727 vs. 518

Looking for some understanding here fellas- I have read that the 518 is an overdrive version of the 727. To me then I would assume that the 518 is just as strong as a 727. Is this true? If not, why?

The front part is as strong if not stronger.. the
rear(the OD section) wont take a ton of torque being
that a 800# spring pressure applies the OD.. but if
you are racing it the OD would be turned off... I keep
the OD switch turned on all the time.. lacking any track
time... the 518 is 47# heavier than the 727 and it has a
bit larger case in front and is longer
EDIT
The coolant lines are 3/8 on the 518.. 5/16 on the 727

Mr P Body,

Thank you for the concise information. You bring a lot to Moparts!

So if I have this right, I can put an overdrive switch in the car, and when it is turned off it will act like a normal 727- no worries on strength.

When the switch is turned on, Overdrive will be active and I would be good to go on the street.

Do you have to manually toggle the overdrive each time, or will leaving the switch turned on allow it to work like the overdrive in my daily driver?

Sorry for all the questions just want to be informed.

Here is a circuit I made to activate mine.

Gary

First you would need to use the RH version of the
518 instead of the RE(the E is the electronic version)..
you can find 2 types of the RH.. if you look at the OD
plug located behind the shift lever on the case.. there
is a 2 pin or a 3 pin plug... some early ones had a single
pin... but you dont want the 7 pin plug... that uses the
computer to operate the trans... I have both a 2 pin and a
3 pin... the 3 pin is a OD and lock up... I changed out the
input shaft and the pump to allow the use of a 727 conv.. I
have a 727 5000 stall in mine... this will eliminate the lock
up.... I use a manual toggle switch to run the OD.. if you
leave it on, when it hits 3rd gear it will go into OD.. turn
it off and its a 727... without the lock up in it I leave the
switch on unless I'm gonna race it
EDIT
If you run a lock up conv then you have to turn that off
when coming to a stop or it will try to stall or lug... but
the lock up conv isnt strong(the lock up clutch is small) and
to get a lock up conv built with any decent stall is pricey

It's the other way around, the spring applies the direct clutch which provides through-drive when not in OD so the torque capacity in direct is limited by the spring. The OD clutch is applied hydraulically so the OD clutch apply pressure can be manipulated.

Ok... I wondered if I wrote it backwards... but
either way that clutch cant take a ton of torque..
its small

i think the clutches in the overdrive are the same ones as used in the main transmission--diesel ones have only one more clutch in the OD and everything else is the same--wonder how they hold up so well.....

When you roll into the power it kicks out of OD..
in my parts book it calls out different P/N for the
OD clutch

PATC sells many upgrade parts for the 518 such as extra capacity clutch packs.

I got some of my parts from them... a lot of the
stuff I get at the local Transtar(which has bought
out most everyone)

How much extra power does a 518 suck up? (Or how much does it slow you down?)

I have the 518 in my 92 D150 which I bracket race on occasion, when racing I always push the o/d off button on the dash if I don`t it goes into o/d which slows the truck quite a bit. I have a Mopar Performance/ Turbo-Action shift kit , the 1st to 2nd shift is quite hard even under normal driving but it works well. I was going to add an off the shelf convertor to try and get the truck to leave better, instead Lenny at Ultimate said he could rework my stock lockup convertor which he did and the truck responded well although it only runs low 15s my 60ft times dropped from high 2 teens- low 2 twenties to low/ mid 2.0s a little over a tenth.

I have the 518 in my 92 D150 which I bracket race on occasion, when racing I always push the o/d off button on the dash if I don`t it goes into o/d which slows the truck quite a bit. I have a Mopar Performance/ Turbo-Action shift kit , the 1st to 2nd shift is quite hard even under normal driving but it works well. I was going to add an off the shelf convertor to try and get the truck to leave better, instead Lenny at Ultimate said he could rework my stock lockup convertor which he did and the truck responded well although it only runs low 15s my 60ft times dropped from high 2 teens- low 2 twenties to low/ mid 2.0s a little over a tenth.

