I don't think you'd want to try to create "half gears" by hitting the overdrive between lower gears. Normally, an overdrive is like having a 5th gear beyond 4th. You go up through the first 4 gears normally. When you're cruising in 4th with light load and the engine's wound up, then you punch in the overdrive which keeps that speed, but brings the engine rpm's down for better fuel mileage (and less noise!).
Edit: Okay, I withdraw my comment. I'm not familiar with these GV units. I guess they really are trying to sell it as being useful for "half gears".
One of the selling features on their website is the fact that you use it for any gear over 20mph (or 15, i forget). The idea is that it keeps you in your power band, and minimizes the big jumps in rpm between gears.
The gear vendors website has youtube video where you can hear the car shifting gears through overdrive in each gear, but you can't see the operation of it.
In principal it reminds me of the 4+3 trans put into late 80's corvette's. Those were 1st, shift to 2nd, push button to 2nd overdrive, shift to third, push button to 3rd overdrive, shift to 4th, push button to 4th overdrive. It didn't require you to unclick the button to go from an overdrive gear to the next higher or lower gear, if I remember right.
It makes a wide ratio trans into a close ratio trans...
i don't think gear vendors makes an od kit for the np435. if they do then it would be clutch granny clutch second/first push button engage clutch push button disengage second/ thrid push button engage clutch push button disengage 3/4 gear push button smile. that is what i remember at least not really a racing application for it but if you were driving around town or hauling it would be pretty nice to keep it where you wanted it but if i remember your biggest jump in gearing is going from granny to 1st which *depending on your rear end* is below the 20mph engage point allowed by gear vendors. just checked and yeah they make the kit for np435 rock on man and enjoy.
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Last edited by carpenter547; 10-30-2010 at 01:57 PM.
Reason: yeah they have the kit
I was thinking about going with a gear4 vendor unit but after the more I found out about them the less I like. #1.thing if you want to to use a used unit that you need to change the adapter for your Tanny. Gear-Vendor will not give any trade in credits or sell you just a new adapter that will fit your trans. They will charge you almost full price for a complete new unit with a adapter that fits your vehicle. IMO This is so they can keep price control over complete unit. So there won't be any lone adapters laying around that a guy could buy for cheap and then just buy the o/d unit..
I called them in South ca. and in a long run around story saying this is what the bottom line was.
They Didn't want any one to copy and adapte it to a Doug nash? O/D unit yeah right. Plus these units have a slow shift lag time. Think of it as the old double clutching trick for the unit to switch gears unless they have improved them. And that's a lot of money by the time your done and got it up and running. And if your not all that handy with tools an so on. Or you have to pay for this installation,
I bet close to 4500-5000 grand to have all those over & under gears to play with.
Me, I just really wanted to lower my rpm at @ 60mph and some gas saving if at all possible. So went the ez way with the dodge/chevy nv4500 5spd o/d.. Have had the np435 tranny in a 4x4 in low range is great for pulling stumps. But did use it a few times 30 yrs. So I figured I didn't need that low of first gear and went with the higher 5.27? geared granny 1st geared tranny. Which is the second generation. Think it was starting in 1995 and up all had the higher 5.27or36 1st gear can't remember it all with out looking it up.. But I'll close with this. I did this tranny swap for just about 2 grand. Just do your home work and find out as much from guys that have do it to the same eng frame model as you want to do..
So with 33" tires in 5gear 4:10 gears, I now tach around 1850 rpm @60mph Was around 2600 And gas mileage came up about 2 mpg But remember it's also how you drive too..
I have a GV O/D in my '68 behind the T19 that I swapped in. It's a divorced unit, meaning that it mounts independently of the tranny and has a short intermediate driveshaft from the tranny to the O/D unit. It basically replaced the driveshaft center support bearing. But I have an adapter to mount it directly to the back of the T19 one if these days, when I finally get around to it. And yes, they do offer a unit to fit the NP435.
Mine is a used unit with a lot of miles on it and so doesn't operate quite as well as new unit is supposed to. A new unit is supposed to build sufficient hydraulic pressure to engage O/D at about 22 MPH regardless of what gear you're in, mine will engage at 25-30 when it's cold but after it's well warmed up or even hot it will drop out of O/D, especially on a downhill when I'm coasting, at sometimes as much as 50 MPH which can really suck as it gives no warning and disengages with a violent bang. It's also very slow to engage, which I understand is characteristic of the unit whether new or old.
In operation I typically run up through the gears till I'm in 4th and then engage the O/D (I have a two-speed rear end pull switch mounted on the gear shift which operates the O/D). I activate the switch, then let off the gas till I feel it engage and then get back on the gas. If I'm back on the gas too quickly then the O/D hasn't had time to engage and it clunks going in. GV recommends using the clutch when you engage it but I can't really feel it engage when I have the clutch in. I've found there's consistently less driveline shock when I use it the way I do. I think they key is to not be on the gas when it engages, though they're commonly used behind automatics as well...
Even though I generally use it to overdrive 4th, I often just downshift to 3rd with it still engaged when needed rather than shift out of O/D and then back in again. Gear Vendors claims you can use the unit to overdrive or underdrive any forward gear as long as you have sufficient speed to build up the needed hydraulic pressure to actuate the unit. I've been able to overdrive 2nd a couple of times when towing up a steep hill at low speed and needed a gear in between 2nd and 3rd, but I wish my unit wasn't so old and worn so I could utilize that ability more often as the T19 has a big gap between those two gears, just as the NP435 does between 3rd and 4th.
To disengage, as I draw near the speed that I know it's going to drop out anyway I push the clutch in, shift to neutral and disengage the O/D all at the same time, then pull it back into 4th (or 3rd) and let the clutch back out. Again, I've found this method to reduce driveline shock, as it really tends to bang hard on disengagement when I do it pretty much any other way.
My main gripe about GV as whole is that I'd like to rebuild the unit myself but GV won't sell you the parts to do it, they want you to send them your old unit and they'll then send you a rebuilt unit at something like half the price of a new one. Also, even though you can buy these units rated to install on a bigger vehicle like a motorhome with a pretty high GVW, I have a hard time trusting them as they're built from the British design and patents of the notoriously fragile Laycock De Normanville O/D unit as installed on many British cars (not to mention Volvos) of the '69s and '70s. In fact, they look almost exactly the same.
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