As many of you know, I have a guy that's making me LeBaron brake swap brackets and a couple other things to sell in the Fiero market. I recently mentioned the Econo transmission and figured out he has a gearing machine as well as a CNC machine! He told me he could make gears for 75 per gear or less. I immediately thought of the Econo trans 4th gear many of us are after and pay/have paid over 500 bucks for a transmission to get.

So, I have several questions.

1. Does anyone have pictures of that gear I can show him? He needs pictures.

2. Would anyone be willing to send me one if I pay for it under the condition that I would return them a brand new gear made with stronger steel than the original and have my payment refunded?

3. What, if anything else would he need to make to go along with the gear and have it work?

4. Are there any other custom gears he could make that would be easily swappable into a Fiero transmission i.e. an "Econo" 5th gear for a Getrag?

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86GT Modded 3.4l Pushrod V6 with Trueleo

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Previous discussion Here

The economy final drive consists of 2 gears - the differential gear and the gear on the output shaft which happens to be made as part of the output shaft. So to replicate the economy gear set, you have to replicate the gear/shaft assy on the right (the left one is the 3.65 output shaft):


Not going to make this for anywhere near $75...

Doesn't look like it.

Any other custom gears that people would want if I can get them made cheap?

Now something that would be cool and beneficial would be a revised 5th gear set for the isuzu... something like a .63 vs. the stock .74. This would further drop the cruise RPM by about 375 rpm to 2000 RPM at 70 mph with 24.6" tires.

On the isuzu, both gears for 5th are directly under the bolt on end cover and can be removed w/o pulling the tranny or tearing the tranny apart. Just pop the cap and loosen a couple of nuts and off they come. They can be removed in under 15 mintues.

Here is what they look like:


The challange is the smaller gear needs to be smaller which will make it thinner/weaker. Since the cover bolts on, you might be able to make these gears wider and use a spacer on the end cover to clear the wider gears.

Great idea...So essentially we'd only have to make 2 gears? 2k RPM at 70 sounds pretty damned good. That would put even the econo to shame...

quote Originally posted by fieroguru: The economy final drive consists of 2 gears - the differential gear and the gear on the output shaft which happens to be made as part of the output shaft. So to replicate the economy gear set, you have to replicate the gear/shaft assy on the right (the left one is the 3.65 output shaft): Not going to make this for anywhere near $75...

Paul,

You could get the 3.32 FD from a Citation 4-speed which gets you the output shaft but that is not the only part of the Fiero Econo gearing. The 4th gear on every Muncie 4-speed that I know of has a 0.81 ratio where as the econo has a 0.73 ratio. IMO it isn't really worth the effort to only change the FD.

quote Originally posted by MadDanceSkillz: Great idea...So essentially we'd only have to make 2 gears? 2k RPM at 70 sounds pretty damned good. That would put even the econo to shame...

Correct.

The isuzu isn't the strongest tranny, but there are many that use them for engine swaps just for the lower cruise RPM. If it could be dropped even further that would be great.

I can donate the gears in the picture and the dissassembled isuzu tranny to this R&D effort.

You know, if you can get custom gears made, you may NOT need to replace this entire shaft assembly:



The new gear could be made with an adequate press fit, and the existing gear could be machined off the shaft....then you press the new gear on in the correct location.

Just food for thought.

quote Originally posted by fieroguru: On the isuzu, both gears for 5th are directly under the bolt on end cover and can be removed w/o pulling the tranny or tearing the tranny apart. Just pop the cap and loosen a couple of nuts and off they come. They can be removed in under 15 mintues.

Are you sure you're not thinking of the Getrag? The Isuzu doesn't have a convenient bolt on end cover... it's the entire case half that must come off.

quote Originally posted by Bloozberry: Are you sure you're not thinking of the Getrag? The Isuzu doesn't have a convenient bolt on end cover... it's the entire case half that must come off.

You are probably thinking of the 4 speeds. The Isuzu has the 5th gear set outside of the main case half and covered with a bolt on cover like this:

Here is the Isuzu gear side case half with the removable cover set to the side (you must pull off the 5th gear set to pull the shafts from the tranny).


Here is a shot of the Getrag (left) and Isuzu (right) bolt-on end caps:

[This message has been edited by fieroguru (edited 01-08-2010).]

OK... forget my last... I think my brain is in a deep freeze. Thanks fieroguru.

Any chance a stronger 2nd gear for the Isuzu could be made or is it like the one mentioned above that is part of a shaft?

charlie

quote Originally posted by Jefrysuko: Paul, You could get the 3.32 FD from a Citation 4-speed which gets you the output shaft but that is not the only part of the Fiero Econo gearing. The 4th gear on every Muncie 4-speed that I know of has a 0.81 ratio where as the econo has a 0.73 ratio. IMO it isn't really worth the effort to only change the FD.

why not? 0.81:1 4th would be fine with a 3.0:1 or less final drive.. it would make 1st gear way more tolerable for shifting, and yield a great overall ratio for economy as well, perfect for V8 swaps...


me personally, i say if you are going to mod anything, Maddancskillz... mod the final drive gears in a getrag.. no offense to all the 4 speed lovers out there, but the getrag shifts smoother, hands down, the gears have better spacing too....its 1st gear defficiencies when mated to a V8 would also be corrected with a taller final drive gearing, and the fuel economy would be fixed as well..

my ideal getrag( 1st through 5th remain the same, just the final drive changes ):

1st gear: 3.50:1
2nd gear: 2.05:1 (MG1: 2.19:1)
3rd gear: 1.38:1
4th gear: 0.94:1
5th gear: 0.72:1
Reverse: 3.41:1
Final drive ratio: anywhere from 2.73:1 to 3.0:1

quote Originally posted by SGS: The new gear could be made with an adequate press fit, and the existing gear could be machined off the shaft....then you press the new gear on in the correct location.

