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Hoses and Hoseclamps

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Old-style clamp

Clamps are used to create a tight fit for a house around a receptacle. Mercedes Benz used old-style clamps which are a band of steel with a pair of loops at one end. A cotter pin is put through the loops at one end, then the other end of the band is stuck into the cotter pin. Using needle-nose vice grips the pin is rotated thereby rolling the band around the pin and pulling it tight on the hose.

Nowadays most people prefer to use modern screw-style clamps, often with rolled edges to prevent them from cutting into the hose material. Well known providers are Wurth (Zebre) and Norma clamps.

History of Clamps and Originality

Although there is some debate on the matter, an expert such as Pete Lesler says:

On 230SL's or early 250 the clamps are most surely Norma's. Look to see if the name Norma is inscribed on the clamp. The mm size should also be inscribed. These clamps are not adjustable like the newer style. They are designed to tighten down to the outer diameter of the hose. Early cars generally use Norma style, later cars used Normas but with a Phillips head screw, rather than a slotted screw. The power steering hose used an altogether different style of clamp, which is NLA. These non-adjustable clamps were used into the early to mid 70's on all cars.
Dealers do not handle the Norma or Gemi style clamps. At concourse judging, we deduct for non German adjustable clamps, but if all clamps were replaced with later style MB adjustable clamps, i.e. no mixing of clamps, we will not deduct. I usually sell a complete set of slotted Normas for around $90 per set, depending on model (2004 prices). A set is usually around 50 clamps.

Others believe that the Norma clamps are a modern-day approximation for the original factory clamps. Their cars have originals "GEMI" clamps which are slightly different in appearance.

Still other people have both Gemi and Norma clamps of various sizes on their cars. MB probably used two suppliers, as you surmised, and mixed both when fitting the hoses and clamps during production.

New-style Norma clamp

Pete Lesler says:

In my opinion: Norma clamps were used mostly throughout the period 1945 to 1975. I have seen them on original SL's from 1964 to 1968. Gemi clamps appear similar, but have Phillips head screws in lieu of slotted crews. There are some other differences as well, but the Gemis are no longer available, the Normas are. In the the case of concourse judging, we allow either Norma, Gemi (1968-1971) and the newer Norma factory adjustable, if all clamps are uniform in application. We do not allow US made open slotted adjustable clamps. In my mind, the Norma clamps look appropriate for W113 SL's.

Clamps for a 230SL

All clamps described below are Norma clamps unless noted and were provided for a 1967 230SL. There are 38 clamps: early 230s may be different as well as the 250s and 280s.

For the purist, the heater hoses originally used the Beru strap and cotter pin type of clamp, not the Norma clamp. Pete Lesler sells the Beru material; most people feel the Norma clamps are tighter and reusable. The brake booster line uses the Beru clamps and are not included in the list below. All new hoses were purchased from Mercedes Benz and the sizes in some cases have changed from the original hoses and are noted. The 12x21mm coolant lines on my car had 19mm clamps on them. Although I used the 18mm clamps but I had to open up the clamp to get them on the hoses. My recommendation: buy the hoses first.

Coolant Hose Clamps

  • Radiator Hoses (6 clamps)
    • Upper: 40 and 46mm
    • Lower: 40 and 46mm
    • Bypass: 40 and 40mm
  • FI Pump (6 clamps): MBZ hose 12x21mm
  • Coolant lines (2): 18mm, 4 clamps
  • Manifold line: 18mm, 2 clamps
  • Heater (8 clamps): MBZ hose 18x27, originally only 18x25
    • Supply: 26mm, 2 clamps
    • Return: 26mm, 2 clamps
    • Expansion Tank to Pipe to Bypass: 26mm, 4 clamps (the end at the Bypass hose is a real tight fit, probably needs a 28mm, the original hose was bigger at this end and is NLA)
  • Expansion Tank, MBZ hose 8x15 (originally 8x13? with 13mm clamp?)
    • to Radiator: 15mm, 2 clamps

Other Hose Clamps

  • Valve cover rubber breather, 26mm, 1 clamp
  • Idle Circuit from FI pump to pipe, MBZ hose 12x21, 18mm, 2 clamps
  • Fuel Tank, with MBZ hoses
    • Tank to Pump: 17mm, 2 clamps
    • Pump to Chassis line: 15mm, 1 clamp
    • Tank to Vent line, 12mm, 2 clamps
  • Fuel Lines in Engine bay (with original hoses, not replaced)
    • Line to Filter: 15mm, 2 clamps
    • FI Pump to Return Valve: 13mm, 2 clamps
  • Power Steering, MBZ hoses, ID 16mm x OD 23mm
    • Reservoir to Box: original is Gemi 20/28, can use Norma 24mm, 2 clamps
    • Reservoir to Pump: original is Gemi 20/28, can use Norma 24mm, 2 clamps

Installing old-style clamps

It would be best if you had an old one as a model, but this is an attempt to describe the installation:

  1. Insert one end of the strap through the rectangular opening and fold back the first inch;
  2. Place the clamp with folded-back strap on the hose. The folded-back part next to the hose, and the head of the cotter pin a little below the end of the hose;
  3. Wrap the other end of the strap around the hose and through the rectangular opening on the clamp;
  4. Wrap the end a second time around the hose, but this time insert it through the cotter pin;
  5. Pull the open end of the strap to remove as much slack as possible;
  6. Hold the strap in place and cut off all but about a half inch of the part that is extending through the cotter pin;
  7. Using an Allen wrench of a size that just fits through the eye of the cotter pin, turn (wind) the pin in a direction that makes the strap pass under the pin;
  8. Stop winding when the clamp appears sufficiently tight, and the head of the pin is tangent to the hose.

