Regearing a tranny - Toyota Tercel

[Daox]

I just talked with the warranty guy here about the failure on the escort. He is sure it was due to misalignment. Most likely this happened when they welded it, but it could have also been machined improperly. He gave me a few tips and thinks that if I can get it machined accurately, and avoid welding it I should be good.

[MetroMPG]

"Luckily I work at a gear manufacturer and I can get access to machinery, or find someone to do it for me (more likely)."

Lucky dog. Nice to get that expert opinion on the possible cause of the Escort failure.

This is going to be very interesting!

[jwxr7]

I just came across this thread, but before seeing this I was talking with minic6 over at GS about changing my metro 5th gear. I wanted to mod 5th gear because I thought it could be changed without pulling the trans.
Here's what I suggested to minic6.

Originally Posted by jwxr7
I may have come up with a short cut to making gears from scratch. I was looking at some service manual stuff on our trannies that someone posted over at teamswift.net. 2nd gear is 1.894:1 so if you could switch the gears around so the input shaft now has the gear from the countershaft and vice versa, you would end up with a .528:1 over drive. This would drop my revs from 3000 rpms at 60 mph down to just under 2100 rpms. That is quite a drop, maybe too much, because currently I use 5th gear around town as low as 25 mph. The majority of my driving is around 45 though and the new rpms would be about 1570 rpms (instead of 2250 rpms).
If we could get ahold of some junk trannies we could remove the second gear set and already have a meshing pair of gears. Problem is, the inputshaft has second gear integrated into the shaft (we'd have to cut the shaft off both sides and bore it out for the 5th gear countershaft) and the bore diameter is probably different for the 2nd gear counter shaft gear and who knows what else would need modified. Could be better than starting from scratch though.

just a crazy thought

Then he suggested reusing the inner diameters of the original 5th gear gears and fitting them to the bored out 2nd gear gears to retain the splines and correct shaft diameters etc.


So it sounds like we are on similar paths Daox (and I thought I had an original idea )

[MetroMPG]

I think the 2nd gear to 5th gear trick is what this ZX2 owner did (bored out, with the 5th gear centers welded in):

Story of a custom 5th gear for a '98 Ford Escort ZX2: +6% MPG

Unfortunately it looks like his web site (linked in the forum post) is no longer active.

[jwxr7]

I remember COZX2 talking about doing gear work on his trans a while back. If I would have paid more attention, or had a better memory, I would have seen that he did the same stuff. Oh well, just started thinking about it recently and was just throwing ideas around with minic6. Neat to see it actually being done.

[Daox]

Yeah, thats where I got most of the info from.

I still haven't gone ahead with any of this yet though. Too stinkin busy atm plus the focus has shifted to the Matrix. However, I do have to get the Tercel back on the road.

[Duffman]

I also agree with the suggestion that a .525 overdrive gear might be to deep. I would run the engine at the target RPM in the current OD gear and see how it responds at that RPM and find a small slope to approximate the increased aero drag from the higher speed you will see at that RPM with the deeper OD gear.

[Daox]

What makes you think .525 is too deep?

[Duffman]

1) Because oriental cars are not known for thier low RPM torque.
2) Other than the T56 speed in a V8 camaro & Corvette or a V10 Viper, none of the manufacturers ever go that deep with their OD gears (maybe a reason).

It costs you nothing to run my simple test.

[Daox]

#1 is a valid concern and I have already looked into this as it was a concern of mine too. At 1875 rpm I have roughly 23 horsepower (65 ft/lbs) avaliable to me. That'll set me at about 70% load (@ 65 mph) which is pretty close to ideal for most engines. The only detriment will most likely be the low rpms since peak BSFC occurs at higher rpms in most naturally aspirated engines. If I need more power I simply have to downshift.

#2 really isn't much of a concern. On all the high mileage versions of cars I've seen they always gear them lower. Examples would be the Honda VX, Honda Insight, Geo Metro XFI, and even the new Chevy models that are getting better mileage like the Malibu LTZ and Cobalt XFE.

The real benefits will have to be seen. It all depends on how the BSFC map is for the engine once I'm done with it. If it has long horizontal sections like the Metro map below I'll be in great shape. If its like the Saturn map I won't see as much benefit. Since the torque output of the engine is very flat I'm guessing its more like the Geo map. The red dot is how its geared now, the purple is after modification.

Geo 1L BSFC map



Saturn DOHC BSFC map