Your BMW's transmission is often one of the most misunderstood components of the car. Very often, owners don't quite understand how the transmission works, and often end up abusing it without even knowing it! This week I will provide you with some hints and tips to keep your transmission shifting smoothly for many years to come.
Let's start by talking about automatic transmissions.
The automatic transmission is one of the most complicated automotive components ever created. I can't go into the specifics of how they work here, but in short, they work hydraulically, which means that they use hydraulic fluid as both a lubricant and a coolant. That said, you can imagine that a loss of this fluid would be detrimental to your transmission's health. Even so, most people don't bother to check their transmission fluid, or don't even think about it when they take their car in to be serviced. Compounding this problem is the fact that many car manufacturers now proclaim to have 'service-free' transmissions. I personally think this is a huge disservice to car owners, because let's face it - there's really no such thing as a service-free transmission.
In the past, I've owned two cars that came with an automatic 'service-free' transmission. While the transmission (sometimes referred to as a 'tranny') itself may be service-free, this is highly dependent upon there being enough fluid in the transmission.
Most transmissions utilize a cooler in the front of the car, which is typically
attached to the car's radiator.
To get the fluid there, it has to run through hoses underneath the car. On one of these cars, the previous owner's wife had dragged the car over something concrete, damaging one of these lines. The result was a slow leak of precious transmission fluid. The owner never noticed, because there is no easy way to check the transmission fluid on these cars. However, when driving the car, if you slammed on the brakes, and then stepped on the gas, the car would pause and then 'slam' into gear, moving forward. This was caused by the low amount of transmission fluid slopping towards the front of the lower transmission pan when you slammed on the brakes. If all the fluid is at the front, then it can sometimes become dry and empty underneath the all-important pickup tube that is located in the center of the sump.
The bottom line:
Don't trust the manufacturers!
Have your automatic transmission fluid checked about once a year, and also change the fluid and filter at least every 30,000 miles.
Moving on, I wanted to talk about...Using Your Transmission to Help with Braking Down Long Hills. When you're traveling down a long, steep hill, you should shift your automatic transmission into a lower gear using the gearshift. Typically, you will have the choice of 'D','3','2' and '1' or something similar to that.
By shifting into one of the numbered gears, the car will stay in a higher gear without downshifting. This will rev the engine higher, and it will slow the car down as you descend the hill.
It's perfectly okay for you to do this to your engine and transmission, although if you are unfamiliar with the technique, you'd swear it couldn't be good for the car. The flip side of the coin is that if you 'ride' your brakes down the mountain, you will most likely overheat them, which will make them lose their effective braking power. Under extreme conditions, they might even fail! I am surprised at how many people don't know this - you can always tell the people who are 'in the know' and who aren't by looking at the brake lights of people in front of you as you descend the hill. The people using engine braking will almost never hit their brakes, while the people who don't know any better will have their brake lights on all the way down the hill. Be smart - use engine braking. Owners of cars with manual transmissions almost always know this tip, but most people with automatics don't.
Now let's talk about...Manual Transmissions. These are much better understood by most people than automatics, but there are still many things people do that aren't good for them. The first thing that comes to mind is having a poorly adjusted clutch cable
(most later-model BMWs don't have a clutch cable, but I'll discuss this
anyways for the owners of early cars). The clutch is responsible for disengaging the transmission from the engine when shifting. This reduces any mismatch in speed between the engine and the transmission and avoids the grinding of gears (more on that next week).
If your clutch cable is out of adjustment, then you may have a situation where your clutch is never fully engaging. What are the symptoms of this? Grinding into first and reverse are sure-fire signs of misalignment. You can also do a simple test to check. With the car at rest and the transmission in neutral, push the clutch pedal in. Now, count to ten slowly. Then try to shift it into reverse. If it grinds, then your clutch cable is almost surely out of adjustment (or one or more of your clutch components are not working properly).
What does this test do? Basically, when the transmission is in neutral, it is not engaged in any gear, but it is still connected to the engine and spinning internally. When you press the clutch pedal in, the transmission is disconnected from the engine, and should start spinning down to a stop internally (that is what you are waiting for when you count to ten). If you go and shift into reverse, the engine should be completely disconnected, and it should not grind. However, if the clutch cable is out of adjustment, then the transmission will never spin down. When you shift into reverse, the transmission will still be spinning, and you will grind some gears.
A poorly adjusted clutch cable will destroy your transmission in very short time, because it's similar to shifting without using the clutch.
You will grind gears and destroy synchros. If the above test reveals problems with your cable or clutch - get it looked at immediately.
It's a lot cheaper to fix or adjust your clutch than it is to rebuild your entire transmission.
