I just replaced the tcc solenoid and it worked without issue for about a total of probably 30 miles or so then one of the old issues resurfaced.
When your going at exactly 35 on the speedo you can feel it engage, but it causes the car to surge, like it didn't fully engage, give it a little more gas it'll engage or hit the brake just enough to trigger the stop, then let go and it'll correctly engage.
It only does that at 35, even just going 40 I can feel it engage and it works fine. It has no trouble disengaging and isn't causing the vehicle to stall or dip in rpms when coming to a stop.
I got it backwards, it isn't disengaging if it engages at 35 - 40 which is causing the stutter when I'm trying to accelerate. Is that definitely the third pressure switch failing to inform the tcc solenoid or something?
I don't feel like taking an engine mount off again unless I have too. Super easy to put on, kinda a pain to take off. Which surprised me, usually it's the opposite.
[This message has been edited by Gizmo0816 (edited 11-25-2024).]
Alright, imma rephrase my question, cause I think I asked it poorly. I know it isn't the solenoid and I know it isn't third gear switch. Both have been replaced, both have been tested, both work as they should. I tested tourqe converter by driving it, depressing brake pedal to see if it disengages and in about 800 miles it has not once stalled or started stuttering when slowing to a stop without hitting the brake pedal. I tested the 3rd gear pressure switch as per theogres instructions on his website. The multimeter and terminal thing. It did what he described.
So, between 30 and 45 mph if you try to very lightly accelerate while the tourqe converter is engaged, you will feel the rear shudder like you are trying to accelerate in too low of a gear. If you give it a little more gas, or enough time, the tcc will let up and let it be in 3rd gear to accelerate.
My question is, is this normal behavior? Is it just an example of older/aging technology being a Lil dumb? I can't imagine it is normal behavior, but if it is then I have been trying to chase a ghost.
Unless its possible that I got a bad torque converter solenoid and thats a symptom of one on its way out.
The TCC solenoid is the only electrical part in the stock Fiero automatic transmission that is used to lock up the torque converter,. Shifting through gears is done by pump line pressure on the clutches. Could be an internal clutch, a defective torque converter or even a worn pump. The TH125 is not a very difficult transmission to rebuild. A while ago you could purchase a video that shows all the steps on a DIY TH125 transmission rebuild. Repair manuals are also available. Rebuild kits are not expensive but the torque converter itself will run a few bucks.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The TCC solenoid is the only electrical part in the stock Fiero automatic transmission that is used to lock up the torque converter,. Shifting through gears is done by pump line pressure on the clutches. Could be an internal clutch, a defective torque converter or even a worn pump. The TH125 is not a very difficult transmission to rebuild. A while ago you could purchase a video that shows all the steps on a DIY TH125 transmission rebuild. Repair manuals are also available. Rebuild kits are not expensive but the torque converter itself will run a few bucks.
I am planning on dropping the subframe, so maybe that wouldn't be a bad idea to look into to. Actually in the process of it now, just gotta get some more money before I continue.
Any idea what a rebuild done by a transmission specialist might be compared to doing it myself? Just a ball park guess would be appreciated.
And of course I read through some of these forums, I will be replacing the water pump and the timing gear with the metal one from the fiero store while the engine is outside of the car. I don't know if anything else should be replaced, but those two have seem to be the most talked about.
I don't think I've mentioned its an iron duke in this post. So if there's anything else I should replace i'd appreciate being told what.
[This message has been edited by Gizmo0816 (edited 07-28-2025).]
Could someone point me into the direction of a compatible torque converter for the th125c? I found one from rock auto, but i'm not sure it's correct and it's out of stock anyhow.
These are the two converters i've found that i think are compatible, " B21HZ2" and "B21FZPB". please correct me if I am wrong.
[This message has been edited by Gizmo0816 (edited 07-30-2025).]
Could someone point me into the direction of a compatible torque converter for the th125c? I found one from rock auto, but i'm not sure it's correct and it's out of stock anyhow.
These are the two converters i've found that i think are compatible, " B21HZ2" and "B21FZPB". please correct me if I am wrong.
Don't have an exact part number to share but the TH125 transmission was used on dozens of GM car models of the 1980's and early 90's. From wiki 1982–1996 A-body 1980–1985 X-body 1982–2001 J-body 1990-1993 W-body 1987–1996 L body 1990–1995 U-body vans (with LG6 engine) 1984-1988 Pontiac Fiero
While all these TC applications should bolt in, the difference would be the stall speed which is different from the 4 cyl and 6 cyl. applications. May have more info to share but it is at home. When I get back tomorrow will look it up but not sure that the TC is your problem.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
While all these TC applications should bolt in, the difference would be the stall speed which is different from the 4 cyl and 6 cyl. applications. May have more info to share but it is at home. When I get back tomorrow will look it up but not sure that the TC is your problem.
Alright thanks for the information, and i would greatly appreciate to hear back when you get the time.
So the reason im thinking its the torque converter, which I'm not saying you are wrong as I don't know anything about the transmission apart from what its doing, but it shifts great, this transmission has given me less problems than the tranny in my 2012 corolla Atf is cherry red, no burnt smell, I opened up the drain pan to see if there were metal shavings on the magnet and I discovered the magnet was missing, I put a new donut magnet back in, but that obviously means a previous owner dug around in there. However a few hundred miles later atf is still cherry red, still shifts really smooth. Just when the tc is supposed to disengage when lightly accelerating between 30 and 45 it's stuttering. Unplug the tc it goes away.
If there is something else that would cause this tho I am 100% willing to chase that down.
Oh yeah forgot to mention, I put 200 miles on her in one day one drive, no stops at all, just for the giggles to see if something would happen, it ran perfect the entire time. It was about an almost 4 hour drive.
[This message has been edited by Gizmo0816 (edited 07-31-2025).]
1987 -1992 Chevolet Beretta Torque Converter should interchange with the Fiero unit. That would be part B21FZPB and its for the Iron Duke 4 Cyl
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 07-31-2025).]
