transmission? problems

[verticalspark]

Started with dropping out of gear and I would have to rev it up for it to catch again. I thought it was the torque converter but then my trans started to make grinding noise so I replaced both of them with a used trans and torque converter. It took a little over a week for me and my schedule to finish the swap and I just finished. Started the jeep checked the fluid levels all ok, try to back up only to find that its doing the same thing as the old transmission??? Anybody have any ideas?

 

[Shorty]

It really sounds like a low fluid pressure problem. Since it's done it with two units, I'd look for external problems that can restrict fluid pressure. The only things I can see are crushed/collapsed cooler lines or a plugged cooler.

Cycle the trans through all gears at operating temp and re-check fluid levels first. I've installed them before and had the level drop ALOT more than I expected after initial fill and check.

Make sure the fluid remains close to the same color as well-- if the trans cooler in the radiator is allowing coolant into the transmission fluid, you can destroy a set of clutches in short order.

 

[verticalspark]

I have checked all the lines and they seem to be good, I havent checked the fluid level today but I dont seem to be leaking anything thing which is a good sign. I have a separate cooler for the transmission and engine due to having those kinda problems with my old pickup so i dont have to worry about that.

 

[Mr. mud]

double check your metal cooler lines directly above your passenger side upper control arm, axle end.... please... Other than that you may have a transfer case issue. Is your XJ even 4x4? Some more detailed rig info may help.

 

[verticalspark]

sorry for the lack of info, I was on my way out the door to work when I posted it. Its a 1990 4.0 with the AW4 trans and a NP231 transfer. Been kinda busy this weekend with working so I havent had a chance to really look at it, but I did check the lines for leaking, dents and a possible flattened line from the trans to the cooler and I found nothing. I dont think the transfer case is the problem because nothing changes from 2 to 4High to 4Low but I could be wrong.

With the cold weather setting in I heard a whistling sounded that sounded like a vacuum leak from in the engine bay but by the time I opened the hood I couldn't hear it anymore. I dont know if these two problems are linked or not.

 

[joe_peters]

Ok, your year, with the NP231, would have come with a vacuum disconnect D30 CAD front axle.

Your grinding noise could be the disconnect collar doing weird things with the inner and outer axles on the passenger's side.

I doubt that would cause transmission to drop out of gear.

You must have a good vacuum system to keep things working, especially due to the D30 CAD--no vacuum, no 4x4.

The vacuum reservoir is behind the front bumper, passenger's side. The vacuum line to the reservoir runs behind or under the battery, and likes to break in that area. Relocate the reservoir into the engine bay. I put mine under the rad pressure bottle. Gets rid of about 5' of useless vacuum line. Test the vacuum system, intall a "T" and use a vacuum gauge. Run the engine for a few minutes, then shut off the engine and see how long it maintains vacuum. There should be a vacuum check valve and you want to "T" in past it. If the system won't hold vacuum you need to find the problem(s) and fix them. The there are three attachments on the shift collar motor on the axle, and the motor itself is problematic. Also, the brake power booster will eventually develop leaks. Test it, engine off, pump the pedal 4-5 times and hold pressure, start the engine, if the pedal drops about 1" under your foot, it is working, if not replace it.

 

[verticalspark]

yea it has the disconnect which has given me problems before but was fixed by replacing the "valve" on the transfer case. dont know the name of it but where the vacuum lines plug into the transfer case. but good idea about moving the vacuum reservoir. Ill have to do that soon.

The grinding was the transmission eating itself. When I drained the fluid it was silver, thats the reason I got a different trans in it now.

And my brakes completely went out while I was driving down the road about 8 or 9 months ago and I had to replace the booster and the master cylinder.
Im trying not to drive the jeep until I get it running right but I have to get to work. Ill try to post a video or a link to a video so everyone might have a better idea of what im talking about.

 

[joe_peters]

That was the transfer case switch, when you move the tc lever the shift rail hits the end of the switch and applies vacuum to engage the axle, when you move the lever out of 4hi/4lo the vacuum is re-routed to pull the axle collar out of engagement. The 4x4 light is triggered off the rear port (closest to the front of the vehicle) of the vacuum motor.

 

[verticalspark]

Well I have given up on trying to find out what it is for now. Im taking it to a local guy I know who has a diagnostic machine that is going to hook it up to see if the electrical crap is ok.