80 Grit!

[Grabinov911]

Finally decided...

Well guys I have noodled back and forth over whether I'd rather convert the car to a four (or five) speed overdrive or bolt on a Gear Vendor. In the end it came down to cost. No matter how you slice it, it's $4,000 to $5,000 to convert an automatic 727 car to a manual overdrive transmission. I was able to get a good deal on a Gear Vendor,and it came highly recommended by a reputable speed-shop I work with here a lot. It's a bolt on two-speed transmission which replaces the tailshaft of the stock 727. The two gears are one-to-one and .78 to one, thats a 22% overdrive, or a 22% reduction in RPM at any speed from my current. If shifted correctly, it allows either an automatic overdrive which comes in at around 47mph, or a full "6 speeds" with first, first-over; second, second-over and third, third-over. You guys probably already know all this, but since I've had trouble locating a good Gear Vendor build thread, I'm going to try to do one here for the next guy considering it. You may remember, my goal is road racing with long high-speed runs like the Silver State, so I need the sustained high speed the overdrive will allow. So here we go:

What's in the box







The tailshaft is nearly 20" and replaces the stock 17" tailshaft. The Gear Vendor goes behind that. The two together are about 29". That's 12" longer than the stock setup, which means a new (or cut factory) driveshaft. For now it looks like the Gear Vendor literally just hangs on the back of the new tailshaft, supported by the tailshaft to transmission connection and the transmission support crossmember. You can see the machined "flat" with the two bolts where the new tailshaft bolts to the factory crossmember. It looks like a lot of weight cantilevered off the back of the new tailshaft, but we'll see. It's certainly a robust looking casting. And I'm sure this is not their first time. The little "digital box" in the center of the picture is their computer, which keeps track of the position of the transmission (overdrive on/off), the position of the in-car controls and the speed of the vehicle.

I started working on the removal of the factory parts tonight but ran into a roadblock when I found I needed a 45-degree or 90-degree snap ring pliers to get the factory tailshaft off. I'll try to locate one tomorrow and keep pushing forward.

You can see the digital signal generator for my Dakota Digital speedometer with the transmission crossmember and the driveshaft removed. I moved the right side exhaust pipe slightly away to get the crossmember out.





I held up the transmission with a floor jack to get the crossmember out, and then lowered it about an inch to make it a little easier to get to the upper tailshaft mounting bolts. The bottom two, which look like nuts which would thread off of the studs coming out of the transmission case, are in fact studs with a fixed nut. When you "loosen the nut", the whole stud comes out. I am not sure what the purpose of that is, but it is...

After I lowered the trans (should have checked first) I put an angle-finder on the air filter just to make sure I could tell if the jack moved. Interestingly, it was perfectly level. Don't forget to check your fan to radiator clearance as lowering your transmission will tilt your engine and move your fan forward at the bottom a little. I had plenty of room but was glad I thought to check.

 

[5.7 hemi]

Whom did ya get the gear vendors thru?

 

[Grabinov911]

More progress, and less...



Once you get the tailshaft housing mounting bolts (6) out, you have to spread the the "lock ring" in order to allow the housing to slide off of the transmission tailshaft. Once you remove the small cover plate (held on by two phillips screws) you can see the lock ring. BUT WHAT YOU CANT SEE IS THAT IT'S NOT A NORMAL LOCK RING. Unlike a normal lock ring which has tiny holes in the end to accept a lock ring pliers, this one has none. All you can do to spread it far enough is to put something between the two "arms" of the ring and spread them apart. This is frustrating as any tool you try will just want to slide out.



I eventually used a Channel Lock pliers with the 90 degree bend extensions. Even so, it's no fun.



With the tail housing off, you can see how the ring sits inside.



And you can see the tailshaft bearing on the tailshaft, with the slot where the lock ring resides. The "gear" on the shaft to the left turns the stock speedometer drive gear.



With the tailshaft housing removed, you need to remove the parking pawl from the factory housing and add it into the Gear Vendor housing. This is described in the instructions, except that the moon-shaped part (shown in the factory housing and then the Gear Vendor housing) under the lock ring really didn't want to line up in the new housing. In the end I had to tap it in with a hammer, worried that if it didn't go I'd never get it out, but it did...





