Hi all!

I have an 86 2.8L V6 SE (about 60k miles on it) and I've decided to go down the road of rebuilding my first transmission. I'm not doing anything fancy, everything is stock. However, let me give you a little background.

When I removed and tore down the engine a couple years ago, I was planning on going down the road of a 4T60 swap but now I decided to rebuild the tranny instead to save time & money. Over the years, the 125C transmission and torque converter have been sitting in my garage collecting dust and suffering from north carolina humidity and now that I am prepping to rebuild the transmission, I have some questions and was hoping yall can give me some guidance too for a first timer.

Here is what I purchased in preparation for the rebuild.

-TH125 Rebuild Kit 125C 3T40 TH125C Automatic Transmission Transaxle Master Overhaul Banner Box Set
-Superior GM TH125 TH-125 TH125C TH-125C Automatic Transmission Shift Correction Kit
-TH125C ATSG Tech Rebuild Service Manual

Here are my questions
-Is there anything else I should purchase here?
-Looking at the torque converter and flex plate, how do I clean this up and reuse it? Should I even reuse it?
-What should I do with the flexplate? Does this simply need a cleaning / resurfacing or should I buy a replacement from the Fiero Store website?
-Regarding bolts for the parts inside the transmission, should I reuse these or is it recommended to get all replacements?

Thank you all!

[This message has been edited by Cunnive (edited 11-03-2025).]

I would recommend purchasing the rebuild manual for that transmission. Would also recommend taking pictures at every stage of disassembly. It is usually standard procedure to replace the torque converter as well. If you want firmer shifts and eliminate slippage I would recommend the transgo shift kit.
The key is to take your time and ensure putting back all parts in the exact same order that they were disconnected. When reassembling the valve body the valve balls must be in the exact same place that they were removed from.

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" 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 "

Thanks Dennis!

Is there anything I should look for in regards to the gears and other components I remove from the transmission that are common failure points?
If a particular gear is in bad shape that should be replaced, can these be purchased from an online store? How would I go about this sitation?
What lube should I use when reassembling? Can I use assembly lube or is there other more specialized lube?
Should I also buy the Auto Lock-Up Solenoid and Auto Trans Pressure Switch from the Fiero Store?

Thank you!

[This message has been edited by Cunnive (edited 11-05-2025).]

Automatic Transmission Rebuild (1st Time)

IMHO
I'm a 'do it yourself' guy too; however, somethings need more knowledge, specialized skills or tools and experience that I don't have...
On these special occasions, like rebuilding cylinder heads, I give them to a shop rather ducking it up!
Due to the complexity, rebuilding an automatic transmission might be over your head.

“Look Before You Leap”

quote When examining automatic transmissions, one must consider the complex network of hydraulic systems and electronic controls that enhance driving convenience. An automatic transmission rebuild requires a thorough understanding of these intricate mechanisms.

Complexity:
Automatic transmissions are more complex and contain multiple components, such as valves, clutches, and electronic solenoids, which require specialized knowledge for proper rebuilding.

Inspection:
When rebuilding automatic transmissions, a thorough inspection of hydraulic systems and electronic components is necessary.

Adjustments:
Automatic transmissions require calibration of the shifting points and pressures.

Good luck and the best on your effort,
VN

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

I've rebuilt automatic transmissions and it is an intense and careful procedure that must be followed. Its just a lot of parts that need to be removed and replaced. That is why I recommend taking pictures every step of the way. It was a 4T60 and I went by the rebuild manual and the rebuild video that was available. A few special tools are needed but you can make them. You Tube has some rebuild videos.
TH125 tear down


------------------
" 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 11-05-2025).]