GV over/underdrive on a 4x4?

[snicklas]

i know around here the 4x4's in the ditch are from overdriving the conditions.

I am the guy in the 7500 lb Excursion running 35 in the right lane on the interstate with the "big trucks". I also point and laugh when I get a couple miles down the road, and the 4x4 that just passed "us" at 75mph is nosed into the ditch.

Worst one I ever saw, was during the Indianapolis Boat Sport and Travel Show that is always in Mid-February. (I garrentee that Indiana has at least one more good snowstorm coming, as there is ALWAYS a big snow during the Boat Show). We were headed home after the show, and had stopped for dinner. The forecast was for a dusting to an inch or so (BULLS**T) we came out to 9+ inches of snow, and more coming down..... HARD! We were sitting at the light at 75th Street and Binford Blvd. headed South (For those familiar with Indy, this is where I-69 "dead ends" on the Northeast corner of Indy). There was a Suburban headed North on Binford approaching 75th. He was in the leftmost lane, and lost control, ended up into the median, across the median, up onto the Southbound lanes (in front of us), did a 180 on the Southbound lanes, across the median again, back up onto Northbound Binford, just missing all the signage for the intersection, and it straightened up and headed back North again. The entire time this was happening, the REAR wheels were spinning for all they were worth..... they NEVER lifted their foot off the gas the ENTIRE time they were careening across the median and into oncoming traffic. If it had been in 4x4, he may have stayed "over there" where they belong..........

We on the other hand, made the 35 mile trip back, in a 2wd E-150 Van and never got "out of shape" once...... but Dad and I both know how to drive on the snow. They live WAY OUT in the country and even once the roads were plowed, there was still and inch or so of snow on the road........

 

[jay22day]

Id like to keep the GV and if i ever 4x4 maybe atempt a mod it in-front of the tcase
I think that would be the best setup, it would jsut be extremely "custom"

 

[Black dawg]

Id like to keep the GV and if i ever 4x4 maybe atempt a mod it in-front of the tcase
I think that would be the best setup, it would jsut be extremely "custom"

I just read your signature, "2 gears reverse". GV wont work in reverse AND DONT TRY!

 

[The Warden]

The us gear is very cool (although noisy)

Is the U.S. Gear noisy when in operation, or are you referring to the shifting process?

I have one waiting to be installed; looking forward to having it in the truck, but I haven' thad a chance to drive one yet...

Thanks

 

[Black dawg]

Is the U.S. Gear noisy when in operation, or are you referring to the shifting process?

I have one waiting to be installed; looking forward to having it in the truck, but I haven' thad a chance to drive one yet...

Thanks

Mine is noisy while engaged, most noticeable through a certain speed range. I plan on tearing into it to make sure nothing is wrong, but I believe it is just gear noise.

I have heard that earlier models had gear noise. I personally have driven a few that made no noise at all.

 

[jay22day]

I just read your signature, "2 gears reverse". GV wont work in reverse AND DONT TRY!

thanks for the advice, i swear i read its functional in reverse some where


i also just read that the guys at GV said that the reverse is the weak link of their splitter and you should avoid backing uphill with a heavy load that same idividual said that if you send GV your malfunctioning/broken overunderdrive that they will ship you a replacement for around $800

does anyone know if theres some truth to that statement? i dont imagine the guy was lying about that. (this was read off a different forum)

 

[Black dawg]

Yes, you can break a GV just backing up with a load (even gv disengaged). GV engaged in reverse is BAD. Dont know for sure the cost on exchange GV, but I have heard of them telling people that they just needed to buy a new one.

 

[The Warden]

thanks for the advice, i swear i read its functional in reverse some where


i also just read that the guys at GV said that the reverse is the weak link of their splitter and you should avoid backing uphill with a heavy load that same idividual said that if you send GV your malfunctioning/broken overunderdrive that they will ship you a replacement for around $800

does anyone know if theres some truth to that statement? i dont imagine the guy was lying about that. (this was read off a different forum)

For what it's worth, I've heard that engine-braking with a GV is a seriously bad idea also...actually, that's one of the reasons I decided not to go that direction (I'm pretty aggressive about engine braking; I can get from freeway speeds to 15 mph before touching the service brake if I time things right). I don't remember the reason, but I suspect it's the same reason why the recommendation to not back a heavy load with a GV is there.

 

[vegas39]

For what it's worth, I've heard that engine-braking with a GV is a seriously bad idea also...actually, that's one of the reasons I decided not to go that direction (I'm pretty aggressive about engine braking; I can get from freeway speeds to 15 mph before touching the service brake if I time things right). I don't remember the reason, but I suspect it's the same reason why the recommendation to not back a heavy load with a GV is there.

