Questions from 4x4 Noob

[Ben-88Comanche]

Hey. I posted some questions about 4x4 on this forum before, but they were hard to understand because i didn't know what i was talking about. Now i have a more complete understanding, so maybe you guys could help me out.

I have a 1988 Jeep Comanche, 4.0, 4x4, automatic. It has a dana 30 in front and a Dana 35 limited slip in the rear. I got in an axident a few months ago, that broke my 4x4 bottle and ruined the vacuum lines that connected it. Once i fixed the body, bumper, and got a new bottle, i tried putting it all together, and my 4 wheel drive didnt work. I Changed the front differential fluid and took apart/cleaned the vacuum shift motor (thing that looks like a tuning fork, i think thats what its called anyway) and put it back together. Now it seems that I'm stuck in 4 wheel High Part time.

I was wondering, is their a 4 wheel drive full time? Part time seems like it spins all 4 wheels at lowish rpms, but if i floor it the light shuts off, and i gain speed more rapidly. Also the truck slows down once i take my foot off the gas faster now then when i had it in 2 wheel drive. WHen i hit the breaks now, it squeaks, which it didnt do in 2 wheel drive.

Ive had the truck in 2 wheel high for like 20 minutes driving around, and its still in 4x4 part time.

Does anyone know if their even IS a full time 4x4 on this truck?

ALso when i was driving in 4x4 high part time for the first time, i could smell something burning at stop signs and lights, maybe the front driveshaft/U Joints/ CV joints need to be lubricated? I can't find any grease fittings on them that i havent already filled.

There is no vacuum diagram in the Haynes manual i have, and I'm not even sure if i have commanTrak or SelecTrak 4x4, though i think i have selectrak. A possibility is that their is something wrong with the selector valve? BUt i have yet to locate that on the car, just in diagrams in the manual.

Anyone have any idea what i should do? or whats wrong?

also- is their a special way you are supposed to shift in and out of 4x4? The guy i bought it from said u can just shift in and out whenever, just go into nuetral if you want 4x4 low, but he was wrong wtih a lot of other stuff about the truck, so maybe with this too. I have never owned a 4x4 before, so i could be wrong about everything lol

[whowey]

Take a look at the transfer case shifter bezel.

 

If it says 4wd full-time on one setting, then you have a Select-trac. If there is only 2wd, 4 hi, n, 4lo thats a Command trac.

 

 

If I was a betting man, you still have a vaccuum leak somewhere.

[Ben-88Comanche]

yea, ok, i guess i have comman trak.

I blew out the vacuum lines with a compressor and didnt find any leaks, once it stops raining I'm just gonna reattach everything see if it works better

[Wildman]

It's a little confusing reading your post.......but I'll try -

 

First off, your '88 will be a Command-Track (NP 231) Part-time 4wd, unless some one change it out to a NP 242.

 

The only way will will be in 4wd all of the time is if you pull the transfer case lever back to 4wd high, unless the linkage is messed up, and not setting into the correct position in the trans case.

 

The 4x4 bottle you talk about, is that the Black "ball" or long "football" behind the front bumper, on the pass side??? That's the vacuum reserve for the heater controlls, nothing to do with the 4wd.

 

There is a vacuum switch on the drivers side of the trans case that switchs the cad on the D30, when you pull the trans case lever. also turn on the light on the dash. If your vacuum lines are in the wrong place, that would cause the light to be on. If you "locked" the cad in the shaft lock postition, that still would not make you have 4wd all of the time.

 

Check ALL of the vacuum line under the truck, and the steel lines where the plastic lines plug in, you might have a leak some where.

 

Here's a link for the FSM you want to look under the 1988 XJ (2nd from the bottom) for areas that you need to address, the XJ and the MJ are about the same for the drive train info.

 

http://www.rol.ac.psiweb.com/jeep/

 

If you had a accident, good chance the linkage got messed up on the transfer case, and needs readjusting. The FSM or your Haynes book will walk you thru the process to adjust this linkage.

 

Your brakes squeaks??? has the truck been sitting for any amount of time?? you could just have some rust on the rotors that need to be worn off.

 

Some thing burning when your sitting at a light.......oh, boy, could be alot of things.......belt rubbing, oil burning off the exhaust????

 

Try to brake down your problems in each paragraph, like I did above, make is easyer for us to read :D

[Ben-88Comanche]

Ok, thanks for the help so far

But i figured something out

 

For SOME reason, having the e-brake on when your off-roading makes it not get stuck... don't ask. The 4 wheel drive wasn't on, the E-brake was, and that was what was squeaking and the burning smell.

 

Still, when I shift into 4 wheel high, the Part Time light on the dash lights up, and it remains in 2 wheel drive.

