84 4 speed trans questions (Page 1/1)
SecretMoparGuy OCT 14, 03:07 PM
I am looking into trans options for my fiero. The plan is a 3800 sc swap with a manual. The car is currently an 86 V6 automatic. I was leaning towards doing an F23 trans - 5 speed; however, I have found a car for cheap near my location. It is an 84 with a 4 speed. I would like to get it as I need the master cyl, pedals, etc for a swap anyway. My question is: how would the 4 -speed work in my 3800 sc swap car if I were to use it instead of a 5 speed? I have heard the 85+ 4 speed was good but is the 84 that much different? I'm not sure if this 84 trans is the econ or the 4:10 (probably econ). Since I want to use this car a daily/commuter car often enough, I prefer a low-ish rpm @ 80 mph. What would the drivability of this 4 speed be like compared to an F23 out of a cavalier?
BadNewsBrendan OCT 14, 03:17 PM
I have been told repeatedly that the 84 4 speed will break under the added torque. The 84's case is smooth and not ribbed. The ribs were added to the 85+ to make the case stronger.

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"America is all about speed, hot nasty bad-ass speed" - Eleanor Roosevelt

Tetanus
1984 3800 II SC Build

[This message has been edited by BadNewsBrendan (edited 10-14-2019).]

fierofool OCT 14, 04:18 PM
Most 84 4-speeds are also the 4:10 gearing. You would be running very high revs at highway speed. Probably in excess of 3500 at 65-70. They are quick on acceleration but as Brendan said, the cases are weak. If you should luck upon an 84 Economy 4-speed, the 4th gear is slightly better than the Isuzu or Getrag 5th gear, but essentially what you are doing is shifting 1, 2, 3, 5, skipping 4th all together. The case is also weak on that transmission.

If you specifically want the gearing of either 84 transmission, remove the gears and put them into an 85 or 86 transmission.
edfiero OCT 15, 01:08 PM
+1 on what the other guys said.

When I did an engine swap on my 84 and put in the SD4 engine, I also swapped in a 4 speed from a 85 V6, for the very reasons mentioned.
1. Stronger Case to hold more HP.
2. Lower RPMs when running at highway speed.
82-T/A [At Work] OCT 17, 12:49 PM

quote
Originally posted by fierofool:

Most 84 4-speeds are also the 4:10 gearing. You would be running very high revs at highway speed. Probably in excess of 3500 at 65-70. They are quick on acceleration but as Brendan said, the cases are weak. If you should luck upon an 84 Economy 4-speed, the 4th gear is slightly better than the Isuzu or Getrag 5th gear, but essentially what you are doing is shifting 1, 2, 3, 5, skipping 4th all together. The case is also weak on that transmission.

If you specifically want the gearing of either 84 transmission, remove the gears and put them into an 85 or 86 transmission.




Want to concur on this. I had a 1985 Fiero GT that had literally no options except the GT steering wheel, and power windows and A/C. It had the 4.10:1 4-Speed swapped in because that's all that was available, and the heads had been decked (because they had warped) which increased compression. It was quick... really quick. But the engine was screaming on the highway at 70.