Any way to defeat the overdrive?

So after a long highway trip with a fully loaded truck through some hilly/mountain areas, I have decided that I want to kill the overdrive in my XJ. When cruising long uphills, the truck stays in OD, unless I push the pedal hard enough to make it kick down. The problem is that it kicks all the way down to third, runs there for a few seconds, shifts to 4th for less than a second, and right back into OD. I want to get this thing to the point that it will shift down to 4th, or at least out of OD, because shifting all the way down to third is a)unnecessary, b)loud and obnoxious, and c)bad for fuel economy(which is already not great).

Someone has to have installed a switch to defeat or turn off overdrive, as I'm sure I'm not the only person to have this issue.

I should probably add info on the truck:

89 XJ
4.0L
AW4
NP 242
2" BB
30x9.5x15 BFG A/Ts

you do not have a 4th gear. 4th IS overdrive.

The 4th gear is overdrive. Maybe the the thing you feel is the TC lockup. Keeping it out of OD is simply shifting to 3rd. Keeping the TC from locking up requires a switch.

Dang, pause to get a cup of coffee and a bunch of you beat me......

Kind of on thread, but when I use cruise control on other than flat ground I always put my auto in 3rd, it keeps the speed much better there. And since it's an XJ, milage isn't a factor in any kind of hills.

jeepcomj said:

you do not have a 4th gear. 4th IS overdrive.

Click to expand...

OK, then what is the short step between 3rd and 4th? It shifts 3-x-4, where x = less than 1 second at that RPM. What I would like for it to do, instead of downshifting all the way to 3 to pass, is downshift to whatever x is to pass. There has to be a way to do this. Honestly I'd rather convert the truck to 5-speed than deal with the AWshifting stuff, as that seems like an awfully expensive bandaid.

Saudade said:

The 4th gear is overdrive. Maybe the the thing you feel is the TC lockup. Keeping it out of OD is simply shifting to 3rd. Keeping the TC from locking up requires a switch.

Dang, pause to get a cup of coffee and a bunch of you beat me......

Click to expand...

I wouldn't recommend defeating the t/c lockup either, as that will generate excess heat in the tranny. Easy enough to do btw, by messing with the white switch high up on the brake pedal.

The bottom line is in the XJ your not suppost to tow in D, only in 3.

maalox said:

OK, then what is the short step between 3rd and 4th? It shifts 3-x-4, where x = less than 1 second at that RPM. What I would like for it to do, instead of downshifting all the way to 3 to pass, is downshift to whatever x is to pass. There has to be a way to do this. Honestly I'd rather convert the truck to 5-speed than deal with the AWshifting stuff, as that seems like an awfully expensive bandaid.

Click to expand...

What you are feeling is the torque converter slipping. In OD it does not lock until 4th gear or when under load unlocks and slips.

You apparently know little about how an auto trans works. Read this and learn http://www.howstuffworks.com/automatic-transmission.htm/printable

I would not recommend bypass the TC lockup either.

Maalox - Are you sure your TPS is adjusted properly?

I have quite a few hilly areas here as well. When I climb up, I recall running around 65 mph at under 3000 rpm in 3rd. This allows me to maintain my speed up the hill when I'm loaded up and still pass slower traffic.

Bear in mind the TC still locks in 3rd.

lawsoncl said:

I wouldn't recommend defeating the t/c lockup either, as that will generate excess heat in the tranny. Easy enough to do btw, by messing with the white switch high up on the brake pedal.

Click to expand...

How bad is it for the trans to do that for short periods(passing on the highway, for instance)? I certainly don't want to damage the truck, but I don't think driving it around in 3rd gear all the time is appropriate, either.

rstarch345 said:

You apparently know little about how an auto trans works. Read this and learn http://www.howstuffworks.com/automatic-transmission.htm/printable

Click to expand...

:laugh: You would be 100% correct, I don't know the first thing about an automatic trans. I've had somewhere in the neighborhood of 30 vehicles over my lifetime, and this is the first one I've ever had without a third pedal. By the looks of it, it may be my last. I know how to drive in an appropriate gear, and I certainly don't need a 20-year-old computer to assist me with it.

