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Sunday, October 23, 2011

How to refurbish SunTour Accushift derailleurs




Suntour derailleurs are solid constructed components that perform troublefree for a long period of time. But as years go by they suffer from wear that ultimately leads to failure. From my experience it´s often the tension spring of the parallelogram cage that breaks and leaves the derailleur useless. But how can this spring be exchanged; after all the derailleurs of Suntour are, like the ones of Shimano, rivetted and not fully able to be taken apart, like the ones of e. g. Mavic?!



This how-to illustrates the complete disassembly of Suntour derailleurs, the exchange of damaged parts and finally the re-assembly of the whole mechanism to form a functioning derailleur. This article further wants to show how one can substitute a broken tension spring with a self-made spring made from hardware store parts.

At the beginning i´ll try to define some terms i will use in the further text. The orientation is set according to the normal mounting position on the bicycle. Parts oriented to the center line of the bike are are referred as "inboard", parts oriented outside as "outboard". The parts of the derailleur that bear the pivots are called "front parallelogram body" (FPB) and "rear parallelogram body" (RPB). They guide the two parallelogram arms (inboard parallelogram arm (IPA), outboard parallelogram arm (OPA)). The entity of FPB/RPB and IPA/OPA is called the parallelogram cage.
The parts of a Suntour derailleur that can be disassembled are the pulley cage and the spring-loaded hanger bolt assembly. The pulley cage can be detached removing the M4 set screw. The spring-loaded cage is unloaded rotating it clockwise up to the "twelve o´clock" position and pulling it out of the FPB. The hanger bolt assembly can be opened removing a circlip that secures the bolt.


The dissassembly of the rivetted parallelogram cage is shown in the following part.




Fig. 1: To drive out out the pivots a small hole has to be drilled in the upper extension of their axis. Using a small stub steel nail and a hammer the pivots can be driven out .



Fig. 2: The required drilling to drive out the pivot under the hanger bolt housing has to be performed meticulously, because the position direct above the pivot has to be reached exactly. The picture shows the relative location of the drilling entrance. Because of the more precise mode of action i use hand drillers of the caliber 1.5 mm.



Fig. 3: After drilling the pivots are driven out using the steel nail and a hammer. As a support i use a wood board with a small recess below the pivot.



Fig. 4: To remove the parallelogram spring a brass bushing in the IPA has to be driven out. To do this an M5 screw is placed on top of the fixated IPA and gentle (!) hammering is applied. After this the inner (serrated), the outer brass bushing and the parallelogram spring can be separated.



Fig. 5: If there are no original Suntour spare springs available, a replacement spring can be formed using a pull-spring taken from a local hardware store (outer diameter 12.5, inner diameter 9.5, wire gauge 1.5 mm). To keep the cylindrical form of the spring during the forming and bending, it is hoisted onto a fitting wood stick.



Fig. 6: After bending the spring is shortened using a bolt-cutter and the IPA is reassembled. The self-prepared spring bears the option to control the preloaded tension in a distinct range. Therefore one can fine-tune the shifter and will be able to build it up using a less amount of operating force. The picture shows from front to rear: the broken original Suntour spring, the newly built spare spring (not shortened) and the outer and inner brass bushing.



Fig. 7: A completely disassembled parallelogram cage. Its OPA has been broken. After exchange of the OPA the derailleur could be newly built up.




Fig. 8,9: After thorough cleaning and lubrication the derailleur can be re-assembled. The IPA has to be inserted into the FPB folded to the inner side and is rivetted. The RPB is connected with the IPA and rivetted. As the last step the OPA is mounted and rivetted, which tensions the parallelogram spring.



Fig. 10: The newly rivetted derailleur.


The drill holes can be left untouched or tinned which masks the the modification of the derailleur. To leave the drill holes as they are bears the benefit that the derailleur can be opened for maintenance very easy. Another application for the dissassembly of the rivetted parallelogram cage is the completion of a derailleur from parts of broken derailleurs. This is a valid option since the last "generation" of Suntour derailleurs are identical in construction (leave out the Superbe Pro derailleur).

How to touch up vintage SunTour index control thumbshifters




Many of you may know them, many still drive them on their vintage mountain bike or randonneur and appreciate them because of their low weight and ability to be run in friction mode when the lever or the derailleur are somehow damaged. But as time goes by and weather and dust keep on having a bad influence on the delicate mechanics inside such a lever one may feel the need to overhaul the lever to re-insure correct indexing. This how-to article mainly relies on the pictures that illustrate the complete "clean-lube-adjust" procedure done with a 1990 7-speed Suntour XC ltd. thumb shifter. But this can be applied to all modern Accushift plus indexed shift levers Suntour produced during it´s last few years before it went out of business, even the road bike down tube shifters that are mounted on braze-on studs do bear the same interchangeable mechanics inside and therefore can serve as a spare part supply.


Fig. 1: The thumb shifter (rear derailleur, 7-speed) connected to the mounting bracket.


Fig. 2: The toggle screw removed which also serves the clamping of the friction/index mechanism in order to adjust the friction of the system.


Fig. 3: The mechanism inside the lever can be opened by removing a circlip in the recession of the cap assembly using a flat head screwdriver.


Fig. 4: The cap assembly opened. The upper part of the friction/index mechanism is visible.


Fig. 5: The ball holder plate with the two indexing steel balls. The balls are inserted into the holes in line with the broad inner noses (not the ones marked with an engraved "ball" symbol!).


Fig. 6: The indexing cam ring. Seven pits on each side serve as resting points for the two indexing balls. This cam ring still looks good and needs only cleaning.


Fig. 6: This cam ring taken from another thumb shifter (Suntour XC Pro) suffers from massive wear. The shifter was unable to "hold gears" and general shifting performance was poor. Note the grooves between the index pits which prevented the correct positioning of the lever.


Fig. 7: The index cam plate can be refurbished by grinding the surface until the grooves have disappeared. The index pits have to be deepened using a dremel tool and a fine abrasive tip.




Fig. 8: The loss of thickness of the index cam plate has to be compensated by an additional washer. I prepared one by cutting and sanding an old credit card type plastic card (white ring inside the lever). During reassembly the new washer is placed under the index cam plate.



Fig. 9: An exploded view of all parts of the thumb shifter


Fig. 10: After thorough cleaning of all parts the parts are greased with a ball bearing grease and the lever is reassembled according to fig. 7. The ball holder plate must be inserted like it is shown in the picture. The friction/index cam plate has two areas, one with a pit which engages the friction mode and one with a flat surface which presses the indexing balls against the index cam plate and ensures the latching of the gears. For reassembly i found it suitable to insert the friction/index cam plate in friction position because the pits help to hold the whole mechanism in correct place. After placing of the cap assembly the whole lever can be secured by inserting the circlip. Although there is some special tool for handling circlips, with a little bit of patience and practice this step can be done using two flat head screwdrivers.


Fig. 11: A scheme of all moving parts (black), the fixed part of the mechanics (blue) and the index balls (red), also visible is the correct arangement of the cup springs and washers.