Thinking about a Gear Vendors OD. Can Anybody Give Some Guidance?

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harrisonm

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I drove my 69 340 4 speed Barracuda to a car show on Saturday. It was about 90 miles each way. Every time I drive my car on the highway, I think about how nice an overdrive would be. I have 205/70/14 tires (25.4” tall) and an 833 with 1:1 final ratio. At 65 miles per hour, I am at about 3100 RPM. I guess that isn’t the end of the world, but after a while, it is a little nerve racking to me. It would be SO much nicer to be cruising at 2200 (or so) instead. I found some older threads about Gear vendor installations, but nothing current. I REFUSE to buy one of Passon’s 5 speed transmissions, and I really don’t want to go the Silversport 5 speed route. That looks like way too much work. The Gear Vendors installation LOOKS easier on paper. Any thoughts?
 
The GV is a lot easier to install but also has an overdrive ratio that isn't that great.
I had a GV years ago. I had 4.10 gears with it at first but changed to 3.91s later. The GV ratio of .78 did make a difference in how the car felt on the highway but the Tremec 5 speed I have now has a .64 OD. Now that really made a difference. That is a 36% rpm reduction compared to the 22% that the GV unit offers.

If you ordered the Tremec, you could recoup some of the cost by selling your 4 speed stuff.

Check out my thread on my Tremec installation. It is very thorough. I even included a list of what everything cost me.

Tremec 5 speed conversion in a 1970 Charger
 
I have a GVOD, LOVE IT. I'd highly recommend one to anyone thinking about it. IT's a game changer.

But...I would not run on e behind a 4 speed. I'd get an OD manual trans first.
 
I have a GVOD, LOVE IT. I'd highly recommend one to anyone thinking about it. IT's a game changer.

But...I would not run on e behind a 4 speed. I'd get an OD manual trans first.
My buddy had the after market 4 speed (4th gear)OD gear set swap using the factory case. It worked well for him. I forget the final ratio, but like Kern Dog said, the gear vendors OD ratio just didn't quite cut it for the $.
 
The new tkx transmission has a midshift shifter relocation option, and without getting that intensive, you can even flip the shifter longitudinal to try and hit the hole and the floor. They are pretty compact, and measurements are avail online. Just something to ponder.
 
The Gear Vendors installation LOOKS easier on paper. Any thoughts?
Your A833 ratios should be 2.66-1.92-1.40-1.00
The GVod has a ratio of .78
With 25.4" tires(79.8 roll-out) and 3.55s, 65= 3050 by the math.
The GVod would drop that to .78, =2380
To get to 2200 you would need 2200/2380 x 3.55s =3.28s, which rounds to 3.23s; and 65=2170rpm.

Your shift splits are/ would be;
.72-.73-.71 and .78 into od.
But I shift mine into 3-od after third and then into 4od. This changes the splits to
.72-.73-.78-.71 giving you a short 4th, and a near-normal overdrive drop. ( the A500/518s have a .69od)

Now, if you were to swap in a Commando 3.09 low gearset, and 3.23s, AND shift like I do; then your ratios would be;
3.09-1.92-1.40-1.09-.78 and an excellent split-progression of
.62-.73-.78-.71 into od. and your roadgears would be
9.98-6.20-4.52-3.52-2.52 compared to the current
9.44-6.82-4.97-3.55.. As you can see, the New Combo, gives you
~6% more First gear,
~9% less Second and Third,
the same Fourth,
and then the deep-overdrive
I love mine.
But, with 3.23s, your 340 is gonna notice the slight handicap in Second and Third.
Possibly a better solution is 3.73s for roadgears of
11.52-7.16-5.22-3.73-2.91 and 65=2500rpm compared to the current
>9.44-6.82-4.97-3.55 of course, with 3.73s you might not need the Commando Low, so then
9.82-7.16-5.22-3.73-2.91
The 3.73s will get you 3.73/3.55=Plus 5.1% in every gear, yet cruise at minus 18%..
Plus 5% TM/Torque Multiplication will make your 340 feel like it just grew 17.3 cubes.
As to cruising at 2500;
it is much easier to give the engine the ignition timing it so desperately wants ( maybe high 50s or more), than is 2200. Once the engine has what it wants, it will be making more power at cruise rpm, more than it needs, much more..... so you can then lean it out for cruising....... and get some decent mpgs. Bonus.