Saudade said:

I would not recommend bypass the TC lockup either.

Maalox - Are you sure your TPS is adjusted properly?

I have quite a few hilly areas here as well. When I climb up, I recall running around 65 mph at under 3000 rpm in 3rd. This allows me to maintain my speed up the hill when I'm loaded up and still pass slower traffic.

Bear in mind the TC still locks in 3rd.

Click to expand...

TPS is newish(last 6 months) and adjusted perfectly, thanks to some of the typical RENIX issues. The truck shifts fine, downshifts when it's supposed to, upshifts when it's supposed to, and all that. I just don't feel that it's entirely necessary for the truck to downshift into third gear at 70mph, just to keep speed up on an incline.

Another thing I noticed is that when cruising under light throttle, the truck seems to shift gears an awful lot, but I guess that's the converter locking and unlocking? And again, this seems unnecessary and excessive.

I agree with ya maalox, if the stupid trans could just unlock the TC rather than dropping back to 3rd, it would work fine for 90% of the (non WOT) situations.

Dave

CantonXJ said:

I agree with ya maalox, if the stupid trans could just unlock the TC rather than dropping back to 3rd, it would work fine for 90% of the (non WOT) situations.

Dave

Click to expand...

I knew I wasn't the only one.

Why not tow in OD? I brought a 3000# box ATL-SJC doing most of the driving in OD without any trouble (switched to direct drive in the Rockies, but that's about it.)

The AW4 can almost be said to have "six" ranges - 1/2/3/3L/4/4L. Torque converter lockup can happen in third or fourth at a steady-state cruise, and it should drop right back out whenever you "blip" the throttle or change speeds. The advantage to lockup is that it turns the TC from a hydraulic coupling with slip into a direct mechanical coupling. This also has beneficial effects on fuel economy, fuel efficiency, operating temperatures, and engine state (the lockup helps to eliminate "hunting" at speeds.)

Eliminate OD? Same way I "eliminate" OD on my BA-10 and my AX-15 - just don't use it. "Third" is "drive" - you have 1/2/3/3L available, but not 4/4L. Problem solved.

As mentioned tho - note that the TC locking/unlocking can feel like a "soft shift" - if you're in OD climbing up to freeway speed from a standing stop, you'll actually feel (if you pay attention) the shifts 1/2, 2/3, 3/4, 4/4L. (You don't hit 3L because you're still accelerating.)

I'd not suggest manually disabling the lock either, unless you are attentive to your driving and vehicle. As mentioned, the lockup will both reduce operating temperatures and increase economy and efficiency, and it should be retained.

CantonXJ said:

I agree with ya maalox, if the stupid trans could just unlock the TC rather than dropping back to 3rd, it would work fine for 90% of the (non WOT) situations.

Dave

Click to expand...

I think this applys if you are NOT towing... but then again, lockup wouldnt really be that much of an issue then.

As i said before, and 5-90 also said... use 3 for towing especially up hills.

When i just recently took my 3400 mile trip in my XJ towing a trailer, i would use D when towing on relatively flat highways... and switch to 3 when i would reach inclines. I only did this cause im a speeder, and went 75-85 as much as i could.

the problem with using OD to tow is 2 fold. 1st is the heat build up of the stress on the cluch packs, eventually the system will fail to the torque of the engine/vs road traction.
the second is that the vehicle (like my old Maxima) will shift in and out of OD however may times it wants. each time it shifts on is what... half a turn on the clutch disks? a full turn? whatever friction material is lost in each shift is multiplied by however many times your tranny shifts from 3rd to OD. Ask me how i know...
and then one day, your auto box might feel a lot like a manual with a slipping clutch... give it a little gas, and instead of downshifting, the engine just revs a little... with no change in road speed... and no shift.
at that point, you wonder if that 1700 dollars you spent last year on the rebuilt trans was really worth it, because someone didn't know to KEEP IT THE HELL OUT OF OVERDRIVE WHILE DRIVING IN THE MOUNTAINS.:bawl:
but i digress, because i love her.

so... the moral of the story? the decision to tow or not to tow in overdrive shoudl really be made the first time the truck or car downshifts into 3rd to maintain steady state cruise speed. at that point, lock overdrive out, and keep it off till you get down the other side. it'll save the trans, and the brakes on the downhill.