Then move the large lock ring to the new housing and push the whole thing back onto the transmission. It's kind of another battle to spread the lock ring as the housing goes on. I got the ring out around the bearing but couldn't get it to fall into the groove. Then I realized that the tailshaft itself moves forward and aft. A little push with a screwdriver and the lock ring dropped into the groove. The lock ring and cover is blocked by the transmission crossmember mount in the next photos.



Strangely, with the new housing in place, it became apparent that it was not centered in the driveshaft tunnel! I thought my way around in circles about this for hours. Was the original housing centered? None of my prior pictures were at an angle where I could tell. Was the Gear Vendor housing offset? Couldn't be. The transmission tailshaft is straight! Nonetheless, you can "clearly" see that the housing is to the right of the tunnel (right of the car).



This played hell with the clearance as I raised the Gear Vendor into position. It rubbed significantly on the right side of the tunnel. I spent this evening with the air hammer trying to make space, but I was left with the question: Why is the tailshaft not centered in the driveshaft tunnel?

 

[Kern Dog]

I hate to break it to you but the speedometer cable is going to be trouble. I had a GV in my Charger and had to bang on the floor to get clearance for the speedo cable and housing. Even so, I still had the GV too low to avoid vibration problems.
The problem is, the GV unit places the speedo hole at approx 10;00 position, pointing a bit up toward the floor. The speedo is NOT at a 90 degree angle (9:00 position) like the stock speedo in the stock tailshaft. The fact that you have to cram the GV closer to the floor to get the right driveline angles, (Denting for clearance) this means that the end of the speedo cable is right against the floor. I had a 90 degree adapter that worked great until it broke, then I learned that nobody was making replacements. Your Dakota Digital pulse generator is not adaptable as far as I know. From here, it looks like you will need to somehow create a space for the speedo cable to reside. Maybe cut the floor and build a small "doghouse" type half-round dome or something. I don't think simply hitting it with a hammer will be enough.
Hate to be a pisser but I feel better when I know the obstacles before I get neck deep in a project.

- - - Updated - - -

I just went back to read some of the earlier stuff in this thread. I like that radiator and shroud. I'm North of you and East of Sacramento. What was the cost of the radiator setup with shroud?

 

[HawkRod]

Thanks for the detailed write up with the GV - very helpful for those considering it. The GV is still a fallback possibility for me although I have a manual transmission (primary is a Passion A-855 5 speed manual).

I have heard that split shifting each gear really doesn't work well. The GV will absolutely allow you to run each gear in regular and O/D mode, giving you 6 total gears as a possibility, but I have read where some say it shifts too slow (from when you push the button until it actually engages) to be effective for drag racing. They just shift it once. Having said that, I cannot vouch for that to be true or false, as I have no personal experience with a GV.

Best of luck with your build.

 

[Kern Dog]

The gear splitting gimmick might be a cool thing for diesels or anyone hauling cargo, but for a fast street car, I just can't see going back and forth with the OD. I agree that the engagement isn't lightning fast, so that surely factors in.
I wish the GV came in a taller ratio, maybe in the .67-.70 range.

 

[Grabinov911]

The problem is, the GV unit places the speedo hole at approx 10;00 position, pointing a bit up toward the floor. The speedo is NOT at a 90 degree angle (9:00 position) like the stock speedo in the stock tailshaft. Your Dakota Digital pulse generator is not adaptable as far as I know.

Answering some questions above and adding to the GV thread:

The latest variation of the Speedometer Drive (I've heard it's been updated over the years) is clocked at approximately the 7:30 position, about 225 degrees from 0 at the top. This is not very well indicated in the instructions, but the part helps somewhat to make it self explanatory. You can see that it has a raised "catch" for the yoke that holds the part into the overdrive unit. It fits in any position, but will only lock down in this one. It's a VERY tight interference fit with an "O" ring. I wouldn't want to push it in clocked incorrectly. You'd break it in half getting it out. You'll also note that it's a 90 degree output right from them.





