Overdrive 727's

nfury8 · Post by **nfury8** » Sat Sep 18, 2004 3:04 pm

I have heard mention of 727's with Overdrives, I think they are reffered to with a different number. Anyone used one, or know if they would be appropriate for use in a Big Block 4x4 Swept?

noemdfan · Post by **noemdfan** » Sat Sep 18, 2004 7:09 pm

The correct designation for the HD overdrive torqueflite is A-518. You need to get a pre-1995 model in order to get a hydraulically controlled version. Anything newer is electronically controlled and you need an engine and tranny computer set. You'll still need a switch to ground the "overdrive" and turn it on. My idea would be to use an extra Emergency Flasher switch in the "Choke" position (Manual transmission trucks only have this. It's right below the Headlight Switch) for a factory look.
As for using it with a big-block, you need a JW bellhousing to adapt a "B/RB" engine to a LA series 727 torqueflite (if you ask them for an adapter for an A-518, they "won't have one." The A-518 will need to be beefed up with parts from an A-618 (used on Cummins and 8.0 Liter V-10 engines) to stand up behind a built big block for any length of time. Also (VERY IMPORTANT), you need to have the radiator altered to use 3/8" transmission lines (5/16" are standard). Otherwise, you'll have to use an external cooler set up for 3/8" lines.
Supposively, you'll need a small block Chevy motor mount for the rear transmission mount.
I've never tried this (yet). This information is from Mopar Action Magazine's tech column (Richard Ehrenberg, editor). I like the idea of a conversion, as it would turn my 3.55 gears into 2.45s for interstate driving. This might be too slow of an engine speed unless you use an Edelbrock SP2P or an Offenhauser Dual-Port and a Spread-Bore carburetor, along with a matched low end cam.

Website · Post by **wideblock** » Sat Sep 18, 2004 9:50 pm

on these swepts, from experience with tall gears, the perfect rear final ratio is around a straight up 3.00 gear for the freeway. anything in the 2's will leave you wishing for more on any hill. my tranny guy here in town says there are kits to upgrade the 518 to near bullet proof staus for anything under 400hp. that covers most mild big blocks and almost all the smal blocks. trans dapt also sells the conversion to run these on big blocks.

nfury8 · Post by **nfury8** » Sun Sep 19, 2004 2:58 am

David,
How long ago was that article? Sounds like it would be a good reference to pick up. The previous owner claimed the rear has 3.23 gears, but I am not sure. The rear came off of an 86, so I suppose 3.23 is possible, but it is a Dana 60, I don't know if they used anything that tall in Danas. Just not my area of expertise.

I doubt they are 3.23, I get about 10mpg on the interstate. It is a 400 with a Edelbrok 650, I try to keep my foor out of it, but...

noemdfan · Post by **noemdfan** » Sun Sep 19, 2004 7:17 am

If it is a Dana 60, it's probably a 3.54 ratio. Only 1990's Ford F-250 Diesels (pre-Power Stroke - i.e. non Turbo Charged) have higher Dana 60 gears, 3.33:1 from what I understand (in an atricle from Hot Rod Magazine - a car had a Ford Computered Fuel Injected 440 with a T-56 six speed and a Dana with a 3.33:1 gear set). Checking the Rear Axle Ratio is pretty easy. Chock the Front Wheels of the truck on both sides. Place a Chalk mark on the drive shaft at 12:00 and a chalk mark on one rear tire at 12:00. Jack up one rear tire (both, if the axle is "Sure Grip Equipped"). Now get a helper to slowly turn the lifted rear wheel one revolution, while you observe the driveshaft. It it turns 5 and 1/3 times, it's a 5.38:1; if it turns 4 and 1/2 times, it's a 4.56:1; just more than 4 times, it's a 4.10:1; if it turns 3 and 3/4 turns, it's a 3.73; if it turns 3and 1/2 times, it's a 3.54 (these are the most common Dana 60 ratios).
I agree about the 3.00 gears being the top set that you want in most instances. Most guys want to run tall tires. Me? I'm running P-255-R/70-15s (White Letter Car tires) and it's relatively flat around here, so 3.55:1 is a bit steep for 70 mph cruising.
With a 4.10 rear and the .69 overdrive from the A-518, flipping the switch will get you a 2.87 ratio.

