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engine braking with an auto

P

paul04tj

NAXJA Forum User
Location
Shelby Twp. MI
We went to Rocks and Valleys this weekend.
Me in the TJ my kid in his XJ.
Down steep hills the XJ wants to upshift from 1 to 2 forcing him to brake more.

Is there a mod to do to keep it in first?
The shifter has D, 3, 1-2

The same hill he has to ride the brakes, I could go down in first with no brakes, no clutch.
 
paul04tj said:
We went to Rocks and Valleys this weekend.
Me in the TJ my kid in his XJ.
Down steep hills the XJ wants to upshift from 1 to 2 forcing him to brake more.

Is there a mod to do to keep it in first?
The shifter has D, 3, 1-2

The same hill he has to ride the brakes, I could go down in first with no brakes, no clutch.
Click to expand...
There are a lot threads on the subject. Here is a good one.
http://jeep-xj.info/HowtoAutoSwitch.htm

Later model OBDII XJs (my 2001 XJ for example) will throw a code, set the CEL and not shift right unless a more sophesticated device is used.
http://montanafab.com/products/
 
By no clutch you mean u got an auto in the tj? How much compression braking do u actually get? I never understood why it doesn't freewheel the torque converter. I have plans for controlling the TC lockup in 1st to act like a clutch on hills and such.
Also I heard they didn't put 4 speeds in the wranglers till 04, only 3 speed autos which I thought was crazy.
 
If I put it in 1-2, my 1998 XJ will hold first until something like 4000 RPM when it will then shift to 2nd. I have never gone down a hill and had it shift into 2nd if I was on the brakes. You can do a modification which will hold it in 1st as mentioned by lazyxj above.
 
Super mud said:
By no clutch you mean u got an auto in the tj? How much compression braking do u actually get? I never understood why it doesn't freewheel the torque converter. I have plans for controlling the TC lockup in 1st to act like a clutch on hills and such.
Also I heard they didn't put 4 speeds in the wranglers till 04, only 3 speed autos which I thought was crazy.
Click to expand...

No no no, my TJ is a 5spd, feet completely off the pedal and it just crawled down the hill.

The kids XJ is an Auto, Selector in 1-2 and it upshifts to second, riding the brakes at about 2,000 RPM.
 
Get deeper gears in the axles or transfer case or both.
 
I had this issue in my 87, and it was very annoying. With the slightest down hill it would change to second and start flying. A transfer case issue caused me to change Tranny's and the new one DID NOT DO THAT! It will stay in first until you are doing like 3500 RPM. I can go down very steep hills with no brakes. I believe that is how it should be. A year or so later my NSS switch stopped working and I grabbed the NSS of my old tranny and the 1st gear issue started again. Cleaned and installed the NSS off of the tranny that shifted correctly and the problem was again corrected.

I have no idea what in my faulty NSS switch was screwing up my shifts, but something was. I keep it as a spare for now. Maybe something you could look into. Also could be the Tranny fuse... I guess I would check that first!

Jeremy
 
paul04tj said:
No no no, my TJ is a 5spd, feet completely off the pedal and it just crawled down the hill.
The kids XJ is an Auto, Selector in 1-2 and it upshifts to second, riding the brakes at about 2,000 RPM.
Click to expand...

This is a typical comparison between auto and manual transmissions.
My auto XJ always need to be braked going down step trails while my friend's manual TJ usually does not need braking. We both have 4.10 gears and 33"s.
I keep looking at the Montana Fab's kit....someday.

I wonder about locking up the torque converter. While it would provide better braking, its clutch surface is very small and might easily be worn out with too much use.
 
jrowell said:
I had this issue in my 87, and it was very annoying. With the slightest down hill it would change to second and start flying. A transfer case issue caused me to change Tranny's and the new one DID NOT DO THAT! It will stay in first until you are doing like 3500 RPM. I can go down very steep hills with no brakes. I believe that is how it should be. A year or so later my NSS switch stopped working and I grabbed the NSS of my old tranny and the 1st gear issue started again. Cleaned and installed the NSS off of the tranny that shifted correctly and the problem was again corrected.

I have no idea what in my faulty NSS switch was screwing up my shifts, but something was. I keep it as a spare for now. Maybe something you could look into. Also could be the Tranny fuse... I guess I would check that first!

Jeremy
Click to expand...

This is interesting, as his reverse lights do not work. I had already been looking at the how to on cleaning the NSS.

I'm going to find a driveline engineer here at work and talk to them about this.

Thanks

Paul
 
paul04tj said:
This is interesting, as his reverse lights do not work. I had already been looking at the how to on cleaning the NSS.

I'm going to find a driveline engineer here at work and talk to them about this.

Thanks

Paul
Click to expand...

The Rev lights did NOT work with my faulty NSS switch either... Maybe on to something here... It could also be a broken or shorted wire/ connector in the NSS, so cleaning it *might* not solve that. just a thought.
 
Super mud said:
I have a hard time beleiving the nss has anything to do with the transmission functions. Though if it also runs back to the TCU I suppose it could.
Click to expand...

I have no explanation other than my tranny shifts from 1-2 completely different with the two NSS's. I can also reproduce it on other XJ's with the bad NSS. just giving my experience.
 
Super mud said:
I have a hard time beleiving the nss has anything to do with the transmission functions. Though if it also runs back to the TCU I suppose it could.
Click to expand...
ummmm... it does. That's the major use for the NSS, and is why it has a handful of wires instead of only 2.

OP, I would bet on a bad or flaky NSS, it should stay in 1st perfectly fine unless you get it up to around 4500rpm on the tach. Also, since you have a 92, you can build a switch setup to lock it into 1st without suffering a check engine light, or if you don't feel like building anything, just unplug the wiring harness at the TCU (it's up under the dash) or the grey rectangular connector at the transmission dipstick. The transmission will stay in 1st when shifter is in 1-2 if you do this.
 
Interesting thread. I also have a '92 AW4 / 241 t'case. I have had the XJ in 4lo/1st on steep hills and thought I was going to die because it sometimes rolls so fast. With 4.56 gears it's better, but not perfect. Recently had to get a new NSS but I haven't made a connection with the 2 issues. And I think it still sometimes rolls too fast ... Wish this question had come up earlier. Now I'll just have to wait until next month when I go back to Rausch to test this out.

Subscribed
 
Yeah a faulty NSS could do this, since it tells the TCU what position the shifter is in. Even in the 1-2 position the tranny is still under computer control if present. It's possible the TCU thinks you are in 3 position and it is telling the trans to shift at the designated points. Some guessing there but not a lot--entirely feasible
 
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