Yes, no engine braking with GV engaged. I did it only once! Mine still works fine but let out a hellava scream when I discovered it was a no no.

 

[jay22day]

Are you guys talking about "engine breaking" with an exhaust break?

 

[The Warden]

Are you guys talking about "engine breaking" with an exhaust break?

More specifically, using the engine to control your speed going down a grade...you basically want to be in a gear where the engine will be close to the governor at the maximum safe speed going down the grade (may be the speed limit, may be slower if you're loaded heavy). Let the engine do most of the work in keeping your speed down, and apply the service brakes as needed. An exhaust brake is a good thing to augment this with if you can run one.

If done correctly, this keeps you from burning up your service brakes, and leaves the service brakes available if you need to make an emergency stop.

Yes, no engine braking with GV engaged. I did it only once! Mine still works fine but let out a hellava scream when I discovered it was a no no.

I was under the impression that, if you have a GV installed on your truck, you're not supposed to engine-brake even with the GV disengaged?

 

[LCAM-01XA]

Interesting thing is they market the GV towards commercial users too (under 25k, but that's still a lot of weight), yet any hot-shot driver we know will engine-brake every chance they get before getting on the service brakes. PacBrake > GV any day, especially if you're running on the West Coast. But seriously, consider your typical 5.13-geared F-Superduty, it certainly can put the GV to a good use even climbing grades, but being limited to service brakes only coming down those same grades to me seems like a major handicap and possibly even a safety concern...

 

[jay22day]

So what your refering to is using the govner and maxing the rpm to keep the truck at a reasonable speed down grades?

Seems like that would beat on the truck pretty good.

I never really heard of "engine braking" with a diesel unless it has an exhaust brake

Its always been my understanding that diesels, not having throttle plates, prevents them from engine breaking. As you cant limit the air into the engine so it breaths(and in turn rotates) as much as it wants.

Seems like alot of the stress is being put on the drive-train rather than the motor by maxing rpm. Think its safe to say thats why the GV doesnt like it? It jsut doesnt seem like a healthy way of attempting an engine brake" to me.

See if your engine braking properly, e.g. with a wastegated engine brake, the majority of the braking force/resistance should be being applied to the exhaust brake, and inturn to the engine (that cant empty its exhaust at more than 15psi through a small wastegate hole).

Seeing as the PO installed the GV and the US GEARS exhaust brake do you think that using these to in conjunction, while towing would be ok? as your not winding out the trans like when (governor/no-exhaust-brake) "engine braking".

I wouldnt think the PO would go to the trouble of dumping $1800 plus install on an exhaust brake he couldnt use with the trans he spent like $4g's on....?

 

[The Warden]

So what your refering to is using the govner and maxing the rpm to keep the truck at a reasonable speed down grades?

Absolutely yes. You want the engine to be doing the majority of the work in keeping your speed from going out of control, and only use the service brakes sparingly. If you use your brakes as the primary method of keeping your speed under control and "ride the brakes", you'll:

1. wear down your brake pads very quickly (possibly dangerously quickly),
2. heat up your brakes to the point where it may create an unsafe condition, and
3. have no practical backup method of stopping if an emergency comes up (keep in mind that the parking/emergency brake uses the same shoes as the rear service brakes on our trucks, and even if it didn't, why have one backup when you can have two backups?)

At the risk of sounding pedantic, I should note that, while you want the engine spinning as close to the governor as practical (more on that below), it IS possible to overspeed the engine...the governor will cut off fuel if the engine goes past a certain RPM, but it cannot control engine RPM if something other than fuel's the cause for the engine to be spinning that fast. You want to avoid overspeeding the engine; especially on an IDI, the valves start floating rather quickly...this is one reason to have your service brakes available.

Seems like that would beat on the truck pretty good.

I never really heard of "engine braking" with a diesel unless it has an exhaust brake

Its always been my understanding that diesels, not having throttle plates, prevents them from engine breaking. As you cant limit the air into the engine so it breaths(and in turn rotates) as much as it wants.

Seems like alot of the stress is being put on the drive-train rather than the motor by maxing rpm. Think its safe to say thats why the GV doesnt like it? It jsut doesnt seem like a healthy way of attempting an engine brake" to me.

See if your engine braking properly, e.g. with a wastegated engine brake, the majority of the braking force/resistance should be being applied to the exhaust brake, and inturn to the engine (that cant empty its exhaust at more than 15psi through a small wastegate hole).

You're partially correct. Since diesels don't have throttle plates, the engine doesn't have anything to suck on and create a vacuum, and therefore a diesel without an exhaust brake cannot be as effective in engine-braking as a g@$ engine is. However, that doesn't mean that a diesel is useless in engine braking.

