The 2nd gear synchro from hell

3A-C Power · Post by **3A-C Power** » Wed Apr 07, 2004 3:45 am

Well I can't sleep, but tonight I was looking at the 4WD tranny diagrams again and I finally got it. How all the ingenious Z54F parts fit and work together. It occurred to me why our trannies have such bad downshifting, particularily 2nd where the synchro has to do the most work. The Tercel's input shaft turns an idler shaft with a giant gear, which turns the counter shaft which is basically what the input shaft is on a RWD transmission. So the synchros have to not only speed up the shaft that they're on, but this intermediate idler shaft with a gear that has lots of rotational inertia, and then the actual input shaft with the clutch disc on it. This extra inertia translates into more force and/or time necessary to synchronize the gears. The design of the transmisson necessitates a strong 2nd gear synchro, and 3rd gear one for that matter, but Toyota didn't use one that's good enough. Toyota's updated synchro design as of 1990 was then an attempt to fix the problem through an improved synchro. Some performance could also be gained in lightening the giant idler gear that takes power from the input shaft to the counter shaft. I started researching to find out more about synchro design and just found a company that makes 'double synchros' for Mitsubishi transmissions. I'll have to find out how that works. To increase performance of a synchro, I can only think of increasing the contact area, increasing the diameter, and improving the friction of the surface.

In RWD/4WD news, it appears there is enough space on the end of the input shaft between the transmission case and the differential housing to add a transfer hub. Furthermore, the space occupied in the rear transfer case that was previously used by the transfer hub could be used for something more useful than a transfer hub that's always engaged. Well, what would you want to add to a tranny? How about a gear? Haven't you always wanted a 6th? Or maybe you could do with an extra, EXTRA low.

When 20V Tercel said that the shop that did his tranny could have added a 6th gear, they likely meant extending the output shaft beyond where 5th is and putting a 6th gear there. That way it would work off of the existing shift fork and hub that's presently only used for 5th. A shift fork can be used for two gears, one in each direction.

The way the Tercel tranny is laid out, the main case is the same for 4, 5 and 6 speed versions. 5 speeds add a 5th in front of the case, and 6 speeds add the extra low behind the case in the transfer housing. They extend the counter and output shafts to mount the extra gears on. This is an easy improvement to a 4-speed since putting a gear right outside the case puts all the force very close to the bearing so as not to stress the shaft very much. You wouldn't want to put any more than one gear on an unsupported end of a shaft. But in the case of the rear of the Tercel tranny, once the output shaft is joined to the transfer output shaft, you get the support of the rear transfer bearing.

I know I'm talking like everyone else has looked at the tranny diagram in the service manual for long enough to understand it. I'm excited because I've always loved mechanisms and mechanical designs, and have been interested in rebuilding this transmission since I was 17 and had my first Tercel wagon. Way back then I tried to take one apart but didn't get very far without access to the factory manual. I eventually took it to a tranny shop, which never called me back and for all I know could still have it. One mechanical engineering degree later, I finally understand the transmission. So what will it be, 6th or EEL?

icE · Post by **icE** » Wed Apr 07, 2004 5:39 am

Would EEL give you more torque? Or would a 6th gear add more horsepower? Don't know much about tranny's but a more efficient design would give you more speed and more power.

WeirdAl · Post by **WeirdAl** » Wed Apr 07, 2004 7:38 am

Which are you more unhappy with, how low 1st gear is or how high 5th is? Do you want your rpm's lower in 5th? I'd think ideally you'd want to change the ratios of all the gears instead of just tack one on on top...

sacwac · Post by **sacwac** » Wed Apr 07, 2004 9:40 am

Isn't the EL gear on the Z54F low enough? The manual states a top speed of 5mph or something. Depends on what you plan to do... If only off road, then I might opt for an EEL. But since I use my tercel for long distance, AND I live in California where I've only seen snow twice, I'd actually rather have a 6th gear. To increase mileage, hopefully.

Also, even with a 6th gear, the RPMs might not change enough to produce that much of a difference in mileage. Depends on the ratio. Would there be any problems in crusing at high speeds for long periods of time at a lower RPM than Toyota designed the car for? I once converted my motorcycle from a chain drive to a belt drive.... drastically reduced RPMs, but the motor would lug on the freeway.

So... 6th gear... that's my vote!

Nice job describing the tranny, I've seen the diagrams... it's a mess.

GTSSportCoupe · Post by **GTSSportCoupe** » Wed Apr 07, 2004 11:15 am

Personally I see no need for another gear in the Z54F. If I had a 4agze in my tercel I might be interested in a 2nd overdrive gear for high speed (150km/h+) highway cruising, but right now I don't have the power in the 3AC to make use of a 2nd overdrive.

I'm mainly interested in the RWD/4WD ability.

It would be so awesome if you could pull this off. An additional gear would be cool, but not necessary.

sacwac · Post by **sacwac** » Wed Apr 07, 2004 6:29 pm

How about a 2nd reverse gear??? That way, I can show the police the awsome fury and speed of my getaway car in reverse.