I have been enjoying mine since 2004.
Having said that, if I had the money to buy an actual 5-speed, I think I would rather have the od in the box. And the reason is this; with the GVod, and the supplied computer module, the shift into od is pretty slow.
You can bypass the module, and it shifts faster than anything you can do, and faster than any automatic I have ever shifted. Now;
You can upshift into od at full power no problem. And you can outshift it no problem, But you cannot allow the driveshaft to have more torque than the engine. So to backshift, you gotta clutch it. If you don't, the unit will instantly toast itself. AND, you cannot have it engaged when backing up; again it will instantly break.
Finally, it outshifts slightly slower than it engages.
The module protects the unit against all these things.
I ran the module for like a day.
Then I hot-wired it, lol. That was in 2004.
Yes I broke it......... But just once lol.
After that, I put a red LED on my tach to tell me when the unit was engaged, and I wired it, thru a relay, to my back-up circuit, so it automatically powers down in reverse. Problems solved.
==================
Until you have the notion to split shift it........
The regular 2.66-low 4-speed does not lend itself well to splitting. The ratios are crappy. So yur Ok on that.
But BOTH the A833od, and the Commando, have a wide-enough 1-2 split to use the splitter more or less to run up the middle. The od unit is better but I found that the 2-3 split in that box is pretty wide, even for my hi-pressure 367. So I more or less, ended up having, that is HAVING, to split every gear all the time. And while having SEVEN usable gears sounds Neat-O, the truth is that for me, Second gear is the gear of choice, and I like the road-ratio to be close to but not much over 7.00, and that is impossible to achieve with the A833-od box, unless I ran 4.10s to 4.30s. I ran the 4.30s, which made the starter-gear to be ~13.29 which I found unacceptable. I tried it for about a year but that was enough.
But splitting works dang good with the Commando gears, and 3.55s.. The roadgears are;
10.97-8.56-6.82-5.32 ; 4.97-3.88-3.55-2.77; GV in red.
When I want to show off, I use the first four in sequence, and 93=6170rpm; this is what the car does in the Eighth-Mile.
The rest of the time, I shift; 10.97-6.82-4.97-3.88-2.77 (65=2240rpm with 27" tires). 3.55 gear is rarely used now. The splits are nicely progressive at; .62-.73-.78-.71into od
The first four ratios split thus; .78-.80-.78 that's pretty tight.
So, I mean, I'm not sorry I ever bought the GVod, cuz it is definitely fun, and versatile; and at the time (2004) IMO it was the best choice.
 
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How much do you wail on your transmission??? If this isn't a drag car with big torque/horsepower, why not just swap in a Chrysler OD four speed? It seems to be the simplest solution. Same driveshaft, all the same hook ups, a lot less cost, one less system to have problems compared to the GV. Don't you have to do some serious floor pan work to use the GV set up in an A body?
 
2.94 rear gears.

You can always drop it down into 3rd gear if you want some more snap.
 
I don't know. That's a lot of jack for "only" a .78 OD ratio. To me, the floor pan mods are well worth a different transmission.
 
