jeff8932612

hey all my gears feel and sound goos when i engage them EXCEPT 5th. When i put it in 5th it makes a quick grind like noise, its very quick and the rest of the gear is fine. It does it with the clutch all the way in so i have no clue what it is. Can anyone help? Thanks

- Jeff

CPA

Very common problem. It is most likely the 5th gear syncro. I had to replace mine. Not sure of the cost since my warrenty covered it, but I think it was almost $700.

legendr35

yup the 5th gear syncro is gone, you should replace it ASAP, before futher damage is done. Make sure you try to stay out of 5th.

jeff8932612

where can i get a new 5th gear synchro and does anyone know if there is DIY instructions on the net anywhere? thanks

legendr35

you'll need to take it to a tranny shop and get it rebuilt. it should run about $500-600.

skunks

one thing you could try to do is to double clutch it (note i have not been able to master this yet and dont even know if it even works), i have the grind but hardly need 5th cuz the power does not comeon till over 100mph. anyways, 4th gear should be good till about 120 so you rarely need 5th.

can anyone tell me if double clutching works?

jeff8932612

hey legendr345, you said takew it to a tranny shop and let them rebuild it....does this mean just rebuild 5th or the whole transmission? thanks alot!

RonKMiller

I am one lazy sonofabitch, since mine went about 5 years ago, and I've been driving around with the repair parts in my storage bin ever since! I'ts quite a job to DIY, the tranny needs to come out, but not completely disassembled. It's not that difficult to replace, just labor intensive and it requires a couple of special tools to do it fast. Between parts and labor you're looking at close to $1K to have someone else do it CORRECTLY. Stay away from tranny shops and find a rotary specialist who has done it before, they might even save you some money on the labor since they should be able to replace the actual ring in about 15 minutes. It's taking out and putting back the tranny that eats shop time.
OR, you can drain and flush the case with LOTS of fluid (you'll undoubtedly get lots of small metal pieces from the broken teeth on the synchro ring). Refill with a quality synthetic, and keep on driving! By holding the clutch in and blipping the throttle (I think around 3K rpm at about 70 mph) you can shift into fifth without a problem, just don't do it really fast. You'll get the feel after doing it half a dozen times. You'll also get a lot of grinding until you do it right. Downshifting should be smooth.
Then again, you could have big chunks floating around in there that COULD cause more damage. If you do a lot of high speed cruising or freeway driving bite the bullet and get it fixed, if not, you'll hardly miss it. If you use 5th under 70mph you're close to "lugging" the engine, which can really be hard on it.

7at11

$500-600 is just for 5th gear, as 5th and reverse can be replaced serparate from dissassembling the whole trans. Expect about $1400 for the whole thing (Full rebuild, all replaced synchros and so on). It's my understanding a thicker fork (5th) was made for the 94+ cars (read the TSBs) and an upgraded part is available for second gear as well (a slider/hub I am told to aid in the 2nd gear grind problems)

Double clutching made no difference for me, but switching to synthetic fluid did help. It has still grinded occaisonally in this state though. My current plan (which has been working so far for about two days) is to slide the shifter towards the passenger, but then wait a second or two before gently pushing it forward. So far so good, hopefully this will buy some time.

skotx

Here's that TSB that 7at11 mentioned: http://www.rx7.org/public/3RD.html. It's #20.

RonK...

So you're not supposed to use 5th gear for highway driving at moderate speeds (70 mph)? Isn't 5th gear in a manual like overdrive in an automatic, where the gear ratio is something like 0.75:1? I thought you were supposed to use this gear to improve fuel economy. I've never heard of what you mentioned, but it sure doesn't sound good.

RonKMiller

Naw, driving at 70 mph in fifth is just fine. If you're doing a wot run to higher speeds and have the throttle mashed you really won't find 5th usefull until about 130 mph or so! I always say live fast, die young and leave a good looking corpse! "Lugging" can cause detonation - although your knock sensor should detect this and prevent it - and we all know what detonation does to any engine and especially rotaries.

Struggly

Double clutching will absolutely work if you do it correctly. I don't know the exact rev-match numbers for my RX-7 because I just got it a week ago, so I'll use numbers from my old Stealth R/T Twin Turbo:

To double clutch from 4th to 5th at 80 mph: In 4th, rpms should be about 3700. At the same speed in 5th, rpms should be at about 2800. So, at 80, you stomp the clutch in and out and pull the stick to neutral. Wait for the revs to drop to 2800, then stomp the clutch in and out and shift to 5th. If you do it correctly, and you have no play in your driveline, the transmission should not grind, no matter how bad the synchros are, there should be no movement of the tach as you pass through the engagement point of the clutch when releasing it after shifting into fifth (this is how you know if you did it right or not).

All you need to do is memorize engine revs in all the gears at any speed, which is really not that hard. Then you can double-clutch constantly, which, while not as necessary on upshifts unless you have bad synchros, is very helpful on downshifts. It saves the tranny. I never downshift without double-clutching, unless I'm going 5 mph.

And just for more evidence: My friend's 3000GT had a 5th gear synchro that had fallen off the spring and was doing nothing. You could barely get it into gear without double-clutching, and it made a terrible clunk, but with double-clutching you couldn't tell something was wrong.

Double-clutching is the proper way to shift a dog-box if you're trying to preserve it, so it can't be a bad thing.

Clint Fralick
Struggly@hotmail.com

skunks

well i compilled a list of rpm to speed, here it is if anyone wants it, its for a stock 3rd gen RX-7 with stock wheels. What rpm should i double clutch at??? im thinking at 70 mph, push in clutch at 4th at 4400 rpm and shift to neutral. Wait for the revs to drop to 3200, then stomp the clutch in and out and back in again and shift to 5th.
is this right Struggly???
also im kinda confused about the then stomp the clutch in and out and back in again and shift to 5th. the clutch has to be in when I shift to 5th right?



