I need to replace my trashed 727 3 speed auto trans in my 89 1st gen.I have access to an a518 with converter with less than 1000 miles since rebuild.I have a few questions I hope someone can answer.
1 - is the 518 a direct bolt in to my 5.9 as far as bolt pattern, line hook ups and linkage, driveshaft length ect ?
2 - I know the 518 is an overdrive unit and I remember reading about a method to install switches and some rewiring to be able to manually apply the lock up, anyone have anymore info on this?
3 - is it possible to just run the a518 at highway speeds as if it were the 727? ( fuel economy is not a concern)I don't tow with this truck just transportation to and from work.

Would really like to find the same trans (727 3 speed auto) I have now, anyone have one for sale???

Thanks in advance ...

 

If they are both 2 wheel drive or 4 wheel then they should interchange, the 518 will run just like your 727. All you have to do is give the overdrive silonoid 12 volt power by switch and its on .....simple

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There's no lock up convertor in the A518. You can lock out OD however. In which case it becomes a 727. As stated above, it's the same tranny with OD.

 

im working on putting in a A-518 in my 89. you will need a drive shaft out of a truck with the A518 tranny. it doesnt have a lock up converter like KD93 said. im going to control the overdrive in my tranny with a adjustable pressure switch. my tranny guy says its about 1psi to about 1mph so i will just set it to what ever speed ill want it to shift into o/d.

 

The driveshaft out of my truck will not work?, I dont know if I can find a driveshaft from an a518

 

Nope, The 518 is longer.

 

Did your 727 make a loud bang and quit or did it fade out and stop working? If it slowly died out, I would bet all you need is some clutches and a cleaning to get another 100K or more out of it. I've rebuilt 5 or 6 automatics in my life and the 727 was one of the easiest. A basic rebuild kit can be had on the bay for under 100 bucks. Might be less than a drive shaft. If you have the talent to swap the 518 in, you'll be able to rebuild the 727. Invest another 30 bucks in a book and take your time. Don't force anything...
If it died with a bang there's broken bits in there that'll cause all sorts of problems and cost who knows what to replace.

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I found this video. It'll show you what you'd be getting into.
He actually knows what he's doing, since I don't, I drilled a hole in my bench and I stack the parts up exactly as they come out so I get them back in the same way. The rear sprag can be assembled wrong, notice at the 6 and a half minute mark of part 4 it turns clockwise and locks counter clockwise.

 

At least on my regular cab 2wd application, the A-518 was longer AND had a spline shaft on the tail of it. The 727 used 2 drive shafts stock along with a carrier bearing, and the splines were between the two driveshafts; the A-518 is long enough that you can use a single driveshaft. BUT, you need a flange yoke with the right splines on it to slide into the rear of the transmission.


I had to find the right flange yoke and get a driveshaft custom made from the friendly local driveline shop. Less than $300 if I remember correctly.



A-518s are lock-up transmissions. DIESEL A-518's are not lock-up transmissions.

 

so if i get drive shafts to go with my A-518 then i have to get the right flange yoke no matter what? they are all like that?

 

I got no idea if they're all that way, just something to keep in mind. If the original application used one driveshaft then it will have a spline yoke in the back of the trans, if it used two then it will not have a spline yoke. If you want to only use one driveshaft, you need the spline yoke in the back of the trans. If you want to use two driveshafts, it's not necessary.