Speed Brake

[TAKPAK]

Well, if I may put in my two cents worth, I too looked into the Banks Speed Brake for my 2008 LMM Duramax. After talking to three different mechanics/dealerships, I have come to the conclusion that it would NOT be worth it. Every single one of them told me that IF anything ever happened to the engine/turbo, etc, and it could be traced back to the Speed Brake, GM would NOT honor any warranty on the damage done to any components, including the engine. With a 100,000 mile warranty on the engine, I am not going to risk it. That COULD be a very expensive mistake. I also called Banks and asked them about the warranty issue. Their comment was they forsaw no problems with the Brake, but also would not cover any warranty items either.

Recently, I had a good chance to really test the "braking" feature of the "plain" Duramax/Allision combination. It was coming back down the mountain into Oakridge, Oregon. It is a 6 percent plus grade for about 5 miles, with two runaway truck ramps on it. With all our load, we weighed in at around 20,000 pounds. After two (spaced apart) depresses of the brake pedal, the tranny downshifted to third gear, truck/trailer held at 45 MPH, and the engine maintained about 3500 RPM the whole way down the hill. Sometimes I even had to accelerate a bit to keep from slowing down too much.

End result, I only had to brake twice to get my "safe" speed set, and the rest of the way down was a "piece of cake" using what was factory installed. Made a believer of the factory system out of me. Sorry Banks, but I will not be buying your Speed Brake, because of the possible warranty issues.

It may work fine, but I'll wait until I am out of warranty, OR GM approves the Brake as a retrofit. Just my personal opinion.

[Art-n-Marge]

Yes TAKPAK, exactly my feelings, AND you describe my experience exactly, but my manual says not to go past the midpoint of the Tachometer (which is 2500). I do go about 45-55 mph down a long hill and get to 3000 but check your book. It probably has a limitation for the RPMs and you are probably exceeding it.

Between you and me a diesel is tougher than they document and it should not be a problem for short periods of time, but how short is short. Unlike an owner's manual for a gasoline vehicle which states unequivocally not to exceed a certain RPM, the diesel manual says you "should not" exceed the RPMs "for very long". There are two different recommendations and the diesel one is unclear.

Another thing. If you talked to your dealer about any mods, I am sure they will not honor your warranty if there is a problem. These include, exhaust pipes, improved turbo instakes, after market air cleaners, air bags, diesel programmers, or any other engine, tranny or suspension enhancement.

I would not mention your story to a dealer if you have a problem. They'll probably give you an invoice under the you exceeded the RPMs story. I'd be interested in what your manual says is the maximum RPMs. It was well hidden in my owner's manual but I did find it. The manual is full of nebulus information.

[Carl n Susan]

quote:Originally posted by Art-n-Marge



Yes TAKPAK, exactly my feelings, AND you describe my experience exactly, but my manual says not to go past the midpoint of the Tachometer (which is 2500).....

O.K. I thought I had memorized the Ford Owners Manual, but I don't recall reading this. Where did you find this documented? Page numbers would be terrific.

TIA

[TAKPAK]

Well Art & Marge, very interesting on the RPM. In several conversations with the GM shop boys, I have been told that the computer on the engine and transmission will NOT allow for engine overspeed. According to GM themselves, the Duramax redlines at about 3900 RPM. The valves start to float at around 4200 RPM. I am definitely NOT going to try that one. Anyway, for what it's worth, they have told me to "let the truck computer do it's thing" it will NOT allow the engine to overspeed. They said it will upshift first...of course at that point you'd better be hitting the brakes and shutting it down, as basically I would say you are now out of control, or close to it. Don't know what else to say, other then I'm following the GM shop instructions. It worked really good on that hill into Oakridge and didn't seem to be straining any. Oddly enough, I was watching the transmission temperature on the way down.....it must have been doing something to help hold back. The temp climbed a bit, settling out at 190 degrees, up from 170 when I started down the hill.
Way back when, I had a 1988 Ford 7.3 diesel. It redlined/was governed at 3500 RPM.

[Art-n-Marge]

For TAKPAK and Carl (of Carl and Susan).

The Ford 2006 F-250 owner's guides consist of two small books:

1. F-Series Super Duty 2006 Owner's Guide
and
2. Power Stroke 6.0 Liter Direct Injection Turbo Diesel Owner's Guide Supplement

Book 1, Standard Owner's Guide - On page 18 the Tachometer description states "Driving with your tachometer pointer continuously at the top of the scale may damage the engine". There is no other text, and this implies that it applies to a gasoline engine since there is a diesel supplement. Keep in mind, my tachometer has no redline indicator. The tachometer starts at 0 and goes to 5 with straight being exactly between the 2 and the 3 (2500).

Book 2, Turbo diesel supplement - On page 5, like everyone has been hinting, "The engine governor is controlled by the PCM (Powertrain Control Module). The PCM controls fuel input to limit maximum engine speed. It will not, however, prevent engine overspeeding resulting from downshifting at high vehicle speed or by descending steep grades at too high a vehicle speed for the selected transmission gear." So what does this mean? All was well until the statements about not preventing engine overspeeding by descending steep grades. This is why I am thinking of an exhaust brake. There is no mention that Tow/Haul prevents this even though one might hope so.

There is specific RPM numbers on the same page under the paragraph "On F-Super Duty vehicles equipped with a manual transmission", where it states, "Do not exceed 3,600 rpm. Maximum engine governed speed is 4,000 rmp depending on engine load. Excessive rpm can only be achieved by manually downshifting at too high of a vehicle speed."

