving as if under pressure from a spring, by themselves..."

I agree with you, Cees.  Unfortunately, I don't have enough MB initial build dimensions to be able to compare to the parts that I have installed.  Therefore, I cannot determine where the problem is.  More discussion after these responses.

Urban wrote (reply #5):  "You may have trapped air in the system. If all the hoses and lines are connected (closed system) and you then push the calipers open you compress the air in the system, Since air is compressable it acts like a spring..."

You would be right, except that the brake fluid hard lines are bolted to the calipers and I have not yet connected the brake hoses.  The piston chambers are open to atmospheric pressure with no fluid inside.

Neil wrote (reply #6):  "Tom, looking at the photos I think  the shim plates should face the other way..."   and
garymand wrote (reply #7):  "...just looking at the picture, something is really wrong with how those bright metal things are arranged."

I have verified from a "before" photo and also from photo 42-10/1 on page 42-10/1 of the BBB that the Girling shims (heat screening plates) are facing the correct direction.  The BBB photo is of a Girling 17/3 (3rd version) caliper like mine, although buried in a 4th version caliper discussion.  The flanges of the shims protrude beyond the edge of the caliper body and cannot interfere.  By way, I have removed the anti-rattle spring clips.  It's better but still dragging.  I also found a discussion on BBB page 42-21/13 of friction pad anti-rattle springs.  Apparently one can use the springs to eliminate rattle (if absolutely necessary), but one must remove the shims.  As you both indicated, the shims and the anti-rattle spring clips are incompatible and mutually exclusive.  One or the other can be used, but not both at the same time.

My investigation and conclusions (pretty weak and not very conclusive) reveal that the friction pads are exactly the thickness specified by the BBB (16 mm each including the  backing plate).  The pistons are apparently completely bottomed in their chambers but the rubber dust seals protrude beyond the pistons two or three millimeters (normal when the pistons are bottomed out, I think).  The rotors are exactly 12.7 mm thick, but I don't know what they are supposed to be when new.  The BBB does not say, or at least I can't find it.  The caliper seems to be centered on the rotor, with neither friction pad dragging more than the other.  I removed them one at a time to verify.  My car is completely disassembled so there are not even a booster, pedals or brake cylinder in the car yet, so I can't go too far with the diagnosis.

As a last resort, before posting this and deciding to wait until the car is finished to continue the investigation, I decided to remove the calipers one more time and verify the flatness of the shims with a legitimate machinists straight edge.  They seemed to be slightly bulged in the centers by the pistons.  Remember that these are CAD plated original Girling shims.  Although I didn`t think they were a problem, I spent an hour with a nylon hammer and anvil, straightening them almost microscopically.  When I could see almost no light between the straight edge and the shims, I reinstalled everything.

The drag of the friction pads on the rotors is now so light that if I spin the rotors by hand, they coast a few degrees before stopping.  In my opinion, they drag no more than a typical disk brake drags when the wheel is removed and the rotor is spun.  Apparently there was enough bulge or warpage in the shims that the outer parts of the shims, beyond the pistons, were bearing against the rubber dust seals and pushing the friction pad against the rotor.  The shims were behaving as if they were about two millimeters thick instead of one millimeter thick.

I'm sorry for the long response but I wanted to answer all the questions, since you all went to the trouble to try to help me.  Thank you all very much.  I'm still not convinced that they are absolutely correct, but I don't think they will be a problem.

I quit!  From this point, I`ll finish the restoration build and wait to drive it to see if the brakes drag noticeably.

Tom Kizer

[garymand]

Tom, very methodical.  I can see in the picture that the springs (clipping over the pads are in interference with the heat sheilds.  I think you foound the issue: use either but not both.  I would prefer to have the heat shielded from the piston seals.  When you 'power up' the calipers and firmly press down on the brakes a few times, the pads and shims and pistons will settle into their intended roles.  I'm sure you will gain a mm or two as they 'break in'

[Tomnistuff]

While it`s true that removal of the anti-rattle spring clips reduced the drag of the friction pads on the rotors, the brakes were still dragging much too heavily after they were removed.  The greatest improvement came with the next iteration of  "flattening and straightening" the replated original shims.  I suspect that the situation was also helped some by my thinning out the grease between the pistons and the shims and between the shims and the friction pads.  That stuff is really almost the consistency of tacky glue.

It's worth noting that when I took them apart the last time, just before straightening the shims, I noticed that there were heavier imprints in the grease from the dust seals than from the pistons.  Two of the four shims (one on each caliper) showed no imprint of the pistons in the grease at all.  All of the dragging was caused by the force imparted by the dust seals on the shims.  As I previously mentioned, the spring-back must have been due to compression of the dust seals because of the distorted shims.  I think there is a valuable lesson to be learned from reusing old parts when rebuilding systems with new parts - make sure they are reconditioned to be like new, or toss them out and use new parts only. 

The comments of you all throughout the thread were really valuable in guiding me through the investigation.

Thanks much.

Tom Kizer