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Old 08-09-2013, 11:41   #1 (permalink)
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F-150 No Overdrive?

I just traded a bike of mine for a 91 F150 that I'm giving to my father. I'm trying to work out the bugs before I haul it out to him. The check engine light is on, I think due to some shoddy wiring that looks like it has been RTV'd in place. It sometimes feels like it hits a flat spot when accelerating. The previous owner said he believes that his "mechanic" friend messed with the timing, so I plan to check to see if that is correct. The A/C was retrofitted to r134a, but isn't working, so I'm gonna slap the gauges on and see whats happening. My old man lives in Phoenix, so A/C is pretty much a necessity.

However my biggest issue was, when driving it home, on the freeway this thing was spinning 2800 rpms at 65mph which I confirmed with my GPS on my phone. That seems about 800 rpms high to me. Feels like overdrive isn't kicking in. The truck has a button for overdrive on/off on the dash and I made sure it is switched on, but still no difference. I haven't checked fluids and such yet, but plan to do so today. It'd be nice if that were the problem, but I doubt it. So I'm hoping maybe someone on here has had experience with this same thing before and can shed some light on the situation for me.

There is also the possibility that one of the previous owners swapped gears out. The truck has a brake controller wired into it, so it was obviously used for hauling, and with the 302, I could see where someone would be tempted to swap to 4:10s or 4:56s to make it pull a little better. - on that note, I guess I need to jack the truck up and check the ratio. It is a 4x4 and I need to be sure both front and rear match. Does anyone know if you can check the gear ratio on the front dif by spinning a tire and counting revolutions of the driveshaft just the same as the rear? I've never tried it.

Also, anyone know where the fuse panel is? I figure I should start there for the A/C and overdrive.
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Old 08-09-2013, 17:29   #2 (permalink)
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Re: F-150 No Overdrive?

Alright I haven't had much time this afternoon to play with it, but so far, here is what I have figured out. I was wrong about overdrive. It is working. At speeds way too low for my liking. If I play with the switch while cruising around town, it works fine, even as low as 20mph. So, I'm wondering if someone has been driving it around in overdrive at low speeds, if it could have toasted something in the transmission causing it not to shift correctly and that be the reason why it is spinning so high at 65mph.

I checked the transmission fluid, and it looks very fresh. Perfectly clean, and, overfull. It isn't slipping, so I'm wondering if I should try and drain some out.

I haven't checked gear ratios yet, but I did get brave and put it in 4x4 in the driveway and it didn't feel like it was binding or anything. So, hopefully, that will be good to go. Tomorrow I will probably jack it up and check the ratios.

Again, anybody with an opinion or an idea, please feel free to chime in!

Thanks!
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Old 08-09-2013, 18:02   #3 (permalink)
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Re: F-150 No Overdrive?

Depending on the size of your tires, 2800 doesn't seem that high for low speed rear end. Smart idea, though on checking gear ratios, don't go just by drive way and binding.
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Old 08-09-2013, 20:59   #4 (permalink)
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Re: F-150 No Overdrive?

Quote:
Originally Posted by CatSkinner View Post
Depending on the size of your tires, 2800 doesn't seem that high for low speed rear end. Smart idea, though on checking gear ratios, don't go just by drive way and binding.
Tires are 31x10.5x15. 2800 doesn't seem too high to you? I haven't been in a gasser in quite some time, so maybe its just me. This thing just feels like its working too hard to just be moving, and nothing more.

I won't be playing with the 4x4 until I confirm the gear ratios are the same front and back
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Old 08-09-2013, 21:05   #5 (permalink)
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Re: F-150 No Overdrive?

I doubt your overdrive will work below about 40 to 45 mph switch on or off.
None are designed to work below that speed range.
The motors don't have enough torque to pull the weight at that low a speed.
Here is an example of why;
If you have a 3:55 rear gear, Od is a .77 ratio.
This means 3:55 x .77= 2.73 final gear from motor to the road.
There is not enough motor torque at that low RPM to pull the truck below 45 mph any place but on the level and then there would be no throttle response causing the trans to down shift in any event to get it'self out of that situation.
The factory has designed the system not to go into OD below about 45 mph because it is useless to allow it.
The larger the tire diameter the worse it gets.
Good luck.
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Old 08-09-2013, 21:12   #6 (permalink)
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Re: F-150 No Overdrive?

Quote:
Originally Posted by Bluegrass View Post
I doubt your overdrive will work below about 40 to 45 mph switch on or off.
None are designed to work below that speed range.
The motors don't have enough torque to pull the weight at that low a speed.
Here is an example of why;
If you have a 3:55 rear gear, Od is a .77 ratio.
This means 3:55 x .77= 2.73 final gear from motor to the road.
There is not enough motor torque at that low RPM to pull the truck below 45 mph any place but on the level and then there would be no throttle response causing the trans to down shift in any event to get it'self out of that situation.
The factory has designed the system not to go into OD below about 45 mph because it is useless to allow it.
The larger the tire diameter the worse it gets.
Good luck.
I know the system isn't designed to work under 40mph, that is why I found it odd that when I hit the button at 20mph the rpms drop when the overdrive engages.

What would you say about my cruising RPMs at 65mph? Without knowing if the gear ratio has been changed, does that seem high to you?
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Old 08-10-2013, 04:24   #7 (permalink)
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Re: F-150 No Overdrive?

