I was putting together some transmission information for Steven Snyder, and decided it would be valuable to share with everyone for customizing transmission gearing.
My hybrid Isuzu gearing in my 98 Cavalier (2.4 DOHC) 1st 3.73:1 2nd 2.18:1 3rd 1.45:1 4th 1.03:1 5th 0.74:1 FDR - 3.94:1
So my transmission in the cavalier is a very close match to the stock fiero transmission, with the major difference being the final drive ratio. I happen to like that gearing setup, but with the power band difference I hope you can find something that would be more to your liking.
I would also point out because of the way these are built, 1st&2nd gears are a set, as are 3rd&4th. Also the isuzu transmissions from IN the isuzus, most of the gears rounded match other gears (1.027 rounds to 1.03 and 1.448 rounds to 1.45, as seen in the other listings). Unless you have a machine press, you will probably need a shop to change gears on the gearshafts for you. The ring gear on the differential is bolted on (you can unbolt it easy enough) and the corresponding gear is pressed onto the output gearshaft. On the side, if you get your hands on one of these older differentials, you can probably find some J-body people that will pay a decent price for one.
Disclaimer: I found all this information in other posts and information online, as far as I know, this information is correct but I ask that you verify any information before trying to assemble your own transmission. I have also had to have gears machined to fit properly in my swap, so not all swapping is a direct fit, but all these should be based on a 76mm isuzu design.
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04:02 PM
PFF
System Bot
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
Ok, I found an awesome combination for the 3.4 DOHC with a 7000 RPM shift point. What do you think of this? It's great close ratio with the most overdriven 5th gear and a moderate FDR so the gas mileage doesn't suck too much, yet it should perform great.
Starting with the Impulse/Storm SOHC gearing we swap in the following:
The end result is (compared to the Fiero Isuzu) a longer 1st gear, shorter 2nd, shorter 3rd, slightly shorter 4th, and very close 5th gear. Cruising @ 75 mph with 225/45/17s is 2675 RPM (the best set would give us 2500 RPM, so its not much worse).
With a 7000 RPM shift point: 1st gear goes to 44 mph. Shift into second and we're at 4371 RPM. Right in the powerband! 2nd gear goes to 71mph. Shift into 3rd and we're at 4961 RPM. Excellent! 3rd gear goes to 100mph. With a mildly modified 3.4 DOHC we should finish the 1/4 mile near the top of 3rd. Shift into 4th and we're at 4965 RPM. 4th gear goes to 141 mph. A decent top speed for a Fiero with some minor aerodynamic modifications. Still shooting for higher? If you've got the power, shift into 5th... and we're at 5044 RPM, right in the peak power range to get a bit more top speed out. Maybe to 150 or 155? 5th gear would go to 196 mph if there were enough torque at 7k to go that fast.
Since Isuzus are inexpensive and readily available in the junkyards this could make a good performance transmission for a Fiero. Crytotreating the internals helps the strength, and the later Isuzus have double or triple synchros for at least 2nd gear so that problem is solved by starting with a later transmission.
[This message has been edited by Steven Snyder (edited 01-18-2006).]
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05:56 PM
Drenyx Member
Posts: 32 From: Concord, CA, USA Registered: Jul 2005
86GT3.4DOHC: yeah, I didn't include the getrag stuff because everything else is isuzu, and I do have a running transmission with swapped ratios.
Steve: sounds awesome, other thing to look at is the rpm in 4th/5th at "normal" freeway speeds, if you're on a long run, never hurts to get decent gas mileage when you're between A and B. I can't say too much specifically about how the height of the gears will do anything with the different synchros and stuff, when I did my swap, I had to cut the 3rd/4th gear for the bearings to sit right so everything fit in the transmission right, at this point I was thankful I had a tranny shop doing the work and someone with some experience could help me figure out what I needed to get done. I have the fiero isuzu sitting around here, if you can find one of those trannys out of the geo, we could talk about what we need to look for in differences swapping gears on the shafts and such.
If I get off my ass here in the next few days, I'll take some pictures (and include some old pictures I had) that should help to illustrate stuff. If you don't see it, someone feel free to bug me as a reminder.
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06:11 PM
Steven Snyder Member
Posts: 3326 From: Los Angeles, CA Registered: Mar 2004
Originally posted by Drenyx: Steve: sounds awesome, other thing to look at is the rpm in 4th/5th at "normal" freeway speeds, if you're on a long run, never hurts to get decent gas mileage when you're between A and B.
The Fiero Isuzu FDR abd 5th gear gives the best possible cruising RPM you can get with any GM 5-speed I know of and these gears I came up with give an RPM barely higher than that.
[This message has been edited by Steven Snyder (edited 01-19-2006).]
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06:27 PM
fieroguru Member
Posts: 12599 From: Champaign, IL Registered: Aug 2003
I am glad to hear that someone has actually swapped the gears between the 76mm isuzus.
