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  1. #1

    Default car shudders on deceleration

    Hey all. So this is the second time I've tried to post this...hopefully works better this time. I'm having a problem with my 86 GT.

    When I let off the gas, such as to coast to a stop sign or light, no matter what gear I'm in, the whole car begins to violently shudder. When I put on the gas again or go to a lower gear, it's fine, until the revs drop on that gear and the car will shudder again. It doesn't feel like the engine is about to stall, but instead feels like I'm learning how to drive stick for the first time.

    The car has just recently had a full tune-up, and the clutch has only been in there for not even 10,000 miles.

    Any advice would be appreciated.



    Second, on an unrelated note. My windshield wipers don't work very well on the slowest setting. They are very jittery and clicky, to the point of being unusable, but are perfectly smooth on the faster two settings.



    Any thoughts? Thanks guys.

  2. #2

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    A shudder or vibration under deceleration is likely to to a driveshaft misalsignment, probably caused by worn suspension bushings or improper install of the engine and trans, meaning the working angle of the driveshaft not correct.

    You said it feels like learning how to drive a stick again, so that sounds more to me like "trailer-hitching" where the car kinda lunges back and forth like your towing something that is loosely attached to the car. Could be to much slack in the rear end, slack in the tranny, or any number of things. Can be caused sometimes if the engine is running too lean. More info on the car would help, like milage, any other repairs done on the car, when the problem started, did it start suddenly or get worse over time, etc.

    As for the wipers, I have the same issue. Haven't looked into fixing the issue yet though. Maybe due to a worn wiper arm assembly, or worn bushings in the wiper arm mechanism.
    '83 Capri 2.3T

    13.08 at 109.5 mph

    http://s466.photobucket.com/albums/r...urbo/?start=40


    I'm on a boat.....

  3. #3
    FEP Super Member NAVYCAT's Avatar
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    For the shuddering and vibration-
    I think its the drive shaft, try raising the car and place jack stands under it get some one to operate the car and you need to observe it.
    2017 Ford Explorer Sport (DD) 1986 Capri 5.0 Silver/Red
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    Both '84 Capri's vin# were 10 away from each other
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  4. #4

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    i have seen worn out rear control arm bushings causing a shudder like described, almost like if you choose too high a gear and lug the motor. also as already indicated, check the driveshaft for tightness, also may be worn u-joint needle bearings. just a thought, tough to diagnose without driving.
    79 Capri RS
    341 rwhp,348 rwtq 11.20@127


    1939 Pontiac Deluxe 6. 73,xxx original miles. Barn find. Currently the secomd owner.

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  5. #5
    FEP Senior Member 895.0's Avatar
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    all the post are probably what is going on but check to make sure your balancer is not coming apart
    1989 Mustang GT " the race car"
    1986 Mustang GT " the dd"
    1985 Mustang LX T-Top " wife's ride"

  6. #6

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    "Can be caused sometimes if the engine is running too lean."

    This would also lead to excessive fuel consumption; right? - and a generally rough idle? I have both of those and think the O2 sensors might be going.

    Could that also, like dominos, cause the shuddering problem?

  7. #7

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    Well, if the car is running lean, it is using less fuel than it should be. But a rich or lean condition could cause a rough idle. So is this more of a vibration/shudder or trailer-hitching? Still need more info to help...
    '83 Capri 2.3T

    13.08 at 109.5 mph

    http://s466.photobucket.com/albums/r...urbo/?start=40


    I'm on a boat.....

  8. #8
    FEP Power Member Mad Max's Avatar
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    Quote Originally Posted by P-51 4B View Post
    "Can be caused sometimes if the engine is running too lean."

    This would also lead to excessive fuel consumption; right? - and a generally rough idle? I have both of those and think the O2 sensors might be going.
    If your O2's are going and are too far out to for the computer to compensate it will defult to a rich setting and run in open loop mode. If your running lean the your headers will glow in the dark. The only way to be 100% sure if your rich or lean is to put a A/F meter on the car.


    also check you u-joints. My buddies car did the same thing before it threw the drivshaft off. Lucky it was the rear that went and not the front
    82 Capri RS, 5.8L, solid drop mounts, areomotive fuel system, 3" exhaust, ROD six speed, MM torque arm suspension, "mathis" 90 k-member, 04 cobra control arms, h&r springs, koni shocks, m-2300-k, caged, battery relocate

  9. #9

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    "You said it feels like learning how to drive a stick again, so that sounds more to me like "trailer-hitching" where the car kinda lunges back and forth like your towing something that is loosely attached to the car. Could be to much slack in the rear end, slack in the tranny, or any number of things. Can be caused sometimes if the engine is running too lean. More info on the car would help, like milage, any other repairs done on the car, when the problem started, did it start suddenly or get worse over time, etc."

