Is it possible for a failing transmission to cause a timing belt to slip?

[wagondragon]

I recently purchased a high mileage 2008 Subaru Outback (200,000 miles) with an automatic transmission. After driving it more, i started experiencing an occasional miss shift. ( only when shifting up into a higher gear would the RPM's climb and then catch hard.) And It always had a hard shift down into 1st gear (or neutral?) only when I'm coming to a stop. This happens almost every time i come to a stop after the car has warmed up, and less often when its cold. I checked the transmission fluid when i bought it, and it didn't seem bad. Ive since done a partial drain and refill of the transmission pan ( about 3-4 quarts worth ) But that didn't seem to help. I also tried adding some Lucas transmission fix ( very thick additive ) Which didn't seem to help, or hurt. A few weeks ago, my wife was driving the car and the timing belt broke, she was unsure if it was the timing belt breaking, or if the car was in the middle of a miss shift. Until the car died a moment later. I have since had the heads done, and have the engine put back together waiting to be put back in the car. But i am superstitious that the transmission might have caused the timing belt to slip, and that im putting all my money and time at risk by re installing the motor into the car with an iffy transmission. Am i crazy? The theory goes like this... Maybe an old tensioner, and a sudden spike in RPM from the transmission failing to find a higher gear, and then a sudden and violent clunk into said gear. May have cause the belt to slip off the sprocket, and ultimately break? As i was putting it back together i noticed there is no timing belt guide above the main crank. ( the manual says that it may not come equipped, or be necessary.)

I think im going to put the motor back in, and test drive it more. hoping to find a solution to the odd shifting characteristics. But wanted to know if anyone had ever even heard of a bad transmission being able to break a timing belt before? IF at least to calm my fears. 

*Forgot to say that the timing belt did not look worn, or dried out in any way before it broke*

Edited July 4, 2021 by wagondragon

[heartless]

well, considering the mileage, it was most likely overdue for a timing belt, and unless you have proof it was changed before you bought it, then i would not necessarily correlate the two issues. Is it possible the extremes of the tranny issue broke the belt? Maybe, but it was most likely going to break anyway, even without the tranny issue.

Timing belts are fairly robust things - the scenario you describe with the tranny would be more likely to end in a slipped belt & out of time, not broken, unless the belt was at the end of its service life. Skipping a tooth or two is quite plausible - have had it happen with a weak tensioner - thankfully the one that did it was a non-interference EJ22, so no damage to heads.

Broken belts come from 2 things typically... 1- end of service life, 2- failed timing component. For the record, they rarely look "worn or dried out" when changed. You don't go by how they look, rather - how many miles/years it has been in service.

Anytime i buy a used Subaru, the FIRST thing I do with it is a timing service - regardless of mileage. Unless the seller can PROVE to me that it was just done... and even then, i might do it myself, just for the peace of mind factor. A timing service is not just changing a belt, either. There are other factors, like the cogged idler pulley that is known to fail, checking the tensioner assembly, and seals behind the cam & crank pulleys, and can't forget the water pump, either.

with all that said.. i would start looking for a replacement tranny... chances are you are not going to resolve that easily.

 

[GeneralDisorder]

Only manual transmission cars have the guide. 

And no - an auto isn't going to break a belt. Even a manual isn't going to break a good condition belt. Skip a few teeth maybe, but not break it in half. 

The belt was old and past it's service life or was off-brand and poor quality if it's broken. 

And heartless is correct - buy a Subaru (or any car with a timing belt and an interference engine) - you are immediately remiss in your duties if you don't change the belt, water pump, and all associated with QUALITY Japanese made components. You generally have no idea if/when it was done or what quality of parts/labor were used.

And it sounds like the transmission/torque converter are garbage. 

GD

Edited July 4, 2021 by GeneralDisorder

[idosubaru]

On 7/4/2021 at 1:56 AM, wagondragon said:

I recently purchased a high mileage 2008 Subaru Outback (200,000 miles)

The timing belt was old, high miles, and/or not a Subaru/AISIN brand belt.  That's why it broke.  It had nothing to do with the transmission. 

[wagondragon]

Yeah, i knew i should have done the timing belt... I thought i "trusted" the guy i was buying it from. And he said that it was done recently, along with the timing belt. And also i got some spiel about the transmission computer causing the hard shifts because of sport mode and learning your driving... Honestly i feel like an idiot now. On both counts. definitely got screwed on the car.

Now to decide what to do about the transmission. Thought about a coolant flush and checking the solenoids, but if its a bad torque converter or clutch packs im not sure if i want to mess with them. Maybe i just need to find a lower mileage used transmission? Like JDM? Ive never opened up an auto tranny before, and i fear parts would be expensive anyways. 

Thank you guys for your responses!

[1 Lucky Texan]

is the trans pan dented?

[idosubaru]

2 hours ago, wagondragon said:

Yeah, i knew i should have done the timing belt... I thought i "trusted" the guy i was buying it from. And he said that it was done recently, along with the timing belt. And also i got some spiel about the transmission computer causing the hard shifts because of sport mode and learning your driving... Honestly i feel like an idiot now. On both counts. definitely got screwed on the car.

Now to decide what to do about the transmission. Thought about a coolant flush and checking the solenoids, but if its a bad torque converter or clutch packs im not sure if i want to mess with them. Maybe i just need to find a lower mileage used transmission? Like JDM? Ive never opened up an auto tranny before, and i fear parts would be expensive anyways. 

Thank you guys for your responses!

No matter what someone says I always check the timing belt.  Even if it's a new Subaru belt I want to roll that lower cogged idler in my hand and see if the tensioner seal is soaking wet.  Bare minimum:  New Subaru or Aisin Belt and new Subaru/NSK timing pulley ~ $35 and check the tensioner seal wetness while it's apart. That's only $100 in parts - otherwise get the entire $200-$300 Aisin or Subaru timing kit and replace it all. 

I'd install the engine and see if it's still shifting erratically.  It probably will but I'm curious if there's any way the failing belt (we haven't seen pictures, dont' know how it failed, don't know what brand it was, etc) could have caused the erratic shifting due to timing glitches, check engine lights, etc....

GD seems to think the trans is trash and he's not too often wrong - so that's your best guess.  Those 4EAT transmissions are reasonably robust and used ones usually aren't expensive. 

That being said - if I didn't know anything about it I'd finish changing the ATF (it needs multiple drain and refills because each drain only removes 1/4 of the fluid or so - so it takes multiple drains and refills to change a significant portion), check for the trans pan being dented, read any check engine light codes, let us know if the AT is flashing at start up, and check your front diff gear oil level and condition (if possible). 

Those 2008 4EAT's can get sloppy with age/miles but still keep chugging just fine - but your symptoms aren't comforting or pointing to that exactly if we are hearing them right. 

 

[GeneralDisorder]

Sounds like a torque converter unlocking problem perhaps - something akin to what happens on the 10/11/12 CVT's with the bushing that was later upgraded to a needle bearing. But a new TC from Subaru is like $700 - cheaper on the 4EAT to just get a used transmission typically since problems with the TC lockup components can also result in a plugged up valve body. If something is eating itself and causing TC lockup clutch and/or valve body problems then the transmission isn't likely long for this world. Not worth rebuilding and special tools are required. 

GD