 

When i put the truck in 4 wheel drive, and have the vacuum lines that attach to the shift motor in the front axle unattached (their only running to the front passenger side black "football" container and back, I can feel the vacuum. Like 5 people have told me that the vacuum reserve has to do with the 4x4, and its attached only to vacuum hoses that have to do with the 4x4, so i don't really understand why that has to do with the heater.

 

2 of the plastic lines run from the axle to the front bottle, i don't remember where the third one runs, ill check tomorrow. I don't remember getting any vacuum on the third one, so that could be it.

 

I'm going to go read the Haynes manual right now and see if i can find something about the linkage on the transfer case. Thank you for the response =]

 

PS- Was this easier to read?

[Oizarod115]

my truck does the EXACTLY what you describe with the 4x4 light and the front axle engaging. don't worry about it, you more than likely have a leak somewhere and the reason the 4x4 light goes off under heavy accel. is the higher vacuum put out in those instances, it will not affect mileage, power, or your 4x4 working when you're actually in 4x4.

 

as for your t-case, unless you pulled the shifter INTO 4x4 (2wheel is all the way forwards) you will not be in 4x4, i seriously doubt you messed up the linkages on it from a front end fender bender. (i destroyed an accord with no visible damage to the truck)

 

as for shifting into 4x4...

don't put it in 4x4 on the road unless there are slippery conditions (ice/snow, REALLY REALLY bad rain) or you are pulling off to go wheeling, put the trans. in neutral and pull the lever into 4x HIGH. put back in gear and you should be in 4x4 (if not you have problems)

 

shifting into 4x4 LOW RANGE should be done at 2ish MPH, NOT AT SPEED. shift trans in N then move t-case lever back, right, and all the way back into 4x4 LOW, (there is a notch you have to go around so that you can't accidently throw it in 4x4 LOW at high speeds)

[Ben-88Comanche]

Aah so the truck should be in neutral when i shift, that could be the problem.

 

Technically my truck was totaled, even though the only damage was header panel, front right fender, and bumper, and it was hardly noticeable. The lady's Taurus had to be towed away so i'm assuming it was totaled too.

 

Ill try shifting in neutral tomorrow, hopefully thats it :cheers:

[Oizarod115]

Aah so the truck should be in neutral when i shift, that could be the problem.

 

Technically my truck was totaled, even though the only damage was header panel, front right fender, and bumper, and it was hardly noticeable. The lady's Taurus had to be towed away so i'm assuming it was totaled too.

 

Ill try shifting in neutral tomorrow, hopefully thats it :cheers:

even with my 5spd when i've tried to shift with the tranny in gear, clutch on the floor its just grinded and not wanted to go in.. i usally shift with tranny in N and clutch on the floor (jsut for good measure)

[DirtyComanche]

Uh, NP231 be shift on fly. Hammer 'er into 4wd, she'll go. 4Lo not such a good idea that way, doesn't have synchros. But it needs movement because of that.

 

 

And find your vacuum leak. Vacuum leaks are never a good thing.

[Wildman]

Dirty is right......"It's shift on the fly" Mine works that way, and no problems, some time's I got to play with it, double clutch, but I can go from 2wd right into 4wd, while in 2nd gear and moving.

 

Do Not drive on dry payment with it in 4wd, you will distroy the transfer case, I hope your playing around with it, you did not do this, well a little wouldn't hurt, but not at high speeds, other wise you will not have any 4wd.

 

You keep saying the light saids it's in part time, forget the light, it has nothing to do with being in 4wd, I got a '89 that the switch is bad, I took the wire off it cause it always lit up, about a $35 part to replace, or the cheep way, take the wire off :roll:

 

Any good jolt/jar could throw off the linkage on the transfer case, I would still check this out, and adjust it. Also, while your under there, check the transmission mount on the cross member, see if the mount is tore up, out of shape, or loose, this could cause the linkage to be out of synk.

 

For SOME reason, having the e-brake on when your off-roading makes it not get stuck... don't ask. The 4 wheel drive wasn't on, the E-brake was, and that was what was squeaking and the burning smell.

 

Well......that answers a few of your questions, Yea most of them, could also be the reason it feels like it's draging. Yea, you don't need the E-brake on when your driving. I guest what your trying to say about the not getting stuck, that's a whole another matter. It has to do with the limited slip diff, applying the brakes help "lock" the spinning wheel to shift the "traction" over to the other wheel. I'm not going to get into that any deeper, just skim over it.

 

The vacuum reserve bottle is for the hearter controll, and cruse controll, if you have that, the only time vacuum is needed on the 4wd is to "switch" on the dash light, and to "shift" the cad on the front axle, the 4wd is a manual operation, your 4wd will work with NO vacuum, if you locked the front cad disconnect. From '91+ they did away with the front cad, and went to solid axle shaft, so the front axle is always locked, and you still shift manually into 4wd. Your thinking, or were told that the vacuum shifts to 4wd, but it don't. It's done manually.