Here is my install;
When I got the unit in about 2002, it was only available with a long-tail adapter,
1) so I had to install a long mainshaft into the box; no biggie for me.
2) So I took the opportunity to also install a Passon alloy box.
3) The long-tail adapter is a B/E clone, so the front shifter pad is right inside the crossmember, and the front shifter boss hit that crossmember. It's aluminum so I zipped it right off.
4) Then I hung the unit and jacked the trans into position. The unit hit the floor-pan before the cross-member could be fully seated. I marked the tunnel by jacking the unit hard into it. It only hit the tunnel in two places. I dropped the unit, and went for my BFH. I clearanced the tunnel with a few well-placed smacks.
5) then re-installed the unit. Good job, the unit now hit the tunnel in a full continuous half-ring so that was gonna be as good as it gets. But the crossmember was still about a quarter inch short.
6) many years prior, I had installed a Milodon Roadrace pan with TTI headers, and to make it work, I had installed the later spool-mount x-member (with a poly mount) and jacked the engine up about a half inch for steering clearance. I chalked the lack of clearance at the GV to the engine not being in the factory place. No biggie; I dug out my die grinder and slotted out the spool-mount holes and bingo, in it went.
7) together with the Schumacher engine torque-strap, the unit has never rattled.
8) so OK, after the driveshaft was shortened and installed, the pinion angle needed to be adjusted a tad to get rid of a mysterious vibration. I took the opportunity to move the rear axle back, to the limit of the studs on the front spring hangers, about 3/8 inch, to install 28" tires.
9) that just left mounting the shifter.
You gotta build a new shifter mount, and you only have the rear mount on the tail left. I could have built that mount to reuse the factory floor-hole location. But I never liked that location in the first place, And, having bucket seats, I thought to myself, that here is a golden opportunity to put the shifter where it shoulddabin in the first place. So I moved the stick back about 7 inches. This opened up the option to also move it laterally, so I did. This opened up the option to raise it. Since I had this ancient Mr.Gasket Bang! short-stick Shifter, I raised the thing high enough to install the top bolt from inside the cabin. So the shifter ended up falling to hand with me in the saddle, and my arm hanging near vertical. So again, I used this opportunity to adjust the height of my bucket, and that was that.
10) Ok that left the shift-rods to deal with. I went to the machine-shop and got me some tubing with the right-sized center-bore for fitting the cut-off parts of some old Chevy shifter rods that I had kicking around. I think the tubing was called "seamless" and maybe "cold-rolled", and it did not have the usual center weld-seam in it. Anyways, I bent me up some nice solid rods, and have not, since that day, ever missed a shift again. I think, IIRC the center hole of that tubing was 3/8; but it mightabin 7/16. In either case, they are quite "robust".
11) finally, I had the Chevy speed-o adapter to deal with, but the GV folks supplied the right parts, the first time, for the 3.55s that I was running. Of course every time I changed chunks, this required a trip to the Chevy place for a new gear. I now have a box full of them, lol.

So OK, it's NOT a straight bolt-in;
but the fact is, that clearancing the tunnel only took a few well-placed hammer-blows, to stretch the metal in a couple of places. This was the smallest problem of all for me, and in my case, was mostly due to the non-stock location of the engine.
My car is also lowered, and on softer street springs, and on a narrowed rear end, with offset springs; so I may not have set the pinion angle quite right in the first place.
So I mean, some of my challenges might have been self-created. But I want to re-iterate;
clearancing the tunnel only took a few well-placed hammer-blows.



As for "only" a .78 overdrive ratio....
Well, whatever;
it drops OP's 3050rpm with 3.55s, to 2380, which is 670 rpm, or 22% of 3050, which is the equivalent of dropping those 3.55s to 2.77s; so ................ I fail to see .78 as a problem.
In fact, if it was any lower, and the engine has a bit of a cam as they say, it would be as good as impossible to give the engine the cruise-timing it needs for optimum fuel-economy. ....... which is more than half the reason I installed it in the first place. I saved the cost of it, in fuel-savings, in less than five years of use as a DD, and, in the meantime, enjoyed the other benefits. If I stopped to do the math, I probable saved it in three years.
Oh, and, my 367 now has well over 100,000 miles on it, and a recent compression test shows that the pressure is still up there. So I mean, the GVod fits into the OP's original post quite well. Like 2380rpm is a very nice cruise-rpm. and I showed how to optimize even that.

Having said that;
OP
rev up your engine, in Neutral, until it the vacuum levels off. Whatever the rpm gets to, you can consider that the lowest efficient cruise rpm of the combo, in it's current state. My guess is that it will peak in the range of 1800 to 2400, depending on your cam.
Say it peaks at 2200.
Now, without regard to the numbers, keep the rpm at 2200 and just keep advancing the timing until more advance does NOT produce more rpm. Now read the timing at that 2200rpm. Write it down, then put the timing back.
Now, my guess is that the number will be in the range of 50* to maybe 56*. Whatever you read is what the engine wants. How are you gonna give it to her?
Your Vcan is worth what? Maybe 12 degrees?
Your idle-timing is what? Maybe 18*?
Your centrifical, by 2200, is bringing in what? Maybe 10*?
for a total of 40*?
How are you gonna stretch that to 50/56? If you don't, your cruise-timing will be seriously retarded; and your fuel-economy will be seriously lacking.
You can modify your Vcan to in the range of 22/24, so from 12, let's say you get an extra 10*, so now you are at 50* and on the lower edge of adequate, but could be still 6 degrees or more, short of optimum.
Can you get it by increasing idle-timing to 24*? Or by increasing the rate of the centrifical? Well maybe; but if this causes detonation under Power, then no.
But increasing your Cruise speed to 2400, might get you 2 or 3 degrees of centrifical, and now yur up to say 53 degrees. Perhaps that is all your engine wants.
Go back and repeat the cruise-timing test at 2400 and see.
Happy HotRodding
 
