Rally mods

[WAM174]

Yeah, I've been reading your efforts to reverse engineer the TCU to see where it would lead. In the red (and brown) mist of competition, I don't think I want to be trying to manipulate a rotary switch especially wearing driving gloves.

I was thinking of maybe hardwiring 2nd gear selection with a momentary pushbutton on the steering wheel to temporarily select 1st. And then a master switch somewhere to revert to stock for when I'm not racing. Nothing against MontanaFab and good on them to have figured it out. But maybe not optimum for race use. Besides...I have to buy everything just now. $150 can be well spent on go-fast stuff.

 

[kastein]

Do you need your horn to work? whipped up a quick design...

Parts:
2 SPST or SPDT relays (the NC contacts aren't used on either relay)
1 SPDT toggle switch (for setting regular auto mode vs rally mode)
1 NC SPST pushbutton switch (for downshift from 2nd to 1st)

Wire it up and it should work... put the SPDT switch in rally mode, the shifter in 1-2, you will be in 1st gear. Hit the horn button (or any other active-ground button connected to the wire marked "horn switch" in the diagram) to upshift to 2nd, hit the downshift pushbutton to shift back down to 1st.

You can leave the horn connected as well, but obviously you will honk the horn every time you upshift :roflmao:

If you don't want to use the horn button to activate it, you can remove the lower relay from the circuit entirely and wire in a normally open pushbutton switch instead.

 

[WAM174]

Actually I was planning something like this. I came across the solenoid logic here somewhere, but I'd have to look it up. Maybe it was both off is 1st and both on is 2nd. Assume that's the case:

So my "race" arming switch would disconnect both solenoids from the TCU and apply 12V to both (2nd gear). And the "downshift" button would block the 12V to both (1st gear).

The button needs to go right where my left thumb "looks for it" in my normal wheel holding position. So my hand doesn't come off the wheel.

Since the TCU only sees a resistive load of the solenoids I wonder if switching that end to a resistor (with a second pole) would fool the computer so it doesn't know anything has changed and doesn't throw a code? That seems so simple that if it worked someone would have already done it.

Obviously the above is just a concept. It will need a little thought and development. And if I assumed wrong on the logic, a simple circuit revision will fix. You've played with it a lot and I haven't, so I may well be missing something.

 

[kastein]

Actually I was planning something like this. I came across the solenoid logic here somewhere, but I'd have to look it up. Maybe it was both off is 1st and both on is 2nd. Assume that's the case:

Not quite, it's a bit more complex than that: http://www.greatlakesxj.com/tech/aw4shiftmod.html

the info you need is that solenoid 1 is ON for both 1/2, it's off for 1st and on for 2nd. If you toss the shifter in 1-2 the TCU will hold solenoid 1 on for you and you don't need to worry about it, just solenoid 2.

The button needs to go right where my left thumb "looks for it" in my normal wheel holding position. So my hand doesn't come off the wheel.

hmmm... that could be annoying to set up. I guess you could rip apart the cruise control switch module and use one of its switches, they have resistors in series with them so you can't use them directly. I'll see if I can figure out a simple circuit to make that work if you want, it shouldn't be too hard.

Since the TCU only sees a resistive load of the solenoids I wonder if switching that end to a resistor (with a second pole) would fool the computer so it doesn't know anything has changed and doesn't throw a code? That seems so simple that if it worked someone would have already done it.

heh... yeah that's what I was hoping for originally. Turns out the 97 TCU acts like you're saying (as far as I can tell, I did not get significant testing time on the 97 that we tried it on) but the 98 and later are smart enough to detect what gear they are in via the input and output speed sensors.

Obviously the above is just a concept. It will need a little thought and development. And if I assumed wrong on the logic, a simple circuit revision will fix. You've played with it a lot and I haven't, so I may well be missing something.

I've played with it a bit... not sure if I'd call it a lot at this point. The circuit I gave will work fine for you if you just remove the lower relay from the schematic and wire your pushbutton in where its contacts were.

