Letting off gas causes truck to jerk

[jeffjb88]

I have searched far and wide for what this could be.

For starters I have a rebuilt transmission and transfer case. Still has a month or 2 under warranty and currently has about 15000 miles on it, so I'm trying to make sure I get all repairs to it before it expires. Recently had the torque converter replaced under warranty as well but this problem has been happening for a while. According to the transmission shop, the transmission is in fine condition after they replaced the torque converter and resealed/flushed the tranny fluid.

What is happening is that when my OD is off at around 35+ mph my car will jerk and make a "bang" sound for a split second as soon as I let off the gas. It feels like I hit the breaks for a fraction of a second then it resumes to decelerating at the normal smooth rate. the faster I'm going the harder it jerks when I let go of the gas and it will get loud/strong enough to rattle my rear window sometimes. It doesn't really happen when stepping on the gas after letting off the gas, at least nowhere near as noticeable as just letting off the gas.

When I have OD on (default condition) there is no jerking at all until 50-55mph+ and even at those speeds it is very light and almost unnoticeable.

What could be the problem? I'm trying to catch serious problems before they happen and before my transmission warranty expires so any insight would be greatly appreciated.

Again this has been happening for a while, I just never went with OD off because I wasn't aware city driving puts stress on the OD (I spend at least 30 minutes to an hour every day between 35-55). I've had this transmission for a year and a half and it has been like this as long as I can remember. (not sure if this goes beyond my transmission rebuild or not.)

Spark plugs and wires replaced, fuel filter replaced, air filter replaced, throttle body and maf sensor cleaned, switched to synthetic oil, thermostat replaced, egr vacuum line redone (small vacuum line that goes under battery was rotted out for a year before finally getting it replaced with a honda high performance vacuum line for <$15 when Ford asked $250~ for their OEM one.)

NO CEL or DTC last I checked after clearing them about a month ago after the thermostat and fuel filter were replaced.

 

[BJH]

Check for play in your u-joints and yolks at the rear end and transmission

 

[jeffjb88]

Thanks for giving me that idea. For some reason it is not as bad now... It's like it has a mind of its own. I took it to the transmission shop couple days ago since my car was vibrating real hard at about 800 rpm and had a metal rattling sound from underneath (all started after they replaced the torque convertor under warranty). I asked them to look at the u-joints while they were there.

They checked the u-joints and said the u-joints were tight and might be dry but did not want to pull the drive shaft to confirm unless I wanted them to (they didn't want to take business from the mechanic I get most of my work done at). they said the normal symptoms of u-joints failing would be a vibration at low rpm and speed along with a squeaking sound when moving slow. Well lo and behold I have squeaking at low speeds (0-20mph) that sounds like it goes at the same speed as the wheels. And I have that weird vibration only at 800 rpm. I told him that after he checked the U-joints as I was under the impression it was 2 different problems. the squeaking started after getting rotors calipers and breakpads replaced in the front and was told it just needs to "break in" even though it's been a month since the replacement and has been steadily getting louder since then... So maybe I will have to get those u-joints replaced soon...

 

[Jasonx521]

I have this same thing.

I have rebuilt my transmission and transfer case as well.

When I let off the throttle, and only if the torque converter is locked up will it do it
If the TC is locked and I accelerate, but not enough for it to down shift or unlock the TC, then let off it gets worse.
If I'm climbing a hill and the TC is locked and slowly accelerate everything is fine; Engine is strong and no noises etc.., but when I let of the throttle, even at a reasonably even slow pace it will do it.

Going down hill it will not do it at all.

The only way to prevent it, when under heavy load w/ TC locked is to very slowly and I mean slowly let up on the accelerator.


History:

I had the transmission rebuilt at AAMCO, and used a Central Valve bodies VB, new servo's with the o-rings, a D-Ring on the First/REV servo, new clutches, steels, resurfaced the drums, 2 of 3 planetary gears are new, new sprags, and of course all bushings, bearings, new gaskets/seals, and new TC. A complete rebuild.

