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Old 06-29-2010, 10:34 PM   #1
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Using the transmission to control descent speed

We have an E350 van, with Quigley 4x4, a V10, and an RB50 interior. It weighs about 8,000 fully loaded, so not too heavy. Just wondering how many RPMs people get using the Tow/Haul feature to help with vehicle braking going downhill. We have been trekking up and down Tioga Pass the last couple weeks and when trying to keep about 40 mph, the engine easily goes up to 4,500 RPM or more. I still have to apply the brakes to keep things under control. Just curious if this is typical for V10s and how it compares to the diesel. I know many of you are even heavier than ours. Tioga Pass loses about 3,000 feet in 10 miles, so it's pretty steep.

Lot's of SMBs out here. Don't see them much at home.

Thanks,
Steve
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Old 06-30-2010, 02:27 AM   #2
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Re: Using the transmission to control descent speed

The diesel doesn't have the tow-haul function or at least never seen it as a possible option.

But diesel engines have a stronger engine braking power than gasoline due to the high compression ratio in the engine.
On a meet and great while on the trails, I noticed that the diesel vans went into lower gear with no break where as the gasoline vans needed to use the breaks here and there to control the speed.
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Old 06-30-2010, 06:56 AM   #3
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Re: Using the transmission to control descent speed

Quote:
Originally Posted by Steve_382
We have an E350 van, with Quigley 4x4, a V10, and an RB50 interior. It weighs about 8,000 fully loaded, so not too heavy. Just wondering how many RPMs people get using the Tow/Haul feature to help with vehicle braking going downhill. We have been trekking up and down Tioga Pass the last couple weeks and when trying to keep about 40 mph, the engine easily goes up to 4,500 RPM or more. I still have to apply the brakes to keep things under control. Just curious if this is typical for V10s and how it compares to the diesel. I know many of you are even heavier than ours. Tioga Pass loses about 3,000 feet in 10 miles, so it's pretty steep.

Lot's of SMBs out here. Don't see them much at home.

Thanks,
Steve
Tioga pass is a challenging environment for any heavy vehicle. We crossed the pass two weeks ago and our SMB weighs at least 10k. There is absolutely no way I'd descend Tioga relying on the brakes alone. I'd smell them within the first 3 miles and they would be fading badly by the bottom.

Initially I tried coming down with OD off, but that was not enough and I quickly hit 50mph. Way too fast for my comfort. I dropped the tranny into 3rd for the remainder of the descent. That worked well and kept me at or below below 40mph with moderate use of the brakes. My RPMs climbed to 2700-2800 several times. Pretty high, but not a worry.

When I have to come down even steeper roads I always switch the transfer case into low range. The SMB can safely descend very steep grades in low range, and speed is generally capped at about 20-25mph.

Rob
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Old 06-30-2010, 07:58 AM   #4
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Re: Using the transmission to control descent speed

Even 40 is too fast for me when dropping down Tioga Pass...I put it in second at the top and never touch the brakes all of the way down except when occasionally needing to pull over to let others pass. I asked a friend who is an RV and trailer tech writer about using the transmission so much in braking and he didn't think it was a problem at all.

Like Rob, I've also used Low range on really steep grades. But I asked Quigley one time about shifting into Low range without also locking the hubs and they advised against that. In such cases (such as dropping down the backside of Sonora Pass), I lock the hubs and use Low range...
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Old 06-30-2010, 01:08 PM   #5
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Re: Using the transmission to control descent speed

I just bought a 2010 2WD Ford E250 V8 gas engine and I too am interested in RPM expectations. While descending from 6500' level in Sequoia National Park I used Drive and 2nd gear quite a bit to avoid wearing out the breaks. Never got above 50 mph in Drive and could get down to 30 or so mph in 2nd gear. Occassionally tried to use 1st gear to get around a 90 degree corner without breaking, but this wasn't easy to time so I relied on the breaks to get down to 15 - 25 mph instead. I never have seen my RPMs above 4500. Seems like went to the 2000 - 3000 RPM range most times slowing down. Not towing anything and don't have a lot of wieght on, but I don't understand how that impacts RPM. Can you guys elaborate a bit more on how you watch your RPMs and what concerns you about it if anything?
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Old 06-30-2010, 02:08 PM   #6
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Re: Using the transmission to control descent speed

I've always thought that, while it's nice to use the transmission to regulate engine braking going down hills, it's a lot more expensive to rebuild a transmission than to re- pad brakes. Especially Ford transmissions which, while OK I guess, aren't even close to being in the same league durability-wise as the Allison that comes with the Dura-Max. Having said that, it's nice to not have to ride the brakes all the way down the hill.
Bill
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Old 06-30-2010, 03:14 PM   #7
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Re: Using the transmission to control descent speed

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Originally Posted by Skywagon
I've always thought that, while it's nice to use the transmission to regulate engine braking going down hills, it's a lot more expensive to rebuild a transmission than to re- pad brakes. Especially Ford transmissions which, while OK I guess, aren't even close to being in the same league durability-wise as the Allison that comes with the Dura-Max. Having said that, it's nice to not have to ride the brakes all the way down the hill.
Bill
I've heard a variety of views on this issue and would like to learn more.

But I've experienced brake fade once before on the SMB while coming down a long hill in DV (down into Panamint valley). It same on very fast and was frightening as hell. After that scare I did the brakman upgrade and resolved to rely primarily on the tranny with assistance from the brakes on long/steep descents. Interestingly, the tranny temps don't get unusually high when doing this, typically about 200deg or less.