The point of the Torque convertor is actually torque multiplication. there are some convertors out there that will actually double the engine torque output when unlocked. thats some serious help in the hills and rock crawling. the drawback is that they build heat when unlocked... not a bad thing for stoplight to stoplight driving, but gets bad pretty quick on extended climbs(esp. with inadaquite cooling). does the convertor lock up in 3rd? probably a reason for it not doing so... that being if you're in 3 already, it's because you need more torque to maintain speed.

drive well,
Sam

5-90 said:

Why not tow in OD? I brought a 3000# box ATL-SJC doing most of the driving in OD without any trouble (switched to direct drive in the Rockies, but that's about it.)

Click to expand...

That's just it, though - I'm not towing anything. The only rust on my truck is on the factory trailer hitch(the reason I made the concession and bought an automatic in the first place), and it's so bad that I don't trust it enough to tow with it. Regardless, this was occurring with myself and one passenger, and the rest of the truck full(to window level) with camping and hunting gear.

The AW4 can almost be said to have "six" ranges - 1/2/3/3L/4/4L. Torque converter lockup can happen in third or fourth at a steady-state cruise, and it should drop right back out whenever you "blip" the throttle or change speeds. The advantage to lockup is that it turns the TC from a hydraulic coupling with slip into a direct mechanical coupling. This also has beneficial effects on fuel economy, fuel efficiency, operating temperatures, and engine state (the lockup helps to eliminate "hunting" at speeds.)

Click to expand...

It doesn't drop back out of lockup until it downshifts all the way to third. If it would drop out of "4L" as you call it, and into "4", I would be thrilled, because that's exactly what I want it to do. Instead it bypasses "4", "3L", and jumps all the way down to "3". And at lower cruising speeds, it does "hunt", as it's constantly locking and unlocking. If I drive the truck in "D" for even a short period of time at 25-30 mph, it hesitates horribly and often times backfires if I give it any more than 1/2 throttle. Not so if I drive it in "3" or keep my RPMs up by speeding(which I try to avoid as best I can).

Eliminate OD? Same way I "eliminate" OD on my BA-10 and my AX-15 - just don't use it. "Third" is "drive" - you have 1/2/3/3L available, but not 4/4L. Problem solved.

Click to expand...

Yeah, but 75mph in 3rd gear doesn't make a whole lot of sense.

As mentioned tho - note that the TC locking/unlocking can feel like a "soft shift" - if you're in OD climbing up to freeway speed from a standing stop, you'll actually feel (if you pay attention) the shifts 1/2, 2/3, 3/4, 4/4L. (You don't hit 3L because you're still accelerating.)

I'd not suggest manually disabling the lock either, unless you are attentive to your driving and vehicle. As mentioned, the lockup will both reduce operating temperatures and increase economy and efficiency, and it should be retained.

Click to expand...

And herein lies the problem. I feel that "soft shift" when it shouldn't be shifting at all(hell, it shouldn't even be anywhere near overdrive at 25-35mph), and it won't give me that "soft shift" when it should(1/4-1/2 throttle at highway speeds).

I am a very attentive driver(this comes from years of driving manual transmission vehicles, including some requiring me to hold a CDL), and I have never in all my years of driving experienced this type of thing with ANY other automatic vehicle I have driven.

maalox said:

... If it would drop out of "4L" as you call it, and into "4", I would be thrilled, because that's exactly what I want it to do.

Click to expand...

Yes, this is exactly what I'd like as well and without having to dip into the throttle more than halfway (which is about what's required to get the 4L to 3 kickdown). There's obviously some switch on the brake pedal that tells the TCU to unlock the TC because if I merely tap the brake with my left foot, the trans will drop out of 4L into 4. I do this regularly when going up mild inclines at 45-50 or so mph, but I don't like the idea of the brake light "flash" for the drivers behind me.

Dave