The biggest down side to the GV is that the OD ratio is not near as good as the 500/518 OD ratio.

Just a comment?
All transmissions get a terrific BANG on the shift (slightly reduced by a loose converter), which beats up the friction material, loads the anchor points, etc. and also shocks the entire chassis. Oh, that's why the car jumps, tries to climb a tree, blah, on the 1-2!
Has anyone dealt with this?
My Lexus DD has factory spark retard to kill some power on the shift using a signal from the shift solenoid. Helps, not adjustable.
An MSD box could do this if it could "see" pressure applied/released on gear change inside a 727 valve body, if some clever person could find a place to tap in? On the linkage might work with manual VB but you'd have to estimate and program the retard time in .001 seconds, etc.

A 518 doesnt have to cost big money

Used to do this on 1-2 for .5 seconds(-10 degrees) found no benefit on the 2-3.
I just used micro switches on my shifter.

Too hard a 1-2 shift and banging into reverse were 2 things I asked A&A to address when they built my 518 valve body. They did and I am very happy with the results. The 1-2 shift is firm, but I no longer worry about pulling the tires loose at the shift. And it now goes into reverse like it goes into forward, smooth with no banging even with the higher idle.

So yes, it can be done.

What is different in the diesel trans that it can take the high loads.. is
it the valve body or something else.. I never messed any diesel auto
stuff.. just my stick diesel
My main concern is why it can take the loads in OD when the 518
cant

As with our 727s, line pressure and valve body play a big role. And really, much of what we do for the 727 applies to the 518. The OD unit does need some attention, but nothing radical. Good clutches, more spring pressure and line pressure, proper clearances, and maybe a better bearing and cooling make the OD unit more durable.

I used a number of internet sources for my build. PATC being one that comes to mind. A Google search will bring up a number of build threads and parts sources. Don't forget to look at what the truck guys are doing. They have spent a bunch more time with these trannies than the car guys have.

The biggest issue I had was getting a torque converter that I liked for my use on the street. Most were just too loose for my liking. Lenny at Ultimate was the one who finally got me as close as I am going to get.

I have dealt with PATC while building my 518.. I did do some things differently..
mainly I used a 727 conv with a 5000 rpm stall which I have Lenny lower
the stall a little for the street.. I also used the correct front pump so the
conv would work.. still have most of the stock parts in the OD and the
valve body.. for what I know the OD spring is pretty much the same as
the diesel one so I just used the stock OD spring with the same clutches
as stock.. so if I want it to hold more power what should I be changing and
what kind of line pressure are you running(I thought the line pressure was
just to take it out of OD and the clutches held it on
thanks

The diesel uses more O/D clutches (not the direct clutches, I believe they are all the same) and better planetary gears with 5 pinions. The V10 uses 5 pinion gears as well but they are helical cut and the diesels are straight cut.

Earlier versions may be different but from the 47RH and up this should be what you find.

If you want more capacity just build the overdrive clutch like a diesel. Line pressure is the same between diesel and gas as is the large spring people call the OD spring. That spring is the direct clutch spring.
It’s used primarily for reverse but is also on in 1, 2, and third.


The 47 diesel has more frictions and steels in both the direct and overdrive clutches. The old 46 diesel had an extra OD disc and same number of direct frictions as the gas.

You don’t need to mess with the direct in a car unless you somehow figured out a way to haul a 20K pound trailer.

The later 48 diesel has even more updates in the OD but again that is driven by the increased GVW of the truck.

There is an aftermarket heavier spring available. I used it, not saying it is even necessary, but there didn't seem to be a down side (other than a few bucks). And it seems like there was a bearing, maybe under that spring, that there was a better version of. There is a cooling mod, too that can be done to the shaft. Again, it may not be necessary, but it got it, just in case. Most of the other stuff has been covered by others here. To be honest, I don't remember the line pressure. It wasn't real high though, seems like 100lbs or so. I discussed that with A&A at the time and took their suggestion.

They also eliminated the OD servo (if that is what you call it) so it goes into OD about as firm as it goes into 3rd. A&A has experience with these valve bodies and trannies and the FMVB they did for me turned out exactly like I hoped it would. I wished everything turned out as well.

As I said before, I am very happy with the 518 in my Cuda. It is a shame though, that we have to cut and adapt a bell and have such a limited selection of street converters for stroker motors. But, in the end, I still feel it was worth the time, trouble, and money.

Do you recall where you got the OD spring from
thanks

I got mine from PATC

Was that the stronger aftermarket spring..when I get ready to pull
the engine and trans I'm looking to put the diesel parts in
thanks

yes is was the stronger spring

How hard are you going to push it when it OD, Mr_P_Body? I don't really push mine in OD, in fact, I have an adjustable vacuum switch that drops it out of OD with a drop in cruise vacuum. Kinda like passing gear. It's actually a lot of fun with passengers. I am not afraid to push it in OD, I just don't need to.

My biggest concern was hitting the clutches in the OD unit that the lower gears must go through at the launch. I know it can handle a lot of power. But like so many other drive train components, the hit at the line will find any and all weak links. I have had it to the track a couple of times, but only made a hand full of passes. Unlike my last combo (440/499, 727) which I beat on unmercifully and therefore needed to work on regularly, this one I am not as anxious to wrench on. Just getting old and lazy, I guess.

I dont pound on it in OD.. thats just for cruising .. I have a switch for
the OD.. I tend to leave it on all the time unless I'm racing then I flip
the OD off.. I know that OD is the weak link so I'm pretty easy on it..
I just wanted to build the OD so I could forget about it and it will
hold the torque

If built right no problems, my 48re in my Ram holds up no problems to dynoed 500hp and 998 foot lbs tourque, and alot of the parts go as far back in time to the 727 transmission. Guys shift the trans while in lockup but have billet shaft through the whole trans. I went with only billet input shaft.