If the engine's turning faster than idle RPM but the fuel lever (controlled by the accelerator pedal) is in the idle position, the injector pump either isn't sending any fuel to the injectors, or the fuel it's sending is minimal (on electronic engines, no fuel is being injected at all; I'm not 100% sure if that's also the case on mechanical engines or not). However, the engine is still compressing air at a 21:1 ratio on each compression stroke. That takes a fair amount of force...while some of that is returned to the crank in the "power" stroke (I use quotes since, if no fuel's being injected, you don't have combustion like you normally would), you're getting nowhere near 100% of your force back (if you were, you'd have a perpetual motion machine ). That will in turn make the engine (and in turn everything attached to it, up to and including the wheels) want to spin more slowly. This is magnified at higher RPM's, hence my comment about wanting to keep the engine close to the governor on deceleration (that's also coming directly from CDL training).

An exhaust brake gives the engine something to push on...instead of the exhaust gases venting through the pipe to atmosphere, the pressure stays in the engine instead, effectively doing the same thing as a compression stroke does in the exhaust stroke. (BTW, an engine compression brake a.k.a. a Jake Brake is exactly the opposite...it pops the exhaust valve open at the top of each compression stroke, so the engine has to work to compress the air but doesn't have any of that helping to push the piston back down.)

FWIW I've never driven an IDI with an exhaust brake installed, but we have a bus at work with a 6.7L ISB and a factory exhaust brake. The ISB's compression ratio is more like 17:1, and I've noticed that, with the exhaust brake turned off, the ISB does not engine-brake nearly as well as my 6.9L does. I suspect that that's due to the lower compression ratio, exacerbated by the larger vehicle mass. Turn the exhaust brake on, however, and it's night and day...with the exhaust brake on, the ISB slows a 26,000lb bus at the same rate as my 6.9l slows an empty 7,000lb truck.

As to putting stress on the drivtrain...I don't think there's any way any sort of engine braking will put more force on the drivetrain than the engine does on acceleration. However, the stress is in the opposite direction, which as I understand it is what the GV has problems with. I don't know how the E4OD handles this stress, but I have a ZF5 and I've been aggressively engine-braking this truck since Day 1 and have had no problems in over 50K miles Also, keep in mind that Ford designed the drivetrain for gasoline engines that turn a much higher engine RPM than our diesels do. The limiting factors in drivetrain RPM are the engine and Smokey Bear

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...the other parts of the drivetrain will happily spin as fast as you want. So, running the engine close to the governor without any fuel being injected won't do any damage to the rest of the drivetrain. I'm actually not sure why the GV units don't really tolerate it; might have to do with how the oiling system is handled on the unit?

Seeing as the PO installed the GV and the US GEARS exhaust brake do you think that using these to in conjunction, while towing would be ok? as your not winding out the trans like when (governor/no-exhaust-brake) "engine braking".

I wouldnt think the PO would go to the trouble of dumping $1800 plus install on an exhaust brake he couldnt use with the trans he spent like $4g's on....?

He may not have known about this issue...I don't really follow GV-related news that closely since I have a U.S. Gear. I don't know if GV explicitly warns people about this or not; what I do know is that people on here have had GV's blow up and determined that engine-braking was a considerable factor. To quote an earlier post on this thread,

Yes, you can break a GV just backing up with a load (even gv disengaged). GV engaged in reverse is BAD.

That sounds to me like GV units don't handle backwards rotation very well, which would fit in with them not liking the reverse stress that engine braking produces.

With all due respect to the PO, he probably had the exhaust brake and the GV installed at different times, and no one told him about the potential problem...especially if the GV was installed first. Just because the PO thought doing something was okay doesn't automatically mean that it is...for that matter, quite a few people buy trucks and spent months undoing things that a previous owner shouldn't have done

 

[jay22day]

With all due respect to the PO, he probably had the exhaust brake and the GV installed at different times, and no one told him about the potential problem...especially if the GV was installed first. Just because the PO thought doing something was okay doesn't automatically mean that it is...for that matter, quite a few people buy trucks and spent months undoing things that a previous owner shouldn't have done

Yeah its hard to say. The trukc had 3 PO, the second was the OO son, third the farmer i got it from. What ive learned since lifting the cab off the frame is the GV unit has a '92 date and the truck is a '93. I think the OO bought the truck and put the GV on when it was almost new/new. The controler of the US gears dates back 15+ years, its the first style, making it 15+ years old. Brake could have came after the trans. I tihnk im going to give GV a call and talk to a tech about it before putting the exhaust brake back into service.

BTW i found the gv contorler mounted UNDER THE CARPET.....(seriously???) under the foot petals....***? seems like an ignorant place to install an electrical controller.... maybe this a popular spot for them? idk?

i plan to move it away from moisture..... ha

thanks for that awesome response and clarification warden!!!!