Hi everyone.

I was just about to pull the trigger on a rear end swap on my 1973 Plymouth Satellite. I have a mild 360 in it right now (318 stock), but I'm planning to either do a 408 stroker kit in it or drop in a 440. I already swapped out the 904 transmission to a 727 with a shift kit. I believe the stock rear end is a 8 1/4. I was going to swap to a 8 3/4 or a Dana 60 but from what I am seeing online, the 8 1/4 can handle up to 500 hp? I need to install a Suregrip either way. For gears I was thinking about 3.23 for the highway, but I just found out about transmission over drive kits. I am thinking a 3.55 rear end with a Gear Vendors might be beautiful. Do any of you have this set up, what are your thoughts? I would like to keep a nice top speed and get out the door fast. Do I really need a rear end swap or should I build the 8 1/4?

In part, it depends on what you will do with the car and tires you run. With common street tires the 8 1/4 will take a lot. With sticky tires or slicks and hard launches the torque in 1'st gear can do it in pretty fast. Axle torque and traction are the limiting factors more than HP. The 8.75 is a bit stronger but would get marginal with a 408 or especially 440 and sticky tires. The D60 would be pretty much bullet proof.

3.23 is a nice all around gear... OK for the highway and decent acceleration. Maybe keep the 8.25" and see how it goes. OD is really nice if you are spending time on the highway. Including with 3.23's. If you want to drag race probably need something like 4.10's for best results.

I agree with most of what ahy says. The only exception that I would take is that he feels that an 8 3/4 would be "marginal" with a 408. I run a 489 8 3/4 in my Cuda. 3,500lbs, 500" stroker, 4000 stall, 3.91s, and drag radials. The car will pull low 1.5s 60 foot. I get years out of my gears before they get noisy.

A 60 is pretty much bullet-proof, but an 8 3/4 would be cheaper, easier to set up, easier to find, lighter and eat a few less ponies while lasting a very long time. And is much easier to change gears in should you want to try a different ratio.

Also, if I am not mistaken, I believe that many Dakotas came with an 8 1/4 with 3.55s and a Sure-Grip. And the junk yards (pick-a-parts) have a lot of them now. $50 will buy the gears and carrier at most places if you pull them your self.

Good luck with what ever you decide.

I don't agree that the 8 3/4 would be marginal, especially with an auto.

HOWEVER, if you are going to buy a new rear anyway, why not just spend the extra and put the D60 in, then no matter what you may eventually do, the rear is done. In the long run it may very well be cheaper.

It is unfortunate you already spent money on that 727. An early 90's 518 transmission out of a dodge rwd truck/van would be the ticket for you. It's basically a 727 with a .70 overdrive gear. It will bolt straight up to a small block (perfect for that 408 stroker idea of yours) or mate to a big block with an adapter. The 518 could be made to fit under your car with a minimum of fabrication(shorter driveshaft, custom transmission mount, possibly some crossmember modification. Also the 518 has a superior overdrive gear to the .80 on the gear vendors. With the 518, you could do 4.10 rear gears and on the highway it would drive like a 727 with a 2.87 rear gear.

Either way, I would get your transmission choices nailed down, and worry about the rear end later.

I'm not a small block guy,...but Man does that package sure sound sweet! I give it a

No biggy,...but wouldn't the 8.75 be a 4.11 though?

The 4.11 ratio was never offered in a Mopar, the 4.10 was. I know, it is only a small difference but we strive for accuracy here, right?

I "sit" corrected.

Wish I would have know about that option back then. But I am happy with the 727. I think the Gear Vendors is .78, but yeah, it only makes a 4.10 drive like a 3.20

However, it looks like 518 is only one extra shift in the 3rd gear high range. Gear Vendors provides 1st over, 2nd over, and 3rd over. The drop down to 2nd over is supposed to be amazing for highway passing power, and the launch mode for 1st sounds like it adds launch speed without needing to jump up to 4.10 gears.

I have the gear vendors unit with 3.55 gears. It works great but you may have to messaage your tranny tunnel plus make sure your pinion angle is right. May have to shim your rear axle for the correct angle.

That being said. I don't see how you will be able to use the unit as a six speed. It has a slight delay when it shifts. How do you expect to shift back down exactly when you shift up to 2nd gear. I just use it as an overdrive and I will use it to split 2 and 3 gear when racing.

You won't use the 1st over, 2nd over. Go read reviews from actual owners, 90% of them say it's useless for anything but a highway OD, with gear splitting too insignificant to produce an ET gain at the track. IMO selling your 727 and doing a 518 would be more cost effective and more useful than the GV. If I was in your shoes I would definitely still consider it.

Also FWIW, I almost never need to downshift to pass with my 1.8L stick shift daily driver. I would have to question the driver if passing downshifts are something you need to worry about with a 400+ cube engine.

