Gear Vendors Over/Underdrive for 68RFE

[PLanciers]

All,

As mentioned in my first thread here on TDR https://www.turbodieselregister.com/forums/showthread.php?t=177716 , I've been looking seriously at adding this Gear Vendors capability to the 3500 SRW Laramie MegaCab I have on order. Learning that they are located in an adjacent town here in SoCal, prompted me to visit with them yesterday to investigate the posibilities. I will share here with you lessons learned as I proceed toward a possible aquisition of their Over/UnderDrive unit http://www.gearvendors.com/ .

First news I can share with you is that they have already adapted one of their units for the AISIN transmission, that's right C&C owners they've already engineered your solution and shown it a Custom Brilliant Red C&C at the 2007 San Diego Auto Show, someone may have a shot of that sharp beast out there the day I attended I spaced and left my camera home, BajaBob maybe you?

Gear Vendors is currently awaiting drawings of the 68RFE case from mother Mopar to determine exactly how to interface both 4X2 and 4X4 applications, but they expect no major hurdles here. We sat down with the Ratios to see what the numbers would reveal and I can share that data here even though it is not yet posted on their site. Understand that this unit is a gear splitter and as such will split rations between all the first 5 factory ratios and overdrive the 6th. That said not all split ratios will necessarily offer utility, the ones that GV feel will, are hi-lighted in the grey bars in the following attachment. Even more eyecatching though are the final drive ratios attainable and their fuel economy implications. Oo.

Pete

 

[EMD-Run8]

Man, I would think that's gettin' awfully tall. Isn't that actually under the torque peak of the engine?

 

[PLanciers]

Man, I would think that's gettin' awfully tall. Isn't that actually under the torque peak of the engine?

P'Cola huh... I spent (or mis spent) a lot of my youth @ Corry Station!



Good thought and it echoed my initial concern but actually the 6. 7L configured for use with an auto maxs out @1500RPM and the stick @1400RPM. Obviously you'd be selecting your unloaded economy cruise settings and gear/OD selections based upon your desired speed... In a loaded condition you'd hold the 68RFE in 4th with the GV overdriving @ . 78 with should give desired performance characteristics while greatly reducing transmission temps while not engaging the orion's OD.



I'm trying to find conceptual weaknesses here prior to a significant cash outlay, so I welcome divergent opinions!



Pete

 

[jelag]

We are a distributor of both Gearvendors and PacBrake... Gearvendors does not approve the use of an exhaust brake with their unit... . they are not designed to transmit power backwards through them... .

If you intend to tow, and use an exhaust brake we suggest you consider some other option... .

 

[PLanciers]

We are a distributor of both Gearvendors and PacBrake... Gearvendors does not approve the use of an exhaust brake with their unit... . they are not designed to transmit power backwards through them... .



If you intend to tow, and use an exhaust brake we suggest you consider some other option... .

Jim,



Trying to understand the issue here and it's scope.



When you say "they are not designed to transmit power backwards through them... . " are you implying a directional design weakness within the planetary gear arrangement? Or an inability within control circuitry to handle load reversal?



Is this a prudent use issue? Who uses the exhaust brake while not towing? Who uses an exhaust brake upgrade? Who needs the benefit of OD downgrade?



Will the 6. 7L VGT integrated brake inherit these issues that seemingly plague aftermarket exhaust brakes?



How wide spread is this issue, in just reviewing a substantial segment of member sigs from the RV&Towing forum the numbers boasting both exhaust brake and Gear Venders Over/Underdrive is somewhat significant?



Not trying to shoot the messenger here just trying to gain insight!



Pete

 

[PLanciers]

Gear Vendor UPDATE

GearVendors does not approve the use of an exhaust brake with their unit... . they are not designed to transmit power backwards through them... .

Spoke at length with Gear Vendors today regarding the above remarks.



"Gear Vendors does not approve of there OVER/UNDER Drive being engaged while compression braking. " Please understand the nuance between this and the above statement it is important and he stated to me that this is the greatest myth out there with regard to their product. The use of their OD unit and an exhaust brake simultaneously engaged can potentialy damage the GV unit. As I suspected it has to do with the helical gearsets in a planetary arrangement's reaction to load reversal.



The next sentance out of the GV rep's mouth was "Hell Pete under what circumstance would you really want both engaged" after explaining that I really couldn't think of any, he assured me that their application techs go to great lenghts to identfy the various exhaust brake manufacturers commands signals from their respective controllers so that they can use that same signal to lock out GV control command engagement. He told they have already requested this technical info from Mopar on the integrated VGT exhaust brake and it would not be an issue.



He also stated that if I knew of any TDR members that do not have automatic Exhaust brake/GV cutout set up and enabled they should contact GV to rememedy their installation.



Pete

 

[ShaneBoone]

"Gear Vendors does not approve of there OVER/UNDER Drive being engaged while compression braking. " Please understand the nuance between this and the above statement it is important and he stated to me that this is the greatest myth out there with regard to their product.





