Getting dust boots on w123 calipers - PeachParts Mercedes-Benz Forum

JHZR2 · #1 06-07-2019, 10:36 PM

Im doing the first caliper, front Bendix, on my 300cd. I’m at the point of putting it together, cannot get the dust boot to fit over the lip on the caliper body for anything. Have wasted around three hours and gotten nowhere.

FSM 42-150 shows images but it’s virtually useless.

Any recommendations? Tricks?

NOT worth the $40-60 for rebuilds.

Diesel911 · #2 06-07-2019, 11:43 PM

Never done the bendix calipers. But, I have had issues on various calipers where the Dust Boot would not stay on the lip of the caliper body. Meaning that I got the boot seal over the lip on the caliper body but it popped back off. But, on those calipers there was no heat shield in the way.

On some the caliper lip and the boot lip needed to be degreased with brake cleaner so it was dry. Then when the boot was installed I needs something like C-clamps to hold the boot down and after letting it sit like 6 hours the boot finally gripped onto the lip.

Other times after the degreasing I have used a high temp rubber cement that I have or used silicone sealant and again used C-clamps to hold the boot onto the caliper lip and waited till it cured and glued them to the caliper.

In the past I have used

Repair Links
Fast navigation Fast navigation Do It Yourself Links

The quality of caliper rebuilding kits varies. You might find that the originals had a separate external metal spring to squeeze the boot onto the caliper lip and the kit you get will have that spring inside of the rubber lip of the boot. The ones with the spring inside tend to slip off of the caliper lip more then the original styles do.

Diesel911 · #3 06-08-2019, 12:04 AM

I am going to suggest a wiled guess.
See the attached pic. Get the boot on the piston as in the picture. Lube the bare piston between the boot and the heat shield with that special caliper lube they sell at places like Autozone.

The boot lip on the caliper body needs to be degreased with brake cleaner.

Degrease the inner boot lip the end that goes onto the caliper with brake cleaner.
Not shown in the pic put some lube on your finger and lube the inner caliper O-ring seal but not the end of the piston.

That should give you working space to push down on the caliper end boot lip to secure it to the caliper lip.

If you get the caliper end of the boot to stay in place let it sit a few hours to be sure it won't pop back off. After that you are going to have to do what is needed to get the heat shield end of the boot up into the groove.

I think if the bare piston area was well lubed and you slowly push in the piston the boot is going to slide at least partly to where it should go. then you can pull the Piston out a bit and see if you can get the boot all the way in the groove.

I know some people hate this Idea but this is where having the two sections of the Caliper taken apart is a huge help in giving you room to work in.

Push the Piston into the seal just barely; enough to get it centered.

JHZR2 · #4 06-08-2019, 12:14 AM

The FSM and other info I’ve reviewed didn’t really help for this. I’ll ultimately construct a pictorial and DIY, though this IME is not a job worth doing unless parts are really poor quality in the aftermarket. I wasted hours this evening trying to get this done.

The issue is that the FSM implies to me that the seal is put over the back end of the piston, then the piston is pressed in, and the seal picked over the flange.

This end of the piston:

This collar or flange (on the left, part of the caliper body)

The FSM shows the boot pressed on the end of the piston, with the heat shield installed at the other end. Then it shows the boot being picked with the piston pressed nearly all the way in... I tried.

But for the life of me, couldn’t get the seal over. I tried with the seal down at that collar, with the piston way out, with the piston way in (Hoping the heat shield would force the seal in that direction), etc. Nothing worked.

What worked was to just barely put the boot on the piston end. Let the other part of the boot, which would ultimately slip over the collar, hang off the end of the piston, splayed open. By doing thst, a portion of the seal can be steered and held in place. The key is to not put the piston in the bore yet. Center it in the bore, but allow it to be mobile. Then start to press the seal in, taking what little ground you can, and then moving the piston a bit more to help steer. Being able to move the piston a bit helps. Picking the seal into place, which is what the FSM mentions, isn’t necessary, because it’s also not useful. Just forcing a bit more slack on one side of the seal or the other, while keeping the boot tight on one side where it’s already under the collar, helps...it will finally go in, on one side, but not want to go I’m om the other side. Just get a tiny bit by tiny bit under that collar, Work around, finally it will be in. Then the piston can be pushed in all the way.

JHZR2 · #5 06-08-2019, 12:18 AM

Quote:

Originally Posted by Diesel911

I know some people hate this Idea but this is where having the two sections of the Caliper taken apart is a huge help in giving you room to work in.

Push the Piston into the seal just barely; enough to get it centered.

FYI no picture loaded in your post.

I agree, in hindsight I should have split the caliper. Don’t think I had anything to lose really. Piston moves in bore, but Imwont know if it is still working 100% until I try...

You’re right, barely push the piston in just for centering, and maybe not even that...

Diesel911 · #6 06-08-2019, 12:24 AM

Quote:

Originally Posted by JHZR2

The FSM and other info I’ve reviewed didn’t really help for this. I’ll ultimately construct a pictorial and DIY, though this IME is not a job worth doing unless parts are really poor quality in the aftermarket. I wasted hours this evening trying to get this done.

The issue is that the FSM implies to me that the seal is put over the back end of the piston, then the piston is pressed in, and the seal picked over the flange.

This end of the piston:

This collar or flange (on the left, part of the caliper body)

The FSM shows the boot pressed on the end of the piston, with the heat shield installed at the other end. Then it shows the boot being picked with the piston pressed nearly all the way in... I tried.