And finally on the same page as its own paragraph is the statement in bold type "Operating the engine beyond the governed speed can cause severe engine damage."

Gee, no kidding.

From all this I will ascertain the following: Use Tow/Haul when towing. On the downhill tap the brakes to keep the rpms below 3,000 so if the trans downshifts it will stay below 3,500 rpms at all times. If the descents are long, I have no choice but to use the foot brake to keep the rpms at or below 3000 rpms (to minimize an engine overspeed condition). In the Southwest, has anyone been on westbound HWY 101 near Camarillo/Thousand Oaks or on northbound I-5 (The Grapevine) or eastbound I-10 between Indio and Chiriaco summit? Those are miles long, steep descents where I get to practice profiency using Tow/Haul and my tachometer while towing my lovely Montana.

I still believe an exhaust brake will help in due time.

Thanks for your support!

[sreigle]

We towed several years of our fulltiming with Ford 6.0L diesel trucks. What I found is that the transmission (automatic with tow/haul engaged) WILL NOT downshift if it will cause the engine rpm to exceed a safe level. Instead, you will require judicious use of the brake pedal. I personally would not worry about a downshift causing an unsafe rpm although I always keep my eye on the rpm anyhow. It just never happened.

Art, you said in several posts that the manual says not to exceed 2500 rpm. That must have been a typo?

[Art-n-Marge]

Hey Steve,

Book #1 (see my prior post) said to not use the tachometer continuously at the top, which is 2500 RPM on my tach, but I expect this is for the gasoline engine! This is what I was referring to and hadn't found a "number" for diesels.

In the same prior post about Book #2 (the diesel supplement), and with help from MOC members, I was able to locate some text that matches what you are talking about, but I still prefer to know a "number", just in case the PCM loses its mind I want to know where the tach should be. The manual transmission has values of the type I was looking for as you'll read in another paragraph in the prior post.

The bad news is if you look at other statements in Book #2, there IS NO downshift protection!

Bottom line, with the cost of an after market exhaust system, I could pay for quite a few brake jobs. I will be monitoring the RPMs on the downhill and use the brakes to help slow me down if I find the rig going too fast and not downshifting fast enough, but I must STILL monitor the RPMs to keep the tachometer below 3500/3600 when this happens and avoid the "redline" of around 4000-4100. Before I started this post I constantly monitor my Tach but I DID NOT know what values to monitor it for. It took a lot of figuring out, instead of being unequivocally stated. If I find I am having difficulty staying in these safety zones, I'll have to find the funds for an exhaust brake.

btw - I looked at my dash tachometer and all the oulined numbers look the same during the day and at night unlike the pictures you posted where it looked like the "1" and the 4" were different. You might be right, camera angles and lighting could have distorted things. Thanks for your help on this.

[sreigle]

Art, I did read your other post and that's why I asked the question. "Top of the scale" does not mean needle pointing straight up. It means needle at the highest number on the scale. Top of the SCALE, not top of the meter.

I am pretty sure the TorqShift will not downshift if it will cause an overspeed situation. I no longer have either my 2003 or 2005 Ford 6.0 so can't run out and test it. In any case, I don't really think it's a problem worth worrying about. We put a lot of miles towing with our Fords and didn't have any overspeed problems. But that's just my opinion.

[Art-n-Marge]

Perfect Steve! You hit on my exact point that semantics is causing this problem. And the lack of a number or indicator like what has been historically provided in most cars and trucks I've owned.

Why don't they just use a NUMBER (a positive integer) like they did for diesels with a manual tranny? This would eliminate semantics and misinterpretation. This way the owner knows EXACTLY what to watch for, in case the brains in their vehicle dies and we need to still know what's safe.

My prior F-250 had a problem with the Tow/Haul when driving slow and towing, that when it downshifted into 2nd or 3rd gear at low speeds the vehicle/tranny made a terrible clunking sound. They replaced a component in the truck under warranty and even seeing I had Banks components and gauges, all was good after that, so Tow/Haul mode has been known to fail for me.

[RCN.Stoker]

First thanks for this thread. I have learned more about the tow/haul system in my D/A GM here than from my manual. Just one question, if I may. When I was descending a long grade my transmission shifted twice. The second time was when I braked to slow further and the tach hit over 3500 rpm. I was a bit worried about braking again so I used the manual trailer brake control to slow down to a more comfortable engine speed. Is this OK? I have since also used it in the city when a driver cut in front of me just as a light changed.

[sreigle]

RCN.Stoker, I've never towed with the GM but I think the tow/haul is very similar to the one in the Ford and Dodge, both of which I have towed with. In ours, there is the automatic downshift (if rpm will not be overspeed) when two things happen. One is that you are not giving it any throttle and the other is the speed climbs a few mph above the cruise setting or the speed when you let off the throttle, if not on cruise. The other way it will downshift is when you are off throttle and you step on the brake. Again, only if it will not overspeed. This overspeed situation is still in debate in this thread but that's how my Fords and my Dodge work. I'd bet your GM is pretty much the same. That would account for the second downshift. On my trucks, you could then apply additional braking, as needed, and it would not downshift again unless doing so would not cause the engine to go over the prescribed max rpm. Again, this is being debated in this thread but that is how mine worked. We've towed up a 14% grade but the highest percentage downgrade we've done is either 10 or 12 percent, I can't remember which. I know we've gone down 10 percenters and climbed two 12 percenters but I don't recall what the downhill side was on those 12 percenters. Those were all in Utah, between Moab and Bryce Canyon NP.