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  #1  
Old 02-09-2014, 10:39 AM
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Top speed for '78 in 4x4?

We got 6" of snow last night, which spurs the question, what's the top speed for a '78 F250 with an NP205 when shifted into 4WD high? I've heard 35mph is the limit on dry roads, but what about in snow?
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Old 02-09-2014, 10:52 AM
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I have run my 205 80mph down the interstate on snow covered on icy roads. (Long Staright Nobody around me) I dont think there is a speed issue. On dry roads, different story
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'65 F-250 4x4 w/ '76 460
Under construction: "Black & Bad" '79 F-150 4x4
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Speed demon, Comp 4x4 extreme cam, edelbrock RPM
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  #3  
Old 02-09-2014, 11:20 AM
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I never heard the 35 mph limit and I've had my '77 a long long time, it has a NP205 and locking hubs .... but if I had hubs locked and NP205 in 4WHI or 4WLO, I wasn't going fast enough to consider it either.
If the roadway was so that I was looking to go 55, the NP205 was in 2WHI, hubs locked or unlocked.

Quote:
I run my 205 80mph down the interstate on snow covered on icy roads.
During my years as a Trooper I always found it "odd" (usually "odd" like funny , not "odd" like rare .... but should have been rare .... and I remember one 4wd snow wreck that was especially sad ) how so many 4WDs (AWD, 4X4, etc) would wreck after long slides in snowy and-or icy conditions (and often a driver explaining later "But I had it in 4WD" ) ....
.... while I operating a always 2WD patrol car with open differential who was required to work (often extended shifts) and get to these wrecks .... never had a snow / ice wreck or spin out ..... in 31 winters .... and over a million patrol car miles.
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Old 02-09-2014, 12:13 PM
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I had my 78 150 np 435 with the 205 tcase in 4hi as high as 55 with out an issues. The reason was purely incidental on my part. Although that does not mean I was without blame. I had let my brother borrow the truck earlier that evening to go to my uncles house from my moms house. He didn't tell me he had it and 4hi and didn't disengage it. And I didn't check before I left my mothers for my house when I got back in it. Yes it was snowing pretty bad that night. But I only use the 4x4 when I absolutely need it. Not just every time it snows. Or I'm in mud. So that's why I say I'm not entirely without blame.
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Old 02-09-2014, 01:09 PM
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Quote:
Originally Posted by tbear853 View Post
I never heard the 35 mph limit and I've had my '77 a long long time, it has a NP205 and locking hubs .... but if I had hubs locked and NP205 in 4WHI or 4WLO, I wasn't going fast enough to consider it either.
If the roadway was so that I was looking to go 55, the NP205 was in 2WHI, hubs locked or unlocked.



During my years as a Trooper I always found it "odd" (usually "odd" like funny , not "odd" like rare .... but should have been rare .... and I remember one 4wd snow wreck that was especially sad ) how so many 4WDs (AWD, 4X4, etc) would wreck after long slides in snowy and-or icy conditions (and often a driver explaining later "But I had it in 4WD" ) ....
.... while I operating a always 2WD patrol car with open differential who was required to work (often extended shifts) and get to these wrecks .... never had a snow / ice wreck or spin out ..... in 31 winters .... and over a million patrol car miles.

Lol... I should have seen that coming. And duely justified might I add. Now I probably have the NSA looking at me too. Lol...

Bryan,
Before I Hi jack here, Let me say I too have never heard of a 35 mph rule on dry pavement. 4wd's and AWD can run at full speed with out issue all the time. PROVIDED there is No Binding between the front and rear axles. AWD vehicles do this with the use of either a viscous coupler or a clutching mechanism in the transfer case. This mechanism allows for slight differences in either travel distance or speed between the front and rear axles. That's why it isn't a big deal driving in 4wd on snowy or dirt roads. If there is a bind going on, it will relax through tire slippage to the road surface.

