7.3 L V8 Ford 53 Chassis transmission shifting

[txc2936@yahoo.com]

I have passed the 8000 mile point on my RV. The engine, transmission have broken in nicely. Oil consumption is minimal and fuel burn steady at about 8.2 MPG.

I am finding that the RV now cruises at 70 - 75 mph at 2500 RPM easily.

However, when needing to pass someone, pressing on the gas pedal causes the RPM to rev beyond 4000 RPM.

Is this normal in Drive mode? I haven't viewed what gear i am dropping down too, I have been pulling foot off the gas pedal. Is this at the max speed of the RV and there is something similar to a speed governor happening

Thanks

[Bill Johnson]

What does your tach say? It's not a problem. Back in the day I had an engine this size and I shifted every day day at 6,000 once I hit 7,000 and it didn't hurt the engine. They say this engine is good for 1,000 horse power. If the engine shifted at 5,500 that's what Ford set it for

[Chance]

Originally Posted by txc2936@yahoo.com

.....cut..... Is this at the max speed of the RV and there is something similar to a speed governor happening

Thanks

The 7.3L V8 makes maximum power at 5,500 RPM when in smaller Super Duty pickups, but when installed in larger trucks and motorhomes, Ford limits maximum power to 3,900 RPM. That’s not to say the engine can’t rev (spin) faster than 3,900 RPM, but it won’t make more power. I would not necessarily call this a governor, but it essentially works like one based on Ford data I have seen.

By the way, if you’re going from 2,500 RPM in 6th gear to over 4,000 RPM from a downshift, you’re going down more than one gear. Perhaps you can shift down more gradually and avoid revving engine over 4,000 RPM if that concerns you.

[16ACE27]

Originally Posted by txc2936@yahoo.com

I have passed the 8000 mile point on my RV. The engine, transmission have broken in nicely. Oil consumption is minimal and fuel burn steady at about 8.2 MPG.

I am finding that the RV now cruises at 70 - 75 mph at 2500 RPM easily.

However, when needing to pass someone, pressing on the gas pedal causes the RPM to rev beyond 4000 RPM.

Is this normal in Drive mode? I haven't viewed what gear i am dropping down too, I have been pulling foot off the gas pedal. Is this at the max speed of the RV and there is something similar to a speed governor happening

Thanks

The V10 F53 chassis was speed limited at 77 Mph. I imagine the new F53s are the same. When speed limited the engine doesn't downshift or over rev, you just get no response from pushing harder on the gas pedal.

[Bill Johnson]

I'm sure staying with traffic I have gone at least 80 mph possibly faster before I noticed and slowed down. I'll try it this spring and see if it's governed, when I get on the expressway

[Sappy2]

You must also note that when downshifting two things happen. The convertor uncouples and the gear ratio changes. Both contribute to increased RPM noted on downshift (and that RPM you cited is fine). But I gotta be honest, cruising at 75+? The tires are really rated for 75MPH (maybe a bit more depending on brand). More power to you, but myself, that is a bit too fast for me. Just my opinion.

[RACarvalho]

Originally Posted by txc2936@yahoo.com

... when needing to pass someone, pressing on the gas pedal causes the RPM to rev beyond 4000 RPM.

Riding @ 4000 rpms is not a problem in itself but, what is the throttle position?
Throttle position is a kind of "measure of effort" for the engine so if you are pedal to the metal at 4000 rpms you need to understand that you are requiring everything that the engine have... Again, it will not damage the engine but usually will not make it last longer either....

That being said, from my previous boating days, I learned to track kinetic energy for safety reasons:
If the wind and waves goes up, the boat speed needs to go down.

The reason is that kinetic energy (what you need to transform in heat to brake) increases with the square of the speed so for example, an increase from 65mph to 75mph is only a 15% increase in speed but a 33% more in kinetic energy (what your brakes need to dissipate in order to stop).

It is "only" a 10mph increase in speed but now the same brake system needs to deal with 1/3 more energy (work) !!!

That is the reason why many people rear end others for they don't realize that a "small" increase in speed translates in a huge change in braking workload....

We have a very nice weight police community but I'm still to see a speed police group...

By the numbers, being 15% overloaded is way less dangerous than being 15% above 65mph...

[txc2936@yahoo.com]

Thanks for quick responses. The RV is in Drive at 6th gear, and at cruise.

Its more like 16 ACE mentioned above, its like the pedal has no more response, and then kicks in a high RPM. I back off totally on the throttle and it seems to have full power again. I'm not advocating operating at max tire speed, i just want to know if FORD has designed something into the RV i should know about. I searched the web and have found some info below.

