Isuzu upgrade report - Transmission Forum

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Isuzu upgrade report
Monday, October 10, 2011 6:56 PM
Maybe there are a few folks interested in my recent experience installing the 4.117 FDR from the DOHC Geo Storm GSI. This was going into my 1995 cavalier base with 2.2.

I used the excuse of a bad shift cable to pick up a used GSI tranny from the nearest bone yard to the Knoxville TN area. I paid 150 for it. They had two trannys available but only one was marked from the GSI. I took the time to stick both of them in 5th gear and count the turns of the input shaft to differential. It became obvious that one was the 3.94 and the other was the 4.11. BTW, if you look on the cases, the 3.94 was a dash 12 and the 4.11 was a dash 13 on the case numbers.

I'd already pulled the trans and disassembled it. Even though it had 278,000 miles on it, the syncros were in good shape, which I found surprising. However, the spiders were heavily pitted and the reverse gear had a number of rounded off teeth. All the shift forks were in good shape.

Once I got the GSI trans home and apart, the next issue was to compare all the parts and make decisions about what to use/not use. I counted all the teeth on the gear sets and put them into a spreadsheet to do some basic math. I decided to see if I could use all the gears/shafts/diff, etc. This is where the adventure begins.

They look like an easy drop in once the bearings are changed on the input shaft, but it didn't work out so well. The GSI trans uses tapered roller bearings on both ends of both shafts, while the Cav trans uses a roller bearing on the clutch end of the input shaft and a roller bearing at the other end. The roller bearing is located via a circle clip that keeps the bearing properly located fore/aft. When the GSI secondary shaft is installed, it doesn't mesh with the primary shaft, even though its length fits well within the case. The secondary shaft is fitted via a shim on the far end.

So, now what? I started by first getting the primary shaft to fit by making a .060 shim under the large roller bearing to get the shaft to not be pulled up as far when the circle clip is installed. Next, I stood the old and new secondary shafts next to each other to see if there were any obvious differences.....there was one. The 1st and 2nd syncro hub on the GSI was thinner. I didn't measure it, but I re-used the hub and dogs from the cavalier. BTW, both trannys had the 3 piece syncros but were in good shape!

The secondary shaft now moved up enough into the bearing bore to no longer need a shim for fitment. The gears meshed just fine and the shifter worked as it was supposed to.
A few other notes:
Although both reverse gears are the same dimension, the GSI gear was about .060 thinner, so I re used the Cav reverse gear.
Who ever invented the interlock for the shift rails should receive a genius award right before they are shot.
Because I used the 5th gear from the GSI, I had to double gasket the cover over 5th. The primary shaft 5th gear is taller by probably .100 and rubs the inside of the cover enough to lock up the trans.
I re used the reluctor from the Cav so the speedo is still as accurate as before.

I now have a close ratio, 4.117 FDR in my 2.2 Cavalier. A couple miles from my house is a 4 lane that I have a "measured" 1/8th mile. It is a bit down hill, but I've driven it enough to know whether any thing changes. Good news, the car picked up 4 mph! Used to go 67mph, but has done 71 mph consistently. That's with AC off BTW. Bad news...still waiting for new shift cables. Supposedly, my local dealer has found them in FL and they'll be here in 2 days.


Re: Isuzu upgrade report- typo correction
Tuesday, October 11, 2011 6:44 AM
Found a typo...i'm sure there are more.

The input shaft has a ball bearing on the far end, not a roller bearing.
Re: Isuzu upgrade report
Thursday, August 26, 2021 5:43 PM
Have a question. Iím doing the same thing. I canít seem to get the storm casing apart. I removed all bolts, 5th gears and plate. Shifter housing. Am I missing something? Something internally seems to be stuck.
Re: Isuzu upgrade report
Friday, August 27, 2021 9:19 AM
, I'm not near my transmission at the moment however I do remember one bolt that holds the reverse shaft in on the side of the transmission I believe it's a 13 mm head
Re: Isuzu upgrade report
Friday, August 27, 2021 12:28 PM
I got that out. Long bolt with mostly threads?
Re: Isuzu upgrade report
Monday, August 30, 2021 7:47 AM

Item 66 is the bolt for the reverse idler gear shaft
Re: Isuzu upgrade report
Tuesday, August 31, 2021 5:01 PM
Good to know but I still unable to get the geo storm casing apart. I havenít needed to disassemble the cavalier casing since I cannot get the storm case apart
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