 

So, check the trans mount, check the linkage, check your vacuum lines, and go thru every thing twice, and keep the E-brake off, and don't drive on hard dry pavement with the 4wd on, and this might get you up and running :D

 

And yes, that's easyer to read :D

[Ben-88Comanche]

Ok, i did some more tests on the truck today and found out some more.

 

 

The front drive shaft IS turning, but the front wheels aren't spinning, because the shift motor is not engaging the front axle. There is 1 vacuum line at the shift motor that moves it one way, and one that moves the shift motor yolk the other way (i think).

 

The red vacuum line Ts off from the intake manifold and supplies vacuum at the transfer case. I think inside the transfer case, depending on the position of the 4x4 shift lever, the vacuum is ported to one or the other side of the shift motor. Is this correct? No matter what position the 4x4 shift lever is in, the vacuum is always at the same side of the shift motor. I believe to enter 4x4, inside the transfer case the vacuum should shift and the other side should gain vacuum, and therefore the ability to move the yolk and engage the front axle.

 

 

I checked the vacuum lines for leaks, and checked the shift linkage. The shift linkage was rusted into place and couldn't be moved much, but it should be close enough that the 4x4 works. I blew air through the entire vacuum line when disconnected from the transfer case,and air came out the other end, with only a slight leak being found. I took that part off of my parts jeep, and theirs a smaller leak in a different spot. Plenty of air still comes out of the end, i don't understand why its not going into 4x4

 

 

 

The only thing i can think of at this point is the transfer case isnt putting out the right vacuum to the right line

 

 

So yea, maybe thatll help

[Wildman]

You say you have a Haynes book, there is a way to test the vacuum on the cad to check that it is working correctly. When you took it apart, removed it from the axle, did you install it so that the sleve sat in the forks?? And your correct that the one line feeds the cad in pulling the forks to lock the axle shafts, and the other line pulls it to unlock.

 

And Yes, you could have the lines backwards, causing the cad not to engage correctly. But you also said you had the vacuum lines off?? did you re-install them correctly??

 

The vacuum switch on the side of the transfer case does not go into the case, only at that switch, there is a ball indent inside the case that opens the switch when you move the lever back.

 

Your other problem seams to be the rusted linkage, get that loosen up, and then you should be able to shift in to 4wd high and 4wd low, there is not a lot of movement in the case between the ranges, only about 1 to 1-1/2 inches, about a quarter turn, that's why the linklage needs to be set correct at the lever.

 

Your thinking right how the whole system works, but your blowing compressed air into the system, when in fact, you need to apply vacuum to the system. Your on the right track, but you got to have a line on wrong, or at worst, the vacuum switch at the transfer case is not working correctly. And do the vacuum test at the cad, I've had a bad one before, and you could "lock" it it to the engaged postition just to get thru this problem, and then leave it locked, or find the right line to feed the cad.

 

If your front drive shaft is turning, that's a good sign, that means the transfer case is engaging and not trashed.

[Ben-88Comanche]

Ok. I'm positive all the lines are in right, and was wondering how i can remove the vacuum switch?

 

If its simple i can take the one off my parts truck and see if that works

[Pete M]

I recommend simply eliminating the CAD and keeping it locked all the time. It's simple and ultra-reliable. :D

[Ben-88Comanche]

To eliminate the cad, would i have to get an axle from a 91+ jeep? And would that mean I'm in 4x4 all the time?

[jaekl]

The vacuum reservoir will have an effect on the 4wd. The lines to the reservoir and 4wd branch off upstream from the reservoir. When the reservoir leaks there may not be enough vacuum to engage the CAD. The reservoir with its check valve is to keep the air flow directed as you choose and not change as the vacuum decreases.

If the 4WD light goes off and on, it typically indicates only a loss in vacuum. Once engaged it stays engaged especially if torque is applied. The CAD needs vacuum to disengage as well. (Normally vacuum is always at the CAD keeping in unengages) The light goes on once the yoke slides all the way and redirects the vacuum to the light switch.

But can anyone explain why my CAD worked fine for 16 years and then after being stuck in the unengaged position only worked after I switched the two vacuum supply lines.

[Pete M]

To eliminate the cad, would i have to get an axle from a 91+ jeep?

 

No, you just need to shim the little shifter fork inside the CAD in the front axle. There are a few ways to do this, including washers, a hose clamp, or installing the CAD cover upside down. You could also install the solid shaft from a non-CAD front axle into your current axle.

 

 

 

And would that mean I'm in 4x4 all the time?

 

No. Your t-case lever is what shifts you into 4wd and 2wd. Engaging the CAD fulltime will make your Jeep just like any other Jeep made after Chrysler abandoned the concept.

[Ben-88Comanche]

So its that simple? I can just install the CAD cover upside down? Theirs nothing else that has to be done?

[Pete M]

That's what I've read. Unfortunately, I buried my spare axle under a pile of crap in the garage before I read it so I've not been able to confirm.