Having dome down Tioga once now, I'd probaby also just come down in 2nd the next time. Slow is good. Just turn on the hazards and occasionally pull out to let traffic pass.
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Old 06-30-2010, 06:23 PM   #8
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Re: Using the transmission to control descent speed

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... it's a lot more expensive to rebuild a transmission than to re- pad brakes.
True, brake pads are cheaper than rebuilding the transmission but it isn't the pads that go, it is the rotors. To expand on my earlier comment, here is my original question to my friend and his response:

Back in May 2008, I wrote to him:

“We got our Sportsmobile back from Ford yesterday after having the transmission replaced with a rebuilt transmission [at around 65,000 miles by Ford under warranty]. The problem started when I got a Check Engine Light while headed up to the Gold Country and then, a 100 miles later, the Overdrive light started flashing. The mechanic's report from Ford indicates that the problem was the Torque Converter Clutch System (my Scan Gauge gave me the same diagnostics trouble codes). The mechanic goes on to report that the fluid level was okay but the transmission fluid smelled "slightly burnt" (the transmission was flushed and the fluid replaced 5,000 miles earlier). He found some metal in the transmission pan and worn bushings in the "...INT BRAKE DRUM", wear at "...NTER CLUTCH PISTON SPRING". He also found brittle seals and contamination.

“So...I'm wondering why the transmission went out so early and what caused the problem. Specifically, I'm wondering if the fact that the van exceeds the GVWR (by about 600 pounds as I recall) could be a factor and/or if downshifting could also be a factor. After warping a rotor at 15,000 miles or so, I became very sensitive to downgrades and take the van out of overdrive on any downgrade. I'll also downshift on steeper grades although I keep the RPMs completely within reason.

“I read somewhere on a post (although the poster might be wrong) that the vans ordered by SMB with the V-10 are equipped with the same transmission as those with the diesel engines (ours is the V-10) and since the diesel has more torque, I would think that the V-10 would be putting less strain on the transmission.

“Any ideas why a transmission would fail at such an low mileage and so completely?”

He responded:

“In a nutshell, here's the reply from my other tech guy. He wants to use your letter in the RV Clinic column in Trailer Life, so here's his reply:

"Based on the number of complaints I’ve received from readers over the years, these transmissions are fairly trouble prone, especially the converter clutches (the aftermarket makes a lot of H-D replacements) and the overdrive clutch packs. Burnt fluid and brittle seals are indications of slippage and excessive heat. You probably do a lot of mountain driving in the steep Sierra Nevada range. I’m thinking that the fluid has gotten quite hot a number of times. I recommend flushing the system and using synthetic fluid, install a fluid temperature gauge and monitor it carefully, keeping temps below 275 degrees on grades. — K.F. "

“In short, you did nothing wrong, per se, it's more like a problem with the transmission, in our experience.

“As you observed the tranny is designed for use in much larger rigs with huge trailers tacked behind, resulting in much higher GCWRs, so overloading isn't a problem.

“One thing to consider: As soon as you hit the uphill grades and start prowling in the mountains, shift out of overdrive. Frequent hunting back and forth between OD and DIR gears will heat up and damage transmission parts as fast as overloading it. OD isn't made for the hills. The little extra fuel you burn is still, at today's rates, cheaper than another rebuild. I seem to recall that you have somewhat taller than stock tires, and that effectively reduces your final drive ratio, and that's also contrary to OD use in hills. If you install the trans temperature gauge and keep an eye on it in the mountains, you can probably see temp differences based on what gear you select. It's a good diagnostic tool.

“Your downshifting and use of the transmission to aid maintaining the vehicle speed on downgrades is fine. Overspeeding the engine is the chief potential problem here, but as you say, you keep the engine rpm within reason so that’s not a problem in this case. Move clear down to 3rd or 2nd on some of those really steep Sierra grades and apply gentle braking now and then as needed to help maintain a safe road speed and engine rpm. Your V-10 can also turn a lot faster than you might think, as these new engines are designed to make power, and thus operate, at significantly higher RPMs than the older big blocks of muscle car days.”
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Old 07-01-2010, 11:38 AM   #9
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Re: Using the transmission to control descent speed

I always use down shifting as braking on steeper grades but only on longer sections of roads. Constantly shifting from drive to lower gears should be avoided when your brakes can be used for short periods. When I'm driving in town where the trany runs through all the gears and into OD only finding I have to stop again, I keep the OD off just like in the hills. It's the constant shifting I'm told by our shop mechanics that's bad on it.

There are other posts on the site that discuss this issue.
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Old 07-01-2010, 12:16 PM   #10
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Re: Using the transmission to control descent speed

Ok I have to add my $.02 to this thread.

How I was taught to drive is to control you speed on long down hills descents using the engine and transmission. Here is why, say you are at the bottom of a long hill and come around a corner to find a stalled car in your lane and traffic in the opposing lane. If you are driving a heavily loaded vehicle and you brakes are really hot you may find that when you jamb them on they have nothing more to give. Heaven for bid someone is serious hurt in this scenario and you are driving a vehicle that is over its GVWR. You better know a good attorney! In my book better a wrecked transmission than a wrecked SMB.

Off road the same applies but for different reasons. If you are going down a steep grade where you should be in low range to control you speed but instead you are relying on you breaks and something happens to your breaks, like a large stick gets kicked up by a tire and tears you break line loose. Now you have no breaks and can't shift into low range because you are moving to fast.

One other thought, with the Ford transmissions you want to keep the fluid temp below 240 unless you want to give the underside of the van a bath in transmission fluid. At 240 they will boil the fluid out the breather vent. I learned this one the hard way.

John
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