What are Push/Pull Cables?
A push/pull throttle is a dual cable throttle operation where the pull cable opens the throttle plates, while the push cable, along with a throttle return spring, closes the throttle plates. The “push” cable is a misnomer as the push cable also pulls.
A push/pull throttle cable is an upgrade to the old standard single throttle cable linkage. The throttle grip works on the carburettors when twisting/throttling up and when releasing/throttling down. This is a step up to the single throttle cable type where only a spring is responsible for throttling down. With a push/pull throttle, should the spring fail, twisting the throttle will pull the throttle linkage back to idle.
In a crash, if the steering stops on a bike and is pushed in a bit from hard falls, the cable can often get caught between the frame and fork tube. This crushes the cable housing a bit, and the cable will bind. If a rock or something gets caught in the carb housing (if somehow the cover fell off) the spring won't close the carb slide. The second cable pulls the carb closed so it isn't stuck wide open. On a road race bike at 165mph+ approaching a tight turn with little run off area, riders want that peace of mind that if they close the gas, it will close. It is for this reason that it is now illegal in many countries to remove the push cable and rely on the spring to close the throttle.
Over time cables stretch and will need adjusting to reduce the amount of free play on the throttle. This adjustment will allow a smoother feed in of the throttle. Most manufacturers recommend 2-3mm of free play. To check the free play, roll the throttle forward until it stops and then gently open it until you feel tension on the cable. The distance between the closed position to the tension position is the “throttle free play”. To measure the distance, two triangles can be cut out of masking tape and one placed on the grip and one on the throttle housing. Then as the throttle is twisted the distance measured.
If the free play is out of specification, there are two places where cable slack can be adjusted. The first is up at the throttle and the second is at the carburettor. The in-line adjustors up at the throttle are for fine tuning the free play, whereas the adjustors at the other end are for bigger changes.
There are a lot of different throttle set ups, the most common of which is to have two cables with one adjuster. The principles to adjustment, however, is basically the same, namely, to slide the cover off the in-line adjuster and release the lock nut. Then turn the adjuster to get the 2-3mm free play. Once that is achieved, tighten the lock nut and spray some silicon on the adjustor before sliding the cover back. Operating at the other end requires the same principles, although access is less easy. When adjusting at the engine end of the cables ensure that the adjustor at the other end is set to the middle so there is scope for fine adjustment either way.
The last, but important stage, is the safety check. Swing the bike from lock to lock to ensure that the throttle doesn’t tighten up. This should also be done with the engine running to ensure that the idle doesn’t rise as the lock positions are reached. If this happens, more adjustment will be required.
Installing Push/Pull Cabling
When installing a new cable, it is important that the routing of the original cable is checked and noted. Also, ensure that the dimensions of the cables are identical, allowing for the fact that old cables do stretch over time.
Prior to installation the cable should be lubricated with some light oil to lubricate the inner cable. By holding the cable upright and moving the inner cable up and down, the oil will be eased down the cable.
In routing the cable, ensure that there is a gap between the cable and any heat source and keep ties loose to allow the cables to move. Always connect and adjust the pull/ open cable first whenever possible.
Where nipples require lubrication in levers or linkages, use a small amount of copper grease rather than heavy greases which attract dirt and restrict the movement of the nipple, causing excessive wear and stress on the nipple and cable.
Once the cable has been installed, check the steering lock to lock and check the operation of the cable at both extremes of steering in the same way as when adjusting the free play.
Maintenance of Teflon Push/Pull Cables
Good cable maintenance will prolong the life of the cable and maintain its operation. In the case of MX bikes, it is a good idea after a race meeting or as often as possible after power washing to remove the cables from the bike and flush them through with a blast of air, either from a pneumatic system or from a can of CO2 (often used to clean computers).
The nipples can also be lubricated, if required, with Copper grease.
The same maintenance regime can be applied to trial bikes.
In the case of road bikes, cables should be removed and flushed through with a blast of air at the beginning and end of the summer. Again, once they have been cleaned, the nipples on the ends of the wire could be lubricated with a light 3 in 1 general purpose oil and Copper grease.
As with the installation, the use of heavy engine oils, chain lubricants or grease to lubricate cables should be avoided as this will attract dirt, increase cable wear and reduce the operation of the cable. Although good maintenance will prolong a cable’s life, they should, nevertheless, be replaced at regular intervals.
Learn More with Venhill
For advice and for the purchase of top-quality cable, including marine grade stainless steel inner wire and PFTE (Teflon) liner for super low friction smooth operation, get in touch with us today or start shopping now.