    You describe trailer-hitching as a lunging back and forth. It definitely feels like that. I should add that the second I push in the clutch, it goes away, or I shift to a lower gear, it goes away.
    This has been happening since I bought the car in July and has not gotten any worse. As far as other repairs are concerned, I haven't touched anything on the transmission since I bought it. As far as the car's history, I can say that the engine was rebuilt about 20,000 miles ago. The transmission hasn't been touched.

  10. #10

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    Based on what you have said about the car using a lot of gas, and rough idle, I would say the trailer-hitching has something to do with the way the engine is running, and is not likely driveline, or suspension related. Be sure that there are no vacuum lines unhooked or split. Maybe check your timing too. I had to help my brother deal with this on his '68, but I'm not familiar with the 5.0 setups, so someone else will need to step in at this point. This is EFI not carbed, correct?
    Last edited by TurboBeater; 12-18-2008 at 07:16 PM.
    '83 Capri 2.3T

    13.08 at 109.5 mph

    http://s466.photobucket.com/albums/r...urbo/?start=40


    I'm on a boat.....

  11. #11
    FEP Power Member
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    If O2 sensors is detecting lean, the sensors will richen up the pulse on the injectors. Even if one injector is stopped up, the computer will compensate for the overall flow by enrichening the entire flow. The EEC-IV processors are not smart enough enough to look at each cylinder individually.

    My 2 cents.... (may not be worth a damn, but there it is)

    Jason

  12. #12

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    Quote Originally Posted by TurboBeater View Post
    Based on what you have said about the car using a lot of gas, and rough idle, I would say the trailer-hitching has something to do with the way the engine is running, and is not likely driveline, or suspension related. Be sure that there are no vacuum lines unhooked or split. Maybe check your timing too. I had to help my brother deal with this on his '68, but I'm not familiar with the 5.0 setups, so someone else will need to step in at this point. This is EFI not carbed, correct?
    I have an '82 Honda Accord and I am having the same problems. Using a lot of gas, rough idle, seems like trailer-hitching, dieseling (run on) when turning off car. The clutch was replaced about 10k miles ago, and radiator replaced recently. I must mention that my car is carbed and seems like it needs adjusting.

  13. #13

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    To isolate the trailer hitching from the u joints perhaps you could see if shifting into a different gear while matching the engine load/rpm which it is at while ithas the problem, changes anything. My money is on U joint weakness being revealed by the other issue, be there done that.
    Last edited by foot2floor; 10-13-2017 at 03:07 PM.

  14. #14
    FEP Super Member erratic50's Avatar
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    My only thought is ive had bad pressure in AOD transmissions cause a similar feeling. About like the vehicle was on washboards in back.

    Kinks in the trans cooler lines. Bad cooler. Filter... etc

    for me A new filter, a new cooler, fresh ATF, and shudder guard cured it for the remaining 60K miles I owned the vehicle and also restored my gas mileage back to normal.

    But, +1 on the U joints.

    Also check both motor mounts and the trans mount. From there inspect upper and lower control arm bushings.

    Ive heard of rear gear problems causing this. Follow proper safety procedures but ultimately end up with the driveshaft disconnected and the rear tires on the ground. When you use a bar to apply rotation pressure to move forward or backwards do you feel a lot of pinion slop?

    With the tires off the ground how does applying forward and reverse rotation by hand feel? Now block one tire and check by trying to move the pinion via rotating the other tire. The limited slip should stop you after a little movement but how do the gears feel? Smooth or like gravel ?

    Just some thoughts.


    or rev it up to the moon and slam it into gear with your foot on the floor. Whatever goes might have been the problem. Lol. (Don't actually do this unless you have the money for new everything in your drivetrain and just don't care anymore!

  15. #15

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    A couple other things to check would be your engine mounts and trans mount. Control arms bushings being worn would allow the rear end to shift under decelleration which could cause the misalignment of the driveshaft. Definitely check the u-joints though, that would be my first thought. Good Luck with it.

    Mike
    1982 GT 351W, retro hyd roller, ported Pro Comp heads, Tremec, M2300K brake kit, Recaros...needs paint!
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    1987 GT in MM&FF May of 97 "Not Fade Away" white and purple. Sold 1999

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