3A-C Power · Post by **3A-C Power** » Wed Apr 07, 2004 7:46 pm

It would have to be a forward gear. On second thought, you can't get much lower than EL already is because the small gear is no larger in diameter than the shaft. They literally made EL as low as they possibly could. I would want a 6th gear to enable closer ratios between all the gears and the 6th gear could be lower for high speeds. I'm thinking more along 4A-GE lines, but the 3A-C could use a 6th gear for if you wanted to go 120 km/h at 3000 rpm instead of 3600.

3A-C Power · Post by **3A-C Power** » Wed Apr 07, 2004 7:50 pm

Don't forget that the 83-84 models had a final drive that was higher so the rpm in 5th gear was significantly lower. They changed it in 85 for more power. So if you had a 6th gear with the 85-88 differential, it would really be like having the best of both worlds.

3A-C Power · Post by **3A-C Power** » Mon Apr 12, 2004 12:27 am

Well I found out why our synchros are so bad - the frictional contact area is so small. It's like a quarter inch thick. Less contact area means more stress on the material for the same frictional force so it wears faster. Given that these friction surfaces don't necessarily obey the classical laws of friction, more force is required to generate friction so in other words the synchros don't work as well. There's not much that Toyota could have done in making just a new synchro ring without changing the gear. They probably improved the material of the syncrho ring to get more friction and last longer. If I want to stick with the original gear changing clutch hubs, which are a bastard to make, I may be able to machine into the sides of the gears and add another synchro cone in there, and make synchro rings to match. I would then research clutch lining materials and have the synchro rings coated with friction lining instead of just having brass on steel contact. That is much better for dissipating the oil film and getting friction between the two surfaces. I've often wondered why car synchros don't use frictional lining, and thought it must be to avoid getting dust from the lining in the gear oil. However in looking at some performance tranny web sites, I saw actual synchro rings that look like they have clutch lining on them. Dust wouldn't be a problem if you changed the gear oil once in a while, and getting parts relined is surprisingly cheap - way cheaper than replacing synchros. The lining would last a very long time also, as it's oil-bathed and bearing relatively small loads. I love this transmission stuff so much, I'm going to ask for a job at some custom tranny shops. It's a stab in the dark but given that I understand transmissions and have so much initiative, maybe someone will give me a chance.

GTSSportCoupe · Post by **GTSSportCoupe** » Mon Apr 12, 2004 2:10 pm

Very interesting. For whatever strange reason, when I shift from 2nd to 3rd (shift up) I get a bit of a burr. I gets worse when shifting faster at higher rpms. As the transmission warms up it gets better.

I'll be going onto my 3rd AE86 transmission (T50) soon too. I don't think it liked the ~180hp 4agze setup I had.

3A-C Power · Post by **3A-C Power** » Tue Apr 13, 2004 6:45 am

yeah, that's what my transmission does. I think that's a problem with the shifting keys, they are what restricts the gear to not shift until the synchro has done its work. 3rd requires a delicate touch to go in smoothly all the time.

20vtercel · Post by **20vtercel** » Tue Apr 13, 2004 11:28 am

GTSSportCoupe wrote: I'll be going onto my 3rd AE86 transmission (T50) soon too. I don't think it liked the ~180hp 4agze setup I had.

perhaps you may want to think of something else like a kaaz tranny or at least getting the ones you have rebuilt with stronger internals....it can be done. The factory t50 trannys are good to 250hp. unless it's how you are driving. It will not last if you are dooing burnouts or launching it down a racetrack all day.

GTSSportCoupe · Post by **GTSSportCoupe** » Tue Apr 13, 2004 11:44 am

Anything is possible with enough money I guess. I find the T50 really doesnt like lots of torque. It was the quick shifts when accelerating that were hard on it. I could feel the whole system torqueing. I might have had more than 180hp too. With full interior etc I beat a 944 turbo and a wrx turbo by about 3 car lengths to 60mph.

3A-C Power · Post by **3A-C Power** » Tue Apr 13, 2004 12:08 pm

What was failing on your T50's? Did you ever have one of them apart to see what the problem was?

20vtercel · Post by **20vtercel** » Tue Apr 13, 2004 8:06 pm

GTSSportCoupe wrote: Anything is possible with enough money I guess. I find the T50 really doesnt like lots of torque. It was the quick shifts when accelerating that were hard on it. I could feel the whole system torqueing. I might have had more than 180hp too. With full interior etc I beat a 944 turbo and a wrx turbo by about 3 car lengths to 60mph.

944=poor man's porsche hahaha

I held a Subaru WRX-i Until I missed and ground my 3rd gear smooth!!! That's when the brass gears came in. You can't grind thoes. You just don't wanna take the chance. They will make the housing fall apart and twist the output shaft into a pretzel when they lock in!!!