It's pretty easy once you have done one or two of them.

Here is a pictorial description of the installation procedure. It differs from the one above with respect to a small loop at the end of the strap through which the cotter pin is fed. Putting both strap parts between the jaws of the pin prevents the strap from pulling through.

Removing the clamp:

About 20cm of strap are needed for a 18mm diameter hose.

Insert the bushing at the end of the strap and wrap the strap around the hose as shown. Note that the end is above the strap that wraps around!

Wrap the strap twice around the hose and then fold it back to make a small loop. Push the pin through the bushing and then over the end of the strap. It is best to insert both parts of the loop into the jaws of the pin but one may be sufficient and is a bit easier.

Insert a narrow rod or nail into the pin head and turn it to tighten the clamp.

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Frank says: they are still available from MB dealers. Pretty sure they were still used on 280 SL heater hoses to the end of production; also on the brake booster vacuum hoses before they went over to plastic lines. We need a table showing what type of clamp was used where, for each year of 113 production. Many of the original types are NLA.

Will Samples says: The clamps you describe are the original band type clamps that came in the 5mm and 9mm wide sizes. They are still available. I carry them new or you can reuse yours and I also carry the strap material. If anyone needs it I can try and scan the original instructions for these clamps and post. It is only a small 1/2 page and in 4 languages with a picture.

My '66 230 SL has wind-up clamps on every last hose except the major radiator hoses. If someone can tell me an easy way to work them, I'll keep them.

Frank Mallory says: Used cotter pins ans straps are not worth anything, because new ones are readily availably & cheap. I've seen one or two cars where somebody went overboard and installed this type clamp on every hose, to replace US-type clamps that they knew were not original. As I mentioned earlier, they were originally used only on the heater hoses (including bottom hose on water tank) and vacuum lines. Radiator hoses, fuel hoses, vent line hoses, water pump hose, air inlet hoses, and cooling water tank overflow line used various kinds of screw-type clamps. I had trouble re-using the original hose clamps as the wire is hard to get back through the pin, the wire breaks, and it's hard to get a tool on the end of the pin to turn it. I think I'll throw them away as they are slightly rusty and I have broken two of them.

Thanks for the info on the hose clamps. Unfortunately, I have not been familiar with enough original 113s to be able to make a list or table of such detail although it would be great to have. I sure would appreciate getting either a part number for the wind up clamps for the heater in and outlet and others (if applicable). Alternatively I would love to get some good used clamps which may be preferable because I want to restore with an original and not brand new look.

Well, that's one approach -- retain the original "patina" on all metal parts. My preference on cars is to make everything look like it did when new. When replacing plain or cad plated metal parts, I first spray them with clear lacquer (Eastwood's Nyalic) so that they will retain their original appearance. Anyway, the part number for the large-size wind-up clamps for heater hoses is 900262 009100, which retail for about $0.56 each; you will also need some 9mm hose strap, 900263 009000.

Thanks for the part number for the clamp. My engine still looks pretty decent so I'm going to wait until I cadmium plate all the parts. Also I'm torn between replacing the discolored plastic containers and replacing them with MB replacements for wiper fluid, coolant overflow and brake reservoir. Anyone know if exact replacements (aftermarket?) are available? Also Frank, would you use the Clear Lacquer you mentioned on cast aluminum parts too? I just cleaned up the support for the brake booster and am trying to protect it without changing the look.

Frank replies: what I do is bead blast cast parts, then spray them with Nyalik. Admittedly, this makes them look a little better than new -- a bead blasted intake manifold will give your engine compartment what I call the WOW effect. The wind-up clamps you get from the dealer now are silver cad plated, exactly like original. You can still get many cable hold-down clamps with yellow cad, exactly like original. Others, like the clamps that hold the rubber fuel & brake line guides, you can only get with black paint. If you find somebody that does real gold cad painting, let us know. Will got some parts plated for me with something close to gold cad, but frankly I think that bead blasting followed by a coat of DupliColor gold paint gives an appearance closer to original. The parts that he had "silver cad" plated came out OK. Frequently, if you will give a corroded gold cad part a light bead blasting followed by the Nyalic, it will look pretty good.

Do you happen to have the part number for the small (not 9mm) wind-up hose clamps. My dealer doesn't want to look up the number, says it keeps changing.

Frank says: Unless it's been changed in the past couple years, the small clamps are 900262 005100, and the small strap is 900263 005000. While you are at it, try to get some 900262 005000 and 900262 009000 clamps; let me know how you make out.

The local junk yard is a good source for clamps off the sedans. I had them replated to look like new. I did have to put in some time with a rotary wire brush though.
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