Great info here, I love my 518, makes the car so much more enjoyable to drive.

http://www.cuda-challenger.com/cc/index.php?topic=84774.0

According to their website, overdrive in 1st is auto when you engage it:

"Another great feature of the GEAR VENDORS is that you will have a full 6 forward ratios when you switch to manual on the dashswitch. Pull into low, then hit our button (on the shifter or the floor), a red light appears indicating our Auto-Launch circuit - as you are accelerating through 1st gear the overdrive will automatically shift to 1st-over. This is directly related to the rear end ratio in the car - so that a 4.56 rear car shifts earlier than a 3.55 etc. If you have a 3.25 or 3.55 rear this brings a whole new level of performance and has a whole bunch more torque multiplication than you have ever felt in your car before. With a 3.55 rear for example the torque multiplication in 1st-over is more than 4.56 diff car would have in 2nd - awesome performance gains. After you have revved up in 1st-over then shift to 2nd and turn us off. Then rev back up and hit the button for 2nd-over for the same benefit (that 3.55 example now get a 4.01 gear)."

I like to keep a balanced view of products I'm researching, could you link me to some discussions? I keep finding positive reviews.

You would need bionic body parts to be able to quickly shift into and out of the GV OD if you expect to improve your times over a standard automatic. The gear splitting feature is a BS marketing gimmick that really only applies to limited rpm mills used for towing and such.
I'd say higher than 90% simply consider the add-on as a 4th gear, not the 1, 1 over, etc.

I'm too lazy to do a search for you, but there's been plenty of discussion about it on this website coming from actual GV owners. Overdrives are great, makes these old cars way more driveable. I wouldn't put too much faith in the gear splitting marketing goodness. Some food for thought, a 408 or 440 has a very broad torque curve. A 2.45 first gear x .8 = 1.96. Second gear is 1.45, close enough that a good aftermarket torque converter should hide most of that difference. A 1.45 second gear x .8 = 1.16. Third is 1.00.

I grew up driving a 2-ton grain truck. When you are hauling 30,000 lb of truck and wheat with a 304 cubic inch engine, split shifting with the two-speed rear end helped to get up to speed faster. You have many seconds between each shift, like 8 or so at full throttle.

The GearVendors overdrive IS the Laycock deNormanville overdrive that was used in British sports cars in the '50s and was used behind Volvo four speeds in the '70s, when they didn't want to have to buy a 5-speed. At the time, even with a 2-liter four cylinder pulling the 245 wagon, no one ever tried to do any split shifting. This is the same as what happened in the States in the '50s with the Borg-Warner overdrive found behind many 3-speed manuals. The shift pattern was 1,2,3,OD. For the Volvo it was 1,2,3,4,OD.

It takes about a second to shift into Overdrive and I think you have to get off the gas a little. On a 0-60 run in 6 seconds, where is the time to shift the overdrive box?

I think the GearVendors people would tell you they aren't advertising that at all. They are advertising the extra ratios that allow one to tailor the gear ratio to conditions. For example, going over a 10,000ft mountain pass in a pickup with a typical granny 4-speed can mean you spend several miles in 1.7:1 ratio Third because it won't pull Fourth at that attitude. So there you are with the engine singing along for mile after mile. Yet every time you stick it into Fourth the truck slows down to a crawl. It'd be nice to have a gear in between. That's what the GearVendors can do. Shift down into Third and regain your speed, then shift into OD. Third OD has an overall ratio of 1.36 which the engine can pull. Everything is so much more relaxed.

That's the other advantage of the OD besides flatland cruising.

Knowing the origins of the GearVendors OD it is amazing to me that they have increased its torque capacity by something like a factor of three.

BTW, the internal workings of the GV look very similar to innards of a TorqueFlite, a planetary gear system with a multidisc clutch. The pressure for the clutch is provided by a pump in the casing. Hint: If the pump inlet gets clogged the OD won't work, but you still will have direct drive.

R.

My Dart has a stockish 318 with A518 behind it and 3.55 gears in the rearaxle.
With a more torqy-er engine I think I would like to use 3.23 gears.

The A518 adds more driveline drag then a A500 transmission which is based off a 904 (which also have a better first gear gearing).

Okay I think I understand now. The Auto launch works well for 11 second or slower cars. In a 3 speed automatic you would engage the overdrive BEFORE you start driving while the column shift is in first. As you take off the electronics automatically shift into 1st over and then you manually shift into 2nd and hit the button again. I see where there would be no time if your car is 10 seconds or faster. I saw one conversation mention that Gear Vendors makes a AutoShift Sequencer to add on to the overdrive if your car is 10 seconds or faster, but I'm not worried about that. At this time I don't plan on building my car into a 6 or 8 second car and like you guys stated, the main thing I'm after is highway cruising rpm with 3.55 gears. That 518 swap DaytonaTurbo recommends is sounding more interesting. Thanks for all your input so far

This is the point where we end the gear splitting discussion. It's not needed in a torquey engine with a broad rpm range.


The only thing I'd like to add to the 518 swap is there are many pros mentioned. I've done it and liked it, from a 904 to a 518 to a 5 speed manual.
The only cons against it is, it's not an efficient transmission. Without taking over the thread with my data I'll condense it. With my 904, excellent mileage but poor acceleration due to tall 1st and tall rear ratio. 518 was quicker due to steeper rear but the mileage was still poor, I blame the lack of efficiency, the only advantage was high cruising speed and low rpm due to tall overdrive. Finally the 5 spd gained me 3 mph in the 1/4 and 3 mpg while speeding.

Just want to add, if you go 518 you need a steep rear gear. The 1st gear is tall and so is the o.d.