Noticeable jerk when letting on/off throttle *VIDEO POSTED*

[harrymaneuvers]

Ok... So when I am cruising down the road at highway speeds... If I let off the throttle, it instantly makes my car have a small jerk or studder (not in the engine but in the actual rolling feel of the car)


If I am off the accelerator and the car is naturally slowing (still going over 65 MPH) and I just barely press on the gas, there is a point where the acceleration will kick in and the car will not just start to accelerate, but I can feel the engine and transmission catch up with eachother... and then start to accelerate.

It is really hard to explain but the only way I can summerize it is to say that there is slack between the engine and tranny and when I speed up/slow down, the engine and tranny speed differences make the car have an instantly noticeable jerk in acceleration or in deceleration if I let my foot off the gas.


Its like when I had a U-Joint go bad in my old mercedes driveline, shifting from reverse to drive would create a slight jerk as the slack in the worn U-Joint was picked up...


Is this just my tranny showing its age?

[csweston]

Manual or auto?

[harrymaneuvers]

Auto

[httrdd]

Tranny slipping? Mine slips then catches some times. Been doing that since I got the car.

[csweston]

My auto does the same thing some times at lower speed. Usually only when im hard on it though. Sounds like the usual slushbox 4 eat to me :lol:

[loganmossmusic]

Is it your torque converter locking and unlocking? When you are driving on the freeway, it will usually lock up, but if you give more than like 40% throttle it will unlock and let the engine speed up about 750 RPM. Thats what it sounds like to me.

[harrymaneuvers]

I dont know... When I really get on the car... the tranny shifts perfectly... almost too good. Haha


Its like If I was going 70 and I started to lift my foot off of the accelorator... It wouldnt really do much until I reached a point where all of a sudden it feels like the engine is now not engaging the tranny. And it is like a switch... I can literally keep my foot right at that point on the pedal and play with the exact point where the acceloration is on or the acceloration is off.

If I try to visualize the sound and feeling.... it is like imagine you have a drive shaft.... connected at the center with a U joint...
https://sl-i.net/FORUM/images/imported/2011/04/uj_dead-1.jpg


Now imagine that instead of that U joint being rock solid... there is so much slack that one side can turn maybe 1/8 turn before the slack is tightening in the opposite direction and it begins to spin backwards.


Now imagine that whole thing is spinning clockwise at 2000 rpm... under acceloration... but as soon as I let off the accelorator, the engine will begin to slow, so the side of the shaft that is connected to that will instantly slow to something below the speed of the other side of the shaft... causing that 1/8 of a turn in slack to switch positions and then continue to rotate at the same speed as the rest of the shaft... until I step on the accelorator and the then the engine side of the shaft speeds up and puts force on it going the otherway and then the slack shifts back to the original position


That is the exact feeling each time I let up off the throttle or start to apply pleasure to the gas while moving at highway speeds.

It is almost certainly "slack in the driveline"... but where would be the likely culprit?

[Huffer]

Could be your torque convertor, driveshaft...

[mike-tracy]

I'll submit that part of the reason it jerks is worn out trans/motor mounts. It would be less noticeable with new ones. But of course that isn't the root cause.

[harrymaneuvers]

So this gives me a good excuse to tear into the driveshaft and the rear diff.


I figured I could do a LSD swap while I am at it...

[Huffer]

Try running the car in FWD mode for a day or so to see if the problem goes away. I'm curious if the driveshaft stops spinning if the transfer clutches are bypassed.

[harrymaneuvers]

That is a good question... I will put the fuse in and see how it goes... I only notice this at hiway speeds though.

[Huffer]

You can run on the highway in FWD mode.

[harrymaneuvers]

Oh and I will. I am just afraid that if it isnt the propeller coupling, then it has to be inside the trans, diff or both...

[harrymaneuvers]

So shopping around for an upgraded trans bushing for the ladies GG made me think...

Maybe the "seat of my pants" feeling IS simply due to a worn out trans bushing...

I think I wouldfeel the an/off throttle jerk if the bushing was worn out and had a lot of slack/play to it.

Is it supposed to hold the tranny stiff to the floorboards?


If it did loosen, what else would I feel?

Also, it seems like this might be cheaper and easier than replacing the drive shaft... any recommendations for an aftermarket bushing that isnt for the track?

[mycargoesvroom]

My transmission does this sometimes as well, it also has the all too common 1-2 jerk. My suggestion is to leave it alone. You'll spend so much time and money trying to track down the culprit it just isn't worth it. These transmissions are pretty terrible from the get go and putting money into it seems silly to me. I plan on driving it till it drops then swapping in a 5 speed.

Just my .02 tho :D

[harrymaneuvers]

Point taken.


Well I am adhd and this sort of thing bothers me. So yesterday I put the rear up on ramps and got under there. It is definitely NOT the U joints or propeller coupling :(

The entire drive shaft is solid... but I can grab it (trasmission in P with E brake on) anywhere on the driveshaft and rotate it back and fourth about 1/8th to 1/16th of a turn... that might not seem like much but it is enough to cause the symptons that I am experiencing.

So if it is not in the driveshaft... is it MOST LIKELY at the rear diff or the front of the car (front diff/transmission)?!?!

I took a video and will see if I can find a USB cord to post it up later today.