At first I called Donnie at CVB's and he sent a new VB, and I put all new solenoids, bracket, and wiring harness on this VB.

That didn't' fix anything, so we completely disassembled the transmission and inspected every part and replaced the torque converter for a new one.

Now the transmission shifts very good, has excellent power transfer, just feels good all around. I would say it is better than when it was new.

The transfer case I rebuilt and I used new case halves with the bushings and sleeves, new bearings & seals, new updated fork & cam, hi/low gear. Everything looked good and nothing stood out to me. I don't hear any noise and it shifts into & out of 4X4 HI/LOW quickly & quietly.

The front drive line is new, and the rear has new Spicer u-joints.

The rear end is as far as I know the original 3:73, I replaced the clutches and filled it with royal purple and Fords additive ~ 20k miles ago.


The engine runs good, except I notice when I let off the throttle it likes to pick back up slightly (or even just level off momentarily) given the right circumstances, and then goes down as it should.

I think the engine is problem, but it has all new sensors, plugs, wires, timing parts, seals, gaskets etc... Runs great. I wonder if there is some kind of vacuum issue when I let of the throttle?

It does not leak any fluids. The PCV hoses, baffle, valve is all new from Ford.

The EGR valve & idle control valve is new as well.

The best I can come up with it; is it is caused by an issue w/ the PCV system or the EGR valve, but I have no way of testing this theory??????


Anyone that can help, I would greatly appreciate it....

 

[colintrax]

I'm pretty sure this "jerk" is just engine braking. If you're OD is off, the truck can't up shift as high. I would assume the transmission also thinks your towing, so it'll act more aggressively (this is just an assumption)
My truck does it, has since we got it with 95,x.. miles.

Quit worrying, your truck shifts through every gear right? Torque Convertor locks? If so, chill out. Cuz it's either just a cork our trucks have, or it's perfectly normal. Either way, no point in dumping money into a problem that most likely doesn't exist.

 

[Petek]

sounds like it could possibly be ujoints.

 

[96eb96]

Also, before tearing anything apart, first check the U-Joints - I suggest match marking the driveshaft to the flange, removing it and checking them by hand for smooth operation. Sometimes they could be tight on the shaft but may bind in a certain position.
You can do U Joints yourself or bring the driveshaft to a Fleetpride(they do this all day for the bigrigs) or a Napa Machine Shop. It is not expensive.

Also, While it is off make sure the slip joint spline shaft is completely lubricated with motorcraft xg-8(Accept no substitutes) grease. Remove the small boot and replace the fasteners with zip ties(this is OK according to a Ford dealer). This is a common issue for trucks of all makes, and will cause symptoms in this post. I believe this procedure is mentioned in the required service list but often overlooked.

 

[jeffjb88]

Just had all 3 ujoints replaced. didnt change anything. Im not worried about it though.

 

[Jasonx521]

~ year ago, I greased the slip joint on the drive line and replaced the u-joints with Spicers.

This really bothers me, as I know it can't be good on the drive train, when I can feel the entire truck shake.

The best way to describe it, is if you have ever had a transmission that shifted hard (either designed that way or not) and you are under heavy loading, say up a hill and held your foot steady on the throttle at say 4k rpms and then manually up shifted at highway speeds. Except with the said issue it is not shifting gears (At least shouldn't be), the TC is unlocking under heavy loading and something making the Thud/Bang sound that shakes the truck.

Its only bad enough to shake the truck under heaver loading, say up a decent hill, with the throttle pressed close to the point of down shifting, and the TC is fully locked, and then all you have to do is back off the throttle slowly and if not really slow it will do it when the TC unlocks.

It so seems like the transmission, but after disassembling it twice and (3) valve bodies and (2) torque converters, its most likely not it.


My plan:

- Remove the rear drive line and check slip-joint and u-joints. (maybe have a drive line repair shop check it out)
- Check the slack in the output of the transfer case, both rotational, and side-to-side
- Check the rear end yoke for rotational & side-to-side slack.
- I planned on rebuilding the rear end soon, so I will go ahead and rebuild it now.