This photo shows the short 14" speedometer cable which they provide. It attaches to the Speedometer Drive at the end not shown. The"output" end hooks to their digital signal generator to run their computer. It has two wires running from it. Attached to THAT signal generator is the (WAY sexier) Dakota Digital signal generator, with it's high-end OEM-type electrical coupler. In place would be your factory speedometer cable if you were running one. There is probably a way to send the signal from ONE signal generator to both computers, but I'm not gonna mess with that for now. With a 493 inch motor, I can afford to spin both!



Still hammering...

 

[Grabinov911]

Not having much fun right now.

I am NOW running into fitment problems with the GV in the trans tunnel. In order to fit the trans crossmember in the original holes, the "bolt ring" around their tailshaft housing is literally touching the tunnel for about 70 percent of the "top half" of the circle. Look at the picture below and imagine the whole thing 3" higher than it is now. The four "top right" bolt holes are touching the tunnel when the housing is all the way up in the stock position.

View attachment 291538

The GV guys are helpful as can be but when I spoke to them today they suggested I lower the crossmember by "100 thousandths" by widening the holes, but I would literally have to lower it an inch from the factory position to get the housing away from the tunnel. THAT isn't gonna work without making a mess of the driveline, and there is no way to do it by enlarging the holes in the crossmember. Only thing I can think of right now is to either shorten the rubber/steel trans mount (seen in the above photo) or cut away some of the trans tunnel. The spot I would be cutting is literally under the center "buddy seat", so totally invisible, but it's a little more than I expected to have to do for this install (as Kern mentioned about knowing what you're getting into). It's actually not the cutting that bothers me, it's the welding of the new part. I have Dynamat over the sole floor of the car, and its going to melt if I try to weld anything. What a mess that would be.

Looks like sheet metal and pop rivets. Hey. Then it would be a REAL race car! OK. You guys are making me make me laugh... I feel a little better.

 

[Kern Dog]

There must have been some changes that mine didn't have. Mine was a first gen design and it had a bolt-on yoke. Here are the pix of the trans crossmember I modified. Mine is an original 1970 B body crossmember. It had the stock cube looking trans mount. I converterd it to the later style spool mount than all 1971 B body cars had.

- - - Updated - - -

Trans mount

 

[Grabinov911]

That's an idea. Here it is from the Schumacher website.

View attachment 291546

I wonder how much shorter it is than the stock mount. By drilling the "cross hole" in the right place on the bolt-in crossmember I could basically set the proper height of the transmission in the tunnel.

 

[Kern Dog]

That's an idea. Here it is from the Schumacher website.

View attachment 291546
By drilling the "cross hole" in the right place on the bolt-in crossmember I could basically set the proper height of the transmission in the tunnel.

Yes.

 

[Grabinov911]

I have a riddle for you:

Riddle: How do you add 27 ounces of fluid to an Overdrive unit and not have it come out any heavier than when you started?

Answer: Add the fluid BEFORE installing the Overdrive and allow it to drain out the front onto your workbench. If you wait 60 seconds, the fluid will have emptied completely and the weight of the Overdrive will be the same as before you added the fluid.

ASK ME HOW I KNOW. The instructions actually talk about filling the Overdrive BEFORE they talk about installing the Overdrive. Given how difficult it is to fill once installed, I attempted to perform the procedures in that order. That's apparently not what they mean, as the front of the Overdrive is full of holes - which I guess allow the fluid to get to the shaft to tailshaft joint. You're gonna want to fill the Overdrive after it's installed on the tailshaft housing - Oh, WITH the gasket in place - probably using a pump like you would to fill a differential.

Oh!

And did you ever hear the one about how you add 54 ounces of fluid to an Overdrive that only holds 27? Drain the first 27 out the front! Hah Hah Hah...