I have a GV unit in the garage, called gear vendors too see if I could use an exhaust brake. The statement above is correct, I received very little information from GV, They said to see an authorized dealer. MMMmmm in this case that sure would have helped... . I guess that why I have not installed yet. Check out gross combination weight what you'll be running. GV has a limit of 20 some thousand pounds. I run 23,500 alot.

 

[betterthanstock]

An overdrive on a 6 speed automatic is like an eight legged horse. They would run into each other. Some of those ratios have a difference of less than 100 rpm.



Every gear has a real friction loss of 3%. So if you get empty mileage of 19, after it passes thru another set of gears, it goes to 18. 4 mpg. Towing, at 12 mpg, would drop to 11. 6 mpg. Are the savings in the engine (by turning more slowly) bigger than 3% to offset the losses in you extra gears? Not at a 100 rpm difference.



That's why the best would be to tow in direct drive, and to drive empty in overdrive. But since there are many towing speeds, from 55 to 80 mph, that is not possible, so having one overdrive gear wasting 3% of your fuel is enough. No need to double that.

 

[EMD-Run8]

That's what I'm wonderin'. I mean, a six speed auto with double OD is covering it PRETTY GOOD. The Cummins has a spread that should more than compensate for the drops between gears which are pretty narrow compared to what has been in these trucks before. Take even the NV5600-----the only "drawback" (if you could even call it that) it had was that even in overdrive it was tachin' over the torque peak of the motor at highway speed. It pretty much handled the rest A-1 ya know?

 

[BGlidewell]

http://www.usgear.com/

Didn't these guys make one a while back?

 

[PLanciers]

Huh ?

An overdrive on a 6 speed automatic is like an eight legged horse. They would run into each other. Some of those ratios have a difference of less than 100 rpm.



Every gear has a real friction loss of 3%. So if you get empty mileage of 19, after it passes thru another set of gears, it goes to 18. 4 mpg. Towing, at 12 mpg, would drop to 11. 6 mpg. Are the savings in the engine (by turning more slowly) bigger than 3% to offset the losses in you extra gears? Not at a 100 rpm difference.



That's why the best would be to tow in direct drive, and to drive empty in overdrive. But since there are many towing speeds, from 55 to 80 mph, that is not possible, so having one overdrive gear wasting 3% of your fuel is enough. No need to double that.

I'm a little confused with the math here maybe you can walk me through this



1. What gear splits result in a 100 RPM difference? The smallest direct drive difference I calculate is 311RPM movement in the direction of the torque sweet spot... in O/D @75mph w/31" tires and a 4:10 gearset it moves engine 458 RPM in the right direction... The basic premise of your argument is why no splits where listed between 2nd & 3rd and 5th & 6th because they fell below a what GV considered a useful ratio...



2. Assuming no consideration for gear type or arrangement how did you assume the 3% frictional coefficent loss? Accepting that number for the moment how exactly does that directly compute to a 3% loss in fuel economy.



Pete

 

[PLanciers]

"Gear Vendors does not approve of there OVER/UNDER Drive being engaged while compression braking. " Please understand the nuance between this and the above statement it is important and he stated to me that this is the greatest myth out there with regard to their product.





I have a GV unit in the garage, called gear vendors too see if I could use an exhaust brake. The statement above is correct, I received very little information from GV, They said to see an authorized dealer. MMMmmm in this case that sure would have helped... . I guess that why I have not installed yet. Check out gross combination weight what you'll be running. GV has a limit of 20 some thousand pounds. I run 23,500 alot.

Shane,



Thanks I think I'm OK with the GCWR issue... Call Nick at Gear Vendors he assures me there's a solution to make Exhaust Brakes and the GV unit co-exsist for every configuration, maybe this fix (the command cutout feature I described) is something relatively new and that is why it seams to be relatively unknown here? Dunno I wasn't smart enough to have asked that question, but I will next week.



Pete

 

[PLanciers]

Found on the RV/Towing forum

Dont worry about the gear vendor overdrive and the use of an exhaust brake..... the newer units have a cutoff switch that turns the overdrive unit off when the exhaust brake is applied... . have used this setup behind my 235 hp/ 605 lbs torque ctd 5 speed for a number of years..... you can split gears with it all day long... works from a switch on the gear shift..... I tow combined vehicle weight of 23,000 lbs often... ... you will learn to like the double overdrive when not towing... . big increase if fuel mileage.

All was hoping to find someone else hear had heard of the Exhaust brake fix, I pulled this response off the RV/Towing forum...



Pete

 

[Tspanos]

Very cool, answers the questions I had in the other thread. Checked out the GV site and am impressed. I just wonder how much this truely would improve fuel economy because at $3700 installed it will need to be signifigant.

 

[Tspanos]

Just did some real quick math, with diesel at $3 and fuel economy increase of 5 mpg it takes roughly 43,000 miles to recoup the cost of the unit and installation. If diesel makes $4 the payoff drops to 39,000.

 

[jcarey]

Just did some real quick math, with diesel at $3 and fuel economy increase of 5 mpg it takes roughly 43,000 miles to recoup the cost of the unit and installation. If diesel makes $4 the payoff drops to 39,000.