I can only hope if I place a video camera under the truck, and record while driving, and shoot different components in action, it will show the problem, at least via sound or motion.

- transmission
- transfer case
- drive lines
- rear end
- rear suspension

Anyone have any experience with slack in the rear end and what it feels and sounds like?

I have not personally seen a rear end with enough slack to make any noise or problems, only seen them break, explode etc...

It is important to note, that this jerk/slam is very quick, with almost no delay when letting off the throttle, this is one of the main reasons I have pointed to transmission as the problem.

 

[colintrax]

~ year ago, I greased the slip joint on the drive line and replaced the u-joints with Spicers.

This really bothers me, as I know it can't be good on the drive train, when I can feel the entire truck shake.

The best way to describe it, is if you have ever had a transmission that shifted hard (either designed that way or not) and you are under heavy loading, say up a hill and held your foot steady on the throttle at say 4k rpms and then manually up shifted at highway speeds. Except with the said issue it is not shifting gears (At least shouldn't be), the TC is unlocking under heavy loading and something making the Thud/Bang sound that shakes the truck.

Its only bad enough to shake the truck under heaver loading, say up a decent hill, with the throttle pressed close to the point of down shifting, and the TC is fully locked, and then all you have to do is back off the throttle slowly and if not really slow it will do it when the TC unlocks.

It so seems like the transmission, but after disassembling it twice and (3) valve bodies and (2) torque converters, its most likely not it.


My plan:

- Remove the rear drive line and check slip-joint and u-joints. (maybe have a drive line repair shop check it out)
- Check the slack in the output of the transfer case, both rotational, and side-to-side
- Check the rear end yoke for rotational & side-to-side slack.
- I planned on rebuilding the rear end soon, so I will go ahead and rebuild it now.

I can only hope if I place a video camera under the truck, and record while driving, and shoot different components in action, it will show the problem, at least via sound or motion.

- transmission
- transfer case
- drive lines
- rear end
- rear suspension

Anyone have any experience with slack in the rear end and what it feels and sounds like?

I have not personally seen a rear end with enough slack to make any noise or problems, only seen them break, explode etc...

It is important to note, that this jerk/slam is very quick, with almost no delay when letting off the throttle, this is one of the main reasons I have pointed to transmission as the problem.

Go up a few posts and read what I said....
It's nothing to worry about

 

[Gormy]

I think this is an old post but I am experiencing the exact same thing in mine. Under load as soon as I let off it hits hard, sounds really bad and shakes the whole truck.

And Colintrax, no disrespect, but stop saying it's nothing to worry about. That's not helping anything. After spending 10 years working for dealerships I know enough to say ignoring this is not alright. This is an issue that needs to be looked at. If you haven't experienced it you don't know how bad it is.

Did you ever figure out what was wrong with it? I would really like to know as I just paid up big for a rebuilt trans in my 2003 and I am now experiencing this as well. I need to know if I should contact the company I bought the trans from or if it is elsewhere in my drivetrain.

 

[LightningStrikes]

Mine is doing the same

Jeff, I have a 2000 Ford Explorer 4x4 and it's doing the same thing. I have replaced everything on it and nothing has helped. It is not the transmission either. I think I know what it is and I am gonna try it tomorrow. Someone told me it is the module under the plug wires. I don't know how to work on cars but I do try. I am gonna try to fix it tomorrow but if anyone can help me, plz do. Mine acts like it's electrical because when it tries to die on me in traffic, the lights and all go out. Plz help.

 

[FIND]

Check your control arms for play.

 

[LightningStrikes]

Fixed my 2000 Ford Explorer

You will never guess what was wrong with it. It was the intake manifold gaskets. It was jerking and cutting out like it wouldn't take the gas. The air and gas has to mix exactly right and mine was getting too much air. I have spent a fortune in other parts trying to fix it and it only took $20 to fix it after all. OMG. Hope this will help others and hope you don't spend money like I did to figure it out.

 

[JusTheUsual]

lol I was about to say brake calipers sticking, happened to me couple times and another one I work on

 

[Mr.Ed]

I think this is an old post but I am experiencing the exact same thing in mine. Under load as soon as I let off it hits hard, sounds really bad and shakes the whole truck.

