Using an automatic from a 2.5 on a 2.8 engine (Page 1/2)
handymanpat OCT 22, 12:00 PM
Can the automatic trans from an 86 2.5 be used on an 86 2.8?
I would assume I need to use the torque converter along with the trans (from the 2.5)
I would use a computer from a v6 automatic.
Right now my v6 has a 5 speed trans that I will use on an engine swap but I am wanting g to use the v6 engine on my wife's 2.5 (it has a bad engine)
I am hoping I can use my good v6 engine in her car and just use the trans and axles that are on her cradle now.
Is this something that can be done if I have the brackets and computer?
Thanks Pat

------------------
pat moody

Blacktree OCT 22, 04:13 PM
The 4-cyl and V6 use the same automatic trans. So yes, it's a direct swap. And I've actually done this swap. But I used a torque converter for the V6. Because the V6 might overpower the 4-cyl torque converter.
handymanpat OCT 22, 06:41 PM
Thank you for letting me know.
I was pretty sure it was the same trans but did not know if they were interchangeable
I will see if I have a torque converter for a 2.8 if not I will see if I can locate one.
The car would be my wife's and we would just drive it in occasion to events now and then, maybe the original torque converter would work?
I will find out for sure before I use it.
Thanks again, Pat

------------------
pat moody

Dennis LaGrua OCT 24, 07:47 PM
With a stock V6 I would guess that the TH125 from the Duke would bolt in,work fine, but the age, use and mileage must be considered. The Fiero transmissions now are 30+ yrs old and won't last forever.

------------------
" 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 "

handymanpat OCT 24, 09:45 PM
I know the trans off my wife's car is good because she drove the car around over the last couple years
The problem is that the guy who did the engine rebuild did something wrong and it burned oil worse than it did before I took it to him!
I pulled the engine and cradle and was looking for another 2.5 but then decided to use a good 2.8 I had with a 5 speed.
I did get ahold of a torque converter for a 2.8 so I should be good unless I can use the torque converter from the original 2.5.
If that torque converter and trans is interchangeable I will stick with the one from the 2.5.
The good news is that I have a parts warehouse and fleet of fieros to choose from so I will kane something work!
Thanks Pat

------------------
pat moody

theogre OCT 25, 12:06 PM
TH125 for year, engine, or both may look same to you but often not true.

Engine choice often have changes to clutches, governor and other things plus often change chain and/or final ratios.
See my Cave, Gear Ratio

IOW While can work, Putting Fiero V6 AT in Duke car will cause reduce MPG and other changes. Worse MPG if TCC doesn't lock up when needed.
And other way around... Putting V6 Engine alone in Duke car will get better MPG but loss some power. If you slam the gas often, Clutch packs etc may fail sooner because factory installed parts expect "weaker" engine.

And that's even when you have the right TC for the Engine. Having the Wrong TC can bite power transfer any time the TCC is unlocked, more so started driving after a stop sign/light etc. even for normal driving.

If some think can look at parts from GM et al... Don't go by repair parts ever was or offer now because "rebuild kits" etc are "made" to have same friction and other parts to have in only 1 part no. to keep inventory to minimum part count.

This is ignoring TH125 have many changes year to year. Is Why If you buy a Rebuild Kit or other internal parts... Many sources will need actual year made of the trans Not Model Year of the Car because some parts won't fit in "wrong" years. Example: 87MY of car can have 86 or 87 year made of TH125 depending exactly when car is made. You Need the Tag on the Trans to have this info when getting many parts.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

handymanpat OCT 26, 12:47 AM
Thank you for the advice and info on the trans and gear ratios and all the other things that might make what I thought would be a simple swap quite a bit more involved and complicated.
I did not know all of this variables existed with doing that automatic trans swap onto a 2.8 from a 2.5.
Especially with the tcc locking up issue and the geer ratio difference.
I will go look at the link you posted.
Thank you again, I may need to rethink this and consider if I am getting myself into another "in over my head" project!
Thanks Pat

------------------
pat moody

Dennis LaGrua OCT 26, 06:53 PM

quote
Originally posted by handymanpat:

Thank you for the advice and info on the trans and gear ratios and all the other things that might make what I thought would be a simple swap quite a bit more involved and complicated.
I did not know all of this variables existed with doing that automatic trans swap onto a 2.8 from a 2.5.
Especially with the tcc locking up issue and the geer ratio difference.
I will go look at the link you posted.
Thank you again, I may need to rethink this and consider if I am getting myself into another "in over my head" project!
Thanks Pat




I only see very minimal problems interchanging the TH125H. It WILL lock up when the computer/chip tells it to and it will shift. The speedometer should work accurately as the sending unit on the trans determines that. You may not end up with the ideal FDR but it will work. Internally except for FDR all the TH125H transmissions are the same.

------------------
" 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 "

Blacktree OCT 26, 11:55 PM
Like mentioned above, the gear ratios are the same. The differences are in the final drive ratio. That's not a show stopper. It just means the shift points will be at a slightly different RPM.

As for the TCC, it's a simple on or off function (controlled by the ECM). As long as the ECM is getting sensor data, and has a connection to the TCC solenoid, the TCC should work.

Once again, I've done this swap. I swapped a V6 into a Fiero that originally had a 4cyl and a TH125. The different final drive ratio didn't create any problems. It didn't have any problems with the TCC function, either. I didn't need to do anything special, or reprogram the ECM*, or anything like that. It just worked.

*Of course, I used a V6 ECM. And as mentioned earlier, I also used a V6 torque converter.
OldsFiero OCT 27, 07:29 AM
The V6 pressure regulator boost valve in the valve body is larger in diameter than the 4cyl one. This increases pressure rise under throttle to handle the extra power. But, unless you really run it hard, you should be fine.

Marc