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My Grand Marquis shudders under very specific circumstances

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Public Alias
New User

Mar 25, 2014, 6:09 PM

Post #1 of 6 (1682 views)
My Grand Marquis shudders under very specific circumstances Sign In

Hello. I need the help of a car diagnostician here, possibly someone familiar with the Panther platform.

The car: A 2000 Mercury Grand Marquis LS with 130,000 miles, owned by me since 84,000 miles.

This all started about 4 months ago.

My car shudders when climbing uphill between 38 - 50 mph. It sort of feels like hitting a bump, and it sounds like something is disengaging for a second - it's hard to describe, but it's like the car's tone sounds like it stopped exerting force for a second.

Sometimes it just happens once, sometimes it will happen a few times while climbing the hill, with each shudder 2 - 4 seconds apart.

The shuddering will stop if the hill is steep enough that the transmission downshifts, or if I depress the accelerator enough so that the transmission downshifts.

It doesn't seem to shudder if I climb hills with overdrive turned off.

This seems to happen just as often regardless of whether the car has warmed up, or if I have just started driving. Also, tank full vs tank near empty, and expensive vs cheap fuel does not seem to make a difference. The CEL does not turn on or flash during shuddering.

Occasionally I will feel a similar shudder when I am accelerating on level ground between 60 - 70 mph, however this shudder is a lot less noticeable, and seems to happen less often.

Two mechanics have looked at the car and said they didn't notice anything. It recently passed inspection.

I've tried researching this problem and I have seen forum posters around the wed suggest the following issues for similarly described problems:

Bad fuel filter
Bad transmission fluid
Transmission is indecisive about which gear to be in
Bad torque converter

Which issue seems most likely and how worried should I be about this?


A few months before this all started the check engine light turned on for about a day. I had the code read and it came from an O2 sensor. Later that day it turned off on its own so I never pursued the issue further. I don't know if this could be related, but I figure I might as well provide any details I can think of.

(This post was edited by Public Alias on Mar 25, 2014, 7:12 PM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Mar 25, 2014, 7:12 PM

Post #2 of 6 (1662 views)
Re: My Grand Marquis shudders under very specific circumstances Sign In

My money would be on a chattering torque converter when overdrive tries to engage.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Ultimate Carjunky / Moderator
Discretesignals profile image

Mar 26, 2014, 4:37 AM

Post #3 of 6 (1644 views)
Re: My Grand Marquis shudders under very specific circumstances Sign In

Either you have TCC shudder or you have an ignition coil problem. Ignition coil problems are more prevalent. Your going to have to get into mode$06 with a high end scan tool and look at the $53 pids to see if any are counting up.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Mar 26, 2014, 4:37 AM)

Tom Greenleaf
Ultimate Carjunky / Moderator
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Mar 26, 2014, 6:45 AM

Post #4 of 6 (1634 views)
Re: My Grand Marquis shudders under very specific circumstances Sign In

First question is there a rust issue where you are or on/under this car anyway?

Torque Converter can do that and not send codes. Knock on wood none came my way but have been told this if true there is an additive (can try to find specific one as I/we don't like magic in a bottle much) or just change out ATF for new should either do it or not and can help or be harmful if never done. This in the absence of any codes lurking at all.

More: Has anyone ruled out plain u-joints? They can be tight just twisting on shaft and seem fine but under load don't twist as intended. Unless rust evidence, play is obvious I only think taking it out to check can know for sure.

If the Panther chassis still used the similar trans support bar as ones just a few model years earlier it is both rubber mounted at frame rails and a motor mount type at the trans itself. Tips at frame rail some could rust clean off inside the rubber. The more common first notice was a loosey goosey feel when driving then if totally broken trans would hang too low! All angles off and actually most still ran along hanging on by exhaust system!

Another that felt as described was usually more obvious was spark plug wire boots that reach long would inexplicably and intermittently sometimes fire outside unseen to valve cover not the plug. If suspect it really should have a code but all that came my way you could see the carbon trace of which one. Handle those with all care if removed for any reason.

