gearbox synchros
 

Seeing that these brass synchros are the weak links in all these 2nd gen boxes,is there anyone building synchros that can take the abuse and that can be installed in the 2nd gen gear boxes and work properly.

Re: gearbox synchros
 

I too, would like to know this.

What's a good material for syncros to be made out of and how much could it cost to have a machine shop do some up?

Good Question....
 

bump....

Re: gearbox synchros
 

I have heard many times before that the syncro rings are the weak part. I personally rebuilt the trans on my RX-7 at 140,000. The shifting was hard and the bearings were going out. But The syncro rings (balk rings) were still within the factory specs for thickness. They were however no longer seating well againt the gear cones. I have read of the 1st gens actually breaking syncro rings but I don't think that is a problem on the 2nd gen.

All I had to do is reseat the rings to the gear cones as sugested by the repair manual. If you get new syncro rings you would want to do that anyway because they need to match the gear cone exactly or you don't get enough friction between them.

Re: Re: gearbox synchros
 

Is it possible that the syncros and the gear cones wouldn't get enough friction if the oil you're using is too "slippery"?

I know that sounds silly, but I'm running Mobil 1 synthetic and I've heard rumors that it is doesn't allow enough friction between parts. I'm going to order some Redline as soon as I get around to it and hope it helps my problem.

My 2nd gear syncro seems to be shot, or something is wrong somewhere that causes me to have to shift to second at high RPM's rather slowly. It'll still shift, but I have to pull it from 1st to 2nd and wait for the cog to spool up before it'll move into place. I never force it in so the cogs won't grind, just put enough pressure on it so the the syncro and cone touch. Sometimes I just double clutch the shift and use the engine to bring the tranny speed down. I always double clutch when I downshift, in every gear.

You know, in all of the RX-7s I've owned, the 2nd gens seem to like a very distinct 1-2 shift, with a slight pause after pulling out of 1 and going into 2.

My 80 (4 speed), 81 & 82 both 5 speeds all were much better in 1-2 shifting in my opinion. I've had 2 86s (a base and a GXL) and now my 88 T2, all have similar feel in 1-2 shifts. I used all kinds of trans oil over the years, Amsoil, Mobil, Redine-- didn't really notice any difference.

My .02

Greg O.

That "distinct" 1-2 shift is because the shifter moves in a "W" pattern instead of the traditional "H".

If you want to see exactly what I mean, go drive a Honda Civic and then drive your car, you'll notice it instantly. When the shifter comes out of first it kinda moves off towards the passenger side a hair, when it moves into second you're actually pulling it a hair to the drivers side of the car.

could it be that the gear ratio between 1 and 2 is so much larger that any other gears? my 91 coupe is over 2k rpm difference from 1 to 2 where it is a little over 1 from 2 to 3 and so on. if this is the case, it would mean that it took twice as long for the 2nd gear to "spool" as you are calling it. my 2 sense

Yes, but my car wasn't always this way. In fact, the problem seemed to pop up out of nowhere.

I was cruising through Baton Rouge on a very hot afternoon and I did a high RPM shift and it crunched, and it has been like this ever since. The night before that it was shifting fine.

I've learned that from now on, there will be no more "speed" shifting in any of my cars.

EDIT
Oh, and I'd like to mention that this is the THIRD n/a FC transmission that I've worn out. Well, actually only two, the first one was fucked when I bought the car. The replacement only had 70k on it, and shifted fine when I put it in but by the time the engine was done for so was the gearbox. I've since learned to double clutch when I downshift to preserve the syncros, that's why I was so surprised when my current transmission developed it's problems.

Problems
 

Mine shifts hard most of the time but smooth somethimes, more noticable in 5th or reverse or 1st. It only has 53,000 original miles on it and is a 87 Turbo. Any ideas what it could be? Oh and it clunks sometimes or doesn't want to go to reverse at all.

Most of the shifting problems described are related to the sycros. It may help to understand more on how they work. I will try to explain it a bit if you don't already know. It is pretty neat.

Basically the shift fork is attached to a sleeve which is splined on the inside and slides over a splined hub which is attached to the output shaft. When you push the shift fork forward it slides the sleeve towards the gear and presses the synro ring onto the gear cone on the gear. The friction between the syncro ring and the gear cone is acts like a clutch and speeds the gear up to match the speed of the sleeve which is attached to the splined hub which is attached to the output shaft. As you keep pushing the spring between the syncro ring and sleeve compresses and the sleeve engages the splines cut on the side of the gear. If the gear is still spinning "GRIND".

It is the same process for all gears except reverse which has no syncro at all. Out put shaft should not be spinning (car stopped) when engaging reverse and the input shaft will spin to a stop soon enough with the clutch depressed.

http://www.howstuffworks.com/transmission.htm

That's where I learned about it. It's a pretty good write-up.

share your knowledge
 

YO 10_ANNIV_

i have a ? for you, how did you tune your safc, im curious about your settings. im about to install one in my 88 turbo II and i would love some advice. i have been reading our tps' suck big time and makes setting the lo, hi point hard.

so can you please shoot me some or your knowledge fellow rotorhead:smoker:

the easiest way to save the wear and tear on synchros is to match revs on all up and down shifts. this can be done with a slight pause between gears on up shifts and a blip of the throttle on downshifts. I have raced my RX2 and turbo II for more than 2 years and the only parts of the transmission I have had to replace are the shift forks, which tend to wear easily(makes shifter sloppy). Quaife makes a dog ring and straight cut gear set for Trust in Japan for the turbo II trans, but this would require the rev matching to shift properly. this setup tends to be more durable but it is also alot louder(bad gear wind sound). try to take it easy on the trans(no speed shifting and downshifting without matching the revs) easy deliberate shifts will be the fastest and also make the transmission last.