I have been doing a great deal of tranny research over the last couple years trying to come up with a tranny with better ratios for higher torque engines - 1st gear is way too low for anything with power. I am not convinced your specified 1st gear ratio of 3.272 for the Impulse/Storm is correct, but that is based on info from http://www.isuzuperformance.com/isupage and it could be wrong as well.
Here are some more gear ratios and final drives from 76mm Isuzu transmissions from the website above: Impulse 83-87 non-turbo (Isuzu gearing) 1st 3.79 2nd 2.17 3rd 1.41 4th 1.00 5th 0.79 FDR - 3.91
Please excuse my ignorance. Regarding all of these different Isuzus... Are all of these trannies basically the same transmission? Can a gearset from any listed tranny be installed in any other listed tranny?
Yeah, like I said it was in my J-body that I have a regeared isuzu, it was *mostly* straightforward, one of the gears had to get machined to keep the same height as the original one (bearing changes over the years I belive). Most of that information I got from other posts on J-body.org, so as I said, I make no guarantees, I just pulled up what I could after talking to Steve. The actual J-body specs I listed though, I worked with those enough that I belive those to be correct. Steve: I think I actually have one of those 2.2 FDR ring gears laying around, I might even know where it is. I didn't get the other side of it though.
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08:31 PM
Drenyx Member
Posts: 32 From: Concord, CA, USA Registered: Jul 2005
Raydar: the biggest differences are basically the casing of the transmission to bolt up to different engines, the internals are *mostly* the same, some slight differences as changes/improvements/bug upgrades get made over the years. The 1st&2nd gears are a set and the 3rd&4th gears are a set in any given transmission. I know of people that have swapped one set of internals into another case, and myself I have swapped the 3rd&4th gears in from another isuzu transmission for different ratios. I still recommend you have someone that knows transmissions in case something doesn't fit right.
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09:05 PM
Jan 19th, 2006
Raydar Member
Posts: 41458 From: Carrollton GA. Out in the... country. Registered: Oct 1999
Excellent! The Isuzu is always looked at as a possible replacement for a worn out Getrag, or as an option when doing an auto-to-manual swap. Unfortunately, the Fiero version also has a huge jump between 1st and 2nd. This could possibly give us yet another option. Thanks for your research and info.
Edit - I wonder if any of the replacement gearsets have a sturdier 2nd gear. That seems to be what most people blow out first, when they push the envelope.
[This message has been edited by Raydar (edited 01-19-2006).]
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02:23 AM
PFF
System Bot
Fastback 86 Member
Posts: 7849 From: Los Angeles, CA Registered: Sep 2003
Careful with the Geo 5spds. We had Geo Metros with 5spds when I delivered pizza and in 3 seperate cars we blew out the 2nd gear synchros. If you're just using the gears it should be ok, but I wouldn't use those synchros if you paid me. If a Geo 3cyl can break it, a 3.4 DOHC will grenade it in the first shift.
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03:14 AM
lanman31337 Member
Posts: 302 From: North Versailles, PA Registered: Apr 2005
I'd like to add a side-note: The Geo Storm differential is WAY stronger than the j-body 96-99 isuzu differential. That's the weak spot for the tranny, and the diff. will swap right in.
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11:40 AM
Drenyx Member
Posts: 32 From: Concord, CA, USA Registered: Jul 2005
I've said it before, starting about 96, they changed the process in which they made the spyder gears in the differential, I've blown one myself on a stock quad 4 (dohc ld9). Which is why I said if you're playing with trannies and end up with an extra differential, you can probably off it to the J-body community for some $$. Win-Win on that one.
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01:21 PM
Steven Snyder Member
Posts: 3326 From: Los Angeles, CA Registered: Mar 2004
Yeah, like I said it was in my J-body that I have a regeared isuzu, it was *mostly* straightforward, one of the gears had to get machined to keep the same height as the original one (bearing changes over the years I belive). Most of that information I got from other posts on J-body.org, so as I said, I make no guarantees, I just pulled up what I could after talking to Steve. The actual J-body specs I listed though, I worked with those enough that I belive those to be correct. Steve: I think I actually have one of those 2.2 FDR ring gears laying around, I might even know where it is. I didn't get the other side of it though.
Do I need a matching drive gear or will that ring gear bolt up to my MT2 diff?
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07:49 PM
Drenyx Member
Posts: 32 From: Concord, CA, USA Registered: Jul 2005
Do I need a matching drive gear or will that ring gear bolt up to my MT2 diff?
Yes, you need the matching gear for the ring gear. someone sent me a differential that happened to have the ring gear on it, so it's extra, but I didn't get the matching gear...but it's here if for some reason you need it.
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09:10 PM
Jan 20th, 2006
Capt Fiero Member
Posts: 7658 From: British Columbia, Canada Registered: Feb 2000
------------------ 85GT 5spd ,93 Eldorado 4.9 Dual O2 Custom Chip, Archie Clutch. Custom Exhaust. MSD Everything 245/50/16's Cant wait for Dyno Time and Track Results. Not Your Average 4.9 Capt Fiero Com --- My Over View Cadero Pics Delta Cam and Allante Intake Soon.