You do understand that torque is transmitted from the splined sections of the shaft to the gear portion correct? I don't think any press fit would be able to transmit the amount of torque which is being transmitted through this shaft. We are talking about ~3.5X of engine torque being applied to this shaft in first gear.

Like I said though. This shaft and differential gear are available from a Citation 4-speed in the 3.32 FD ratio.

quote Originally posted by Jefrysuko: You do understand that torque is transmitted from the splined sections of the shaft to the gear portion correct? I don't think any press fit would be able to transmit the amount of torque which is being transmitted through this shaft. We are talking about ~3.5X of engine torque being applied to this shaft in first gear.

Yep. Some manual transmissions are actually made with press fits. The T-56 used in Camaros, Vettes and Vipers uses gears that are pressed on to a shaft.

I know it seems counterintuitive, but you can make a press fit hold a LOT of force. A shrink fit (where in this case you would heat the gear and cool the shaft and assemble them, taking advantage of thermal expansion) can be made so strong that the parts CAN'T be separated without physical damage at the interface of the fit. The parts actually friction weld themselves together as they move, and breaking those friction welds results in pitting and extreme fretting of the mating surfaces.

I just thought I would throw that out there as an option. Obviously, it would take some expertise to set up, but when you're to the point of wanting to change ratios in a transmission, it may be worth it.

quote Originally posted by fieroguru: I can donate the gears in the picture and the dissassembled isuzu tranny to this R&D effort.

Wow. an improved gearset for the isuzu 5 speed would be a wonderful thing. Maybe someone can do the math and spread out all the ratios - 1st is wayyyy to short and too close to 2nd . i bet a lot of the V8 guys are watching this thread and i hope somethign comes of it.

[This message has been edited by PaulJK (edited 01-09-2010).]

quote Originally posted by PaulJK: Wow. an improved gearset for the isuzu 5 speed would be a wonderful thing. Maybe someone can do the math and spread out all the ratios - 1st is wayyyy to short and too close to 2nd . i bet a lot of the V8 guys are watching this thread and i hope somethign comes of it.

Making all new gears for the isuzu would be very cost prohibitive just for the gears, then the end user would have to pay someone to essentially rebuild the tranny with the new gear set... by this time you are well past the cost of the F40 tranny and Archies plug & play kit.

The nice thing about just changing just the 5th gear set on the isuzu is it can be swapped out with minimal work and no special tools in probably less than 2 hrs. Most people with the isuzu have it for the 5th gear cruise RPM anyway and this would just make it even better... I could see a market for this upgrade.

Now if you want to modify the rest of the isuzu gearsets, you are far better off to find the other 76mm isuzus gearboxes that used different ratios for each gear.

Rumor has it that the 87 turbo spectrum 5 speed isuzu (76mm) had a 2.83 final drive vs. the 3.35 in the fiero. I looked for years trying to find one with no luck. About 5 years ago there was a lady in MO that has a 87 turbo spectrum 5 speed, but she hasn't been able to get me the info needed to confirm if it has this ratio - I try every few years.

The rest of the gear sets can be had in the following ratio depending on application:
1st: 3.50 or 3.73 (fiero)
2nd: 1.92 or 2.04 (fiero)
3rd: 1.33 or 1.45 (fiero)
4th: 0.92 or 1.03 (fiero)
5th: 0.83 or 0.74 (fiero)

The 87-89 Turbo Isuzu I-Mark has these ratios
1st: 3.50
2nd: 1.92
3rd: 1.33
4th: 0.92
5th: 0.74

The 85-89 non-turbo Isuzu I-Marks came with these two sets of ratios:
1st: 3.73 -------3.73
2nd: 2.04 ------2.04
3rd: 1.33 ------1.45
4th: 0.92 ------1.03
5th: 0.74 ------0.83

Rumor also has it that GM cheaped out and had Isuzu do a lower grade heat treatment on the gearsets for the GM boxes, so the original Isuzu gearsets are said to be stronger.

Rick (The Machinist) thinks the Isuzu idea is very doable.

These gears would be cut and hardened, not forged. Just wanted to get some opinions here. Obviously we will strive to make the strongest gear we can, but seeing as how it's a 5th gear and someone obviously wants it for fuel economy, strength should not be as much of an issue as the low gears, correct? Please don't think I'll tell him he can skimp out more if you say it won't be as much of an issue, just need to know what I'm dealing with.

Don't forget that those shafts are hardened steel.

To cut new gears on them they may need to be annealed and then re-hardened after the machine work.

Also,

Is the 2nd gear weakness in Isuzu transmissions because of a literally weak 2nd gear or a design flaw? If the 2nd gear is simply weak my idea regarding cutting down a larger gear with the same spline should work just as well for this purpose if there is a stronger gear of a larger diameter that could be used...

If the guy is going to have an issue with the internal splines, then he might not be able to make these gears. I need to take a pic of the other sides because there are more slines on the back side (for the synco I think).

2nd gear is weak because of its size, but the excessive gear split between 1st and 2nd means it takes a larger than normal beating during the 1/2 shift.

His ability is not an issue. It just has to be worth his time to make them. Realistically, what could I sell these for? 250 or 300 MAYBE? If it takes him 10 hours to make a set and get it just right I don't know how excited he will be about making them.

Everyone's valuation of this upgrade will be different. Some would only do it if you paid them and installed it for them, others would be willing to pay up to maybe $400, and there will be people everywhere in the middle. Most will not be willing to front any $$$ until the part proves to work and is in stock.

Here are some better pics of the gears. Notice on the small gear the cone is splined on.