Three days ago I was rear ended while sitting at a stop sign. No damage to either vehicles other than a few scratches (maybe a 5 to 10 mph hit). Since then, I've been getting progressivly louder noises from the transmission. The noises only occur when no power is being provided to the rear wheels (during costing or maintaining speed where only the front wheels are being used). Also, while sitting at a stop and releasing the brake (without pressing the gas) the acceleration is jerky. Doing the same in reverse is worse. If I were not driving a hybrid, I would say that the cause was a warped or damaged brake rotor because that is what it feels like (rotors are all inspected and fine). I've even read on a different post about U-Joints causing this so I replaced them and that wasn't the cause either (although one u-joint was going bad).

I have an appointment in 2 days, 37 hours from now, to have it looked at but before I go in, could being rear ended cause this? I was in drive with my foot on the break which maybe got released for a moment. What other issues could this sudden acceleration cause?

 

The issue is how much force was transmitted by pushing on the body (the hit) to the power train. Since the hit pushed the car and thus rolled the wheels, force was transmitted to the rear axle. So what damage could occur?

As I see it there might be damage in the rear axle (& maybe the CV joints out to each wheel). Then there might be damage in the PTU, if it was engaged when you were struck. Lastly, if the PTU was engaged when hit, then there might have been damage to the transaxle.

Alternatively the transaxle might be damaged since its wheels were also pushed (separately from the rear wheels). The larger motor/generator in the transaxle is directly geared into the ring gear of the planetary gear set of the transaxle. So if the wheels rolled, this MG rolled. Probably not a big deal.

But, this also rolled the Planetary gears a little and thus attempted to roll the engine. Probably no big deal either. And finally this sent some force to the sun gear which is the smaller MG. Don't think that was a big deal.

My bet is that the transaxle (or rear axle too) ring gear took nearly all of the force and could have damaged it.

So how hard were you hit? What did your rear bumper look like?

I'd look at changing your transaxle & rear axle oils. When you do, drain the oil into a clean pan and look carefully at the drained oil. See what's in there: shiny particles, gritty stuff, or whatever. Look to see if there are any very fine particles that remain suspended in the oil. Probably ought to drain quickly after warmed up operation so as much "stuff" is still suspended in the oil when you drain it.

 

I am a prosecuting attorney and a victim of a minor rear end car accident reported a broken motor mount as damage. you might check mount points.

 

Thank you both very much for the replies. I took it in last Friday. The tech found loose front sway bar links but that was not the problem. So the tech went for a ride with me and he could neither hear it or feel it (it was raining which doesn't help). He claimed it was road noise and nothing more but it never used to do that.

I believe the person who hit me was accelerating. There was a left turn lane and a right turn lane. I was turning right and I eased forward a bit to see around a car turning left. The person behind me must have thought I was going, started looking left, and hit me on the back drivers side. I just had a few scrapes of paint and slight bumper deformation. This person never came to a complete stop until after hitting me. After impact, there was about 9 feet between us. They were probably going about 5 to 15 mph when they hit me.

I will check the motor mounts to see if they are damaged. Thank you for the advice.

I will also change the transaxle and rear oils and run a magnet through it as it drains to see if I collect any particles. On the transaxle side of the drive shaft for the rear wheels, there is another transfer case with oil of some sort in it. Does anyone know if that is fed from the transaxle or is that separate and I should check that as well?

The reason I'm asking is because my gut is telling me that is where the noise is coming from. It is worse when it is warmed up so before I take it in again I'm going to get it good and hot and make sure it isn't raining.

Also, it doesn't make the noise a speeds greater than 60 mph. The loudest is between 35 and 45 mph. I assume that the rear wheels are staying somewhat engaged at speeds above 60 mph or I am just traveling to fast to hear it.

I have a great audio file where you can hear exactly the noise I'm talking about. It is a tinging rattle sound coming from the transaxle. I will try to find a way to post it here or post a like to the noise. You can hear it stop when accelerating and start when slowing down.

 

The noise got much worse so I took it back to the Ford service center and within a few hours they deduced that the issue is the PTU and needs to be replaced. They said there was a bearing that sheared which is not related to being rear ended.

I did ask if it would be covered under the eCVT warrantee and was told it will not be because they have never had to replace a PTU on a MMH before and the failure must be from towing too much or overloading the vehicle which is a good guess because I have an aftermarket trailer hitch installed but their guess is wrong. I explained to them that the trailer hitch is used for a bike rack because I didn’t want to put our bikes on the roof (aerodynamics and stone chips on the paint of the bikes) and I didn’t want to put on a bike rack that connected by putting straps through the rear hatch back and rested against the paint so a trailer hitch bike rack was the best option.

The Service Manager then asked about replacing the U-Joints in the drive shaft and I told them that I did that only after I started getting the noises from underneath.
I then showed them TSB 9-4-4 which is for the PTU vent bolt leaking. I said that while changing the U-Joints that I found this bolt was loose and I tightened it. After that was when I found the TSB for the vent bolt. With only 12 oz. of oil in the PTU, I would guess that a significant percentage of the oil leaked out judging by the dirt/oil mix on the side of the PTU and on the frame cross bar under it. Again, this was all after the noise started and on page 296 of the manual, it clearly states that this fluid level does not need to be checked unless a leak is suspected and by the time I suspected it, the damage was already done.

We ended with him, the Service Manager, saying that low fluid wouldn’t have caused the bearing damage and it will be up to Ford if they decide to replace it under warrantee or not.

So my new question is, if low fluid isn’t an issue, why in TSB 9-4-4 do they tell you to check the level and add 75W-140 oil if needed? Isn’t a bearing something that would wear out from not enough lubrication? Finally, has anyone else had to have their PTU replaced?

 

How can you miss this, 10 posts down from yours: https://www.greenhybrid.com/discuss/...i-first-21743/

 

Yes. I see that. That is the post that lead me to replace the U-Joints as a first test. I posted the reply quickly and asked the question about the PTU as an afterthought. Sorry for the mistake.

 

You might search for "PTU" and find some more topics.