RX-7 5-4 Downshift

[Eagle7]

S4 RX-7.
Not a new issue for me, but still trying to solve it. I don't heel-toe downshift (I've tried, but might be too old to learn ). The two tracks I most commonly run require a 5-3 downshift at the end of the long straight. I prefer to row through all the gears on the way down - when I try a straight 5-3 shift it sometimes turns out 5-5 . The problem is that it won't reliably go into 4 - sometimes yes, sometimes no. So often, there I am in the middle of the braking zone struggling with the shift lever. Either I blow the corner when the shift doesn't happen or brake early every time.

So my preferred pattern is brake on, clutch in, 5-4, clutch out (schreech), clutch in, 4-3, clutch out (schreech), brake off, throttle and turn-in.

I've tried double-clutching - clutch in, 5-N, clutch out, clutch in, N-4, clutch out ... It's better but still not reliable.

I had hoped it was an issue with the one transmission I keep rebuilding. I switched to another transmission, planning on a problem solved and a good specimen to compare against when rebuilding the problem child. But this transmission is worse then the original.

So the question: is this inherent in the design of this transmission, or should I be able to fix it with a proper rebuild. If it's fixable, what specifically should I be looking for? And would proper heel-toe downshifting be a reliable solution?

TIA,

 

[Drew M]

Sounds like it could be a shifter problem Have you replaced the shifter bushings?

Yes, proper heel-toe shifts would most likely improve the problem some. I learned by doing it everyday in my streetcar. Now, it's not even something I have to think about.

Another fix would be to leave it in 4th and go faster.

 

[seckerich]

When you do the quick 5-4-3 downshift with the Mazda just push the clutch in and go to forth, do not let clutch out and then go to third and rev as you come out on clutch. Stop with the heel toe and just roll the side of your foot on the gas.

 

[TomL]

Is the screech when you let the clutch out (what you wrote) or when you try to do the downshift (seems more likely)? And does it occur on both downshifts or is it just the 5-4? And does it not happen on a regular 5-4 only downshift? If it happens pretty much all the time, and with multiple transmissions, it's more likely a problem with the clutch not releasing completely. Either the hydraulics are leaking, or you just aren't depressing the pedal enough (I've done it myself).

I'd also vote for what Steve said, and recommend a straight 5-3 downshift where needed. It's all I ever use and I end up with a 5-5 about once a year.

 

[Eagle7]

Sounds like it could be a shifter problem Have you replaced the shifter bushings?

Yes, proper heel-toe shifts would most likely improve the problem some. I learned by doing it everyday in my streetcar. Now, it's not even something I have to think about.

Another fix would be to leave it in 4th and go faster.

Pretty sure the shifter bushings are good.
Not sure what you mean by leave it in 4th. I'd need a different rear gear to do that.

When you do the quick 5-4-3 downshift with the Mazda just push the clutch in and go to forth, do not let clutch out and then go to third and rev as you come out on clutch. Stop with the heel toe and just roll the side of your foot on the gas.

Not letting the clutch out in 4th would not solve the issue. The problem is that it won't go into 4th. Do any of your transmissions have or develop this issue? Could it be a worn 3-4 shift hub? I changed the synchros but probably not that hub.
When I said heel-toe I meant the foot roll. I just can't seem to get my brain to do all four things at once.

Is the screech when you let the clutch out (what you wrote) or when you try to do the downshift (seems more likely)? And does it occur on both downshifts or is it just the 5-4? And does it not happen on a regular 5-4 only downshift? If it happens pretty much all the time, and with multiple transmissions, it's more likely a problem with the clutch not releasing completely. Either the hydraulics are leaking, or you just aren't depressing the pedal enough (I've done it myself).

I'd also vote for what Steve said, and recommend a straight 5-3 downshift where needed. It's all I ever use and I end up with a 5-5 about once a year.

Yeah, the screech is the tires when I let the clutch out, because I didn't rev-match.
The clutch is good (and the problem also existed with the prior clutch). Every shift is very smooth except the 5-4 downshift.
Maybe the 5-3 shift is my best option, along with another attempt at mastering the rev-match.

Thanks to all for the feedback.

 

[joeracerx95]

Yes, all RX7 transmissions I've used are touchy going from 5th to either 4th or 3rd. I've been told, and take this for what it's worth, that the shift forks are usually bad in these transmissions. I don't know what that means or how to fix it, but if it's true it may be related.

Now, how to solve the problem? Here's the method I've found that works pretty much 100% of the time.

As soon as you hit the brakes, put the clutch in and take the transmission out of 5th. Then either let go of the shifter completely or, as you get used to this method, simply release any pressure on the shift lever from your hand. Let the transmission "settle" for a moment and the shift lever will automatically align itself with the 3-4 slot due to the internal springs pushing on the shifter. This takes very little time and you will still be in the braking zone. Now push/pull the lever into the gear you want. You will find that it does so without any problem. Trying to muscle or force these transmissions just doesn't work.

Double-clutching or heal and toe will not have any affect on this. Double-clutching helps the transmission gears match speeds and is only really needed if your syncro's are bad. Heel and toe matches engine revs to tire speed and will get rid of that screech you are getting when you let the clutch out. You need to learn this, otherwise you will loop the car at some point. If you haven't looped the car when the rear tires screech, you probably aren't hitting your brakes hard enough to begin with.

 

[lateapex911]

My method is to stomp the brakes, get it out of 5th and into N, pop the clutch out while rolling the right foot onto the gas to zing it, then clutch in and straight into third, and more zinging as I ease the clutch out. At certain tracks like Lime Rock, it's all about trailbraking and being smooth as you roll back on the throttle. Can't do a fast lap there any other way that i've figured out.
I don't have any grinding, screeching tires or spinning. I also pause in my shifts a millisecond, as a rule, to be nice to my transmissions.

Learning proper heel toe and double clutching is useful.
In a sense we are lucky that our cars don't brake like F1 cars and we have plenty of time to get all the shifting done.