Sachs clutch modifications

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Manual clutch

Many sachs performance enthusiats will opt for the manual shift, 2-gang or 3-gang sachs/hercules motors (505-2B(or D) or 505-3B) ordered from ebay Germany. Helpful search terms include: "2-gang" or "2 (zwei) lamellen" sachs/hercules "Prima 5" and "kupplung" meaning clutch. Unfortunately, even the 2 speed manual motors have trouble with clutches slipping.

The standard clutches consist of:

  • 2x pads [#18] 3.2mm thick
  • 3x plates [#16] 1.7m thick (on an standard 2 pad automatic clutch you instead have one 1.7mm plate and 2 2.6mm plates)
  • spacer [#15] 4.5mm

for a total 16mm thickness

Additionally the manual clutches use a spacer at the bottom of the bell and a spring washer to press the clutch together when engaged, and three 15.8mm long x 3mm diam pins [#14] which go through the plates and push back the bottom plate against the spring to disengage the clutches when the shift lever is pulled.


Manual clutch performance

One option to prevent slipping is the so-called "uber clutches". These are available through ebay Germany, however the cost is 150+ Euro, plus shipping, and the seller doesn't ship to the US, so you need a contact in Europe. These have been tried and provide good action with no unwanted slip.

The "uber-clutch" consists of:

  • 4x New "uber" pads [#18], 2.15mmx4
  • 5x clutch plates [#16] 1.7mm
  • no spacer

for a total 17.1mm (meas 17.3) total thickness It also includes a stiffer base spring [#20]

The second option is to make these uber clutches yourself. If you find any second clutch pack even from an automatic, grinding down the clutch pads is all you'd need to do. 1.7mm plates should be thin enough as-is. The manual engines already have 3 and the automatics usually have 1 plate of desired 1.7mm thickness. Grind the pads on the side where the oil channels don't go all the way out the teeth, this should be apparent when looking at them. This is so that you dont loose oil turbulence. It's also very important when grinding to keep the 2 sides absolutely parallel.

There is more work required to make it fit into your clutch. Even when milled down to the uber clutch sizes, it still doesnt quite fit. You can mill the bottom spacer [#21], to leave room for more clutch to fit in the bell. You may also remove the spacer [#15] on the end. Another option instead of milling down #21 is to space out the cover. If you just flip the inner spacer [21] and get rid of the outer spacer [15] it buys you enough room to fit it all in the bell, but it pushes the engagement bell [#11] too far out so the clutch cover causes the clutch to disengage when the cover is tightened on. A few extra gaskets or a custom spacer works to alleviate the problem. So either you gotta mill down #21 about .5mm or flip it and add some extra gaskets on the clutch cover. I did the latter and have 3 clutch cover gaskets.

The second problem number 2, the new uber clutch pack is too thick for the old pins. The clutch disengages when you pull it by pressing the set of 3 pins [14] thru to push the back plate and spring [16,20]. The pins are only 15.8mm which works because the normal outer spacer [15] is recessed. With the new setup at 17mm thick, you need longer pins. These can be found (3mm diameter 18mm long) from McMaster Carr. They work, I have a ton extra, if you want some, they’d be free. PM wdaloz.

Another option used by Nick K with his 3 speed Sachs is to maintain cool oil temperatures. A simple pump and radiator cooler setup is used to circulate the transmission oil and dump int back into the top of the clutches. This is reported to also alleviate problems with slipping. It is also worth noting that the 3 speed motors have a 4 plate 3 pad clutch with greater surface area. Transmission oil also has an effect on the clutch performance. I run a belray gearsaver 85w gear oil but have tried everything down to ATF with no noticeable affect. Sachs recommends 90w oil for it’s manual transmission engines.

It also could help put a little whirly piece to whip the oil around and keep everything lubed and cool. that's equally or more important than friction area. it's just a cut piece of tin can with bent out tabs bolted in there. pins go through it. i havent any pics but get creative.


Automatic Clutch

By far the most common Sachs motors have the 1 speed Automatic sachs clutch (504,505-1A,B,C,D).

These consist of:

  • 2x pads [#18] 3.2mm thick
  • 2x plates [#16] 2.6mm thick
  • 1 plate 1.7m thick
  • 2x spring washers
  • Donut spring
  • Ramp plate

in the clutch bell


The pads are engaged with the clutch bell and the chain drive and pedals, while the plates at engaged on a toothed piece and move with the engine crankshaft. They are by default separated by the spring washers, so when the engine is off or idline the rear wheel and drive spin freely from the engine. When the starter clutch is pulled, the engagement bell presses the pads and plates together, forcing the pedals via the clutch bell and pads to engage the plates and thus turn the crankshaft and turn the engine over. When the starter lever is released the pads and plates again separate allowing the motor to idle without the wheel turning. As gas is given and the motor accelerates, the spring washer expands due to centrifugal force. As it expands is it presses out against the ramp plate and is forced against the rear clutch plate. This presses the plates and pads together and allows the motor to drive the wheel. Upon stopping the donut again retracts and the bike can idle again when stopped.


Automatic clutch performance

The automatic clutches are a weak point in the Sachs motors. They are prone to a number of issues, most notably slipping under load which over time causes the pads to overheat and "glaze" or loose friction and the problem consecutively gets worse. In order to alleviate this problem it's important to improve the friction between the pads and plates, which may be achieved through increasing contact area. Parts from two standard 2-pad/3-plate clutches may be milled to fit 3 pads and 4 plates for more friction area and less slip. The center plates are the thinner 1.7mm (usually one in each clutchpack is this size), outer 2 plates are standard 2.6mm thickness. The pads can be milled milled down to 2.3 from 3.4mm. When doin so it's good to recut the oil channels in the pads for proper lubrication. After that you just have to add shims to make sure the center toothed piece [#19 above] has proper clearance so it grabs only as the donut springs out or the starter bell is pulled in. See also: setting sachs clutch preload

Another problem people have with the sachs auto clutches is the nut backing off the end of the crankshaft. The reason for that is that the clutch attaches to the crank via the toothed piece. That piece is only attached to the crank by the nut on the end; whereas most clutches are taper fit. That means the sachs clutch can spin on the crankshaft against the nut and in many instances can spin the nut free. To correct this, a taper would be ideal, a woodruff key would be great but neither are really easily doable.

What I did was to take the toothed piece [#19]and drilled and tapped a 1/8 in. hole through the side of it and then got a short allen set screw for it.


-somethin like that. I lined it up on the crank and drilled a tiny divit into the crank where it would sit normally, making sure that's alligned right. Then drilled a big hole in the top of the clutch case to get to the screw and tighten it down through the slits in the side of the bell once the bell and spring and everything behind #19 was in place. Then i just put a cover over the top hole, theres no pressure on it, just to hold the oil in. Assembled the rest as usual. Red loctite on the end nut is still a good idea. clean it with brake parts cleaner 1st to get any oil off.