[mycargoesvroom]

I feel you for sure about the ADHD thing, but there are so many demons in these transmissions it just isn't worth it. By the time you fix one thing you'll notice something else and so on until you've spent enough money you could have swapped and been done with the issues.

Keep us posted though, if you find out what it is it might be worth looking into in my car.

[harrymaneuvers]

http://www.youtube.com/watch?v=krXoQ1R4BNc

Car is in Park with E brake pulled...

Where do I go from here?

If it was play in the rear diff, would it be able to move that much at the front where it goes into the tranny?

If it was play in the tranny, would I be able to move it that much in the diff?

I just spoke to trusted friend of mine who looked at the video and said that from his experience as a mechanic, it doesnt look like an abnormal amount of play...

Can anyone confirm or deny that their car has the same amount (roughly) of play or gear lash?

[harrymaneuvers]

Ok so after talking with MULTIPLE trans shops and subaru speciality shops, it seems that the amount of play in my driveline is appropriate.

First suggestion was the rear diff bushings, which apparently need to be pressed in/out.
Next suggestion was the trans mount...

I cant seem to find anything whiteline or other as a good replacement for some reason... Can someone point me in the right direction??? Kartboy?

[Huffer]

Hold on - are any of your driveline mounts ORIGINAL? Your car has 200k+, so even brand new factory parts will be much stiffer than what you have.

My suggestion is to pull your stock mounts and see how soft they are. You can also DIY a polyurethane auto trans mount.

[Dead91silvia]

I would agree with the other guys on the driveline play. It's the same with all the S13's and Toyota trucks I work on.

As for the mounts, if your car has a leaky trans, it might have saturated the mount to make it super soft. Every now and then I can feel some jittering with my BD, but not much and it has 235K on the trans.

Have you looked at your CV joints also? If they are toast, that could be part of it. I have a vibration from my right front wheels and I know its because the axle is FUBAR. I'm just too lazy to change it out... haha

[harrymaneuvers]

Yes I am sure they are all original mounts...

I am not concerned with the axles because they all seem solid when I give them the twist/shake test.

I am mainly looking for the rear diff bushings at this point... the ones that the two horizontal stubs go into the rear crossmember...

I found some from whiteline but they dont specify the BD...

http://www.whiteline.com.au/product_det ... ber=KDT905 (http://www.whiteline.com.au/product_detail.php?part_number=KDT905)

Can anybody confirm that these will work?!?!

[Dead91silvia]

I think anything different from BD/BK/BG for chassis is the sway bars, brakes, and coil springs/struts for the suspension (different spring rates). Maybe a couple other things, but all the mounts should be the same. It should all interchange.

I could be wrong, but I dont think so. The only things not interchangeable is everything from the back seat back (seats and body), but even at that, the chassis is all the same.

[harrymaneuvers]

Well I know the wrx's dont mount the same way... at least not the newer ones... the older impezas might be the same but the newer ones bolt into the rear subframe which bolts to the crossmember... or the other way around.


I need a solid answer from someone before I buy this...


So besides new Diff bushings and a new trans mount... anything else that I should do while I am at it??? Yes I know I should be doing a LSD swap but I want to make sure I can get replacement bushings first... The dismantler by me, specialized parts planet, has TONS of 4.11 lsd diffs for like $150... axles would be another $50 total so I am not really worried about that.

[Huffer]

Here's Whiteline's selection for the BD: Note that in Australia, Legacy = Liberty

http://www.whiteline.com.au/do_segue.ph ... F94-8%2F98 (http://www.whiteline.com.au/do_segue.php?make=Subaru&model=Liberty&vehicle=BD%2C+BG+MY95-99+6%2F94-8%2F98)

[harrymaneuvers]

Huffer - I have read through their list... no rear diff bushings... that is why I was asking about the other set...

[loganmossmusic]

Im sticking with my original idea, and maybe post a video of your RPMs while you are on the freeway experiencing the problem.

[harrymaneuvers]

There is really nothing to post as it is really only felt in the seat of my pants.

The RPM's are not affected at all.


I am crawled under the car and felt the bushings and they are REALLY loose and squishy... I could almost pull them out right now if I wanted.

[loganmossmusic]

Exactly, when the RPMs do not move at all, the torque converter is locked, so its like driving a manual and lifting off the accelerator, the engine bucks a bit because it is solidly connected to the transmission. It gets worse over time because of bushings. So you are right about your bushings and also it is not really a problem unless you like to be really hard on your engine and transmission in which case you should think about maybe getting OEM replacements or polyurethane replacements. I would say you need engine and transmission bushings, your rear diff bushings are probably not going to affect it alot.

[harrymaneuvers]

Well I know I need the rear diff bushings because I just looked at them. My engine mounts are fine but I was going to replace the tranny mount.

Back to my question though... Can someone point me in the right direction for some aftermarket rear diff bushings?

[loganmossmusic]

http://store.powerflexusa.com/legacy-19 ... p1184.aspx (http://store.powerflexusa.com/legacy-1995---1999-urethane-bushings-p1184.aspx)
This?
Also maybe this, but I dont know if Impreza bushings will fit a Legacy.
http://www.rallitek.com/Whiteline-Rear- ... ngs/p-4460 (http://www.rallitek.com/Whiteline-Rear-Differential-Bushings/p-4460)