ZF5+GEARVENDOR VS T19+GEARVENDOR

[Ray Cecil]

Moral of the story, a ZF5, or a t19 plus a gearvendor would save me about 200 rpm over the c6, according to this chart up to 4th gear. The T19 1st 2nd 3rd gear ratios look closer to the wide ratio Zf5, and actually keep the rpms up a little more until 4th, where wide/close ZF5 and the T19 are same ratio. That 5th gear on the ZF5 really drops those rpms at 65mph with a gearvendor to 1677rpms!!! A whole 1000rpms lower than my c6. I spend the majority of my driving in that truck on back country roads. Not sure if the ZF5 is worth the extra gear for my purposes. A good ZF5 is soooo much more expensive than a T19. 

[Gary Lewis]

If you don't need 5th, maybe by adding the Gear Vendor's OD, then the ZF isn't needed.  But I go into 5th at anything over 35 MPH.

[Gary Lewis]

What tach do you have?  I've had several different stock tachs and they all had different readings, none really matching the spreadsheet.  But they are close so it is pretty obvious in my case that it is an error in the tach.  

[Ray Cecil]

On 10/6/2024 at 6:22 PM, Gary Lewis said:

What tach do you have?  I've had several different stock tachs and they all had different readings, none really matching the spreadsheet.  But they are close so it is pretty obvious in my case that it is an error in the tach.  

Factory tach. 

[Ford F834]

I have owned and driven the T19 & GVOD combination and it is clumsy. I am not a fan. Unlike a 2 speed differential, it drops out of OD at lower speeds. You can’t split the lower gears because you are not going fast enough for it to engage. I could do 3rd over, but mine was the close ratio T19 so 3rd over was essentially the same as 4th. And like Gary said, I would be in 4th + over at 35 mph (4.10 axle gearing). The final drive ratio of 3.20 (4.10 x 0.78 GVOD) was okay, but it still needed another gear in my opinion. At least for the low rpm IDI. If you already have the GVOD, I would put a ZF5 and have double overdrive. That’s what mine will have when it goes back together. I would rather nix the GVOD if I could, but I don’t really want to re-gear the axles. 

[viven44]

On 10/9/2024 at 1:43 PM, Ford F834 said:

The final drive ratio of 3.20 (4.10 x 0.78 GVOD) was okay, but it still needed another gear in my opinion.

I can agree with that. I have 3.07 axle on my 84 and I am turning roughly 2500 rpm going 70mph with a C6. I feel I can do better.

[85pig]

On 10/6/2024 at 11:52 AM, Ray Cecil said:

A good ZF5 is soooo much more expensive than a T19. 

And why I just quit looking for them and bought Gary's old T19.  I've got a T18 now, but that ugly grinding into 1st and reverse is annoying, not to mention it's a good hard yank to get it out of 1st once you're moving.  The T19 solves that.  I've read of too many issues with the ZF, plus the initial price of what may or may not be a good transmission.  

[Ray Cecil]

On 10/9/2024 at 2:43 PM, Ford F834 said:

I have owned and driven the T19 & GVOD combination and it is clumsy. I am not a fan. Unlike a 2 speed differential, it drops out of OD at lower speeds. You can’t split the lower gears because you are not going fast enough for it to engage. I could do 3rd over, but mine was the close ratio T19 so 3rd over was essentially the same as 4th. And like Gary said, I would be in 4th + over at 35 mph (4.10 axle gearing). The final drive ratio of 3.20 (4.10 x 0.78 GVOD) was okay, but it still needed another gear in my opinion. At least for the low rpm IDI. If you already have the GVOD, I would put a ZF5 and have double overdrive. That’s what mine will have when it goes back together. I would rather nix the GVOD if I could, but I don’t really want to re-gear the axles. 

I already have the GV. I really like it. I can do 1 + OD with the C6 anf 4.10 gears. Not sure why you couldn't at least do 2nd + OD with the T19. Maybe the 1st gear in the C6 is just a lot longer than the 1st in the T19. 

[Ray Cecil]

On 10/12/2024 at 6:08 PM, 85pig said:

And why I just quit looking for them and bought Gary's old T19.  I've got a T18 now, but that ugly grinding into 1st and reverse is annoying, not to mention it's a good hard yank to get it out of 1st once you're moving.  The T19 solves that.  I've read of too many issues with the ZF, plus the initial price of what may or may not be a good transmission.  

THIS!!

I get so sick and tired of people thinking the ZF5 is made of Gold. $1000+ for a crummy old 5 speed with bad synchros??? Yeah right. Its more up front cost, but buying a F Superduty 2WD with the trans brake ZF5 I can often find for like $2000-$4000.....but if I do that, Im still using a ZF5 that MIGHT brake a bell housing.....THis is why Ive often just thought about keeping my GV C6 setup. Its reliable and it works in all 6 gears. 

You can bypass the GV Control unit, and just run a floor switch with 12v to the unit. Just remember to manually shift it when coming to a stop. I do it all the time.

[Ford F834]

The Ford C6 three gear ratios are essentially identical to the close ratio T19’s 2nd, 3rd and 4th. I am sure I could split 2nd if I revved it high enough, but there isn’t much reason to since the gears are already close. I can’t speak to splitting gears with the C6 since there is slippage and different rpm’s than the standard. My hunch has always been that the GVOD would work smoother with an automatic. 
 

The ZF-5 is a really good transmission as far as full size pickup overdrive transmissions go. But high demand drove the prices up, and over the years fewer and fewer can be used as-purchased without a rebuild…. While the prices still seem to reflect what a good drop-in would be worth. The gamble is increasingly against the buyer. I bought mine at junkyards at a price that won’t upset me if it turns out to be a core.