 

[Goatman]

On the KOH racers we have push to talk buttons on the steering wheel for the radio, mounted on a wheel spoke. The button is wired with a coily cord that's wrapped around the column. Since the wheel only rotates 3 turns back and forth the coiled cord works fine. This would be a simple way to do a downshift button on the steering wheel.

 

[WAM174]

There you go. Thanx Richard.

BTW Richard, if I remember correctly you said the car I'm buying was a 98 but could be a 97. So maybe the simple resistor trick will work? Not critical, just a nice-to-have. If it throws a CEL I can live with it. Or install the MontanaFab thing.

 

[WAM174]

the info you need is that solenoid 1 is ON for both 1/2, it's off for 1st and on for 2nd.

Did you skip a word or two there???

I downloaded a FSM and on Pg 21-169 it says this:

-------------------Sol-1-----------Sol-2
1st gear---------ON--------------OFF
2nd gear---------ON--------------ON

So
1) disconnect both wires from TCU
2) connect 12V to Sol-1 via simple toggle ("ARM")
3) connect 12V to Sol-2 via momentary normally-closed pushbutton ("DOWNSHIFT")

ARM switch on, DOWNSHIFT pushed, I have ON/OFF = 1st gear

ARM switch on, hands-free, I have ON/ON = 2nd gear (default race position)


Somehow I think doing this will be easier than writing it.

 

[tbburg]

I wonder if we're putting too much brainpower into this. Could the stock computer programming work for Rallycross?
Most of our problems with the 1-2 programming on the XJ stem from not wanting to be tooling around on the dirt roads at 30MPH in 1st gear. 'Not as much of a problem in competition.
In the stock mode: Stick it in 1-2 on the line and hit the gas. It's going to stay in 1st until about 4500RPM, then shift into second. It'll stay in 2nd until the vehicle speed drops to about 25MPH, downshift, then stay in first again until you rev back to 4500. For flat out competition, this might be perfect. Thoughts?

 

[WAM174]

Well I'll need to play with it a little before I can say. Fortunately I live in the desert and have a mini test track only a mile away. With 4.56 gears and 26" rally tires 1st gear is going to be really REALLY short. Might be kinda useless in a pickup truck granny gear kinda way.

But even more concerning might be an unwanted downshift in the middle of a corner. If I'm getting 100% out of the tires and it suddenly downshifts I'm thinking all hell might break loose.

Or like you say...maybe all the stars will align and this will be slicker than...:shocked:

If I do decide to go with a wheel mounted switch I found an AC coiled cord on EBAY, and McMaster-Carr always has a nice selection of switches with all the specs, ratings and dimensions. $10 will git-r-done.

I'm assuming I'm going to want to spend 95% of my time in second gear. But if that's wrong and I want to shift it a lot, the RADesign stuff looks promising.

BTW, when you were screwing around with it, did you ever determine the equivalent resistance for the solenoids? I've got quite a few power resistors sitting around. I may want to see if I can fool the computer just for grins.

 

[Goatman]

What's annoying about the stock 1-2 position is that unexpected 25 mph downshift to 1st. Could calculate what the computer will see as "25 mph" with the smaller tires and 4.56 gears and see if that is acceptable in any way....probably not. The downshift has nothing to do with throttle input, only the speed.

What we're talking about is why I like my Compu-shift on the buggy, when the switch is on it holds 2nd, even from a dead stop, but if you give it more than 3/4 throttle and the rpm is low enough it will downshift into 1st. That works for me since if I'm going slow enough for a downshift and I'm giving it that much throttle I want it to downshift......and I don't have to think about it. But, I'm a lazy driver wanting less to have to think about and keep track of.

 

[WAM174]

Okay, Goatman got his part done and I've got a week to prep for the first event. Not enough time to do everything, but that's okay. I'll catch some of the biggies and develop it throughout the season. Goatman geared it, installed Bilstein HD's, cut the front springs, installed Deaver rally rears, and beefed up all the known weak points. We put in a home-built 2-stage progressive spring-insert soft/hard bumpstop. Fancy. Seems to work in testing.

