A500/A518 overdrive mileage / cost/work..worth it ?

[rustytoolss]

Just trying to decide if installing an A500/A518 overdrive trans is worth the work and cost involved. After all the money was spent. And the work was complete. Do you feel this was worth doing ? How much of a change in gas mileage did you gain or loose ? What rear end gear/tire size are you using ?
Like I said just thinking things over. Thanks

 

[Kern Dog]

You will not lose fuel economy at freeway speeds but I wonder what the extra weight and rotating mass does at lower speeds? does the extra mass result in a slight loss, offset by gains when in OD? I do not know.
An opinion that I have seen printed around the forums is that the cost of the aftermarket overdrive transmission kits (SST, American Powertrain, etc) will likely never pay for itself in fuel savings. The benefit is in better driving conditions, quieter cruising, less wear on the engine, etc. Adding a Mopar overdrive setup on your own cuts the costs by a bunch, so given that, it makes the swap even more attractive.
Floorpan modifications are the drawback here: The 518 is fat around the tailshaft area, an area that is skinny in most classics.

 

[Fran Blacker]

This was asked in a thread about getting better mileage. You need to look at cost to do vs gain in mileage. IMO not worth unless you put on over 5,000 a year and gain 10 or 15% in mileage.

 

[2quick]

Gear Vendors!

 

[rumblefish360]

Gear vendors = bigger money spent.
Compact and easier though. Also holds a lot of hp.

 

[SDCoronet]

I about when compared to a taller ratio in the rear?

 

[rumblefish360]

I about when compared to a taller ratio in the rear?

???????

 

[rustytoolss]

Gear vendors is not within my budget. I may be able to do a mopar overdrive for less than $700 or even less. I'm not running big power. That's why I asked about the chrysler AOD transmissions.

 

[wyrmrider]

Which motor
small block is a no brainer especially if you are looking at a trans rebuild anyway
I've built several 518's let me know if you need any suggestions
think about 92-95 RH models

 

[rustytoolss]

Yeah, small block (318) 71 RR. The big block was removed before I got the car. Is there a difference between v6 and v8 A500's ? , Thinking of A500 to get lockup , and no balance needed.

 

[rumblefish360]

Internally the trans am be a but beefier but this I do not know for sure. The 318 produced a good amount of more torque than the V6.

But! It can be beefed up and beefed up well!

Lock up converters of any decent performance stall rating are basically zero. What ever converter you have with it should be sent out and modified for performance useage. Otherwise, any size cam you look at is very limited in duration. Pretty much at or under 218@050 is it. Unless you get crafty. IE numerically higher gear ratios.

Since the OD ratio is IIRC, .69, multiple that by the gear ratio used for the final drive ratio.

IE 4.30 X .69 = 2.96.

Also remember the first gear ratio in the OD vs. the standard trans.

 

[rustytoolss]

I have the small summit cam 204/214 @.050 .421/.444 . Performer intake, Edelbrock 650AVS. gears are 3.23 , tires 27.4 DIA. stock dual exhaust. Electronic ign. The only thing that might change is gear ratio (3.55 if I got to an overdrive)
the lower 2.74 gear set should help slow speed power (over the 2.45 gear set, that have in my current 727 trans). And would also hope the it would offset low performance converter. (maybe not ?)

 

[Detroit Iron]

Horsepower robber.

 

[wyrmrider]

are you towing?
don't change the 3:23 you may like it
I've run OD with 3.08 (I have 3.54 but it's a truck and I tow)
The late trans has a 2.78 low vs your 2.45
IDK if there are any 318s with the small 500 -42RH trans
My 92 318 has the 518 46RH 3WIRE not the 46RE
if someone gave you an A500 without the E -pre 95 it would work about the same as any 904 as far as durability was concerned- you could find a 998-999 and use all the guts as far as more planets and number of clutches
THE OD's ARE ALL the same except the drum snap ring is cut for more clutches in the V8 I have 9 in mine
the Diesels were the same as the V8- they just squeezed the spring a little more and stuck an additional steel and clutch in
That said if you have to get one out of the boneyard get one from a 93-95 360 (have to re-balance the converter) or a 92 95 318
your old school cam will work fine
now if you want to beef up your 518 get the guts out of 97RH
The week spot with either trans is the od planetary thrust washers- if you do decide to do it I'll tell you the easy fix
I have a quarter million miles on mine and it's just starting to get soft

 