So you have just a bit over stock stall... I checked into
a lock up high stall conv.. 5000 stall and it was
$1800 for a conv.. and he didnt know if the LU clutch
would live... he wanted to make it about a 1" thicker
so I would have needed a 1" spacer between the engine
and trans... most of the conv places that I talked to
wanted to go thicker if I wanted the stall I was looking
for... right now I'm using the old J-conv from T/A and
when I talked to Paul about the slippage it didnt know
for fact what it would be in OD... he said 10%... he was
close... its 9% at 75 mph.. I havent seen any issue with
trans temp.. I normally see about 180* on a long run(75 miles
or more).. but I run a nice size cooler.. and if I needed more
I have another with a fan that I would add to it also
EDIT
This slippage data was when I was still having issues
with the trans.. it was eating itself up due to no
torrington bearing in the OD.. so I will need to do
a new set of numbers since this last time of going
through the trans.. I expect it to be better now

Yes Mr P a little better than stock and it was only a few hundred dollars to convert my stock convertor. Off course I don't have much power just a 5.2/ 318 with a few bolt ons and 4.10 gears. Is the 518 in your trick Rampage?

Yes it is... I finally have it working right.. I had issues
with the rebuilds( 3 times before... so I finally did it myself)
and it seems to be fine... it has all the gears now but I havent
put it on the road as of yet on the build.. now it has injection
on it also which is working nicely(Holley multi point)

You have a sweet looking '92 and 15s are respectable for what you have and in bracket racing, if your vehicle can repeat and you cut the light, you win.

My '87 D100 will have the Dana 60-2 in place by the spring time with the 4.10 PowerLock. I have the original 318/727 with an E-brock Performer and a #1406 E-Brock on top and it feels strong though it has never been to the strip...yet. It was planned to be my tow vehicle for the Ramcharger, but I may be using it in next years Car Club Challenge while I work on the Ramcharger and I may want to upgrade to a 518 like you have for the gas mileage, but I only have to drive 20 miles to Pacific Raceway and a little farther to Bremerton Raceway, so with a real tall tire it probably won't make any real difference. I have a fresh 3,000 stall 727 converter and a used Hemi converter that I can experiment with. I just love working with junk.

Like John K said the large 800 lb spring applies the presure to the direct clutch in the O/D unit and all power goes throught the direct clutches in first , second and third. It does also have an overrunning clutch in the overdrive that holds if the direct clutches slip. It actually has that overrunning clutch (sprag) to prevent shift flare going from third to overdrive but it would hold if the direct clutches slip. I just dont really know how much power it can handle. Ron

PACT sells a heavy duty overdrive spring for $70. That and some good OD clutches along with the oiling mods to the shaft should support quite a bit of power? Not sure how much though, the 518's I have built were all stock replacements.

Not sure if you have a big or smallblock engine to put in front of it, but don't forget all 518 transmissions have a smallblock bellhousing.

A friend of mines 440 Duster is running 121 mph through the traps with a 518 with Ultrabell. Full street car with steel wheels and power steering.

Good catch, this will be behind a Gen III hemi so at least that part is figured out.

Thanx Polara Pete, I have fun with my D150, I am the original owner as I bought it new in 1992. It ran its lowest E.T. to date last weekend going 15.12 @ 87 mph with a 2.03 60ft but averages 15.20s-30s. I have been very successful with it with many round and eliminator wins, including r/u in Street at Chryslers at Carlisle back in July and a Win in Bracket 3 ( 14.00 and slower) at a Mopar Meet at my local track a few months ago.The 518 has never been apart ( only out a few years ago to have the shift kit installed) even after all these years of racing and towing as it used to be my tow vehicle.

Just a matter of time before it grenades. It's a shame Chrysler didn't build a better OD Unit. They were no doubt the weakest OD units of all Makes ever made. I know you can beef them up a bit but they won't take a beating especially behind a big block. Hell you can even make the Ford AOD stronger than the 518.I debated about putting a 200r4 behind my car but I was too proud to GM it. So I'm putting the 833 back in it.

