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Crown Victoria Shimmies when accelerating at 35 mph

I have a 1994 Automatic Ford Crown Victoria with apx. 120,000 miles (the odometer stopped working about 20k miles ago, what can ya’ do).

Recently it has started doing a subtle vibration/shake/shimmy when accelerating from (I believe) 1st to second gear at about 35 mph. It doesn’t happen when decelerating, and i think it might happen the same way at around 65 mph…not always though. It isn’t a rough vibration, but it lasts for about 3 seconds. it is definitely coming from the engine, it isn’t the tires or brakes

I just want to know what it might be before I start throwing money at it. Thanks in advance!

A shimmy is coming from your engine?
Are you sure?
When I hear the term “shimmy”, I look to the suspension or the steering components as the probable source of the problem.

If the problem seems to be coming from the engine…is it possible to describe it with some terms other than “shimmy”?

The car could be checked for any DTCs that may exist as a first step and if there are none then one has to proceed on with more diagnostics. I have no idea if throwing money at it means as a DIYer or if you’re throwing it at someone else.

Wild wild guessing, I might say a fuel flow problem (fuel filter or pump), intake manifold vacuum leak, intake tract air leak, or MAF sensor fault.

This is where you start getting into basic diagnostics and your mechanical abilities and/or tool situation as a DIYer is the unknown to me.

What would I do first? Check for DTCs followed up with the use of a vacuum gauge. At 20 years of age a vacuum leak or intake tract leak is a real possibility anyway.
If the fuel filter hasn’t been changed in a millineum I’d also consider that. The filter can be checked once off the car. It should be drained and allowed to dry for an hour minimum. Then try blowing gently through it. It should be easy to do; much like a soda straw.

@VDCdriver It is a vibration, maybe like going over rumble strips on the highway but not nearly as violent.

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@ok4450 I have a fairly competent dad with most of the tools we could possibly need, when i called a car shop and described the problem to them and suggested a fuel flow issue the man said that if that were the problem then it would always be vibrating, not just at 35 mph

Your car is old enough that fault codes, if any, probably won’t lead you anywhere. From what you describe, I would suggest a complete tune-up, including spark plugs, wires, fuel filter, air filter, PCV valve. If the trouble is still there sounds like you might have a torque converter shudder, these transmissions were prone to that.

An experienced qualified mechanic should be able to determine the cause of your problems as well.

is this shimmy when the transmission is shifting gears?

@asemaster ooooh I just looked up a torque converter shudder and I’d bet anything that that is the problem, it describes it perfectly. hopefully a transmission flush will fix it. Will update once I get the work done to let future this-problem-havers know if that fixes it!

Torque converter lock-up. Worn. Red Lube Guard may help.

I was going to suggest a converter shudder as that’s common with Ford transmissions of this era. That rumble strip effect, if that’s what it feels like, is pretty common with aged fluid.

I change the fluid in my Fords about every 30-35k miles. If allowed to get into the 40-50k miles range the subtle signs of it start appearing; usually a barely detectable shift flare.

Don’t just flush the fluid. Drop the pan, change the filter, and check the pan for excessive debris while it’s off. Debris means metal flakes or an excessive amount of blackish sludge.

I kept mine clean with fresh fluid and filters, and it did that anyway. It’s a wear effect.
After changing the fluid as per ok4450, add Red Lube Guard. I know that at least Napa used to carry it.

Concur w/ok4450 above, don’t do a flush. Do the drop the pan thing, as OP describes. Refill w/the exact fluid the manufacturer recommends for this car. If that helps, but doesn’t solve it, repeat the same procedure after driving a few days. It’s not possible to get all the old fluid out the first time.

Just wanted to update-
I was scared off of the idea of doing a flush by everybody i spoke with, and I could not determine if transmissions totally crapping out after a flush was an old wives tale or not, so I decided to do the easy, safe, cheap thing of adding red lube (or whatever it is called) from the auto parts store. It’s been about 2 weeks and the shudder has not come back yet. Hopefully it stays this way!

^
Yes, hopefully it stays away.
However, you did fall for an old wives tale regarding the supposed danger of doing a trans fluid change.

Just pouring in an additive is a crutch and should not be considered a long term fix.
You really need to drop the pan, change the filter, and drain as much fluid as possible at a minimum.
Some Fords of this vintage have a drain plug on the torque converter and if so fitted the converter should be drained. With the converter drained a fluid replacement/flush could be omitted and refilling the fluid to the correct level should be sufficient.

My preference would be to do the pan drop and filter change and then do a fluid replacement; or flush being the term used most often if there is no drain plug on the converter.

Yes my crown Vic is doing as you describe… do you know a probable cause?

Did you read any of the previous posts?