If you're running 4.11, you're in the ballpark:
Calculators
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Old 08-10-2013, 04:28   #8 (permalink)
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Re: F-150 No Overdrive?

Damn... I calculated for a 5 speed. Sounds like OD's not kicking in.
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Old 08-10-2013, 06:56   #9 (permalink)
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Re: F-150 No Overdrive?

It would seem at that speed and RPM the trans is in 3rd a 1:1 ratio, and the rear gear ratio is around 3:55.
The specific rpm is based on tire size and accuracy of the Tach.
My 02 with 3:55 will run about 3000 rpm at 70 mph 'out' of OD.
There is nearly a 1000 rpm difference between OD and 3rd.
Upshifting to OD then drops the RPM back to about 2100.
My speedo in known to be about 2 mph fast.
In between this is the converter lock which is a difference of about 300 rpm on to off.
You can still be in OD but the converter can be either locked or unlocked depending on how much light throttle is applied and the load on the motor.
It's all a matter of throttle angle as determined by the TPS sensor, VSS and motor RPM.
From these values the PCM makes the decision as to what to do with trans gearing control with a little timing delay thrown to prevent hunting, as applied to an electric controlled trans.
Older throttle control and govenor shifting is done differently to arrive at the same results such as the old AOD trans or even earlier the C4 and C6 types that were total vac and govenor control to arrive at about the same results.
The OD switch only signals the PCM for the intent then the PCM passes the action to the trans.
I don't know what you got going there but it 'ain't' right if it's happening at very low speeds.
Nice when you buy someone else's troubles thinking you get a bargin. That's why they sold it.
Turns out that even if something is obtained free it 'ain't' free after you get it and have to fix it..
Good luck.

Good luck.
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Old 08-10-2013, 15:23   #10 (permalink)
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Re: F-150 No Overdrive?

Quote:
Originally Posted by CatSkinner View Post
If you're running 4.11, you're in the ballpark:
Calculators
Checked and sure enough it has 3.55s so that means it is a transmission issue.

Quote:
Originally Posted by Bluegrass View Post
It would seem at that speed and RPM the trans is in 3rd a 1:1 ratio, and the rear gear ratio is around 3:55.
The specific rpm is based on tire size and accuracy of the Tach.
My 02 with 3:55 will run about 3000 rpm at 70 mph 'out' of OD.
There is nearly a 1000 rpm difference between OD and 3rd.
Upshifting to OD then drops the RPM back to about 2100.
My speedo in known to be about 2 mph fast.
In between this is the converter lock which is a difference of about 300 rpm on to off.
You can still be in OD but the converter can be either locked or unlocked depending on how much light throttle is applied and the load on the motor.
It's all a matter of throttle angle as determined by the TPS sensor, VSS and motor RPM.
From these values the PCM makes the decision as to what to do with trans gearing control with a little timing delay thrown to prevent hunting, as applied to an electric controlled trans.
Older throttle control and govenor shifting is done differently to arrive at the same results such as the old AOD trans or even earlier the C4 and C6 types that were total vac and govenor control to arrive at about the same results.
The OD switch only signals the PCM for the intent then the PCM passes the action to the trans.
I don't know what you got going there but it 'ain't' right if it's happening at very low speeds.
Nice when you buy someone else's troubles thinking you get a bargin. That's why they sold it.
Turns out that even if something is obtained free it 'ain't' free after you get it and have to fix it..
Good luck.

Good luck.
I'm gonna be honest, I can't make much sense of what you are saying. I'm trying, but I don't speak transmission I guess.

Seeing that the gears are 3.55s, overdrive isn't working right at highway speeds. Or at least that is what I am assuming based on what you said. So, with all the different things you mentioned, where do you think I should look to figure this out? Could the transmission being overfull cause this? Or is this more likely to be an electrical issue? Or mechanical? I'm more confused now than I was in the beginning.

*Edit* Another note about the transmission issue. On the highway when cruising at 65mph with overdrive on, while it is running 2800, if I let off the throttle, the rpms drop to about 700.

In all honesty, I bought a $550 motorcycle that needed a little work and traded it for this truck. So i'd say overall I'm still not doing too bad. I always expect used stuff to need some work.

My other project today was trying to figure out what is going on with the A/C. It was retrofitted to r134a, but the compressor isn't kicking on, and I can't find any obvious leaks. I tried pulling a vacuum, but had no luck. Couldn't get it to pull anything at all. But between the noise the vacuum pump and my compressor make, I couldn't hear where it might have been leaking. So, I decided to buy a can of r134a with leak detector in it to see if I could get the compressor to kick on long enough to get the dye through the system to see anything. So I hook it up to the gauges and start adding the can, pressure is increasing like normal, then all of a sudden, nothing. No pressure, no hissing, NOTHING. Again, no obvious signs of leakage. So, I decided I'd jumper the ac clutch for a couple seconds to try and pull some dye through the system. When I did, the system pulled almost 20inHg of vacuum instantly. I didn't want the compressor to burn up, so I didn't do it for long. I'm sort of at a loss at what to do now. Also, Any suggestions?

*Edit* I forgot to mention that when I was charging the A/C, I never read ANY pressure on the high side. Nothing at all.
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