And Colintrax, no disrespect, but stop saying it's nothing to worry about. That's not helping anything. After spending 10 years working for dealerships I know enough to say ignoring this is not alright. This is an issue that needs to be looked at. If you haven't experienced it you don't know how bad it is.

Did you ever figure out what was wrong with it? I would really like to know as I just paid up big for a rebuilt trans in my 2003 and I am now experiencing this as well. I need to know if I should contact the company I bought the trans from or if it is elsewhere in my drivetrain.

~ year ago, I greased the slip joint on the drive line and replaced the u-joints with Spicers.

This really bothers me, as I know it can't be good on the drive train, when I can feel the entire truck shake.

The best way to describe it, is if you have ever had a transmission that shifted hard (either designed that way or not) and you are under heavy loading, say up a hill and held your foot steady on the throttle at say 4k rpms and then manually up shifted at highway speeds. Except with the said issue it is not shifting gears (At least shouldn't be), the TC is unlocking under heavy loading and something making the Thud/Bang sound that shakes the truck.

Its only bad enough to shake the truck under heaver loading, say up a decent hill, with the throttle pressed close to the point of down shifting, and the TC is fully locked, and then all you have to do is back off the throttle slowly and if not really slow it will do it when the TC unlocks.

It so seems like the transmission, but after disassembling it twice and (3) valve bodies and (2) torque converters, its most likely not it.


My plan:

- Remove the rear drive line and check slip-joint and u-joints. (maybe have a drive line repair shop check it out)
- Check the slack in the output of the transfer case, both rotational, and side-to-side
- Check the rear end yoke for rotational & side-to-side slack.
- I planned on rebuilding the rear end soon, so I will go ahead and rebuild it now.

I can only hope if I place a video camera under the truck, and record while driving, and shoot different components in action, it will show the problem, at least via sound or motion.

- transmission
- transfer case
- drive lines
- rear end
- rear suspension

Anyone have any experience with slack in the rear end and what it feels and sounds like?

I have not personally seen a rear end with enough slack to make any noise or problems, only seen them break, explode etc...

It is important to note, that this jerk/slam is very quick, with almost no delay when letting off the throttle, this is one of the main reasons I have pointed to transmission as the problem.

Hello, Did you ever figure this one out. I have the exact same problem - going uphill on rebuilt trans (only 15,000) with a shift kit put in, it was trying to down shift with TC on and Bam it finally blew up the OD Solendoid - and it was Extremely LOUD. So now I'm still getting the bump roll thing going foward - and I'm certain this is whats causing the stress on the Trans and OD. Let me know - I know this post is very old but I've been trying to figure this out forever.

 

[Mr.Ed]

Hello, Did you ever figure this one out. I have the exact same problem - going uphill on rebuilt trans (only 15,000) with a shift kit put in, it was trying to down shift with TC on and Bam it finally blew up the OD Solendoid - and it was Extremely LOUD. So now I'm still getting the bump roll thing going foward - and I'm certain this is whats causing the stress on the Trans and OD. Let me know - I know this post is very old but I've been trying to figure this out forever.

Also, I have not done any rear end work, change the U-Joints, I have put the grease in the slip yoke though. If anyone DEFENITELY KNOWS THAT ANSWER TO THIS ONE please reply.

 

[Mr.Ed]

Also, I have that Idle thing going on where is goes up a bit at after I stop and then drops back down, but I don't think that is related. I could actually feel the trans trying to upshift to OD (it would knudge a little - you could feel it), on this long hill I have near my house (and it would only do it on this particular long hill with about 18 - 24 degree grade I would say but long, until Finally, BANG the OD solenoid blew up in there. Now I only have a C3 (three speed) - which is OK, but what burns me is I can't figure this one out, because the driveline shop said my ujoints were fine. I might have slack in the rear end but I checked it after having the driveshaft off to lube the splines - so this one is a complete mystery to me. And yes you have to release the gas pedal until almost at top to do it. Sheesh.