In The Shop: Clutch Spring Plate

Harley Davidson Clutch Spring Plate

Starting in 1991 until 1997, Big Twin model Harley Davidsons used a spring plate (37977-90) in their clutch pack. Sportster models used the same spring plate until around 2019. The spring plate is positioned in the middle of the stack of clutch plates (8 friction plates & 6 steel plates) and is directly sandwiched between 2 friction plates.

The spring plate consists of two outer steel plates which sandwich 8 small, slightly concave, springs. The assembly is held together with 8 brass rivets. These rivets are known to wear and break loose. When this happens, not only will the spring plate fail to function, but the loose rivets fall out of the spring plate and completely wipe out the two friction plates on each side of the spring plate assembly.

This week, In The Shop, we had a 2007 Sportster 1200 come in for a set of handlebars and cables. Upon completion of the job we start up the XL and prepare for a short test ride. Unfortunately, we immediately notice the clutch is inconsistently lurching.

So we get the bike back inside and try to re-adjust the clutch. This is the obvious first thing to check. However, we know that we are only avoiding the inevitable as we have diagnosed many Harleys with this same clutch lurching condition before. The clutch adjustment renders no change so we drain the primary/transmission fluid and prepare to remove the outer primary cover. We immediately notice brass metallic in the drain oil which reassures us that we should be looking for a bad spring plate. With the primary cover removed, there is even more evidence of larger brass debris.

With the clutch pulled apart, we can see what we had expected. The spring plate has broken apart, completely wiping out 2 fiber plates and contaminating all of the other plates. For this repair, we prefer to install a Barnett extra plate kit. This kit eliminates the weak spring plate.

However, the customer was not anticipating this additional expense and we will have to work with her. In order to make the repair as inexpensive as possible, we replace the spring plate and clutch fiber plates only. The steels are to be cleaned, inspected, and reused. Everything is thoroughly cleaned and we also go back together with a new shift shaft seal, outer primary, inspection, derby seals and fluid.

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Harley Clutch Assembly Upgrade

Below are some photos of this job.