727 truck question

[Niki]

It's been a while since I owned one, but I'm thinking of getting another one due to knee problems, and their simplicity/reliability/cost effectiveness compared to later OD trans'. With 3. 07's, what would be the cruising RPM going say, 75-80? Is this too much cruising RPM, and will my fuel economy suffer? Thinking of a truck w/ a 366 governor spring, upgraded turbo and intercooler. I used to have an early 91 w350 auto, it was great, sold in a fit of stupidity!!!

 

[dpuckett]

ACtually, the 727 and 518 have the same internals, just an OD is added to the 518. There are threads here that tell you various options about bypassing the bad electonic components of the OD system.



The 3. 07 with no OD would be real similar in RPM to 4. 10s with OD. In my 91, I think 80 was 2800rpm or so- I KNOW 70 was 2400 and change. I can almost guarantee that your MPGs will suffer at that RPM. Plus, I think 65 is about it for aerodynamic efficiency in these bricks we drive.



Daniel

 

[Niki]

Even so, isn't a 518 much more costly to rebuild, as well as getting a converter, or are the converters the same? I've owned 2 518 trucks and have driven a couple of others and I prefer the way my 727 shifted and drove, but all of the 518's still had TPS' on them. I remember holding my foot almost to the floor to hold 65-70 on my 727 truck, that RPM is probably close. I know they aren't very aerodynamic, but I can cruise my current truck empty at 75-80 and still get high teens/low 20's, better than a lot of newer trucks out there! And my truck isn't at the dealer 6 times a year like my buddy's 6. 0 powerstrokes...

 

[dpuckett]

As far as I understand, someone correct me if I'm wrong, but the only difference between the 727 and 518 is the OD and controls thereof. There are differences in transmission in varying trucks- my mom's has one of the sloppiest stock converters I've ever driven (even sloppier than the supposedly terrible 2nd Gens out of lock up), while Philip has a pretty tight convertor in his. All aftermarket convertors I've seen were listed as 727/518.



DP

 

[cerberusiam]

Even so, isn't a 518 much more costly to rebuild, as well as getting a converter, or are the converters the same?

Not really that much more. The only difference is the addition of OD in the 518. If somebody is charging significantly more for the same rebuild they are just padding their pockets.



Me thinks you would eat up the difference in cost between the two with fuel costs. There is no reason a 518 will not shift just the same as a 727 as it is the same internals. Might have to tweak on it a bit to get it there but it is capable.

 

[Gary - K7GLD]

I had an early '91 with the 727 and 3. 07 - 80 mph was top speed, then the governor took over. I installed a US Gear OD on mine for better cruising RPM in freeway travel.



Problem with the later OD units was DC's attempt to operate the OD unit using only the fluid and pump that originally only had to operate the basic 727 - the added drain of the OD was too much, and that plus the low speed torque and typical low RPM operation just simply did not provide enough fluid PSI to keep the clutches engaged - they'd start slipping under load, and the game was all over...



The 727 with an add-on US Gear or Gear Vendors is a far better and more reliable way to go - they provide a good OD function, and WILL live behind the Cummins - as will the plain 727...

 

[DieselTweaker]

A stock 727 will not stand very many engine mods before they crap out. But on that note they are cheap to rebuild and upgrade to with stand alot.



Aslo billet output shafts are being produced right now for the 727 4wd's.

 

[Headshot zod]

slightly off topic but.....



what do you think of a beefed up 727 behind a lightly modded 4bt. I'm thinking of my 74 ram.

 

[cerberusiam]

The 727 with an add-on US Gear or Gear Vendors is a far better and more reliable way to go - they provide a good OD function, and WILL live behind the Cummins - as will the plain 727...

The 518 is every bit as capable and reliable as an external OD and will live a long happy life with a few external adjustments. Several small internal adjustments that don't neccessitate a rebuild will enhance that further. A significant amount of OD falures can be contributed to incorrect setup clearances, incorrect external adjustments, and driving habits that were simply not conducive to transmission life.



From a cost persepctive, the GV is another transmission at about the same cost as the transmission. It is really hard to justify twice the price for the same functionality.



Don't be scared of a 518 equiped truck as long as you keep the power levels sane and the loads within reason.

what do you think of a beefed up 727 behind a lightly modded 4bt. I'm thinking of my 74 ram

Same as a 6bt. It will work fine but be short on gearing. If the 4bt runs like the 6bt, you need to shoot for a cruising rpm at 1900-2100 rpms. You have much better effective leverage with a lower final drive and an OD than a higher final drive. Easier on the drive train as whole and much more flexibility in use.



The biggest problem with the diesel 727 is it is a compaively rare item. IF you ever hurt the case you may NOT be able to find a replacement. While the internals are the same the case itself will not interchange with the gasser versions.

 

[DieselTweaker]

slightly off topic but.....



what do you think of a beefed up 727 behind a lightly modded 4bt. I'm thinking of my 74 ram.

A beefed up 727 will take the beating from a 4bt with out any problems.



As stated about cases this is very true ive been lucky enough to come across a spare case. But there are changes in cases Dogde made alot of changes in the early year's trying to figure out how to keep them together.