Again it is the bind that causes damage. Like TBear says, he'll drive at speed with the hubs locked in but with the T-case in 2wd. Doing so, spins all the pieces and parts at full speed, but no binding at all. it's just a little extra wear and tear on the front end and wastes abit of fuel. But provides the convience of simply shifting into 4wd with out having to get out and lock in the hubs. I'll shift mine in and out of 4wd on the fly up 50-60mph. I'm not suggesting you do that, just saying it can be done

Going around corners, different size tires front to rear will cause binding. Put it in 4wd going 2mph with the steering wheel turn all the way one way and your truck will buck and jump. That is binding. Slow or fast it is not good. If you have a full load (great Traction) on your truck, dry pavement, turn the wheel to the lock position and go slow, You will break something. If the front and rear go different speeds in 4wd, something has to give.

here's another thread on the topic.
http://www.ford-trucks.com/forums/12...-into-4x4.html

Now for the Hijack.
TBear You are absolutely Right. I would feel absolutely terrible if someone was hurt of killed due following some dumb *** direction from me.
With that said, I was trying to convey there is no top speed for a '78 in 4wd. At least that I know.

Back to TBear's Point,
4wd is NOT safer than a 2wd in any winter or limited traction condition. I believe there are substantial statistics that show they are more dangerous as drivers become over confident and do venture into speeds that can unravel very quickly. Safety is in the driver (like the gun Owner).


Quote:
Originally Posted by tbear853 View Post
never had a snow / ice wreck or spin out ..... in 31 winters .... and over a million patrol car miles.
because you understand the principles and know how to drive. I too have done extremely well with winter driving for 31 years. knock on wood. I really wish we could say the same for others, as i have seen far too many tradgedies along I-196 this year.

You dont live in Florida, do ya? Kidding

I'm no expert, but I did stay in a Holiday inn Express once

Shawn
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'65 F-250 4x4 w/ '76 460
Under construction: "Black & Bad" '79 F-150 4x4
351w, 435np, 205np, TFS Twisted Wedge heads,
Speed demon, Comp 4x4 extreme cam, edelbrock RPM
AirGap, NOS Powershot, detriot locker, w/a '73 grille
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  #6  
Old 02-09-2014, 01:19 PM
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Thanks guys. I'm a firefighter and have plenty of first hand knowledge of folks doing stupid things behind the wheel. I'm not looking for how fast I can get away with, but simply whether or not I'll have issues pulling up a snowy pass at 50 in the snow in 4wd. That helps, thanks!
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  #7  
Old 02-09-2014, 04:23 PM
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Haha Drac .... I wasn't flaming you. I was just pointing out observations of mine over the years. Some of those I mentioned maybe did hit 80, 70, maybe just 50, most just whatever the speed limit was probably .... but you noted the point .... "overconfidence" as you say.

I am not without my dumb stunts either, like the snow / sleeting evening many years ago as a young Trooper when I had a 4WD SUV pass by me on I-81, roadway looked mostly wet but snow was sticking to shoulders and trees and stuff .... and I paced it at near 80 and then activated the lights and when I stepped out imagine my "self criticism" when I could hardly stand up on the icey road. It was just starting to freeze, not glare ice, but not just "wet" either. It didn't matter to that driver, the limit was 55 and anything from 75 up was reckless even on a dry road then. I didn't pace anymore that evening, that experience taught me to pay closer attention before taking action, like "let it go and be there to work the wreck" next time it's maybe slick. I've been lucky to have survived to gain some experience and better judgment.

I live in The Shenandoah Valley, we get some good snows between these mountains.

This was me cleaning some before marking on for duty Saturday early AM after working 16 hours Friday December 19-21, 2009 .... police car is sitting in distance where I managed to get it parked night before.

Click the image to open in full size.
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There's 2007 and there's 1977...
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...
and whatever you do, Have a Safe Trip!
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  #8  
Old 02-09-2014, 05:52 PM
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Its all good. I tend to try keeping myself under control, as my 600+ posts in 12 years may suggest. I know one of my weakness is not thinking before I speak therefore I tend to shutt'er up.
I was raised to think i am being one of those patriotic, one the fringe, American exceptionalist believing in personal responsibility and harm to non. in today's day and age it called being an outlaw. Lol...