 

[Hemirunner]

I ended up buying the shorter 8" version of the GVOD for a 727. I wanted to keep the driveshaft as long as possible and I didn't want the tunnel issues most have. The shorter version keeps most of the mass forward and in the larger area of the tunnel. I modified the crossmember to lower the trans a little and then all I had to do was a little hammer work to get the housing to clear the tunnel. Zero vibration issues and the car has been 10.90 at 4200# so I assume it works lol.

 

[Kern Dog]

For those that worry about the GV being cantilevered so far past the trans mount: The 727 in the Full Time 4wd trucks from 1975-79 had an iron case model 203 Transfer Case mounted the same way. THOSE are some incredibly heavy units, all being supported by 7 little 3/8" bolts!

 

[Grabinov911]

For those that worry about the GV being cantilevered so far past the trans mount: The 727 in the Full Time 4wd trucks from 1975-79 had an iron case model 203 Transfer Case mounted the same way. THOSE are some incredibly heavy units, all being supported by 7 little 3/8" bolts!

I actually wondered about that myself, but once you get the thing bolted up it is pretty clear that it's not going anywhere. Objectively, you're talking about a 30 pound weight hanging 12 or so inches behind the last support on a frame-stiffened 6" aluminum tube (the new tailshaft housing) with 1/8" wall thickness. It's nothing from a pure engineering standpoint.

I ordered a custom 3.5" diameter 0.125 wall aluminum driveshaft today from Inland Empire Driveline Service. They appear to know a thing or two about driveshafts. The distance from the pinion yoke on the diff to the tip of the GV tailshaft is 39.5" so that's the length I gave them. They of course know how to get the tubes and yokes welded up to make that length. I supplied them with the slip-yoke provided by GV, which uses a Spicer 1350 U-joint (rated for 1,200 ft-lbs.), for the front of the driveshaft. The rear will be a combo-joint which is a Spicer 1330 on the driveshaft side and 7290 on the pinion yoke side (stock big block Mopar size). Unfortunately no one manufactures an aluminum 7290 yoke for the back of the driveshaft, so if you are going aluminum, you need this combo joint. It'll last more than the number of miles I'll ever drive in this car I'd guess.

I went with the 3.5" aluminum because of the critical velocity (driveshaft rpm) issue when using an overdrive transmission. All of a sudden your driveshaft is turning at 22% greater velocity than your engine. The stock 3" steel driveshaft turned one to one with engine RPM (in top gear) regardless of the transmission you were using (auto or manual), so it was unlikely to see much greater than 5,500 RPM, and only that for short bursts. At the same engine RPM, in overdrive the driveshaft now sees 6,710 RPM! Andy Finkbeiner says that the critical velocity for the stock 3" shaft is about 6,300 RPM. The only question then becomes: Can you actually pull 5,500 engine RPM in overdrive - if not, your driveshaft type may not matter anyway. For me, 5,500 RPM in 3rd is just about 120 MPH. In overdrive it would be about 145 MPH. I don't know if I'll be able to pull that top speed, but I don't want to grenade my driveshaft trying to find out.

Again according to Andy, The 3.5" aluminum shaft has a critical velocity of 7,400 RPM at the shaft, or 5,772 at the crank in overdrive. That is probably where my redline is anyway, and in any event equates to 160 MPH, which is probably faster than I'm gonna get to in overdrive without some additional horsepower. In other words, No Worries...

 

[Kern Dog]

The math is impressive. I wish i did more research when I had mine. I dealt with vibration that I'm sure Id have better luck with what I know now.

My GV was a 1st gen version. It had a bolt on yoke and I thought I was stuck with using a "slip & spline driveshaft like you see in the front of an old style 4 wheel drive truck. I figured that I'd sell the GV because of the vibration issues I had. The guy that bought mine told me the yoke unbolted to reveal a splined output shaft! I could have used a traditional drive shaft all along. Also, the shaft I had was based on a 3 inch core. I had 3.91 axle gears at the time with a 28" tire...Talk about some driveshaft RPM !! The leaf spring hangers I had in the car were modified Super Stock units. I drilled holes to mount the front spring eyes up higher to lower the car. I wasn't aware of what this did to pinion angle. Ahhh... The things that I know now!

