Transmission Grinds

[johnl]

My experience with the notchy shifting was that it occurred regardless of how fast I attempted to shift. Even when shifting slowly and carefully, the added resistance in the shifter made it hard to differentiate between 2nd and 4th when shifting out of 3rd. Normally, the 2nd gear downshift would require a bit more force, and the 4th gear upshift would slide naturally into place. With the short shift modifications (I've tried numerous types), both gears felt similar. After nearly blowing my engine while racing and shifting ham-fistedly into 2nd instead of 4th, I put it back to stock!

I have no problems like this with the way I have the shifter set up. I don't really know why your experience is different. All I have to do to select either third or fourth is not apply any lateral force on the lever, just let the spring loading do that job for me as I push forward or backward. If I want second gear then I apply lateral force to the left (not much), and if I want fifth gear apply lateral force to the right. Works every time, I never have to think about it.

This is why there is a spring loading in the third / fourth plane, so the driver can orient themselves by feel as to which plane the shifter is in. This is only needed with five or six speed boxes because there are three laterally disposed planes, with four speed boxes there are only two planes and a light lateral pressure on the lever will put you in the correct one (without any spring loading).

This isn't possible with more than four gears because you can get caught out when trying to shift from (e.g.) fifth to fourth, easily selecting second instead (etc.), so you need a spring loaded plane when there are more than four gears. This is more important the closer the three planes are to each other.

Once the cables were back in the stock position, the shifts felt natural again.
It's not "notchy" in that it feels like it's clicking into gear. The "notchiness" I refer to is the added difficulty getting into any gear. I'm wondering if further modification as you specified, john, would eliminate the bad parts, and leave the good.

Changing the height of the cable / lever attachment also changes the angle at which the cable rod enters / exits the cable sheath. From memory the sheath is mounted in rubber bushes which help to some extent, but when I was messing around with my shifter I found that if this angle became too acute (as the cable is raised at the lever) it could produce a side load between the cable rod and the sheath that created some degree of 'stiction' in the shift action.

If this happens you need to work out how to get rid of any cable rod 'stiction' because you can feel it at the lever and it makes the shift 'feel' less than satisfactory. Rod / sheath stiction may also affect how well you can feel the lateral spring loading, which could be the root of the shifting problems you found with the short shifters you've tried...?

The cable rod needs to be well greased where it enters the sheath. I've also just remembered that I had to bend the rod between the sheath and where the cable attaches to the lever (this for the fore / aft cable, I can't recall if I had to do this for the lateral throw cable). Without the bend (call it a 'curve') in the rod the cable would become 'bindy' as third gear was selected because the top of the rod would rub hard(ish) against the inside of the sheath. The rods are very stiff and hard to bend, and no part of the bend can enter the sheath at the most forward part of the rod travel (or sever bind may result).

Thinking back on it, it was quite a fiddly job eliminating all the stiction between the cable rod and the sheath, involving some lateral thinking that would be hard to describe, assuming I could accurately recall what I did. You need to look very closely at what is happening between the rod and the sheath as the different gears are selected, there will be a tendency for the rod to try to move the sheath up and down as the rods is pushed into and pulled out of the sheath. You need the rod to move as freely into / out of the sheath as possible, with the least pressure from the rod acting against the inside of the sheath.

It's also possible that my transmission is already damaged.

My box has very weak synchromesh on third gear. If I'm ham-fisted it will crunch shifting into third. It's no big deal, I very rarely get it wrong, just experience with this particular gearbox. The problem was there from the day I bought the car, it hasn't gotten any worse in the next 170,000km. I should mention that I've had the short shifters (i.e. the one at the shift lever and the modified levers at the gearbox) on the car for about 100,000km, and the gearbox still works very well (ignoring the synchromesh on third, but that was already like that).

I had an axle replaced at a Chrysler dealership (before I was confident enough to do it myself.) and the mechanic put standard gear oil in my transmission. The extremely thick type that smells like eggs and crap. Until it was warm, grinding occurred. Once warm, it shifted fine.

The "eggs and crap" smell is caused (I think) by the substantial quantity of zinc used in some specialised gear oils. RWD hypoid differential oils smell even more strongly of it (it's a very good 'anti-scuff' agent, which hypoid cut gears need). With some relatively high zinc engine oils you can smell it a bit too.

When I was young and less experienced I used some thick oil (about 80W from memory) in a Fiat 124 Sport gearbox, which made for a rather stiff shift action (especially when cold), but other than that it didn't cause any noticeable problems. This box was in my Lotus 7 style car ('NOTA', if you want to look it up), that had a very short gear lever, if the lever were standard Fiat length it would have been less of an issue.

I chose the oil it because it said 'for manual gearboxes' on the bottle...