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Old 09-21-2003, 07:52 PM
David Speed's Avatar
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Location: Brisbane, Australia
Posts: 81
Question Bolts -? when to replace or ok to reuse

In the process of replacing to front brake disc rotors on ’78 280 CE (W123) 60k miles -first post on this forum, but have been posting my progress on the re-birth of my 280CE on the Vintage Forum

Caliper mounting bolts and rotor / hub bolts very tight & blue ? loctite ? anti-seize on threads

Can the threads be cleaned up and these bolts be reinstalled with new blue loctite or should they be replaced?

I have read about stretch bolts -how do you identify them ?

The caliper bolts look like they could be stretch type…..but why use the ‘blue’ unless it is just anti-seize

The rotor / hub bolts have thread all the way to the 10mm Allen Head

I have read on the Pindelski site that the rotor to hub bolts should be installed to 115Nm with no anti-sieze, no oil, no loctite, but mine had had the ‘MB blue’ on them when removed for the first time since manufacture……….no indication re need to replace bolts noted on this excellent info site

Will probably replace all the bolts as safety is my prime concern……….but I would appreciate Tech advice.

If anyone has a MB CD or Manual for this type of brake / hub setup (W123 or W124 I think -later ones seem to just have one small locating bolt) -what do they advise with regard to these bolts ?


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Old 09-21-2003, 08:16 PM
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Location: Evansville, Indiana
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The lug bolts hold the rotors on in the W124 chassis, front and rear. No need to replace.

Basic rule on bolts is to re-use unless they are subject to stress or head that would change the material characteristics.

That means stretch bolts (these are always tightened to a torque and then some degree of rotation) and critical fastners like the bolts on calipers should be replaced unless integrity can be verified. Mind you, I've never replaced a caliper bolt and never had one break, but if the factory manual says replace, it's a good idea. Some manufactures (Volvo, on the TD) require replacement for head bolts each use, others have a length spec.

The newer cars have many bolts "glued" in with Loctite, and it's a good idea to either replace the bolt with a new one coated with the microencapsulated adhesive OR to clean it off and use the appropriate color of loctite. On large bolts, you also need to clean the threads with a thread chaser in the body so that you can correctly torque the bolt.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
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Old 09-21-2003, 08:37 PM
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Location: Ontario, Canada
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Just to answer one of your questions.
Loctite blue = re-usable, i.e. something that you take apart ocassionally.
Loctite red = "permanent, i.e. something you want to keep together.
Loctite green = high heat applications.
2007 C 230 Sport.
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Old 09-22-2003, 04:44 AM
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Location: Newcastle upon Tyne, UK
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Whenever I've bought MB or good quality aftermarket brake pads they have included new bolts with the blue locking adhesive.
Cheers, Neil
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Old 09-22-2003, 09:04 AM
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Location: New York City Burbs
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Great Book on Nuts Bolts & Fasteners

I highly recommend the book "Carroll Smiths Nuts Bolts Fasteners and Plumbing Handbook". It is written in laymans language and you dont need a phd in math or mechanical engineering to appreciate it. It is also pretty entertaining. And short.

All bolts stretch to a cetain extent, that is what keeps them tight. But at a certain point, the metal wont snap back from its stretched position. High strentgh bolts are harder and more prone to breaking as they are less elastic. Over tightened fasteners are a big no no with any fastener.

Its available from Amazon Books, 15 bucks or so.
Patrick Leber
'84 190E 2.3
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Old 09-23-2003, 07:42 AM
David Speed's Avatar
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Location: Brisbane, Australia
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Thanks for the responses

This is a link to the Rotor / Hub bolts I am talking about on W126 -mine are similar on W123

I would be interested to know from an MB Tech if these bolts and caliper bolts are routinely replaced in a MB Workshop
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Old 09-27-2003, 10:08 AM
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Join Date: Jun 2001
Location: CA
Posts: 531
Repalce the bolts

David -

If you read my piece more carefully, specifically here and here, you will see that my parts list includes replacement bolts and that I do advocate replacement.

I got into a big discussion (argument?) with Stu Ritter on the subject of bolt replacement 10 years ago, and ended up concluding that the small cost of replacement exceeded the risk of ignorance. Stu is right. Even if you drive conservatively, you do not know the extent to which the PO subjected the bolts/calipers to thermal stresses and those bolts exist in a very hostile environment. Can you think of a more vital part on your car than the brakes? This is not an occasion for frugality especially when you crash and kill your child or mine.

The reason I say 'no Loctite, no anti-sieze, etc' is that the OEM bolts come with blue Loctite on them. The factory manual specifically states you should replace these. Want to argue with the world's best engineers?
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Old 09-28-2003, 09:07 AM
David Speed's Avatar
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Join Date: Aug 2003
Location: Brisbane, Australia
Posts: 81
Thomaspin........I am very grateful for your informative MB repair site

The Haynes Manual is 'better than nothing', but I was certainly more confident to tackle the rotor repacement with your info

"A picture is worth a thousand words"

PM or Email me if you are interested in any (I hope constructive) feedback on your sequence

I certainly have a lot of respect for the MB Engineers

I don't have a factory manual and find a lot of the other info conflicting.


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