Transmission problem - won't go into reverse

[sopwith21]

Howdy all;

My 74 260z **racecar** has been retro-fitted with a 2.8L and a 5-speed tranny. I don't know which 5-speed it is.

When putting it into reverse, the shifter grinds and will not stay in place. I can use a great deal of hand pressure to hold it in - just enough to get the car barely rolling - and then it pops out of reverse and into neutral again.

My mechanic thought it was a linkage problem but it is not - the shifter goes straight down into the tranny housing. What could be causing this? Should I swap back to our original 4-speed before the race in case of failure? The 4-speed is not as fast, but maybe that's the more reliable way to go.

Your opinions are appreciated!

[Zed Head]

How does 5th gear do? It shares half the shaft, on the backside of the adapter plate, and a shift fork, with reverse.

[sopwith21]

Don't know... we never use 5th gear on the track and I've never shifted it into 5th.

The car is up on a lift for a few days but maybe we can at least see if it will shift into 5th cleanly. That's a good thought, though.

Edited March 3, 2014 by sopwith21

[Zed Head]

If the 5 speed is pre-1980.5 it will have the same 1-4 ratios as the 4 speed. The 77-80.5 5 speeds were just the old 4 speeds with an extra gear added. If it has two exhaust hangers on the tail-shaft housing it's the pre-1980.5 5 speed.

[sopwith21]

That's very helpful! I had a new engine put in at the same time as the new tranny, so it is possible that the increase in speed was due to the engine alone and not the tranny at all. I'll check for the exhaust hangars and hope its a pre 1980.5 model.

This site seems to claim that there is a difference in the ratios of the 260z vs. the 75-79 280. I can't figure that out? Scroll down the page until you see the Transmission Ratios and tell me what you think.

Something to remember... I use 2nd gear twice per lap, but I use 4th gear either 3 or 4 times per lap. So a closer ratio between 3rd and 4th would theoretically help more than a closer ratio between 2nd and 3rd.

Edited March 3, 2014 by sopwith21

[Zed Head]

A look in the FSM's shows that they are different. I have a 280Z so kind of forget about the early 4 speeds, which were used with the 3.36 rear diff ratios, generally. 3.592 1st vs. 3.321. They all have a 1:1 4th gear though, so probably quicker but not faster.

Here's the ratios from the FSM's (MT chapter), looks like the 260Z 4 speed would be the one, if 3-4 closeness trumps:

260Z - 3.592, 2.246, 1.415, 1

280Z - 3.321, 2.077, 1.308, 1

[sopwith21]

That's what I thought. Not only is 3rd to 4th about 0.01 closer than 2nd to 3rd, but I can use it nearly twice as often in the race.

I still need to figure out what trannies I have exactly. I know I have one four speed and one five speed... that's all I can say for sure.