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I have had one behind the Passon aluminum 833 / street Hemi in my Duster for over a decade. After initially driving around doing the split-shift thing, that got shelved and now is only used on the expressway where I am going over 60MPH.

Small mod (cutting ,no BFH) to the trans tunnel to keep my driveline angle at 1.5 degrees down towards the differential.

It is pretty simple, drive it like your standard Mopar 4-speed until you go over 60, engage the OD and drop the revs. I have a 30" tall tire with a 4:30 gear. 65 MPH is around 2400 RPM....the sweet spot.

I like the A855 5-speed, but for me, it does not carry the time tested reputation of the 833.

I would do it again.

20220714_124829.jpg
 
Having said that;
OP
rev up your engine, in Neutral, until it the vacuum levels off. Whatever the rpm gets to, you can consider that the lowest efficient cruise rpm of the combo, in it's current state. My guess is that it will peak in the range of 1800 to 2400, depending on your cam.
Say it peaks at 2200.
Now, without regard to the numbers, keep the rpm at 2200 and just keep advancing the timing until more advance does NOT produce more rpm. Now read the timing at that 2200rpm. Write it down, then put the timing back.
Now, my guess is that the number will be in the range of 50* to maybe 56*. Whatever you read is what the engine wants. How are you gonna give it to her?
Your Vcan is worth what? Maybe 12 degrees?
Your idle-timing is what? Maybe 18*?
Your centrifical, by 2200, is bringing in what? Maybe 10*?
for a total of 40*?
How are you gonna stretch that to 50/56? If you don't, your cruise-timing will be seriously retarded; and your fuel-economy will be seriously lacking.
You can modify your Vcan to in the range of 22/24, so from 12, let's say you get an extra 10*, so now you are at 50* and on the lower edge of adequate, but could be still 6 degrees or more, short of optimum.
Can you get it by increasing idle-timing to 24*? Or by increasing the rate of the centrifical? Well maybe; but if this causes detonation under Power, then no.
But increasing your Cruise speed to 2400, might get you 2 or 3 degrees of centrifical, and now yur up to say 53 degrees. Perhaps that is all your engine wants.
Go back and repeat the cruise-timing test at 2400 and see.
Happy HotRodding [/SIZE]

Either add vacuum advance (I have seen 24 degree cans, and I think there are ADJUSTABLE cans available) and adjust it to come in earlier, or reduce centrifugal advance and add initial timing (1 for 1) to compensate.

For a cruiser, considering the significant costs of the GV and the work required to install it, I would probably swap to either an 833OD or tall (2.94, 2.76) axle gears.
 
I love my GVOD. #.91 gears behind a 727. My 70 mph went from 3500 or so to 2700 or so. Much better all around.
 
You can buy the 18-spline heavy duty OD conversion gear set from Jamie Passon and add it to your existing 4 speed. You will have a heavier duty transmission and a better OD ratio than the GV. I had a GV unit on a 727 in a 71 Challenger. If I had that to do over again, I would have used a 518 and done the mods to the transmission that @1WildRT came up with years ago to just bolt it right in place.
 
You can buy the 18-spline heavy duty OD conversion gear set from Jamie Passon and add it to your existing 4 speed. You will have a heavier duty transmission and a better OD ratio than the GV. I had a GV unit on a 727 in a 71 Challenger. If I had that to do over again, I would have used a 518 and done the mods to the transmission that @1WildRT came up with years ago to just bolt it right in place.
Funny this popped up now.. I did my first 518 install about 25 years ago, two weeks ago I got the car back, the O/D still works great, and trust me it's good that it does, the car has 4:30 gears... But in O/D it acts like 2.94's....

