New Jeep owner... couple things I need some advice on
 

Hey all,

Just picked up a '96 Jeep Cherokee 4.0L automatic at a city auction and I have a few things going on that I need advice on:

1. When shifting from Neutral to Drive I have a clunk and the car jerks forward. All the shifting to other gears and during driving all feel normal. Checked tranny fluid level and all good. Fluid looks almost like new.

2. When I hit 45mph I get a noise coming from what I think is the engine area (maybe back of engine). Sounds like a low rumble and there is a vibration (so much vibration I can't use the rear view mirror cause everything is jumbling around. I thought it might be tire balance, but steering is fine and doesn't vibrate much.

Thanks for any help you can give!

Mike

Check all of your driveshaft u joints they tend to go causing that clunk and vibration that is taking place.

Anytime a vibration or shutter happens at 45mph go check your brake light switch. It controls the locking & unlocking of the torque converter at, you guessed it, 45mph. This is often over looked as a suggestion on threads. Both of my jeeps have had hard shuttering at 45 mph and this was the cause.

The brake light switch is located up under the drivers side dash near the brake pedal. Just press the plunger in and out to make sure it ain't stuck. If you have any trouble let me know and I'll try to get you a video.



https://cimg3.ibsrv.net/gimg/www.che...ad72f29525.png
Should move in and out the direction of the arrows.

Also check your engine and transmission mounts. How are the rear springs? Shocks?

All possibilities.

Huh, that's a new one. Easiest way to check that switch and the lockup solenoid is to get to an even highway speed and tap the brake with your left foot. You should see the rpm jump a bit when the t/c unlocks.

A lot of these jeeps don't have RPM hands but that is second way to test it if you have one. I still like to get down and move in and out just to make sure, of course when you feel that shutter you'll know something ain't right haha.

Yeah. When you press the brake pedal it lets the plunger on the switch extend and make contact. The trans computer interprets this as you having your foot on the brake and then unlocks the torque converter. If iit gets dirty or sticky and doesn't fully extend then the contacts don't touch, and trans computer doesn't unlock the t/c on braking. I suppose the trans computer not knowing you've got your foot on the brake and unlocking the t/c could cause some shuddering. I've also seen the switch really mis-adjusted or knocked completely loose and the trans computer thinks you have your foot on the brake all the time and never locks up the t/c.

Also if you have cruise control on an older non-HO Jeep, there is a vacuum line on this switch that releases the vacuum on the cruise control solenoid when you hit the brakes. So this switch can be the culprit in cruise control issues as well.

Ah, my 89 has cruise control but has never worked and to be honest I have never even looked into fixing it. I did not know the brake light switch had any effect on that so now I learned something else new about the switch.

And yes, if that pluger sticks in, it causes extreme shuddering. If you let off the gas it immediately stops. Unsticking the switch solved it on both my jeeps.

Hey I took some video of the switch I think you guys are talking about (click on this Switch it's about 20 secs into the video)

Is this it? It looks like it is not extended when I let off the breaks.

Yours appears to be going in and out just fine, so the plunger is working

Here is my brother in laws 92's. I just took this video for you. They look a little bit different on my 89 but same idea.

Thanks for the video and yep it looks like it’s fine. Next stop.... checking the u joints

unless its proven to have been changed out, you can be almost certain your LH engine mount is completely shot (on most vehicles that age)

same with XJ trans mount, sags too

makes sense to change all 3 mounts as a set

dont ever use the cheap ones though, very soft rubber

hey thats good advice... any recommendations on brand of mounts??

I like Rusty's because they are built around an easily located easily installed suspension bushing and are rubber instead of polyurethane, I've got a set coming for my latest XJ. YOu can get them for about 100 dollars shipped from their website. Others prefer other brands. Some stick with OEM. Honestly it depends on your budget. I've had luck with the cheap 10 dollar a pop Anchor mounts and I've had high end mounts, the stock design on the mounts just isn't very robust.

Thanks for that. Lotta threads I read sat the aftermarket stuff just turns to dust after a few months like Thanos snapped them into oblivion :) I like the idea of performace mounts that use the polyeurthane but I don't know I need all that since not really off-roading that much. Might stick with OEM. Guess I'll see what the local auto parts store recommends too :)