Track tested it and found the antilock braking obnoxious. Caused me to overrun the final turn of the track. I assume I can disable that by pulling a fuse or circuit breaker or something. Anyone know the specifics on a 98 XJ?

With 4.56's it really launches. Turning, not so good as yet, but something to work on. Although I bought the RADesign Baja shifter, I didn't mind the standard 1-2 automatic shift. It upshifts at 27mph (GPS) and downshifts at 14mph. That's slow enough I don't think I'll get caught out by a surprise downshift. We'll see. I'll run the first race as is.

Priorities for first race are a race-bucket, the other seats and bumpers removed. Rally tires fitted. Even though they won't tuck, it looks like I might not need to mod the fenders. I'll eventually try some extreme mud terrain LT's, 235/75 and those will require trimming because I'm running 3" wider track.

Anyway, help with the ABS would be appreciated. Otherwise I'll just start pulling likely fuses an see what happens.

 

[kastein]

You are correct, on a 98 (any 92 and later) XJ you can disable the ABS by simply yanking out every fuse and relay related to the ABS subsystem.

 

[98xjse]

Okay, Goatman got his part done and I've got a week to prep for the first event. Not enough time to do everything, but that's okay. I'll catch some of the biggies and develop it throughout the season. Goatman geared it, installed Bilstein HD's, cut the front springs, installed Deaver rally rears, and beefed up all the known weak points. We put in a home-built 2-stage progressive spring-insert soft/hard bumpstop. Fancy. Seems to work in testing.

Great to hear you got the this thing going, it has been fun reading about you and the Team Petty Cash Cherokee (two similar goals with different approaches).

I am assuming that you are running 2wd (I didn't see it previously mentioned, if not NP231 or NP242?). Also could you give a little more info on the Deaver rally rears (how much drop, how many leaves, custom?).

How much travel are you able to maintain with the shorter springs and I'm assuming shorter bump stops and smaller tires?

Anyways, sounds like it's a fun project.

 

[WAM174]

Great to hear you got the this thing going, it has been fun reading about you and the Team Petty Cash Cherokee (two similar goals with different approaches).

I am assuming that you are running 2wd (I didn't see it previously mentioned, if not NP231 or NP242?). Also could you give a little more info on the Deaver rally rears (how much drop, how many leaves, custom?).

How much travel are you able to maintain with the shorter springs and I'm assuming shorter bump stops and smaller tires?

Anyways, sounds like it's a fun project.

4WD, open/open. The drivetrain is stock 97 XJ except for 4.56 gears to match the engine to the typical course speeds with 26" rally tires.

The Deaver springs are approx stock rate, about 1.5" lower, three leaves I think. I found them, didn't spec them.

Jounce travel is about 4", with 3" being on Prothane progressive bumps front and rear. And then a custom hard-stop up front just before the steering hits the pan. And I've been using every inch of it.

Most unusual piece is a twin-handle cutting brake. Makes it a very nimble contender easily out-turning the rally cars. Can't stay with them on the fast sweepers tho.

 

[WAM174]

New livrey



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[Brown Dog]

NICE!!

 

[hubs97xj]

Very cool.

 

[bjoehandley]

Were those Prothanes for for stock height trucks by chance? I need new ones for the back of mine and would like something better than stock.

 

[WAM174]

Were those Prothanes for for stock height trucks by chance? I need new ones for the back of mine and would like something better than stock.

They're available in various lengths. You select or cut them to the proper size to get a certain amount of free height above them. I think I'm using about 1.5" of free height. Maybe you should start with an inch and if you feel they come on too soon or too harsh, start cutting them back. Easier to shorten them than lengthen them

 

[bjoehandley]

Thanks WAM, are you also running their bump stops in the front by chance and do you think it would be safe to run bump stops of two different materials front to back on a street only truck?