Hi All,
I'm doing the rotors on the front of one of the 123's. Is it OK to reuse the bolts that hold the rotor to the hub? Will a nice whack with an electric impact wrench remove them (having been previously soaked with PB Blaster).
The bearings are fine so just a repack but i will replace the seal at the back of the hub. When putting it all back together, on other cars I would generally "pre-load" the wheel bearing by tightening up until the wheel wouldn't turn anymore than back off a bit and stake the nut. Would I do similar here? How far to back off the hub clamp thing, 1/4 turn? 1/2 turn?
Thanks for any and all advice.

If the impact wrench doesn't do it go with heat.

Sixto
95 S420
87 300SDL

This may sound weird, but I couldn't get those bolts loose until I stood the tire up, attached the assembly back on, sat on the tire and used a breaker bar. They all came loose that way. Prior to that, I couldn't get any of them. Of course, I didn't have an impact wrench which might be the better way to go.

Len

My thoughts are to avoid the impact wrench if you wish to reuse the screws. The chances of slight damage to the hex socket heads is great. If you reuse the screws, make sure you sell the vehicle before the next full brake job.

You can get the screws to come off with brute force if you do the following:

Thread three lugs into the hub and set the hub on a table with the three lugs downward. Shove a two foot bar in between two of the lugs and let it come to rest against your thigh. Get an 18" breaker bar and the screws will break loose with just your arm strength. The risk of damage to the screw is minimal and you can reuse them.

You would not do similar here. You are speaking of a typical American vehicle that can easily live with .010 clearance.

With the M/B, the specification is .0005 axial play in the hub. Now, you won't be able to feel .0005, so, unless you have a dial indicator, you can't set the clearance properly. But, what I do is to tighten the clamp until there is no play and the bearing is dragging the rotor. Then, back it off, very slowly, until you can barely feel the slightest bit of axial play in the bearing. The smallest possible amount of axial play that you can feel is too much, but, you won't notice it while driving the vehicle and it won't harm anything. In reality, you probably can't feel anything below .0015". The spec is 1/3 of this value.

The bolts zipped right out with the impact wrench. Small sledge hammer and the hub popped off too. I am going to use new screws to put on the new discs and hand tighten them and use blue loctite. I do have a question about the seal, will it come out using say a claw hammer? Don't much care if it's wrecked as I've got new ones. I just bought a dial gauge for another job and will set the wheel bearing play with that. I was surprized how well the impact wrench worked. Not violent at all, less than 10 seconds per bolt. One bolt was stubborn and I hit it with a bit of heat and that did it. The PB Blaster stuff works very well. I've been using it instead of Liquid Wrench and it hasn't let me down yet. Found a set of new rear rotors in the garage, probably do them too while I'm suffering in the heat anyways. Question, is the seal the only thing holding in the inner bearing? I want to re-grease the thing well as this job won't be done by me again. Looks like one 123 is going to my son, the other is just plain going. Time to trim the herd. I'll be left with my old ponton and a recently acquired Jag for toys.

out the seals from the other side. they are the only thing holding the inner bearing in. the loctite is fine, the red stuff.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Excellent. Normally, they are not that compliant. Tigthen the screws more than hand tight, BTW, even if you use Loctite. If you tighten them to specs, you don't need Loctite. You clearly noticed that they are not going anywhere on their own.


Be very careful with a claw hammer. You can use the claw to get behind the seal, but do not use the hammer as a lever. The bearing is right behind the seal and you cannot use the bearing as a place to apply force from the hammer. Better to hook the seal and be able to hit it upwards in some fashion. IIRC, I used a prybar that had a horizontal surface to smack the hammer against.

That's certainly the best option. Set it anywhere between .0005 and .0015 and you will be fine.

That's it. Once the seal comes out, the bearing comes out. Just be careful not to damage the bearing in the process of pulling the seal.

that the factory uses a form of locktite, so i always do too. theirs is blue.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

FYI the end play is 0.005", not 0.0005", according to my Haynes manual. I'll double check this with my MB manual, but if you set it to .0005, it'll be WAY too tight.

Jay.

I'm using the W126 FSM. The end play is .01-.02 mm.

.005" is 6.4 X the high side limit.

I thought I had a dial gauge, not, it was something else. I was rummaging around in my dad's old tools and what I thought was a dial gauge (years ago) is actually some kind of temp measure for submarines.
So, here's what I did, I put the new disc and hub back on, tightened the living crap out of the end nut thing until the wheel would barely move. I then backed off the adjuster until slight play could be felt. I then snugged up the adjuster until I could no longer feel any play, but the hub would still spin free. only spins for a couple of seconds and make no noise whatsoever. Am I ok like this? Is the end-play so critical the the wheel will fall off if I'm wrong? I really doubt I'm going to have trouble with this as I've had these hubs off before and never had trouble after remounting like this.
A PS here. The second wheel's disc bolts would back out easily. An 18 in breaker bar and a small sledge hammer like the ones used on knock-offs, worked GREAT. Wack wack, loose! Real easy. this was on a hub that had been badly overheated due to a frozen caliper.
Thanks Much.

Personally, I would guess that the wheel would work perfectly well with .005 end play. The wheel won't fall off and the bearing won't care. So, the M/B spec of .0005 seems a bit ridiculous.

That said, a tapered roller bearing is intolerant of preload. If you tighten the nut and the bearing has less than zero clearance (preload), it causes the bearing to run considerably warmer than it would otherwise run. In the environment of the brake system, this is not a good thing and could shorten the life of the bearing.

I've had one of those bearings disintegrate while the vehicle was moving. It's not pretty.

there is a formula in the haynes i believe which says tighten til it no longer spins freely then loosen 1/4 turn or some such. i usually do it by feel, but a formula is comforting to a beginner.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Rediculous or not, the spec IS 0.01-0.02 mm (0.0004-0.0008"). If Haynes indeed has 0.005" written in its procedures, it wouldn't be the first time I saw an error in a manual.

Yes, end play is critical. Your wheel will not fall off if the axial clearance is off spec, but it will have a definite affect on bearing life.

If you must set the preload without using a dial gauge, this is the procedure I recommend:

1. Tighten the nut while turning the wheel until the wheel is difficult to turn. This will squeeze out the excess grease and seat the races.
2. Back the nut off until slack. (Don't turn the wheel).
3. Turn the nut finger-tight.
4. Tighten the clamp bolt.

__________________
95 E320 Cabriolet, 159K

In step #3 you state to turn the nut "finger tight". A procedure such as this is grossly inadequate to come anywhere near a axial clearance of .0005".

If I tighten the nut "finger tight", I can assure you that the axial play will be completely gone and the bearing will be under some preload.

It would be far better to tighten the nut slowly, while checking for axial movement, until you can't feel any axial play. Then back the nut off by 10 degrees. This will put .001 axial play into the bearing and ensure that there is no preload.

10 degrees is 1/6 of one wrench flat. Not very much.