[rustytoolss]

are you towing?
don't change the 3:23 you may like it
I've run OD with 3.08 (I have 3.54 but it's a truck and I tow)
The late trans has a 2.78 low vs your 2.45
IDK if there are any 318s with the small 500 -42RH trans
My 92 318 has the 518 46RH 3WIRE not the 46RE
if someone gave you an A500 without the E -pre 95 it would work about the same as any 904 as far as durability was concerned- you could find a 998-999 and use all the guts as far as more planets and number of clutches
THE OD's ARE ALL the same except the drum snap ring is cut for more clutches in the V8 I have 9 in mine
the Diesels were the same as the V8- they just squeezed the spring a little more and stuck an additional steel and clutch in
That said if you have to get one out of the boneyard get one from a 93-95 360 (have to re-balance the converter) or a 92 95 318
your old school cam will work fine
now if you want to beef up your 518 get the guts out of 97RH
The week spot with either trans is the od planetary thrust washers- if you do decide to do it I'll tell you the easy fix
I have a quarter million miles on mine and it's just starting to get soft

I assumed that the A500/42RH was used in "some " 5.2/318 trucks and vans. But have not looked in to it much yet. The only reason I was more interested in the A500/42RH is for less rotating mass/ and less overall weight and lower first gear set ratio, and maybe less parasitic loss? than the A518/46RH. But maybe those are not good reasons IDK ?
And yes I do tow a small camper less that 800lbs.

 

[wyrmrider]

all valid reasons to run the 42rh
with the 998-999 parts you are not going to break it and most likely not even with the 318 parts
the 727 was put behind 6 cyl and 318 more to make them last longer especially in taxi and police work
my 68 Polara C body 318 has a 727
but remember they used the 904 based 999 trans behind 360 police cars later on
I took the guts out of a 360 AMC National Park Service 4 Door and put it in the 77 Pacer
we live at the bottom of a long steep driveway and I never lost reverse after switching to the double wrap band of the 999 trans
I just picked up off the floor the 86 techtran A999-A904T manual which covers the first year of lockup and I have one for the 92 vintage 518-46RH plus teh Factory 92 Dakota shop manual
you do need something but these trans are DIY except squeezing the big od spring- takes a press
couple of other things but all doable
Transtar parts manual helps on interchange

 

[rustytoolss]

all valid reasons to run the 42rh
with the 998-999 parts you are not going to break it and most likely not even with the 318 parts
the 727 was put behind 6 cyl and 318 more to make them last longer especially in taxi and police work
my 68 Polara C body 318 has a 727
but remember they used the 904 based 999 trans behind 360 police cars later on
I took the guts out of a 360 AMC National Park Service 4 Door and put it in the 77 Pacer
we live at the bottom of a long steep driveway and I never lost reverse after switching to the double wrap band of the 999 trans
I just picked up off the floor the 86 techtran A999-A904T manual which covers the first year of lockup and I have one for the 92 vintage 518-46RH plus teh Factory 92 Dakota shop manual
you do need something but these trans are DIY except squeezing the big od spring- takes a press
couple of other things but all doable
Transtar parts manual helps on interchange

Thanks for all your input.

 

[rustytoolss]

Horsepower robber.

Just asking...why do you say that the A500/A518 are hosepower robbers ? Would like to know why the might be a bad choice.

 

[rlem1977]

Just asking...why do you say that the A500/A518 are hosepower robbers ? Would like to know why the might be a bad choice.

All of the "beefy" auto trans have higher parasitic horsepower loss. The Ford C6 about 55hp vs C4 about 25hp; 727TF about 45hp vs 904TF about 25hp; TH400 about 45hp vs TH350 about 35hp. You can see the difference between the "beefy" and "less beefy". More rotating mass to get moving. I think rusttoolss wants an idea if he'll see a ROI through fuel savings with an overdrive. So many factors to consider.

Here's a very rough outline, meaning my math is probably fuzzed:

Assuming you drive 10,000 miles a year @ 16 mpg = about 625 gallons of fuel. At $2.40/gal. = about $1,500/year. Assuming the upgrade to a 4-speed auto gets you the same 10,000 miles @ 19 mpg = about 526 gallons of fuel. At $2.40/gal. = $1262/year. A savings of $237. Divide that into the total upgrade cost and you'll have your payback time in years. If you spend $2,000 it'll be about 8.5 years; which will be 85,000 miles and time for a trans rebuild.

I did all of this fluffy crap already for my car. For me the price will not be justified in fuel savings as much as in drivability, as I have a 3.91 rear gear ratio. Good luck, have fun.

 

[MJF_]

So, anyone actually installed one? I have A500 from 1989 Van with 318. I am interested to install it to my 69 Satellite with mild 318. At the moment interior is pretty much empty. If there is floor cutting involved, now would be time for that. The question is: does floor pan need to cut?