Mike Frye

So I've been contemplating how I managed to apparently break a brand new (and possibly the last one Porsche had in stock at the time, anywhere on the planet) shift centering spring in my '85 5-speed.

I had replaced it and the reverse lockout spring about 14 months ago and then about a month ago it apparently snapped again. (I can get every gear reliably, but there's no resistance when going left or right in the shift pattern. I drained the trans but the piece isn't coming out, so it could still be something else, but it really feels like the spring again).

Anyway, so I'm trying to figure out how, in less than 15k miles, I managed to snap a second one.

Then in discussing the operation of the spring with Colin (Lizard) in another thread I realized that the spring is flexed in all positions except the 2/3 plane. Anywhere it provides resistance, it's flexed (slight flex in 4/5, more flex in 1/R).

So then it dawns on me: I park my car in 5th gear! I had been thinking that the spring is really only flexed in the 1/R plane in the S3 and is 'unsprung' in all other gears. For this reason I didn't even like to keep the car in 1st at a stop light. I would only go over that way when I had to for the shortest time possible, hoping to extend the life of the spring. Then I realize that by parking the car in 5th gear (all winter in the cold) I've probably shortened the life of the new spring considerably.

I'm still not 100% sure this is the cause, but it kind of makes sense when you think about it.

Anyone else think this is a possibility?


EDIT: Well, that was a short discussion.

GregBBRD

There is actually preload in every position, even when in 2/3...although it is much less.

My guess with your problem would be that you have mixed pieces from different years and you have thus induced both twist on the "cam" and have too much preload.

The '85 spring is actually a different spring than used on the later gearboxes...there are actually three different versions of that spring...even though Porsche only lists only two. There is an early spring (stopped somewhere in the S3 cars), a middle version (took over the early spring), and the late spring (which Porsche just ran out of and Colin has built a replacement....although I haven't seen one. However, I am very intriqued that Colin has developed a method of welding on spring steel without ruining it....this is very new/unique technology that no one has ever accomplished.)

You have to be really careful, in the early boxes, when swapping springs. The shape of the "cam" is different on both early springs and there is a version that requires cutting of the lower pivot to fit.

My guess is that you are using a late spring in an early gearbox and have both the wrong shape "cam" and too much preload...either way, it will break the spring in very short order.

The only possbile way to run a "late" spring in an early gearbox is to modify/change pieces to accept the later spring.

Mike Frye

Greg,

Wow, that's the first I've heard that there were 3 springs. I was aware of the S3 and the '87+ version which has a different profile to apply spring resistance and keep it in 2/3 rather than just out of 1/R mostly (which would require a different roller as well).

I'm not a very happy camper that I have to pull the transmission again. I did test for free motion of the new spring when I put it in there, which is how I figured out how the whole thing works. I put the very smallest amount of pre-load on there that would keep it in the groove of the roller in all positions for the sole reason that I wanted it to last as long as possible and remain 'unsprung' in the 2/3 plane (or very nearly so).

I didn't compare the two when I got the new one because I could tell right away it wasn't the '87+ one by the profile and didn't know there was a third option to watch for.

Thanks for the feedback.

GregBBRD

The two early springs have the same shape, where the piece touches the roller. The difference is at the pivot. One style had a washer...this requires a spring with a "thinner" pivot piece.

Mike Frye

Cool, thanks.