An Import Car Garage
Tech Dept. ( for all brands of Import Cars) Tech # 4
Tips to make that std. trans last longer
Standard transmissions have parts called synchronizers in them. These "synchros" as they are called are actually little clutches used to smoothly engage two gears that are or can be rotating at different speeds. Without synchros, the two gears would "grind", "crunch" or "clash" as they tried to engage each other. The synchro (little clutch) gets the two turning at the same speed just before they engage. In a current 4 speed gearbox, the gear teeth no longer engage and disengage each other. They are engaged all the time. This is referred to as a constant mesh trans. Instead, one of the two gears is riding on bearings and is not attached to the shaft it rides on. Next to that gear is a unit called a "sliding hub assembly". The inside of this hub is attached to the shaft by a spline. The outside of the hub is also splined with a slider on it that can slid toward and away from the gear. On the side of the gear is a corresponding spline. So when the slider is forced over to the spline on the side of the gear it engages the gear and thus locks it to the shaft that it had been spinning on. The engagement of the slider spline and the spline on the side of the gear can still "clash" so the synchro (Little Clutch) gets the gear spinning at the same speed just before engagement. When your synchros are worn out you hear the "clash" of the slider splines trying to engage the splines on the side of that gear.
You may be asking now. "What has all of this got to do with me and making my gearbox last longer?" Well, if you understand what is doing small and large damage to your gearbox EVERY time you use your gearbox, You can extend the life of the box substantially. Let us continue.
This only applies to the synchro gears. 1 to 4 if it is a 4 speed synchro box. Some older boxes did not have a synchro on 1st. gear, the gear teeth actually engage and disengage with no synchro. The same is true of all "Reverse" gears. There are some 5th gears that are not synchro on some 5 speed boxes.
Lets look at the biggest gear saver first. THE ENGAGEMENT OF REVERSE YOU CAN USE A SYNCHRO TO PROLONG THE LIFE OF A REVERSE GEAR. I see you asking questions again in your head. You ask; since reverse does not have a synchro, how can I possibly use a synchro to prolong the live of "Reverse"? You definitely can but first we must look at what is happening in your gear box just as you engage Reverse.
We will go from Start up. You should start the engine in Neutral with your foot off the clutch. There are only two reasons to start an engine with your foot on the clutch. One is if this is a late model vehicle with a starter interrupt switch. A system designed to make the vehicle Idiot proof. I doubt you are one of those Idiots because if you were you would not have read this far. The other is in the dead of winter if the vehicle was outside the oil in the gearbox is rather thick and it takes a lot of power to turn all the gears and that is what you are doing with the starter with the gear in "Neutral" and foot off the clutch. You may ask; "Why don't I hold the clutch down in the summer then? The oil may be thinner but it still must be a load for the starter." Yes it is. However, you have another evil to contend with. When you push the clutch down, you are applying about 400 lbs. pressure on the end of the crankshaft and this load in on one very small "Thrust bearing" on the crankshaft and this bearing is most likely dry of oil at this time and will not receive any until the oil pump builds pressure. Also you will probably find the load on the starter is higher then turning all those gears under warm weather circumstances. So it is; which is the lesser of the two evils?
Lets get back to how to use a synchro to save reverse gears. You start the engine with the box in neutral and foot off the clutch. The engine starts and goes to a fast idle. 1000, 1200 RPM or what ever you have it set at. At this point the clutch disk and input shaft in the trans. is spinning at engine speed and all the gears inside are spinning at close to engine speed. The clutch disk, the input shaft and all the gears in the gearbox make a good flywheel. So even when you depress the clutch peddle, Everything in the gearbox is still spinning. The gear you are about to engage with is attached to the output shaft which is stationary at this time. When these teeth engage, CRUNCH! even if you don't hear it. The load on the teeth to stop all the gears, the input shaft and the clutch is tremendous. This load and damage can be brought to almost "O" by first engaging a synchro gear then quickly shift to "Reverse". The synchro (little clutch) will stop the spinning of all the gears, shaft and Disk. While everything is stationary and you shift into reverse there is no damage to the gear teeth. In the winter, if you use the clutch down start procedure the oil will be so thick the disk and gears will probably be stationary anyway so reverse can be engaged easily without going into a synchro gear first. To make a synchro last longer avoid fast shifts on up shifts and if you down shift practice revving the engine a little before shifting to a lower gear and never shift direct from a higher gear to a lower gear bypassing the next gear down. Down shifting is an art and needs to be practiced to be good at it. Some mechanics and race drivers get so skilled at getting the engine speed close to the correct road speed on a up shift and a down shift that they can drive a car through the gears shifts without grinding the gears without using the clutch. Don't try it unless you are very skilled at it or you have a very large bank account.
Some cars are notorious for bad synchros. One that comes to mind is the early "E" Type Jag. Even with new synchros (w/gears) they still needed care in shifting. The best synchros I ever ran across was the Fiat 124 coupe and spider. No! I would not trade a early "E" for a "124", I would just learn to shift the "E".
The neutral to reverse procedure should be applied to 1st gear of a non-synchro 1st gearbox.
As for what oil to use. you should use what ever the factory recommends unless you find otherwise. The only two examples I can give you is: On seventies Chryslers the factory said use gear oil, but the synchros will not work so many of the dealers went to ATF (automatic trans. fluid) and it worked fine. On British MGs in the early 60s they used engine oil, but British Leland said to switch to gear oil. However, this caused more problems then it solved so most dealers went back to engine oil. Also, DO NOT add STP to a trans. oil. I had a customer that did and none of the synchros worked afterward. We were able to flush it several times and got the synchros to operate again.