Put the big 6 pinion planet in the OD out of a 48RE, add an extra strong spring and a diesel clutch pack with an extra clutch and it will be fine. I block the OD acumulator (the spring is usually broken anyhow)and open the feed passages in the case and VB to apply the OD quicker, seems to make OD go in and out quicker when you hit the button both timing and firmness. No reason chrysler should have let them leave the factory like the piece of crap they were but with minor mods they are very good.

A fellow club member has an original '70 Superbird with 426 Hemi and he runs the Aluminum case 833 with OD 4th gear to cruise to car shows...but he does not race it, of course. He saved the OEM 833 on the shelf so that when it comes time to cash in his "401-K" Superbird he can say it is numbers matching and mean it. Some years ago, he and several other club members drove the car from Everett, WA to Talladega, AL. There was an event to celebrate the NASCAR reunion for all the aero cars including the Phords. Most of the participants trailered their cars, but Bob Kropp (AKA SuperbirdBob) drove his. They were made to be driven, weren't they???

Just a matter of time before it grenades. [/quote]

Been driving it for two years now, it was built to be a true street car hence the back seat and power steering. It even has a flat hood.

He drives it to work and takes the kids out in it all the time.

Problem with that is the extra pressure has to be overcome when the OD is engaged and this robs apply pressure from the OD clutch pack along with putting extra load on the bearing that carries the spring pressure. This is what makes the Mopar OD trans inferior to most others.

do you have any pics of the feed passage mods ? is the 6 pinion planet a steel case ? i have never been inside a 518, but have been contemplating an ultrabel/518 build for a big block project.

Why not use the NAG1 5-speed transmission? I know the controller is expensive, but the transmissions are supposed to be pretty tough?

Someday, I need to get going on my 6.1L NAG1 transplant project...

I would like to use a nag-1 , but the controller I have read about has been deemed less than reliable by Dave Webber from Modern Muscle.

I do not know of an easy way to run a Nag-1 in the way that a 4l80E is run.

Since the new site "up date" I have not been able to post pics, I can't even get them off my phone onto the confuser any more! I have a ton of pics to share like this and how to tell if your magnum heads are gonna crack or not...

The 6 pinion planet is steel caged, there are heavier doody ball bearings also to take the load better.

so if I want to put a 518 in my 70 Cuda with a smallblock, what donor vehicle should I look for? What is the OD ratio? Will I need to make any modifications to the floorpan or crossmember, or just a shorter driveshaft?

You will have to do major surgery to the crossmember to get it to work. Not sure about the floor pan.

I had a 90 dodge pickup with overdrive that could be turned off.

I went the gear vendors route.

I have a 73 cuda 340 with an A500 which is the 904 version of the 727/518. I love the lower first gear and the OD which is simply turned on and off when in high range via a toggle switch. It is dimensionally the same as the 518 at the case to tailshaft overdrive split and rearward, and thus posed the same challenges at clearing the crossmember that the 518 will. I did not want to butcher my crossmember, but took a cutting wheel/grinder to clearance the tranny itself as much as I could stand, especially at the case to OD flange where there are pipethread pressure test plugs. I also "bulged" my floorpan and dented the upper crossmember a bit in a couple places where interference was still a problem. You can cut the lower crossmember cradle to weld in a new rear tranny mount system, or try and buy a GearVendors crossmember cradle and mount which is what I eventually did and run to this day. Did this mod in the late "90s and still using it today tho with a non lockup 904 hi stall converter and modified (additional clutch plate) front clutch and front pump system from a 904. I always wanted to do this with a 518 but could not find one and convinced myself the lower first gear ratio of the A500 was more suitable for getting my somewhat heavy Cuda out of the starting gate. I did shorten the driveshaft by about 2.75 inches as I recall and had to mess with drivelshaft angles a bit to prevent an annoying vibration. Love it and it was a worthwhile mod. Now I want an 8 speed!!!!