 

[Grabinov911]

Driveshaft In

It's BEAUTY FULL!



I've included pictures of the 1350 U-Joint end (front) and the combo 1350/7290 end for anyone building one who wants to see. Length ended up being 39 1/3" from the joint-center on the yoke to the end of the tailshaft on the GV unit. That leaves 3/4" of "plunge depth" for the driveshaft to move in as the suspension compresses.





All together the shaft ended up centered nearly perfectly in the driveshaft tunnel (or under it at least).



I have one additional problem to contend with in terms of the installation, and that is that the right-side exhaust pipe contacts the bottom bolt on the GV unit (you can see it in the pic), and since both are essentially hard mounted to the same place - the block - there is no adjustment to be had. The main pipes in the exhaust need to be moved anyway as they hang down too low and rub on my driveway. One is about half-way worn through. They never really did fit right with my Schumacher headers.

I was dying to get on the road but couldn't see doing it without a way to power the GV unit so I ran a hard wire through a switch and a fuse straight two the solenoid. The switch is just zip-tied under the dash for now, which turns out not to be so great as it takes one hand to move the column shift lever and another to flip the switch. You should see me going up an on-ramp with my foot on the floor, leaning forward to reach the switch while shifting with my other hand and steering with my chin! I was able to sort-of split second gear, going from second to second over and then third direct and third over. That's gonna take some practice, and would be MUCH better with a floor shifter with an overdrive button on it. That's gonna be the way to go I think, or the GV -supplied "high-beam-style" floor button at least. I have a couple of electrical things I want to do so if I'm going to pull the gauge console out of the car I'll do them all at once and install the GV computer then.

I'll tell you this: Second to Second over sure feels faster than second to third, and that shift is easy. It's getting the OD off while shifting to third on the column that's tough. Third over on the freeway makes a big difference in the feel of the car even if the RPM change is only from say 3,000 to 2,400. Try it in your car. 2,400 is WAY quieter.Oh, and 3,000RPM in Overdrive is now about 85mph.

The OD doesn't seem to care where the throttle is (how hard on the gas you are or are not) when shifting up into overdrive, but it does shift more smoothly down if you are on the gas. Seems unintuitive, but if you blip the throttle as you shift down, as you would in a manual, you can actually "match revs" and barely feel the shift out of OD.

My electronic speedometer is out of whack due to the gear on the GV being different than the one I was calibrated for, but that would be an easy fix. I don't have any vibration problems that I can identify so far, but I do have one weird driveline problem. When I get off the gas, I get a "whine" from the driveline. No problems under acceleration or constant throttle, only when the rear end is turning the motor rather than vice versa. Driveline angles maybe? Need to look into that. Open to advice if anyone has it.

 

[Kern Dog]

I had that same type of whine on decelleration! I thought mine was due to excessive backlash in my diff!

 

[Cranky]

Typically, gear whine from the rear end on coast down is caused by the pinion gear being set too deep into the ring gear. Were you driving the car before the installation of the OD unit and hear a whine at that time? I've also heard people saying that they experienced some whine on coast down and it got louder when a new larger drive shaft was installed. I've never experienced that myself so I don't know if it's even possible. Usually gear whine is gear whine no matter what your angles are and I would hope your angles are not so bad that it would cause something to whine.

Kern Dog, how much slack do you have? I've seen some with a lot of back lash and yet still didn't whine. If you are checking with the axles in the housing and drive shaft attached, you may be seeing the slack in the splines too. Also, if the rear has a lot of miles, you may have other issues going on. I had one where the cross pin and carrier was badly worn and that by itself was showing up in nearly 1/8th turn in the drive shaft. Gear back lash vs spline clearance and wear are different things. Back lash on the gears is usually around .008 but with everything installed in the car, your spline clearances will show up to be a lot more than that so grabbing the drive shaft and twisting it back and forth won't give you a good feel of what your back lash really is. The ring gear has to be held still in order to check gear lash correctly.

 

[Lets Roll]

From what I have heard the pinion angles have to be adjusted. Something about the angles being equal.. I think.