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Gearvendors length

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77crewcab

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Wondering if anyone here has gotten one of the gearvendors o/d units that bolts to the back of a t-case. I am trying to find out the length added. I emailed them and got two conflicting answers. One email said that they replace the output shaft and made it sound as though it was then 13 inches from the back of the t-case to the new yoke position. I emailed back to verify this and was told that no it was 13 inches added to the the position of the stock yoke. This is on a 205. They also specify that the 205 must be fixed yoke or converted to a fixed yoke before bolting on their kit. So can anyone verify the length added from the back to the case with the GV bolted onto the back of the 205. This is going on a Burb chasis so I am not really concerned about the length but want to get the information right so I can make a decision.
 
Hmmm okay so it would be 12-13 inches longer than a fixed yoke 205. Anybody know off the top of their head the measurement from the back of the case to the yoke face on a fixed yoke 205? Off to search!
 
Looks like 19.5 inches from the back of the 205 case, with a total of 51 inches from the back of the engine to the rear driveshaft yoke.
 
It was my understanding that the output shaft housing is removed and the GV unit ( and adaptor ) bolts and couples up to the output shaft of the 205. The speedo cable is relocated to the GV output shaft. I investigated this 4 years ago but haven't made the change yet.
If you are going to add the GV unit, make sure you have a resonable OD ratio.
Example: Stock tires, 4.11 : 1 rear axle, and GV 0.75 : 1 OD = 3.08 final drive. If you went from stock 30" tires to 33" tires your rear axle is now 3.70 : 1 , now times the 0.75 OD = 2.775 final drive. If you went to 36" tires your rear axle is now 3.24 : 1, and GV 0.75 OD = 2.47 final drive. The engine will not pull this ratio on a level road.
Don't get me wrong , GV OD is the best, you should look into buying a unit that has a 0.86 ( or other ratio ) that will work with your system. In general a final drive ratio of 2.70 - 3.08 will not overload your engine or transmission. With the price of gas now I will probably change my 205 within the year.
 
Huh?? I am going to be running the GV, 3.73, and 35 inch tires. Cruise rpm at 70 will be 1880. That about the same as my stock burb with 700, 3.42, and 31 inch tires. What formulas are you using for your calulations, and what would final drive with the OD have to with anything if I am hitting the same RPM at cruise?
 
I do not have access to the formulas I used 8 years ago, however I based the data I posted on my truck. Please follow allong. 1981 Chevy truck ( 350 cu.in.,Turbo 400, NP 205 ) with 4.11 rear axle and 30" stock ( I measured ) tires. I changed to a 33" tire and noticed my speedometer about 9 mph too slow. Therefore the engine was running slower. Going from 30" to 33" tires is about 10% therefore my effective axle ratio now is 4.11 - 0.41 ( 4.11 x 10% = 0.41 ) = 3.70 . Does that make sense?
In your case the difference in 35" tires vs factory 31" tires is about 12%, Therefore your engine sees an axle ratio ( not counting the GV OD ) of 3.42 - 0.41 ( 3.42 x 12% = 0.41 ) = 3.01 . If you incorporate the GV OD (0.75:1 ?) Then your engine sees 3.01 x 0.75 = 2.26 axle ratio. A 454 cu.in engine will not pull a vehicle with that low a ratio. PERIOD. You would never be able to engage OD in high gear without the engine shaking and bucking. There is no mph where it will be effective. The only GV OD ratio that will work effectively is 0.90 : 1. With that ratio the engine sees 3.01 x 0.90 = 2.71 . That will work.
Find out what the ratio is in the GV OD. If it is 0.75:1 , or 0.8:1 don't waste your time and effort. If it is 0.90:1 it will work.
Your current set up with 3.42 and 35" tires is already an economical 3.01:1.
Don't screw with perfection!
 
I think you are misunderstanding completely. I have a burb with 350/700/208 with 3.42 rear and 31inch tires. I am at 1820 rpm at 70mph. I am building another burb chasis that will have a Cad 500/465/205/GV, 3.73 gears and 35 inch tall tires. RPM calculator puts this combo at 1880 RPM at 70mph. I was just comparing the two in that the cruise RPM would be similar.
 
Not saying it's right or wrong, but GM had 305's turning 1400RPM's in these trucks, a 454 would have a heck of a lot less problem doing the same.

Really doesn't matter in this case, 1800RPM is plenty for cruise, probably more than enough with a 500. :)
 
With out the GV what would your rpm's be ?

I have 4:10 and 35's with a TH400 and mine isn't all that bad, I think cuz I don't have a tach hooked to it, but its manageable.

