Truck lurches after hard stop

[EUREKA]

For a while I've noticed that after coming to a very abrupt stop, there is a delay after pressing the accelerator, then a thunk before it will begin moving forward. The harder the stop, the longer the delay and more pronounced the thunk. Today the truck began lurching while driving around town. Feels like a momentary loss of power then the same thunk sound.

 

I'm kinda suspecting the torque converter. I replaced it last year with one from O'Reilly when I had to remove the transmission to replace the freeze plugs on the back of the engine.

 

I've had the fuel pressure regulator go out on a 93 ZJ 4.0, and experienced spider gears slipping, it doesn't feel quite like either of those. I'm going to inspect my transmission shift linkage, and install this since it's already sitting around new in the box in my garage,

 

https://www.azzysdesignworks.com/shop/p/xj-linkage-mopar

 

[pizzaman09]

I think I am following your description and what I'm going to suggest doesn't quite align with what you are describing.  However do you by chance have a sticking/hanging break caliper?  The usual symptom is an unusually stiff pedal.

 

Else, it's probably worth crawling under the truck and feeling around for the slop in the drive line, like is it in the diff, u joints or transmission.  Also are the transmission bell housing bolts tight?

[EUREKA]

Could be a hanging caliper. I do not have a stiff pedal. No uneven wear, no pulling to one side. These knuckles do tend to

 

No slop in the driveline. U-joints are all new as of last summer. Transmission and t-case were inspected and serviced last year by a transmission shop.

 

I could check the bell housing bolts but I'm not seeing how lose bell housing bolts would relate to the symptoms I'm having?

[EUREKA]

Well my trans fluid was low. Hardly touching the stick. Looks like my local trans shop left it low last time I had it in there. Not sure if that is my problem.

[gogmorgo]

I was actually going to suggest that. 
If the fluid level is low the transmission may not build enough pressure to engage the clutches at low engine speed, but when you rev it up the increased pressure will make them grab, the “thump” is essentially a neutral drop. Having the intermittent pressure loss isn’t great, slipping clutches can burn out quickly, plus the potential for shock loading the drivetrain, and if the level is low enough you may also have issues with cooling and lubrication.

Top it up, and double check for leaks, on the trans itself and the cooler lines. Keep an eye on the fluid level. The AW4 is a tough transmission and will take some abuse, so hopefully it’s okay once the level is corrected. 

[EUREKA]

I definitely have no leaks. Test driving  it today.

[gogmorgo]

That may be more concerning. If there’s no leak it means you’ve been driving in the danger zone for a while now. Fingers crossed though. 

[EUREKA]

Right, like I said, looks like my local trans shop left it low last time I had it in there. Really pisses me off.

[gogmorgo]

It’s upsetting, yeah. In their defence it can be tricky to get it right, because there’s a pretty big difference in level between cold and hold, and it has to be checked running and hot. And for someone getting paid flat rate it’s not necessarily profitable to go and drive it until it gets hot. This is unfortunately getting pretty common, with techs not wanting to spend time on a job that isn’t going to pay much. Which, I mean, hard to blame them if they’re not taking home a ton of money as it is. Some shops don’t pay well at all.

And you also had the capacity to pull the dipstick out and check at any point between now and then. Its not a “sealed for life” transmission that doesn’t have a user-verifiable level indication. 

 

But it also doesn’t take a huge leak. Its very common to get sweating from cooler lines which can be enough to cause a problem given enough driving time. 

[ghetdjc320]

Sounds like the torque converter is starved or failing

[EUREKA]

After adding 2 quarts, I can't get the issue to occur today.

[gogmorgo]

Good stuff. But keep an eye on the level, and keep an eye out for spotting underneath it. If a shop had left it two quarts low I think you would have started noticing problems on the drive home. 

[EUREKA]

I am fairly certain that I do not have any transmission fluid leaks. I park inside a garage with a concrete floor, and would have noticed any significant leak. I also just got under the truck and see no signs of leaks. I can't explain why/how I had no symptoms until the last few weeks, or why this issue only occurred after a hard stop.

 

It could be that my problem is intermittent and will return, and that the low trans fluid had nothing to do with it.

 

Maybe once the pavement is dry the problem will return. For now I can lock up the brakes and slid to a stop without the issue occurring.