Which transmission gear oil should I use?
Without a doubt, the best transmission gear lube to use in manual transmission cars appears to be Swepco 201. Normally, I don't make blanket recommendations like these, but my customers simply swear by it. I've had many of them insist that the addition of Swepco 201 can forestall a transmission rebuild for several thousand miles. While I'm not exactly sure what magic stuff exists in the Swepco 201, I can indeed tell you that it is the number one choice amongst our Porsche and BMW customers. Particularly with the racing crowd, the Swepco
oils have a somewhat legendary status.
Be sure that you check with your owner's manual first though - some special transmissions require a slicker, synthetic formula than the Swepco.
Bad shifting habits that will hurt your transmission...
Hmm, there are hundreds of things you can do that will hurt your
transmission. I only really have space here to talk about a few though.
Here are two of the worst:
- Leaving the clutch pedal pressed in while at a stop light.
This one is both bad for your clutch and your engine. It places a load on the pressure plate spring and your throw-out bearing. In addition, it places forces along the center of your engine's crankshaft, which can lead to premature wear of flange bearings in the engine. When you put your foot down on the clutch and leave it there, you are 'stretching' the spring that is used to control the clutch, and that spring then pulls or pushes on the crankshaft of the engine. Only doing this once and a while is fine, but repeating this over thousands of miles will cause both your engine bearings and your clutch to wear out prematurely.
- Slamming your transmission into 1st gear.
Let's say you're at a light, day dreaming about what you're going to have for lunch. You don't realize the light has changed, and someone honks at you from behind. So you super-quickly push the clutch in and slam your transmission into first gear. Crunch! This (as you might have suspected) is very bad for the transmission - even if you don't hear it crunch. The transmission needs time to 'spin down' as you engage first gear. Slamming it into gear right after you let the clutch pedal out is simply bad for it. Push the pedal in for a moment, and let the transmission 'spin down' a bit before you shift into first. Another trick is to shift into 2nd or 3rd prior to shifting into first gear - this will help spin the transmission down without grinding your 1st gear synchro. The same principle applies when shifting into reverse. Wait a few seconds after pressing the pedal down, before shifting into reverse.
Improving a poorly shifting transmission...
I won't tell you how many people have talked to me about how they had their transmisison rebuilt (expensive), only to find out that the problems was actually with their shift linkage bushings. Very often on older cars, the shifting ability deteriorates as the years go by. While many people blame their transmissions and prepare for a full rebuild, their worries may be needless. In many cases, the shift linkage bushings have simply worn out and need to be replaced. Worn bushings can result in sloppy shifting, misplaced shifts, and grinding when engaging gears.Most people are amazed at the improvement that occurs when they replace their bushings. A mere $45 spent on new bushings is a heck of a lot cheaper than a $1500 transmission rebuild.
Shift linkage bushings are different on every car, but the results are often the same when they are replaced - the transmission shifts a lot smoother. At a bare minimum, replace your shift bushings prior to having any major transmission work performed - that way you will eliminate them as a potential problem When you have all the bushings replaced, and the shifter adjusted, the car should show a remarkable improvement. If you are still having problems with shifting and grinding, you might want to check your clutch adjustment, or your motor and transmission mounts, or the fluid level in your transmission.
Myths and truths about short shift kits...
One of the most popular additions to many cars is the installation of a short shift kit.
The kit shortens the length of throw on the shifter, theoretically giving you the ability to shift faster. Installation is relatively easy, and typically takes the better part of an afternoon.
However, many people install short shift kits in their cars thinking that it will fix problems that they are having with their transmission. This will not solve any problems, and will in most cases make a poorly shifting car shift even worse. The reason for this is that with the short shift kit, the torque arm on the shift lever is much shorter, giving you much less 'resolution' on your shifter. It's similar to having a gas pedal that only travels 1 inch over its range instead of 2-3 inches. You have less precision in how much throttle you want to give the car. In a similar manner, with the short shift kit you will have less precision on where the
shift rod is placed. It's a wise idea to tackle the core problems with your transmission (synchros, shift bushings), prior to the installation of the short shift kit.
Ironically, many people install a short shift kit onto a poorly shifting transmission, and then magically proclaim it 'cured.' In fact, in most cases, they didn't fix anything with the transmission - the short shift kit is simply 'muscling' the transmisison into gear using more force and more leverage. The bottomline?
Only install a short shift kit into your car if your transmission doesn't have any shifting problems.
Well, there you have it folks, parts 1 and 2 of my tips and
tricks on transmissions.
Thanks again for your support!
Wayne R. Dempsey
Pelican Parts Inc.