Any of the mk1 or mk2 trans will be plenty reliable.
They are all 020 series. Proven through the test of time.
Keeping proper lubricant level is about the only vital element on them.
90mm flanges - and the correct mounting provisions - will be the most straitforward for sure - most all of us prefer a direct replacement.
You can convert 100mm flanges, over to 90mm flanges.
But the mounting provision deal is non-negoitable.
ACN is the "hot code" for most mk1 diesel owners.
But it comes with 100mm flanges, and that requires a change of flanges, or knuckles, or hybrid axles.
I think about all the 1985 and 1986 020 trans have both mk1/mk2 mounting access, maybe further in some cases. But an 85 code ACH is a direct bolt in for sure on mk1. Still verify anything before purchase, never say never. You could be the new owner of a needle in a haystack otherwise.
The final drive ratio is usually a big part of choosing what to buy. And sometimes availability will limit your choices. So it's good to have as many choices (codes) to choose from as possible.
Take a look at the tranny charts on these links:
Both have some really good info on codes, ratios, flange sizes, and original applications.
www.a2resource.comhttp://www.scirocco.org/gears/If you do a lot of highway driving, you'll want a final drive number that is numerically lower than 3.00 if possible.
You take the ring/pinion ratio (3.67 for instance) and multiply that by the 5th gear (0.75 for instance) to arrive at the final drive number.
Code FF is a good Mk1 5spd code, and you will find others listed too.
Limiting to 4_ codes might make the hunt tougher.
Just depends on what is around in your area.
Good to have as many codes that are satisfactory to your needs as possible, when you begin the hunt.
There was also a nice 4spd called 3+E.
I "think" it was code GC, from memory.
2 years ago i never planned on owning a mk1, and could have scored a 3+E on the cheap cheap. oh well
I have an 82 4spd Truck - it has the crap code GN.
My 81 Truck was also originally 4spd code GN.
It was converted to the 1985 ACH 5spd.
You will probably have to make some mild mods to your existing shift box underneath the vehicle - unless you can source the shift box from an original 5spd mk1. I had to make some relief cuts on the outer perimeter rim, and bent the rim flat in the area where the shifter fork was rubbing/binding when shifted into 5th.
I didn't do the 4spd to 5spd conversion.
A previous owner did that.
Shifting into 5th was a hassle, and that was the cure I applied to it.
It will probably hamper the use and/or lifespan of an underbody (protective) shift boot if you have to do that modification. fwiw
I doubt the majority of mk1 owners have this underbody boot in place anyway. Many never knew there was one there. Usually the original is long gone. Replacements are $40+.
Good luck on finding the tranny you want/need.
Was very wise to do this research First.
BrokeVW.com is a top-flight guy.
Don't hesitate to contact him if you need to, for anything.