[gogmorgo]

The symptoms you described are definitely consistent with low transmission fluid.

And you’re correct that it would be tough to miss a two-quart leak. 

Hopefully it solves it with no further issues. 

[cruiser54]

With an AW4, it's simple to do yourself.

 

Drain it with the plug.

Reinstall plug and begin with 3.75 quarts of ATF. DEXRON!!

 

You'll be so close.

 

Now, and this is on you. It's not on the transmission shop. Everyone needs to heed this!!

 

You should be checking your fluid levels periodically on your own. 

How often do you guys check the engine dipstick? Check trans fluid at the same time. 

 

 

Checking ALL the fluid levels should be done at every oil change minimum by whoever is performing the oil change.

 

Across the forums I see this over and over again. Posts and threads outlining some odd vehicle behavior that has a root cause of low or worn out fluids. 

Or a lack of someone who cares about your Jeep doing an undercarriage visual inspection. They're more interested in selling you a cabin air filter or an unnecessary and potentially damaging fluid flush bull$#!&. 

. 

[EUREKA]

I had them do far more than a fluid change. A previous owner had installed a "clamshell".

But you're correct a fluid change is easy, and I should have checked the level long ago.

[pizzaman09]

Don't feel bad, I ignored noise in the transmission of my old BMW M3, for about 6 months including a lot of autocross racing.  Eventually the noise got bad enough that I figured I'd check the fluid level, it was basically out.  A new output shaft seal and some fresh fluid and at least is makes less noise.  Still makes bad noises with enough fluid, I'll drive it until it dies, which could be a long time.

 

The fortunate thing about the situation is it motivated me to fix the leaking t case in my Comanche as well as the leaking power steering pump.  I may even fix the leaking engine.  

[EUREKA]

Problem is not gone. Occurred a couple times cruising around 35 - 35 mph yesterday. I can't see anything wrong.

 

I do feel that the problem initially only occurring after very hard stops should be diagnostic of something. All I can think is maybe the u-bolts holding leafs to the rear axle need to be tightened, and as I stop hard the axle is rocking downwards, placing the drive shaft in a bind. Haven't checked that yet, but I've never loosened them for anything. And now that it has occurred while cruising at a constant speed I'm not sure how that would make sense.

 

Might just have to break down, tow it home when that happens, then I'll be able to fix it. Intermittent problems are the worst!

 

 

[cruiser54]

Maybe do a complete drain and fill on the trans. Perhaps the geniuses that didn't fill the trans also used the wrong fluid.

 

Use Dex/Merc only. NO CHRYSLER ATF+4!!!!!

 

Check u-joints etc. 

[ghetdjc320]

4 hours ago, EUREKA said:

Problem is not gone. Occurred a couple times cruising around 35 - 35 mph yesterday. I can't see anything wrong.

 

I do feel that the problem initially only occurring after very hard stops should be diagnostic of something. All I can think is maybe the u-bolts holding leafs to the rear axle need to be tightened, and as I stop hard the axle is rocking downwards, placing the drive shaft in a bind. Haven't checked that yet, but I've never loosened them for anything. And now that it has occurred while cruising at a constant speed I'm not sure how that would make sense.

 

Might just have to break down, tow it home when that happens, then I'll be able to fix it. Intermittent problems are the worst!

 

 

Just a thought, but check the wiring to your TCM and make sure it isn’t loosing power. 

[EUREKA]

I'll do both those things.

[cruiser54]

I think that would be good. 

[EUREKA]

So the u-joints are all in great shape, and they should be since they are relatively new. Haven't looked at the TCM wiring yet, but I have needed to rebuilt the t-case mode indicator switch for years so I will do both of those this weekend (dash light indicates part time for a couple hours after I shift back into 2wd)

 

I pulled the receipt from the trans shop from my truck folder and it was actually back in August of 2021 that I had it in. It reads "10qts ATF Jeep type".

I'm going to stop by there next week and make sure that it was DEX, but I suspect that it was.

[cruiser54]

I may suspect the opposite.....

[EUREKA]

2 minutes ago, cruiser54 said:

I may suspect the opposite.....

Yes, but I have a very good impression of this shop owner. Nevertheless, I'll be checking this.