I think Mike's point is that with 3:73 and a overdrive and 35's its going to be to low of an rpm to run the big block, well it will run but it will want to run at 80 mph.
 
Sorry about the mix up in numbers, I am just getting old.
3.73 - 0.45 ( 3.73 x 12% = 0.45 ) = 3.28 effective axle ratio ( without GV OD ). Now iif the GV OD is 0.75:1 ,then the effective axle ratio the engine sees is 3.28 x 0.75 = 2.46 . Like I stated before the engine will not pull the vehicle on a level highway. The minimum ratio is 2.70:1 .
If you could obtain GV OD gear ratio of 0.83:1 , Your net effective axle ratio will be 3.28 x .083 (OD) = 2.72 . Now that will work.
If you already have a GV unit check out the cost of changing the OD ratio to 0.83:1
By the way, what is the GV OD ratio if you already have it? They make a lot of overdrive ratios. Look, if it is 0.75:1 and you install it, you will have to drive it in gear # 3, not # 4.
There is nothing more frustrating than installing something and the result is worse than if we never started it in the first place.
 
Mike D said:
Sorry about the mix up in numbers, I am just getting old.
3.73 - 0.45 ( 3.73 x 12% = 0.45 ) = 3.28 effective axle ratio ( without GV OD ). Now iif the GV OD is 0.75:1 ,then the effective axle ratio the engine sees is 3.28 x 0.75 = 2.46 . Like I stated before the engine will not pull the vehicle on a level highway. The minimum ratio is 2.70:1 .
If you could obtain GV OD gear ratio of 0.83:1 , Your net effective axle ratio will be 3.28 x .083 (OD) = 2.72 . Now that will work.
If you already have a GV unit check out the cost of changing the OD ratio to 0.83:1
By the way, what is the GV OD ratio if you already have it? They make a lot of overdrive ratios. Look, if it is 0.75:1 and you install it, you will have to drive it in gear # 3, not # 4.
There is nothing more frustrating than installing something and the result is worse than if we never started it in the first place.
Click to expand...

I think your math is flawed, tires have nothing to do with gear ratio.
3.73 x 0.75 = 2.7975 and for an OD gear that is just fine.

to figure out the MPH use this equation:

(RPM) x 60
(Final drive ratio) x number of tire revolutions per mile
 
Tires have everything to do with final drive ratio though which effects gear ratio. The point is if I have a 29" tall tire with a 3:73 gear ratio then put on a set of 40" it in effect changed my gear ratio, well my final drive ratio. I would need to change my gears to a 4:88 or so to keep the same final drive ratio. Which is Mike's point, a 2:73 final drive ratio is way low a 3:08 is better.
 
kgblazerfive said:
Which is Mike's point, a 2:73 final drive ratio is way low a 3:08 is better.
Click to expand...

I'll disagree a bit here...final drive ratio can be whatever you want it to be, as long as you can cruise in gear.

I don't know why 2.73 would be bad for cruise. If the engine is efficient at whatever cruise RPM is, then it's fine. It could be 2.29 (another factory GM ratio, albeit for 3500lb cars) as long as the engine is efficient when at your cruise speed.

Having overdrive is pointless if you can't drive the RPM's down a noticeable amount at cruise. A numerically high final drive ratio, coupled with a very efficient overdrive ratio, is the best of both worlds. (which is why I poo-poo the GV unit, OD is not effective enough) Numerically low ratios (2.73, 3.08) are horrible for crawling and compression braking, great for high speed cruise.
 
The overdrive for the GV unit is .78. Wit 3.73 gears in 4th over the final drive is 2.77. I have yet to find a formula online to figure in the effective ratio of the tire other than the formulas to tell you the efective ratio change when switching tire size. On the other hand the final drive of my burb with the 700s OD of .70, 3.42 gears is 2.39 and with 3.73 gears is 2.61. I actually have my daily driver burb with the 3.42 gears and a parts burb with the 3.73s which is the chasis I will be building up. Both with 700s and 31 inch tires, the parts burb with 3.73 has a much stronger feel when you press the pedal and is fine cruising at 70. The daily driver cruises fine at 70 as well. I understand that changing the tire size will change the effective final drive ratio. But I fail to see how the vehicle will suddenly be undrivable and not pull itself down the road. Especially when going from a worn 165hp 350 with maybe 250ftlbs max, to a 350-400hp(conservative) CAD 500 with over 300ft at cruise speed and over 500ftlbs max. Sorry I just don't see how it won't pull itself in OD.
 
With the 465/205/GV, 3.73 gears and 35 inch tires the rpm at 70 would be 1955 (I had to make a correction, I origionally had the OD at .75)
 
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