7mge Auto to w58

[elpolloloco]

Hi everyone, ive been here a lot the past two years but this is my first post.

I have an automatic 1987 mk3 NA. It needs a catalytic converter and now the transmission is going out (skipping from 1st to 3rd) and it has gotten progressively worse over the past few months. I found someone on Craigslist with a 1987 mk3 NA five-speed with a blown head gasket some body damage for pretty cheap. Most of the threads I find are about turbo model auto to manual conversions, but I just want to know If i buy the 5speed NA junk car, will it have everything I need or will I still be missing any parts?

 

[AGsupra]

Look at buying new seals, clutch, master & slave rebuild kits, and havong the flywheel resurfaced, and ballanced with the new clutch.

While your at it, use the 5-speed harness & ECU.
The auto ECU will work just fine with the 5-speed, but getting the harness to work is anoher problem, as the plugs that pick up the reverse & nuetral are different, and would require some modifying. Almost easier to just get them off the parts car.

You should also look at using the diff out of the 5-speed, as it has a lower ratiom and the 5-speed has the correct speedo gears to match it.
The 4.3 gears will make the car a little quicker, and that diff most likely has an LSD in it.

 

[hvyman]

^not correct.

Auto harness and ecu will work fine with a 5 speed.

Yes the donor car would have everything needed. just swap over everything including the drive shaft.

Also all n/a cars came with a 4.30 gear diff. sport models got 4.30 lsd.

 

[HighlandsSupra]

I just finished my 87 NA auto to R154 over the weekend. I have an 88 GTE as a donor car. All I bought to do the job was front and rear transmission seals, and a full length clutch hose from Driftmotion. A few things I found out when doing this job. Auto and manual harnesses are the same as far as transmission plugs. There are 4 plugs. The speed sensor plug is different between transmissions and one is left hanging depending on the transmission installed. I just cut the complete harness off the old auto trans and spliced in the reverse light pigtail and clutch start switch. Someone on here has a very basic diagram of this. Also, the hole that the shifter goes thru on an auto car is smaller than a manual. As far as ECU's, as said before either will work. The only thing I did was open the left kick panel and unplug the silver, A340 ECU. If not the overdrive light will flash on and off. I did swap out diffs too, as the speedometer would have been off if not. If you remove the drivers seat and lay on your back, it will make doing the pedals much easier. This was a very straightforward job, just took a few days to complete.

 

[akito]

Yea it's pretty straight forward. The auto shifter hole is smaller but the manual shifter mount will fit just fine, at least for my 89 when I did the swap in 08'. If you were to use an auto harness there's this one round plug that needs to pretty much ground itself, I don't quite remember which one but it's one of the 3-4 plugs on the right side of the trans under the intake manifold.

 

[Nick M]

Unplug the transmission control and see if it still shifts from 1 to 3. Does it shift into O/D?

 

[Nick M]

Since he has not posted since his opening post in February I will point out that it is more likely he is shifting from first to O/D, as that would happen with a solenoid number 2 malfunction. If number one malfunctioned, it would sit in direct with an upshift to O/D.