225/50 16" = 24.86" diameter

RPM Speed in 1st gear.
200 1.04
400 2.07
600 3.11
800 4.14
1000 5.18
1200 6.22
1400 7.25
1600 8.29
1800 9.33
2000 10.36
2200 11.40
2400 12.43
2600 13.47
2800 14.51
3000 15.54
3200 16.58
3400 17.61
3600 18.65
3800 19.69
4000 20.72
4200 21.76
4400 22.80
4600 23.83
4800 24.87
5000 25.90
5200 26.94
5400 27.98
5600 29.01
5800 30.05
6000 31.08
6200 32.12
6400 33.16
6600 34.19
6800 35.23
7000 36.27
7200 37.30
7400 38.34
7600 39.37
7800 40.41
8000 41.45
8200 42.48



RPM Speed in 2nd gear.
200 1.79
400 3.58
600 5.37
800 7.16
1000 8.96
1200 10.75
1400 12.54
1600 14.33
1800 16.12
2000 17.91
2200 19.70
2400 21.49
2600 23.28
2800 25.07
3000 26.87
3200 28.66
3400 30.45
3600 32.24
3800 34.03
4000 35.82
4200 37.61
4400 39.40
4600 41.19
4800 42.98
5000 44.78
5200 46.57
5400 48.36
5600 50.15
5800 51.94
6000 53.73
6200 55.52
6400 57.31
6600 59.10
6800 60.89
7000 62.69
7200 64.48
7400 66.27
7600 68.06
7800 69.85
8000 71.64
8200 73.43


RPM Speed in 3rd gear.
200 2.59
400 5.19
600 7.78
800 10.38
1000 12.97
1200 15.57
1400 18.16
1600 20.76
1800 23.35
2000 25.94
2200 28.54
2400 31.13
2600 33.73
2800 36.32
3000 38.92
3200 41.51
3400 44.11
3600 46.70
3800 49.30
4000 51.89
4200 54.48
4400 57.08
4600 59.67
4800 62.27
5000 64.86
5200 67.46
5400 70.05
5600 72.65
5800 75.24
6000 77.83
6200 80.43
6400 83.02
6600 85.62
6800 88.21
7000 90.81
7200 93.40
7400 96.00
7600 98.59
7800 101.18
8000 103.78
8200 106.37


RPM Speed in 4th gear.
200 3.61
400 7.22
600 10.83
800 14.44
1000 18.04
1200 21.65
1400 25.26
1600 28.87
1800 32.48
2000 36.09
2200 39.70
2400 43.31
2600 46.92
2800 50.52
3000 54.13
3200 57.74
3400 61.35
3600 64.96
3800 68.57
4000 72.18
4200 75.79
4400 79.40
4600 83.01
4800 86.61
5000 90.22
5200 93.83
5400 97.44
5600 101.05
5800 104.66
6000 108.27
6200 111.88
6400 115.49
6600 119.09
6800 122.70
7000 126.31
7200 129.92
7400 133.53
7600 137.14
7800 140.75
8000 144.36
8200 147.97


RPM Speed in 5th gear.
200 5.02
400 10.04
600 15.06
800 20.08
1000 25.10
1200 30.12
1400 35.14
1600 40.15
1800 45.17
2000 50.19
2200 55.21
2400 60.23
2600 65.25
2800 70.27
3000 75.29
3200 80.31
3400 85.33
3600 90.35
3800 95.37
4000 100.39
4200 105.41
4400 110.43
4600 115.45
4800 120.46
5000 125.48
5200 130.50
5400 135.52
5600 140.54
5800 145.56
6000 150.58
6200 155.60
6400 160.62
6600 165.64
6800 170.66
7000 175.68
7200 180.70
7400 185.72
7600 190.74
7800 195.76
8000 200.77
8200 205.79

Struggly

Damn man, that's an extensive list. But yes, that's basically the idea:
Let's say you're at 4400rpm in 4th. By your list you're doing 79.40mph, which we can round to 80 for simplicity. If you want to double clutch into 5th, release the throttle, push the clutch down, pull into neutral, release the clutch. Ideally, you want to do that as fast as you can. When the revs are at 3200, which, by your list is 80.31mph in 5th, push the clutch in, shift to fifth, release the clutch. Again, do this as fast as possible. Since the flywheel is already spinning at the same speed as the transmission, you do not need to release the clutch slowly. Just lift off. If the revs are matched perfectly, you shouldn't have any lurching, nor should the tach jump around. You can e-mail me if you have anymore questions, but it's not as complicated as it sounds. If you just drive around in the car a little bit you'll get it. Find a small neighborhood with lots of right hand corners and practice going from 4th to 2nd and 3rd to 2nd. You'll get the feel and then driving the car is a hell of a lot more fun and you wear down the trans less. Remember that the only difference if you're going to downshift is that when you're in neutral and the clutch is engaged you've got to throttle up to the correct revs.

By the way, I'm saving your rev/mph list. Good resource to have because now I know where all the gears end.

Clint Fralick
Struggly@hotmail.com

7at11

Not to question but just to make sure, can someone verify those numbers? My tach is screwed, but I didn't think it was off that much! I show redline in third is about 87 mph, and in 5th 80mph is (or was in my case) "exactly" 3000 rpms. Is this extremely wrong?

skunks

those numbers are for a bone stock system i pulled off some where, it seems to be relativly accurate but its gonna change/be off a little with airpressure and other varibles. they seem to work for me.