Thanks to both of you for your service
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Shawn
'65 F-250 4x4 w/ '76 460
Under construction: "Black & Bad" '79 F-150 4x4
351w, 435np, 205np, TFS Twisted Wedge heads,
Speed demon, Comp 4x4 extreme cam, edelbrock RPM
AirGap, NOS Powershot, detriot locker, w/a '73 grille
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  #9  
Old 02-09-2014, 06:15 PM
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Quote:
Originally Posted by Drac View Post
Its all good. ... etc ... I know one of my weakness is not thinking before I speak therefore ... etc ...
No doubt! .... and I do that too, I just use the edit feature ....
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and whatever you do, Have a Safe Trip!
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  #10  
Old 02-09-2014, 06:43 PM
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Why would the driveline bind with the hubs locked and making a turn in 4x4? Shouldnt the differential allow one wheel to rotate faster and prevent binding in a turn? Assuming the pinion gear ratios are the same and the diffs are not locked, what else is left to bind up.
?
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  #11  
Old 02-09-2014, 06:57 PM
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The front of the truck makes a larger circle than the rear, so it travels farther. It's the 2 drive shafts that bind up in the T-case.
Look at the tracks it makes in the snow or dirt. The front tire makes a wider arc.
The rear of the truck trails behind and takes a short cut to catch up. Like a Semi tractor trailer, the trailer cuts a smaller radius. That's why they alway are going over the curbs or cars when they turn.

The open style differential corrects this problem within a given axle, but not between the front and rear axles. Think about it like the two drive shaft are the axle shafts and they are locked with a spool. They will turn evenly. (unless it is an awd T-case or a NP203, which I reecently heard has an open type differential inside it)

True, it is not much, but it is enough to bind up the gears.
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'65 F-250 4x4 w/ '76 460
Under construction: "Black & Bad" '79 F-150 4x4
351w, 435np, 205np, TFS Twisted Wedge heads,
Speed demon, Comp 4x4 extreme cam, edelbrock RPM
AirGap, NOS Powershot, detriot locker, w/a '73 grille
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Old 02-09-2014, 07:05 PM
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I have just put my 77 highboy on the road after a ton of work and it has been siting for along time, I have noticed when in 4x4 at anything over 50mph it seems to buck ? kind of kick back through the driveline, I have checked and re checked everything u joints driveline phasing etc so not sure on how fast to you can drive in 4x4 I just know my truck does not seem to like it at highway speeds for some reason
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Old 02-09-2014, 07:24 PM
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Quote:
Originally Posted by 64rarebird View Post
I have just put my 77 highboy on the road after a ton of work and it has been siting for along time, I have noticed when in 4x4 at anything over 50mph it seems to buck ? kind of kick back through the driveline, I have checked and re checked everything u joints driveline phasing etc so not sure on how fast to you can drive in 4x4 I just know my truck does not seem to like it at highway speeds for some reason
2 things come to mind quick

The tires have to perfectly the same size, meaning wear also. Jeep would not warranty a newly installed T-case on our AWD Grand Cherokee unless we put all new tires on it.

Not sure about the 250's, but the ford 9" rear end and the Dana 44 would have different ratios at the 4.10 ratio. one of them ( can't rememer which is 4.11 the other is a 4.10.

Does it do this on Wet, snowy, Icy roads? If so, then it's something else.
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'65 F-250 4x4 w/ '76 460
Under construction: "Black & Bad" '79 F-150 4x4
351w, 435np, 205np, TFS Twisted Wedge heads,
Speed demon, Comp 4x4 extreme cam, edelbrock RPM
AirGap, NOS Powershot, detriot locker, w/a '73 grille
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Old 02-09-2014, 07:43 PM
64rarebird 64rarebird is offline
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Truck has new 35" matching tires front and rear, new u joints all 3 driveshafts, cleaned and lubed slip yokes , matching gear ratios etc, I also just replaced the divorced transfer case mounts, I am sure this is not normal as a 4x4 should be able to be driven at highway speeds when in 4x4, for me the road conditions do not seem to make a differnce, the only thing i have noticed on my truck , is the previous owner has put new front leafs in and the truck sits slightly higher in the front so maybe my pinion angles are not correct. I have owned and driven several 4x4's and awd vehicles with no high speed 4x4 issues however this highboy is new to me so still working out the bugs
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Old 02-09-2014, 08:00 PM
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Does it shake?
With the hubs locked and T-case in 2wd does it do it?

If you're on and snow covered road and it does it, then its not going to be a binding situation. Maybe a balance issue. Any dings in the drive shafts?

They do all have personalities, and will tell you what they don't like.
It's not the full time 4wd - NP203 Is it?
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'65 F-250 4x4 w/ '76 460
Under construction: "Black & Bad" '79 F-150 4x4
351w, 435np, 205np, TFS Twisted Wedge heads,
Speed demon, Comp 4x4 extreme cam, edelbrock RPM
AirGap, NOS Powershot, detriot locker, w/a '73 grille
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Old 02-09-2014, 08:00 PM
 
 
 
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