For increased mpg (and some added increase in torque), a box or downloader is a whole lot cheaper way to go.



Even for towing, I would prefer a box... too much button pushing to maintain proper gear. Mot to mention too many $$$



IMHO

 

[betterthanstock]

I'm a little confused with the math here maybe you can walk me through this



1. What gear splits result in a 100 RPM difference? The smallest direct drive difference I calculate is 311RPM movement in the direction of the torque sweet spot... in O/D @75mph w/31" tires and a 4:10 gearset it moves engine 458 RPM in the right direction... The basic premise of your argument is why no splits where listed between 2nd & 3rd and 5th & 6th because they fell below a what GV considered a useful ratio...



2. Assuming no consideration for gear type or arrangement how did you assume the 3% frictional coefficent loss? Accepting that number for the moment how exactly does that directly compute to a 3% loss in fuel economy.



Pete

4th overdrive to 5th normal, an 89 rpm difference at 2000 rpm. So you lost 3 useful gears already. 3rd over to 4th is only 200 rpm @ 2000 rpm. How much use will you have for that speed? Maybe one slow long hill where you will go 200 rpm slower. And what if the automatic then does not like your overdrive gear selection and downshifts on its own?



The 3% is a typical loss for any gear set, including the factory overdrive, and underdrive gears. So if in a gear, like 5th over , which they don't list, you have the same rpm as 6th, then 5th over will get you 3% less power at the wheels, and you will need to push the engine harder by 3%, which costs you 3% fuel economy. Differentials have hypoid gears, which I believe waste about 5%. My truck shows 3% loss over repeated dyno runs in 6th (overdrive) compared to 5th (direct drive).

 

[PLanciers]

4th overdrive to 5th normal, an 89 rpm difference at 2000 rpm. So you lost 3 useful gears already. 3rd over to 4th is only 200 rpm @ 2000 rpm. How much use will you have for that speed? Maybe one slow long hill where you will go 200 rpm slower. And what if the automatic then does not like your overdrive gear selection and downshifts on its own?



The 3% is a typical loss for any gear set, including the factory overdrive, and underdrive gears. So if in a gear, like 5th over , which they don't list, you have the same rpm as 6th, then 5th over will get you 3% less power at the wheels, and you will need to push the engine harder by 3%, which costs you 3% fuel economy. Differentials have hypoid gears, which I believe waste about 5%. My truck shows 3% loss over repeated dyno runs in 6th (overdrive) compared to 5th (direct drive).

Okay now I see the > than gear split your reffering to, but had not considered it since I don't suspect anyone would ever use the Orions 5 not normal but O/D and 6 O/D in a loaded tow condition... the value of the GV . 78 gear is to allow you to leave the orion in 4th w/the GV in O/D (much less heat and we all know what heat does to efficiency). Third O/D over to forth will not have value in a empty condition obviously, however I suspect you'd agree that could change on a grade fully loaded. Not disputing any particular Dyno results your observing on your truck, you do not state 3% HP or Torque? Regardless the remainder of your lineal computation toward fuel economy figures would seem to indicate that Gear splitter users out there are not realizing fuel economy savings in either loaded or empty conditions... This is not what I'm gleaning from postings on this and other forums but obviously is the crust of the biscuit so splitter users please chime in here.



Pete

 

[cerberusiam]

the value of the GV . 78 gear is to allow you to leave the orion in 4th w/the GV in O/D (much less heat and we all know what heat does to efficiency).

Your kidding, right??? A 3% difference is not even worth looking at. Less heat? C'mon! It doesn't matter what combination you make it will generate the same amount of heat, just in different places. The trans coolers are pretty good on these trucks. With the TC locked you will not be able to see a difference on a gauge.



Let me put this in perspective, $3700 to get ONE AND ONLY ONE split that is any good. Thats a no brainer considering the TQ the engine has.



The rpm's for 70 and 75 are ridiculous. :-laf I seriously doubt the trans will allow that unless its downhill or under coast. From what I hear the 68RFE doesn't like to hold 6th under very much throttle and/or load. The trans will be downshifting to 5th every time the throttle is bumped, if it even manages to upshift. THATS way worse than a little rpm.



There is just nothing in economy to be gained running under 1600 rpms. Its the back side of the TQ curve and with the emissions design its severely defueled. I seriously doubt the TQ peak is that low anyway as emissions plays a large part of the fueling at low rpm's. I'll withhold judgment until I see a dyno sheet but I would guess it will show a TQ peak around 2200 rpms and HP peak around 28000 roms. All thats gonna happen is it will coke the injectors faster and cause more issues.



All I see is a big expensive toy that does little or nothing to enhance what looks like a decent gear split from the factory, and, possibly lead to other problems by letting the motor run under the high idle limit.

 

[betterthanstock]

Just did some real quick math, with diesel at $3 and fuel economy increase of 5 mpg it takes roughly 43,000 miles to recoup the cost of the unit and installation. If diesel makes $4 the payoff drops to 39,000.

Did you mean 0. 5 mpg? Because you'll never see 5.