Right now I suspect a u-joint and it's not very hard to take shaft out on these to check especially if no data shows trans or engine issues is found,


Public Alias
New User

Mar 26, 2014, 9:56 AM

Post #5 of 6 (1628 views)
Re: My Grand Marquis shudders under very specific circumstances Sign In

Rust is certainly an issue where I live - New England. For a 14 year old car mine doesn't seem too afflicted by rust.

Out of these three replies Torque Converter shudder came up in all of them, so I plan to address that first. Next time I bring my car to the mechanic I'll ask to have the ATF changed. I don't know when, or if the previous owner ever did that, and I've never done it, so I'm guessing at 130k miles it would be a good thing to have done anyways? I think I'd rather get fresh fluid and see if anything changes than try adding additives to what's in there.

No one has addressed the u-joints. Are they something that a mechanic will typically look at during routine maintenance? If not, I'll ask that they be checked out when I bring the car in.

I guess that leaves the ignition possibility. From how you addressed it in your post, I get the feeling it is the least likely of the three, so I'll ask my mechanic to look at it if nothing changes after addressing the ATF and U-Joints.


I just called a local transmission repair place. They said they can flush and change the fluid, and change the filter tomorrow. Fingers crossed that this fixes it!

(This post was edited by Public Alias on Mar 26, 2014, 10:09 AM)

Tom Greenleaf
Ultimate Carjunky / Moderator
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Mar 26, 2014, 12:43 PM

Post #6 of 6 (1617 views)
Re: My Grand Marquis shudders under very specific circumstances Sign In

Rust - I'm in MA so no stranger to rust OR the Panthers - own two right now, all others lost running new to rust so bad you could see the rear tires thru the trunksMad No I'm not pleased about that.

U-Joints: Some have lasted forever and some just don't. Should just be 2 "U" bolts, 4 nuts at differential and whole shaft is out and NO that wouldn't be in any regular check without a complaint. Shaft is indexed or was when new so even if you aren't doing this mark the shaft and the yoke so it's back in same position. Almost never matters but should do that just because.

With a shaft out front should have no free-play and swing without any resistance in all directions. Back one is 1/2 in a yoke and two caps NOT to fall off (tech's know) and inspected same way. Tech decides on how good they are and to do both or just a bad one. I'll stay out of that as tech's will disagree on what I do. If they are replaced the replacements will have grease fittings and OE ones never did TMK. Mostly IMO what kills them is water/moisture getting in or hard use or a redo was just a cheap junk one OR hammered in vs pressed can wreck new ones. Simple dang concept.

The lock up of converter can what I call "chatter" you said "shudder" = same I think. It really should quit it if you select non overdrive. Owner's manual should suggest if your particular speed is constantly right at the lock and unlock point just use non overdrive for that stretch of a drive.

If driveshaft was bent or damaged the misbehavior should be constant and predictable.

OK - could be none of this and back to trans and converter: By 2000 get codes. Mine are older but same chassis idea. If the thing is getting confused it may show a code.

Trans service: 3 ways to choose from. Drop pan, clean and inspect it replace filter. That really only changes out about 1/3rd of total ATF but you get to clean the pan of a clay like mud that some is normal - chunks of metal is game over. If a filter is clogged from junk that trans has plain worn out so it's done mostly because you are there. Another is flush thru such that pretty much 100% of ATF is new. Has it's advantages but doesn't clear out pan as I would also like if mine. A recent to me way suks is done at the while you wait places will just suck out what they can and refill that amount. Fast, cheaper and frightened by usually less than well rounded techs.

Changing fluid can either fix something just for renewing the additives that come with new fluid or cause a lurking worn one to give out sooner in some cases if never done before in an older vehicle. Jury still out on much of this.

In any case this is just a forum with real tech's all free for you with the challenge of not having this car in front of us for inspection in person so has its limits.

Just seek out if not doing all or any of this yourself the best help you can. Most IMO will mean well on all fronts just this is trans and you must know there's bucks at stake for doing something wrong!

Rust if the mounts or metal parts simply has to be seen to know what to do. Used cross bars might be just fine even from New England. Once an aftermarket one was available but doubt it now. Simple phone call to a local trans shop would be a good idea.

Again - if you choose an additive for converter chatter it's still AYOR and would rather see it have new fluid than some unknown junk,


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