I have an 85 SE that pulls 2200 at 55, but I just got this 86SEand it does 3k. Im guessing this is bad It seems to shift firmly, and doesnt feel like its slipping. Ideas? were there diffrent gear ratios put into Fieros?
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07:54 PM
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donk316 Member
Posts: 1952 From: Red Deer, Alberta, Canada Registered: Mar 2003
I have an 85 SE that pulls 2200 at 55, but I just got this 86SEand it does 3k. Im guessing this is bad It seems to shift firmly, and doesnt feel like its slipping. Ideas? were there diffrent gear ratios put into Fieros?
Are you serious? Over a 1000 posts here and you dont know about gear ratios? and which ones there are?
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08:25 PM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
I can tell you all about all the manual trannys they used, but Ive never payed much attention to articles about the auto trannys. Ive never heard anyone mention diffrent gear ratios used in the autos, in fact im pretty sure they're mostly the same....
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08:28 PM
donk316 Member
Posts: 1952 From: Red Deer, Alberta, Canada Registered: Mar 2003
Hi! They offered THREE gear ratios for the Automatic through all 5 production years.
2.73:1 3.08:1 and 3.33:1
You can check which one YOU have in your car by referencing the RPO sticker on the front drivers side inner wheel well fender (under the hood).
The only one that I know by heart is the "GX3" RPO, this designates the 3.33:1 final drive.
This is supposedly the more sought-after one... however, it kinda sucks on the highway.
The only other thing I could think of is that your torque converter "lock-up" might not be engaging.
Does your check engine light ever come on?
Anyway, when accelerating casually to say.. 65 miles an hour, you should feel what "seems" like 3 shifts.
1s, 2nd, 3rd, and then the TC lockup. It feels like a 4th gear even though it isn't.. it also usually drops the RPMs by around ~500 or so, but I suppose that depends on your gear ratio.
If you want to keep it an automatic, but want the extra gear, there is a fairly inexpensive 4-speed swap that you can do.
Actually there are about Twelve ratios offered in TH125c. The RPO codes for them are listed in the transmission section of my cave.
While there are only three final drives, there are 4 chain sets. The chain sets have the same effect as altering the finals. They can be used with the finals to offer more gear combinations from the same parts. GM didn't offer all the possible chain/final ratio sets but you can make them easy enough if you want.
------------------ The only thing George Orwell got wrong was the year.
I agree, the RPMs at highway speed are the worst thing about the Fiero automatics. I'm used to 2800 @ 70 MPH in my Beretta, which also had the THM125..... The Fiero would probably be about 4000 if I took it to 70. And, yes, I've verified the TCC lockup solenoid works. I think these old cars are just geared for the old 55 MPH limit we had at the time.
[This message has been edited by css9450 (edited 09-04-2004).]
either your speedo or your tach could be out of wack too -. I once had an 88GT that would read about 4500 at 60 mph. If you put your foot into it , the thing would show 7K at the shift points.
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06:26 AM
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1MohrFiero Member
Posts: 4363 From: Paducah, Ky Registered: Apr 2003
Do this test: On a nice level stretch of road, gently accellerate up to 50 or so MPH. You should feel each gear engage firmly, 1st, 2nd, and 3rd. At around 45 mph you should feel what appears to be a shift to "4th" and the RPMs will drop a few hundred. That's the torque converter locking up. Tapping the brake pedal slightly will disengage it, and a few seconds later you should feel it engage again.
If you don't see the RPMs drop and don't feel the lock then your converter isn't locking, most likely due to a faulty TCC solenoid or the wiring to it.
Don't assume the transmissions match the RPO codes. The high reving one may have been replaced or rebuilt with lower gears. Both are posible in older cars. If the build tag is still present on the transmission, it may help you determin the ratio as well. Starting with 87, i think, you will also find the last part of the VIN stamped into the trans, so if you see that it could mean you got one in there from a later car. (On mine it's easily seen on top of the valve body.) Even if the gearing is the same, a replaced trans could have the wrong VSS gears in it. They pick those based on the tire size.
You can scan the ECM and see what speed/rpm it says you are going. That will tell you if the speedometer or tach is wonky. It won't help you if the VSS is messed up or VSS gears are wrong.
Tachs often go nuts in the V6 and older L4 thanks to that wonderfull little turd known as the Tach Filter.
You should also check for TC lockup function. If the TC isn't locking that will add to the problem by a couple hundred RPM or more.
I don't think it is a slipping problem. That would likely burn up the high gear parts quick. It's not like a slipping lower gear that you are just passing thru. Low gears can slip for a fairly long time in some cars before failing completely.
Do not assume that the tranny in your car is the one from the factory either. It is all posible that a shop replaced the original tranny with an "equvilent" (spelling) from a differant car altogether. I was running a isuzu 5spd from an olds calais and it was geared differant than the fiero isuzu thats in my car now. If you can check the code on the tranny's tag (if tag is still there) to get a more accurate indication of the build of your trans. Good luck.
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12:01 PM
82-T/A [At Work] Member
Posts: 25530 From: Florida USA Registered: Aug 2002
So maybe this is wy when I swapped the engine and trans in my other Fiero, its seemed like I lost a lot of low end torque, but it feels stronger on the top end.... man I miss that low end
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12:46 PM
DylansGrandpa Member
Posts: 140 From: Franklin Massachusetts Registered: May 2004
Lock out only drops em 200 RPM. I ran winaldl on it, and its actualy only pulling 2500 w/o tcc lockup the tack is fluttery and a little high. I think the lack of lockup might be due to the fact that I dropped molten metal onto the harness right where it joins, into the crack. I was hoping it didnt hurt anything, but I guess it did.
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08:52 PM
css9450 Member
Posts: 5572 From: Glen Ellyn, Illinois, USA Registered: Nov 2002
Do not assume that the tranny in your car is the one from the factory either.
Yeah, in my case someone long ago pulled out the broken Getrag and swapped in a THM125 automatic. Really! The RPO sticker still has the MG2 code for the 5-speed BTW...
Yeah, in my case someone long ago pulled out the broken Getrag and swapped in a THM125 automatic. Really! The RPO sticker still has the MG2 code for the 5-speed BTW...
Exactly ! I bought an 85 gt with a 4spd when i removed the blown engine and trans i found trans fluid lines that run up front to the radiator. It was originally an auto. Someone coverted it at some point in its life. Weird i guess that car is meant to be modded because its the one gettin the v8