But for the life of me, couldn’t get the seal over. I tried with the seal down at that collar, with the piston way out, with the piston way in (Hoping the heat shield would force the seal in that direction), etc. Nothing worked.

What worked was to just barely put the boot on the piston end. Let the other part of the boot, which would ultimately slip over the collar, hang off the end of the piston, splayed open. By doing thst, a portion of the seal can be steered and held in place. The key is to not put the piston in the bore yet. Center it in the bore, but allow it to be mobile. Then start to press the seal in, taking what little ground you can, and then moving the piston a bit more to help steer. Being able to move the piston a bit helps. Picking the seal into place, which is what the FSM mentions, isn’t necessary, because it’s also not useful. Just forcing a bit more slack on one side of the seal or the other, while keeping the boot tight on one side where it’s already under the collar, helps...it will finally go in, on one side, but not want to go I’m om the other side. Just get a tiny bit by tiny bit under that collar, Work around, finally it will be in. Then the piston can be pushed in all the way.

All of the above means your time was not wasted.

JHZR2 · #7 06-08-2019, 12:37 AM

Quote:

Originally Posted by Diesel911

All of the above means your time was not wasted.

The pain of my fingertips from messing with pushing the pistons in and out, sharp,edges on those heat shields, etc, would make my brain say otherwise

I love diy, but still lingering is the question of if it will still bind. All of this could be for naught.

I did learn how to do it, that’s something aim happy about. But I’m still not done with one side rebuild, let along the other side, the rears, or my 240, which is likely prudent....

All that makes me tired. For $40-ish a piece, subsequent ones will need to be much faster, or else not worth the hassle and hand pains, IMO.

JHZR2 · #8 06-08-2019, 09:44 AM

I guess it works. Now on to paint.

https://youtu.be/T7C-jy8GZu0

Diesel911 · #9 06-08-2019, 11:00 AM

Quote:

Originally Posted by JHZR2

The pain of my fingertips from messing with pushing the pistons in and out, sharp,edges on those heat shields, etc, would make my brain say otherwise

I love diy, but still lingering is the question of if it will still bind. All of this could be for naught.

I did learn how to do it, that’s something aim happy about. But I’m still not done with one side rebuild, let along the other side, the rears, or my 240, which is likely prudent....

All that makes me tired. For $40-ish a piece, subsequent ones will need to be much faster, or else not worth the hassle and hand pains, IMO.

If you ever exchange your calipers you could get ATE Calipers instead of the bendix ones. The ATEs are easier to rebuild; you insert the Piston, install the Boot and then the Heat Shield goes on last.

hercules · #10 06-08-2019, 05:00 PM

Rebuilt many,That shield goes on last.
Worked for Mercedes Benz of North America for twenty some years, discovered the
manual to be less than best way often,some times just plain incorrect.
Corrections or updates to many manuals.

Diesel911 · #11 06-08-2019, 11:38 PM

Quote:

Originally Posted by hercules

Rebuilt many,That shield goes on last.
Worked for Mercedes Benz of North America for twenty some years, discovered the
manual to be less than best way often,some times just plain incorrect.
Corrections or updates to many manuals.

There is a difference between the ATE and the Bendix Heat Shelds. The ATE Heat Shields grip on the inside diameter of the Caliper Piston and the Dust Boot has nothing to do with the Dust Boot.

The Bendix Heat Sheilds grips on the outside of the Piston and the heat shield end of the Dust Boot overlaps over the that part of the heat shield that grips the piston.

JHZR2 · #12 06-08-2019, 11:39 PM

Quote:

Originally Posted by hercules

Rebuilt many,That shield goes on last.
Worked for Mercedes Benz of North America for twenty some years, discovered the
manual to be less than best way often,some times just plain incorrect.
Corrections or updates to many manuals.

Thanks for the insight. The goodness of putting it on first is that it gets the geometry of the raised part of the piston, which has to face one way, to be correct. The FSM makes a big deal about that.

I tried boot installation both ways relative to having the heat shield on. Ultimately I did leave it on for orientation.

The boot was best installed hanging off the front like this:

The challenge is that when seated nicely on one side:

The other side is way off and falls in the bore.

So you need to get the boot hanging off with minimal slack in the overhang part, so just enough is there, then hold the seal in place in some amount of the circumference, and move the piston (it’s not pressed in yet) to generate the stack.

JHZR2 · #13 06-09-2019, 09:04 AM

Quote:

Originally Posted by Diesel911

There is a difference between the ATE and the Bendix Heat Shelds. The ATE Heat Shields grip on the inside diameter of the Caliper Piston and the Dust Boot has nothing to do with the Dust Boot.

The Bendix Heat Sheilds grips on the outside of the Piston and the heat shield end of the Dust Boot overlaps over the that part of the heat shield that grips the piston.

True, but the crux of it is that the heat shield can be put on last (and save your fingers dealing with sharp edges, IF, you can actually get the shield on in those close quarters. First try getting the FTE (notionally German made; the boots were f.a.g. FWIW) heat shields on, I had to use a block of wood and hammer to get them on... and I don’t think it’s possible to get the piston to rise 0.1mm at all.

So putting the boot as I show can be irrelevant of if the heat shield is on, except that as the FSM shows, it’s a convenient way to index the raised section of the piston if you don’t have the tool and don’t want to eyeball it.

Once the dust boot is seated, the heat shield could be applied, and the fsm says that the piston must be fully compressed to seat the seal perfectly, which does slip it over the heat shield in the piston groove on the top.

To me the big issue is getting those heat shields on the first time. It was hard!