Chapter 1 – “Do I even need a rebuild?”
What external things to inspect It is usually a surprise to the bewildered owner of a poorly shifting transmission to find that the cause of the poor shifting is actually external to the gear box. The concept is fairly straight forward. The engine and transmission (drive-train) are solidly bolted together as as single unit, and they are suspended from the chassis with flexible rubber mounts. The shifter assembly is solidly connected to the body at the stick-shift (which is bolted to the floor in the cabin) and at the firewall bushing. This solid link to the body continues aft until it is connected to the transmission at the shift console. As such, any slop in the drive-train mounts, or the shift linkage, will cause the orientation between the drive-train and the chassis to change and subsequently the shift pattern location to shift making your shifting suck.
So, with that concept in mind, here is a list of things to check before blaming the transmission.
*Engine mounts – both side and tail shift 901 configurations in the 914 have rubber mounts incorporated into the engine mount bar. The side shift configuration has solid mounts from the bar ends to the chassis and rubber mounts between the engine and bar, the tail shift configuration is exactly the opposite. The two rubber mounts are intended to isolate drive-train vibrations from the chassis, but they can break causing the whole drive-train to shift. The common symptoms experienced when an engine mount fails are a “clunk” or “thump” when revving the motor or driving, and a shift pattern that continues to move around on you (gears are once in one place, then in another).
*How to test your engine mounts; side shift - Testing your engine mounts is pretty easy. First, realize that the side shift engine mounts are pressed between the engine and the engine bar. Thus, you need to lift the engine a little to see if the engine mounts are still in one piece. I have a method that I use and find to be pretty easy. First, jack the car up and place it securely on jack stands or ramps. Then, take a piece of wood and a jack and placing the wood under a solid part of the engine block on one side, and atop the jack, lightly jack under the engine to see if the engine easily lifts away from the engine bar. You are not trying to lift the car with the engine, you are only trying to see if the engine is still attached to the engine bar. Repeat this on the other side of the engine case. If the engine lifts a little from the bar, that is fine as the rubber mounts will yield a little bit. But, if the engine lifts very easy and any more than a little, consider changing your engine mount(s).
*How to inspect your engine mounts; tail shift - On the tail shift 901 in a 914 it is easy to check the engine mounts as they are located at the ends of the engine bar and are bolted to the frame. Inspection of these is pretty self explanatory and simply requires that one support the engine bar, pull the bolts, and inspect the rubber in the mounts. A good upgrade for these are the 911 engine mounts which tend to be cheaper than the 914 stock mounts, are solid rubber, and are overall better for enhanced stiffness and resistance to failure.
*Transmission mounts – transmission mount failure presents as a changing or sloppy shift pattern. The transmission mounts are straight forward and easy to inspect. Just support the transmission, remove the bolts from the mounts, remove the mounts and inspect.
*Shift bushings – shift bushings differ from side shift, tail shift and '70-72 914s that have been converted to side shift.
Side shifter:
Bushings are found in the firewall, in the joint just aft of the firewall in the shift linkage, at the side shift console where the rod passes through, and in the cup at the end of the shift rod. The majority of bushing issues are found when the firewall bushing deteriorates and disappears. Excessive looseness in any of the bushings will cause your shifting to suck.
Tail shifter:
The tail shifter has a cup bushing under the stick shift in the cabin, a firewall bushing (same location, different size than a side shifter), and one at the back end of the transmission where the rod mates up.
Converted '70-72 to side shifter:
For those wishing to convert their early 914 to a side shift, the only special thing to mention is that you must use a conversion bushing at the firewall. The firewall hole where the shift rod passes through in these earlier cars is larger than the one for the side shifting later model cars, and the hole in the middle of the bushing is smaller for the side shift rod verses the larger diameter tail shift rod. Thus, only the adapter bushing will work. Many times I have seen where one has used the standard side shift bushing in an earlier car only to have it be very sloppy in the firewall hole. The conversion bushing is readily available currently (01/22/10) and inexpensive.
*Cone Screws (side shifter only) – There are two cone screws to consider when your shifting gets crappy. One cone screw is located where the external shift rod joins the one sticking out of the fire wall. It is used to couple these two rods together and if it backs out the rods will have slop in them. The second cone screw is located at the aft most part of the external shift rod where it retains the shift cup. Again, if the screw backs out a little then play will be induced into the coupling and shifting will subsequently be affected. Cone screws come with a nylock deposit and should be replaced with new ones each time you remove them lest you suffer lost shifting. They are cheap, I am cheap, and I do it.
*Clutch cable – The clutch cable being too loose is probably one of the most common reasons that peoples shifting sucks. If your cable is too loose then you will not be able to fully disengage the pressure plate from the clutch disk/pressure plate and you will keep power to the transmission. If it is really loose then reverse will grind when shifting into it from a standstill. There is no way that this should happen if the clutch is fully disengaged. To properly adjust your clutch, you need to tighten the cable until the clutch disengages at about 1/4-1/3 pedal travel (see figure). If the clutch disengages too early then it is too tight, too late then it is too loose.
*Clutch tube – if your clutch cable seems impossible to adjust, you may be suffering from a separated clutch tube. The clutch tube runs through the center tunnel and is welded near the front to the drivers side of the tunnel and to the firewall where the clutch cable exits. Often, one of the welds brakes causing your tube to shift when you clutch in. This will cause your cable not to pull enough on your clutch and thus not fully disengage your clutch. Repairs for this issue are many and beyond the scope of this article. Search www.914World.com for information and advice on how to tackle this and other and other 914 related problems.
Inspecting a core transmission So, you are considering buying a used transmission and the owner tells you that is shifted properly when before it was pulled and stored. So what? Unless someone can provide you with irrefutable evidence that the transmission was in good shape or has had some work done to it, it is a core. Feel free to violate this rule at your own financial peril. But, the box shift just fine by hand or in the car. I don't care. That and $3 will get you a beer at most bars, but it will not prove that your core transmission is any good. However, if it does not shift that doesn't mean anything either. More on that point later after rebuild. The output flanges should turn independently and together. If they do not turn independently, but do turn together, you may have a welded diff or a rare LSD. Not likely, but I don't want to dash your hopes
Definite signs of concern include, but are not limited to: drive shaft has much axial play, output shafts do not move at all, output shafts make a grinding noise when turning, current owner looks nervous and deflects your questions, etc.
A word on reading used transmission oil A lot can be deduced from the oil you get out of a core transmission. However, you can not rely solely on this method as it is easy for someone to change out the oil and then let it sit leaving the oil relatively clean. Giant gold or other metal chunks are concerning for bearing failure. Gold flake in the oil is often indicative of normal wear and tear on the consumable parts in the stack. Oil that is gooey or burnt is indicative of a neglected box and may mean lots of parts to be needed to rebuild. Lots of shavings on the magnetic drain plug is not cause for concern as it is often due to normal wear and tear.