Fine. Now i know there is a limitation, and will drive accordingly. My aeroplane has what we call a Vne never exceed speed. A line on the speedometer would go along way here on the paved highway.

[Beau388]

Originally Posted by Sappy2

You must also note that when downshifting two things happen. The convertor uncouples and the gear ratio changes. Both contribute to increased RPM noted on downshift (and that RPM you cited is fine). But I gotta be honest, cruising at 75+? The tires are really rated for 75MPH (maybe a bit more depending on brand). More power to you, but myself, that is a bit too fast for me. Just my opinion.

Due to heat generation the 6 speed's computer does not unlock the computer in 5th gear. You must be in 4th gear or lower for the computer to unlock the computer or at least that the way mine works. If you do a full throttle acceleration from about 30 mph, you can feel and see (on the Tach) computer lockup in 4th before shifting into 5th.

[FloridaFlyer]

Originally Posted by txc2936@yahoo.com

{snip}

I am finding that the RV now cruises at 70 - 75 mph at 2500 RPM easily.

{snip}

Thanks

Wowzers! 75 mph in your 33’ Classs A?

What, if I may ask, if anything do you have to mitigate the blowout of a front tire?

If nothing, I suggest looking at Safe-T-Plus steering stabilizer and/or Tyron Bands. The latter are more expensive than the former, but provide better protection. The life you save may be your own.

[txc2936@yahoo.com]

I don't drive that fast and would never advocate running these RV at max tire speed. The original intent of the post was about the engine or speed limit i was noticing.

Your in FL and see I-95 where im in the right lane at 68 mph, and travel trailers on those small tires, Large Diesel pwr RV with trailers attached are zooming by on my left. I'm like SLOW down dude....

65-68 is the sweet spot on the RV. There are pretty good video on front tire blowouts, and it goes against just slamming on the brakes. Actually, adding pwr to stablize the side loads, and steering clear. Good educational video.

[Chateau_Nomad]

Originally Posted by FloridaFlyer

Wowzers! 75 mph in your 33’ Classs A?

What, if I may ask, if anything do you have to mitigate the blowout of a front tire?

If nothing, I suggest looking at Safe-T-Plus steering stabilizer and/or Tyron Bands. The latter are more expensive than the former, but provide better protection. The life you save may be your own.

Agree! And what's the rush?? Slow down and enjoy the trip. Don't get me wrong... I'm not the speed police... you go as fast as you'd like. But... as stated above, you are responsible for unfortunate situations you put the people around you into.

I have my rules which work for me... you do the same. I guarantee driving 75 - 80mph in a motorhome is going to give you extremely poor fuel economy. So if 8mpg is your style... go for it. I simply prefer a much more relaxed pace... less stress. After all, it IS a "recreational" vehicle, not a cross-country racing vehicle.

[txc2936@yahoo.com]

Thanks and i will be more cognizant of the speed. This 7.3 L engine is alot of pwr for me. Ive done even better, i have a big red line on my dash now. ...like the Nascar guys on pit lane speeds.

[ducksface]

I have no idea why a tach was put in an rv.
Worthless. It only adds distress.
An actual billion vehicles were built without a tach.
Rev limiters and computers make a tach just a visual toy.

About speed.
If you can't keep up with traffic, get out of traffic.
Mazzillions of mile, at highway speeds on an rv sized vehicle happen every. Single. Day. Worldwide.
Front tire blow out? I posted a video a while back if an rv running on a front rim at 85mph for about 30 miles. She was very drunk. Excellent driver though. Be excellent.

Do the speed limit. It's easy.
A speed limit is designed so the worst half blind, partially drunk person can navigate the road at that speed.
A speed limit isn't an upper tier...it's the lowest common denominator.

The hurry isn't mine.
The hurry seems a hurry if you're afraid of your vehicle.
The hurry is actually just the flow of traffic... That 99.9999% of drivers accomplish.
I will not impede.


Not trying be mean, just trying to understand how being an impediment is some right of retirement.

[RACarvalho]

Originally Posted by ducksface

I have no idea why a tach was put in an rv.

I actually use the tach. but it is a shame that vehicle manufacturers don't spend time educating people on how to use it.

I use it when going up a long incline that I know the MH will not be able to keep the cruise control set speed.
If you leave it on its own, the cruise control will just floor it, downshift to the gear that gives you maximum speed and then you will be stressing/wearing out your engine @ almost the maximum rpm all the way up and burning more fuel.

