RPM, Downhill, Exhaust Brake

svoshop · 03-22-2021, 11:00 AM

Ok, so I used the title as search terms I looked for first.

I am using a Toad for the first time. 20 Wrangler. I have a Blue-Ox and Air Force One system.

I went out for a little test run, and when using the exhaust brake during a decent grade, at 65 MPH, the transmission downshifted to bring the engine up to 2500 RPM.

That did a great job of slowing the coach and reduced me having to use any brake input. However, I felt like I was really winding the motor up more than I wanted to ask some of you with more knowledge than me.

Thanks

Mike

Grumpy · 03-22-2021, 11:34 AM

Quote:

Originally Posted by svoshop

I went out for a little test run, and when using the exhaust brake during a decent grade, at 65 MPH, the transmission downshifted to bring the engine up to 2500 RPM.

Red line is 3,400 if I remember correctly, so your not in an over-rev. What would the RPM be going up the hill at 65?

svoshop · 03-22-2021, 11:43 AM

Quote:

Originally Posted by Grumpy

Red line is 3,400 if I remember correctly, so your not in an over-rev. What would the RPM be going up the hill at 65?

I don't think it will pull 65 up hill LOL...

I usually take control up hill and keep it 1800-2000, as the stock programming will let it lug around 1400 rpm and gain ( more than likely lose ) speed.

It was a pretty good grade. I would be lucky to pull it at 60 MPH uphill.

Grumpy · 03-22-2021, 02:06 PM

Quote:

Originally Posted by svoshop

I don't think it will pull 65 up hill LOL...

I usually take control up hill and keep it 1800-2000, as the stock programming will let it lug around 1400 rpm and gain ( more than likely lose ) speed.

It was a pretty good grade. I would be lucky to pull it at 60 MPH uphill.

The other thing to remember, a diesel normally tolerates red line when you are not on the accelerator adding fuel.

Drv · 03-22-2021, 04:23 PM

2500rpm for the ISB typically isnt an issue. The 6.7L ISB tend to be a little more rev happy then the ISL. Your experience is similar to mine when I towed around 8k of trailer and load.

SloPoke · 03-22-2021, 04:50 PM

Quote:

Originally Posted by svoshop

I don't think it will pull 65 up hill LOL...

I usually take control up hill and keep it 1800-2000, as the stock programming will let it lug around 1400 rpm and gain ( more than likely lose ) speed.

It was a pretty good grade. I would be lucky to pull it at 60 MPH uphill.

When we are loaded (almost all of the time) at 33k# and decending 6% grades in/out of our home towns... we will kick it out of cruise and let the engine brake do it's own - we try to stay at about 60MPH and about 2,200 RPM with the exhaust brake doing all of the slowing. We could let it go a little faster, but most of our steep grades include a lot of curves too.

Drv · 03-22-2021, 04:56 PM

Quote:

Originally Posted by Drv

2500rpm for the ISB typically isnt an issue. The 6.7L ISB tend to be a little more rev happy then the ISL. Your experience is similar to mine when I towed around 8k of trailer and load.

I should add I did not and do not typically let it rev over the 2500rpm mark without brake application as needed. Brakes are cheaper to replace then an engine.

miles ahead · 03-22-2021, 06:32 PM

I must be doing something wrong; I'm pulling a 1/2 ton 4wd pickup and can't decend a 6% grade without riding the brakes even when i first slowed and put in 3rd gear?

Rustynuts · 03-22-2021, 06:56 PM

Quote:

Originally Posted by svoshop

I don't think it will pull 65 up hill LOL...

I usually take control up hill and keep it 1800-2000, as the stock programming will let it lug around 1400 rpm and gain ( more than likely lose ) speed.

Are you aware that you have 2 programs for your transmission? This is often not known by new owners as the dealers usually know nothing about it and unless you read the manual yiu don’t realize it....I stumbled across it myself when I first bought ours. Upon startup you are in Eco mode which is default programming. If you press the “mode” button so Mode lights up, then you are in performance/tow haul/superduper...whatever you want to call it, program and there is a significant difference in the shift patterns and rpm. I pretty much run in mode, every time I drive and have fount that if I leave it on cruise control and running mode, it usually pulls the hills better than manually shifting.

staineous · 03-23-2021, 02:44 AM

Quote:

Originally Posted by miles ahead

I must be doing something wrong; I'm pulling a 1/2 ton 4wd pickup and can't decend a 6% grade without riding the brakes even when i first slowed and put in 3rd gear?