Website · Post by **wideblock** » Sun Sep 19, 2004 9:30 pm

1/2 ton trucks you got 2 choices, 1= 8.75 has the removable center chunk, no rear removable plate and does have the 3.23 as an option. 2= spicer unit, made by dana, but not a 60, has removable rear cover( used in most later modle trucks), and also would be possible, and most likly a 3.23. the dana 60 for these trucks was an 8 lug axle, and as mentioned above, didnt have a 3.23 gear unless it was a aftermarket install. 4.10 and 3.54 were the most common ratios on these big boys. but i will add, if the axle has been played with, there are many manufactures that will, and do, make any gear ratio for almost any common axle you can imagine. so, is yours a 5 lug or 8 lug? one more thing, the dana 60 was available in a 5 lug, but these were in hemi cars and such, really rare, really strong also. if indeed you have a dana 60 5lug, you got a hell of a good axle that should be held on to, its worth as much as the truck its under. and 3.23 was a common gear on them as well. but my money is on a later modle spicer rear. they came in somewhere around 70 and went on from there for a lot of years.

noemdfan · Post by **noemdfan** » Sun Sep 19, 2004 10:05 pm

I'd actually bet on a 10 bolt Chrysler built 8-1/4" (actually 8-3/8" ring gear). If by chance the rear was out of a big block truck, it will be a 12 bolt Chrysler built 9-1/4" rear, which is damn near as indestructible as the Dana. This is what comes under late model Durangos and last generation Ram 1500s. Checking the ratios is the same procedure but the ratios are a little different (2.71 instead of 2.76, 3.21 instead of 3.23, etc.). Both rear ends have circular/octagonal bolt patterns on the rear housing. The 8-3/8" tends to be lighter duty. The Dana 60 rear has an elongated octagonal cover shape, stretched to the right. It's quite possible that someone has fixed up a 3/4 tom Dana 60 with 5 lug axles and yes! that would be one hell of a deal.

nfury8 · Post by **nfury8** » Mon Sep 20, 2004 12:26 am

The rear is a 5 lug, 5 on 5.5", but not an 8.75". I am told it was a Dana 60 by the previous owner, but I am really only familar with the 8.75's from my cars. So I took his word. I know the front is a 44, I saw it stamped in.

The rear supposedly came out of an 86 with the front axle, transfer case and tranny. The tech at Aamco told me it was a come style sure-grip when I had them inspect it after I bought it. I told them it was a 60 when I dropped it off, but never asked them to verify; and they didn't correct me. The back cover looks like the Dana covers, but I suppose it could be a weaker unit inside.

Here is a pic of the rear:

noemdfan · Post by **noemdfan** » Mon Sep 20, 2004 3:33 pm

Looks like a Chrysler 9-1/4" Rear Axle. These are nearly as strong as a Dana 60. Good score!

nfury8 · Post by **nfury8** » Wed Sep 22, 2004 12:46 am

Thanks for pointing that out. Now that I go back and compare, it does look like the 9 1/4". I should have figured that one out myself.

Now to check that ratio.

Guest · Post by **Guest** » Wed Sep 22, 2004 4:34 am

If you're going to go this route, I'd hunt for a 4wd automatic truck. Then use the tranny with the tranfer case as a single unit. The advantages of this method are a simplified operation and installation. Be sure to get the driveshafts from the "donor vehicle," in case the driveshaft length is different when using the new assembly. Of course, the 4wd lever placement might be different. But you'd probably have the same issue using the 2wd tranny and old transfer case.
If you're "beefing up" the transmission by using A-618 internals and a shift kit, I don't think that you'll kill it with a 400.
BTW, if you're only getting 10 MPG on the interstate, I'd bet that you're running a 3.91 ratio ring and pinion set. Sounds like fun; until you have to fill it up again!

Post by **oneowner71** » Wed Sep 22, 2004 11:11 am

I thought the 9.25 were considered weaker axles than the 8.75? Man, now I am confused... So by strength, we get Dana, 9.25, 8.75 (489), then 742, then 741... right? Man, I need more sleep in my diet.

Jeffc · Post by **Jeffc** » Wed Sep 22, 2004 4:39 pm

The 9.25 axle is a good axle and has some good points and some drawbacks
also......
The 9.25 is based on the older 8.25 and has C clip retaners to hold the
axles in, the 3rd member is strong but not as easy to swap out a
a 8.75 and because of the C clip use the axles will not handle side loads
as well as the earlier 8.75. Now don't get me wrong there good axles
but do tend to wear out faster than a 8.75 in 2 areas; differantial bearings
and at the C clip groove (if the C clip groove wears to far it will snap
the axle and you see the axle leave the housing, about the only time you
will see that happen on a 8.75 is if the axle bearings are not serviced
for many years (repacked at brake job time)).
Because of this, the 9.25 is not recommed for high side load applications
such as Autocross or road racing, but fine for the strip.
In these areas the 8.75 beats it hands down as a all around better axle
type road or track, which is why it has stayed around, as far as parts aftermarket, for so many years since they stopped producton of it in the early 70s. Given a
choice between the two, I would choose the 8.75 any day, but that is just my point of view on the subject.

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