Instead, I know that maximum torque in my engine is around 3500rpm so I take cruise control off, give it 75% throttle, keep 3500rpm and go up the mountain whatever speed this condition give me.

Because the gear ratio is designed for this, I usually will get a speed that is higher than the semis and not too slower than simply flooring it.

The difference is that the cruise control will try to keep maximum power which, in a gas engine, tends to be closer to maximum rpms, while I keep it at maximum torque, which will give me the minimum fuel consumption and wear...

BY the end the time to the top difference is almost nothing but you preserved your drive train, used less fuel and had less stress...

Because the MH transmission has only 6 gears, you don't need to manage the transmission but just for information, in my previous rig, that had a 400hp V8 and a 10 speed transmission, I would limit the transmission while towing on flat to 8th gear (1st overdrive) and when towing on the mountains to 7th gear.
The reason is that the wacko that programed that transmission set it to upshift as soon as possible (3rd overdrive while towing 9000lbs!!!) and when downshifting while towing skip a gear and that resulted shifting all the time and when, for example, going up IKE in Colorado it would be shifting up and down all the time with the engine running at 5000rpms (it could keep 60mph towing 9000lbs going up though).
That is just terrible.
More preferable was going up in 5th gear, w/o any shifting, at ~3500rpm and 50mph...

[ducksface]

When I'm driving the rv instead of cruising I don't use the cruise control.
Hills and inclines call for me driving. I'm in charge of the pedal.
Seat of the pants, not specific rpm dictates to me.
If I'm 100 yards from an apex I'll react differently to a high rpm than if I were 1,000 yards from it.

[RACarvalho]

Originally Posted by ducksface

When I'm driving the rv instead of cruising I don't use the cruise control.
Hills and inclines call for me driving. I'm in charge of the pedal.
Seat of the pants, not specific rpm dictates to me.
If I'm 100 yards from an apex I'll react differently to a high rpm than if I were 1,000 yards from it.

Yes, hills and mountains require control, one more reason to turn if off beyond what I said, but if you have 400 miles of flat terrain to cover in a day, cruise control helps to reduce stress and fatigue.
I drive at 65 mph so basically semi speeds.... can spend hours w/o passing anyone here in midwest...

[Chance]

Originally Posted by RACarvalho

I actually use the tach. but it is a shame that vehicle manufacturers don't spend time educating people on how to use it.

......cut.....

Because the MH transmission has only 6 gears ....cut....

Average drivers lack sufficient understanding of how engines work to be educated in this area, and especially by manufacturers they probably don’t trust. Two themes are repeated constantly: something must be wrong when transmission has to downshift at highway speeds, and ideal engine speed must be around 2,000 RPM.

Crowd-sourced internet misinformation is repeated so often by so many that educating anyone is pointless. In my opinion those who can know probably already do, and the vast majority of others either don’t care, can’t learn it, or won’t believe the manufacturer anyway.


Regarding “only 6 gears”?

3-speed manual transmissions were quite common when I learned to drive, and forced young drivers to use RPMs correctly; and also to appreciate higher RPMs for power when needed. New transmissions with 8 ~ 10 gears are more for minor gains in fuel economy than anything else.

Before long we will be forced to drive fixed-gear vehicles with no shifting at all. Electric vehicles don’t need tachometers, no one will complain about downshifts, or that the motor is revving well above 2,000 RPMs.

[txc2936@yahoo.com]

Thanks, i use the TACH constantly and have my favorite RPM for speeds. You can hear and feel the sweet spots easily now that the machine is broken in.

I have one for 55mph and about 66-68, the engine sings at those speeds,

I always disconnect the cruise control going up and down hills, wet pavement. It gets the long flat stretches on I-95.

Also, I am amazed how fast it wants to shift thru the gears to 6th gear, ugh.

Question to the Transmission Guru's? What is this Automatic Transmission Adaptive Learning programming statement in the FORD manual, page 49? Does the transmission really track your driving style and adjust the transmission?

[RACarvalho]

Originally Posted by Chance

Regarding “only 6 gears”?

Yes,
My first car had a manual 4 speed transmission and dad had a Chevy SW with the shifter in the steering wheel column... only 3 gears...

Probably you didn't pick from my previous comment that I hated that 10 speed transmission in the truck.
The first vehicle I ever had I really wanted to get rid of a few months after buying it.
Loved everything about the truck but could not stand the transmission and... the reason I love the 6 spd in the MH....

As for electric, I'll not comment on that in order to not be the reason for "another tread ruined by politics"..