I posted the photos of how I'd trimmed excess material off the trans & fabricated a crossmember once about 22 years ago and since then those photos have popped up probably 50+ times in posts I was reading. At one point US Cartool posted about a project they were getting ready to cut the floor and crossmember out of to allow a 518 to be installed.... I PMed him and sent pictures.... Eventually they wound up marketing the crossmember/mount... Still being sold on their website...
 
For anyone interest Passon has over drive gear sets for the 833 back in stock...$2800
 
I love my GVOD. #.91 gears behind a 727. My 70 mph went from 3500 or so to 2700 or so. Much better all around.
How much surgery and expense is that to install...especially compared to an A518, or even a Silver Sport "A41" swap?
Funny this popped up now.. I did my first 518 install about 25 years ago, two weeks ago I got the car back, the O/D still works great, and trust me it's good that it does, the car has 4:30 gears... But in O/D it acts like 2.94's....

I posted the photos of how I'd trimmed excess material off the trans & fabricated a crossmember once about 22 years ago and since then those photos have popped up probably 50+ times in posts I was reading. At one point US Cartool posted about a project they were getting ready to cut the floor and crossmember out of to allow a 518 to be installed.... I PMed him and sent pictures.... Eventually they wound up marketing the crossmember/mount... Still being sold on their website...
Nice. I hope you get royalties. :thumbsup:
 
How much surgery and expense is that to install...especially compared to an A518, or even a Silver Sport "A41" swap?

Nice. I hope you get royalties. :thumbsup:


This was all I needed to do on my 73 scamp. Air hammer worked great. I had a little trouble because my tailshaft retaining clip was on the side of the transmission, but that was all. Still doable. See that thread to know what I was up against. As to expense, I had to have the driveshaft shortened and that was maybe $200. I got mine new from a member here for $2000.
 
I have had one behind the Passon aluminum 833 / street Hemi in my Duster for over a decade. After initially driving around doing the split-shift thing, that got shelved and now is only used on the expressway where I am going over 60MPH.

Small mod (cutting ,no BFH) to the trans tunnel to keep my driveline angle at 1.5 degrees down towards the differential.

It is pretty simple, drive it like your standard Mopar 4-speed until you go over 60, engage the OD and drop the revs. I have a 30" tall tire with a 4:30 gear. 65 MPH is around 2400 RPM....the sweet spot.

I like the A855 5-speed, but for me, it does not carry the time tested reputation of the 833.

I would do it again.

View attachment 1715994618
Would you happen to have photos of this installed, or the mods required to install it?
 
the gear vendors is a Laycock de Normanville overdrive, a constant on british cars of 50s -70s taxis luxury cars and small trucks.

which used a long obsolete double latching relay and a bunch of switches on the gear linkage, made by lucas to switch it out when you were doing something that would break it, as per situations mentioned above.

the main market these days is pickup trucks with truck gearing for day to day use and the overdrive for traveling economically to "site" of work.


latest versions made by Laycock enginerring/GKN for mitsubishi and Volvo P-type i think
believe gear vendors must have a nice collaborative arrangement with GKN
and who knows if they take units as manufactured or they toughen them up...
Volvo 740 turbo was a heavy car with decent torque so maybe not...hard to say

P version is a big shaft version J is a small shaft version
all previous versions designed really for small capacity motor use.

one thing you used to be able to get was a stand alone unit that had a splined input and output.

the unit was mounted somewhere in the middle of the chassis in the middle of the tail shaft

i think the unit on some mitsubishi pickups was like that.

if you could find one for low $$$ that might be a way in to OD for say a slant or 318 with no transmission work at all

Dave

remote_overdrive_unit.jpg
 
oh yeah early versions of the Range Rover used 904 based trans...laycock from one of them might be an option as well. but you would be looking for a rare 1970s car where someone went mad on the options order form
 
I have run the passon 18 spline hemi overdrive gears in my a833 for a bunch of years. No complaints
28" tire and 4.30 gears. Cruises awesome.

I just finished my install of a t56 into the same car but now with a big block. I have not run the car much due to other issues. I swapped in a dana 60 with 4.10 gears now.

The passon od is now going into a different vehicle.

I have another passon od gearset for another future project. Just have found the project yet :-D
 
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