If I activate the engine brake I do not manually shift. I let the transmission handle the shift for the coach.

Like rustynuts says, I use the mode button on the transmission when merging on to the interstate and when in the hills. Sometimes in mountainous terrain I will manually shift, but it’s usually not necessary. I had read the Allison manual before I picked the coach up after purchasing it and I specifically asked the dealer about the mode function during pdi. The guy had no idea what I was talking about.

As an FYI, when the engine brake is active (switch in the on position and foot off of the accelerator) the brake lights for the coach are activated to let vehicles behind you know that you are braking.

svoshop · 03-23-2021, 03:45 AM

I had read this on this forum. However, I never saw and tow/haul or indicator come on. So I assumed mine didn’t have this software.

As I look at it this am, I see that when I depress the mode, the right indicator gets smaller and “mode” comes up.

I assume “mode” means tow/haul or the less economical setting has been selected.

I work on passenger cars all day. So I guess I assumed this vehicle would comply with my previous history and knowledge base ��

staineous · 03-23-2021, 04:08 AM

Quote:

Originally Posted by svoshop

I had read this on this forum. However, I never saw and tow/haul or indicator come on. So I assumed mine didn’t have this software.

As I look at it this am, I see that when I depress the mode, the right indicator gets smaller and “mode” comes up.

I assume “mode” means tow/haul or the less economical setting has been selected.

I work on passenger cars all day. So I guess I assumed this vehicle would comply with my previous history and knowledge base ��

Yes you will see the word “mode” appear and the gear indicator get smaller. This it to indicate that the transmission is in the secondary mode, which in our case is programmed to be ‘power mode’. It changes the shift points to be at higher rpm’s so you get more performance. Also, in normal mode you can hold the accelerator to the floor at highway speed and the transmission will not downshift. In performance mode it will downshift.

svoshop · 03-23-2021, 04:57 AM

I appreciate all the feedback.

I am anxious to see what "performance" mode does

Mike

miles ahead · 03-23-2021, 06:32 AM

thank you to all who have posted to this subject, I am learning a lot. I do use the Mode function but where is the exhaust brake switch?

staineous · 03-23-2021, 07:46 AM

Quote:

Originally Posted by miles ahead

thank you to all who have posted to this subject, I am learning a lot. I do use the Mode function but where is the exhaust brake switch?

I have a 2021 S2RV chassis and it is located right next to the regen button below the window buttons.

I don’t know if the 2018.5 and earlier models have it or not, but I’m sure someone can weigh in on that.

miles ahead · 03-23-2021, 08:43 AM

Thanks, it's in storage so I'll have to drive over and take a look.

Rustynuts · 03-23-2021, 10:45 AM

Quote:

Originally Posted by svoshop

I appreciate all the feedback.

I am anxious to see what "performance" mode does

Mike

Oh you will notice a significant difference. Personally after trying both default and mode programming on the same roads, towing or not towing, I saw no difference at all in fuel mileage but the drivability is so much better in "mode" program, I drive in mode all the time. I did ask Freightliner about it and they said they actually suggested driving in mode all the time. I did ask if mode could be programmed as the default and they said it could but would have to be handled but an Allison dealer for a charge.

Rustynuts · 03-23-2021, 10:54 AM

Quote:

Originally Posted by miles ahead

thank you to all who have posted to this subject, I am learning a lot. I do use the Mode function but where is the exhaust brake switch?

The exhaust brake switch looks like in this picture. Really it can be in a slightly different position on the dash depending on how the assembler was feeling that day but most have been in this position that I have seen.

CAG · 03-23-2021, 11:44 AM

Quote:

Originally Posted by miles ahead

I must be doing something wrong; I'm pulling a 1/2 ton 4wd pickup and can't decend a 6% grade without riding the brakes even when i first slowed and put in 3rd gear?

What are you driving? Do you have tow/haul?

Another item with this issue, the computers in the vehicle in most all cases with kick you out of gear before they will allow the engine to overrev.

EA37TS · 03-23-2021, 06:10 PM

Quote:

Originally Posted by CAG

What are you driving? Do you have tow/haul?

Another item with this issue, the computers in the vehicle in most all cases with kick you out of gear before they will allow the engine to overrev.

No tow/haul on the Seneca’s. Tow/haul is a Ford gas chassis feature and not on Freightliner diesels.

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