C70 S70 V70: Transmission problems - solutions

[yevgeniy]

I know this has been chewed out by many, but nobody usually says what actually fixed their transmission problems - here is my story -

About a month ago i found a 2001 Volvo C70 Convertible for 2500$, it has 125k miles. Sounds too good to be true? exactly what i thought, and well on a test drive i knew the transmission was going out. ( keep in mind that the only volvo i ever had was a 1986 740 GL) and that was a long time ago. I was hooked as soon as i saw it , and simply knew that it will be my next project.

Here are the problems and things done.

When the car is cold it shift perfect, but as soon as it warms up it would start flaring on up-shift from 2nd gear into 3rd, and 3rd into 4th. after few more minutes of driving if would SLAM into all the gears with such force that it shook the whole car. after another 10 min of driving if would not downshift from a 3rd gear sometimes and stall out the car.

1) I decided to try AT fluid first - flush made no difference , then i started looking at forums - found out that the shop used Castrol 3309 , and it needs Mobil 3309, so i put a bottle of Lucas stop Slip additive ( i normally am against those, but i figured can't harm it any more). this seemed to resolve the problem for a few miles . and then it was back to "normal". Called Volvo dealer they said a new transmission was needed, took it to transmission shop, they checked for codes - none popped up. their answer was "Needs complete rebuild"

2) Learned about software update and B4 Servo Cover, decided to do two at the same time, took it to a local Volvo Only shop, Mechanic that drove it, and looked at software came back saying that TCM has the latest software, and B4 Servo Cover has been updated. I told him to go ahead and put in a new B4 Cover. On way home i noticed something interesting, although it still slammed into gears, it did it at the somewhat right time, and it downshifted from 3rd as was needed. when i got home i took a closer look under the hood, the top torque mount seemed a little worn.

3) Got a new top torque mount, when i took the old one off it has simply fell apart! It looked OK when installed. So i figured it needed to be done anyway, New mount went on........ here is the kicker .... IT STARTED SHIFTING SMOOTH!!!! now i knew about possible vibrations from broken torque mounts, but how transmission being warm has anything to do with it? well, i opened a hood, and it was insanely hot - the mount - more so than i imagined. rubber gets soft when warm - sooo simple huh?

4) this is unresolved - after a much longer drive i get a hint of hard shifts, not nearly as bad as it was. So i will purchase a new lower torque mount and do believe that it will make a big difference.

5) this is unresolved - Still get flares on 3rd gear - as i get a bit more money i'll go ahead and flush the transmission with the Mobil 3309

I will report on progress and what made the biggest change as i go along - but at this point i am 80% positive that a new transmission will not be needed. and that a lot of people replaced or rebuilt their transmissions for no reason - so far the repair rounded to 250$

Sorry for a long post, but i wanted to be clear on the problems, hope this post helps someone.

Anybody has any more ideas about this? please let me know. I am an amature mechanic, so far restored 1984 MK1 Volkswagen Cabriolet, 1995 VW Cabrio, 1995 BMW Cabrio, and now doing a Volvo. as much as i like it i think it will not be my last

[TurboZutek]

When the ATF is cold, the TCU dials back the speed and pressure used to change gear; and holds the gears and the torque converter ON for longer to get the ATF up to temperature.

Once it's reached operating temperature, the TCU goes to a more aggressive change pattern with quicker changes and higher operating pressure. That's why sometimes a cold transmission behaves itself and a warm one doesn't.

By the sounds of what you are saying (car stalling and failing to change down from 3rd, then improving with a change) it all points to dead / defective ATF having clogged the box up in the first instance. The symptom you relate is common with a stuck or slow LPR solenoid and new fluid and some exercise should improve that. I imagine if you'd pulled the valve body at that time, you'd have seen it gummed up with crap and several blocked filters also.

I think you did correct in flushing out the old oil and I suspect you'll start to see improvement as you replace what's in there just now. The detergents in the Lucas will have started to remove the varnish from around the transmission internals and when you do your next flush / drain and fill more and more of that stuff will come away. Keep an eye on the fluid colour as it drains (silvery tinge = dead box, forget about it) and a good look at the magnetic drain plug.

As for the engine mounts, the mounts can make a HUGE difference to the transmission 'feel'. Check the lower buckle too (I recommend you remove that buckle to inspect it, they can pass all the tests en suite and still be knackered. And check the front engine mount (at the crank end) too: when I replaced mine shifts were a lot smoother.

Chris...

[yevgeniy]

The strange thing is that the old fluid was not very dirty, it wasn't as clean as new, but was changed withing the last year or so. my guess it was the wrong fluid too. I ordered a new lower torque mount, should be here within a week or so. I checked the fluid level and i'm about 1 quart over, so i'm in the garage right now, will drain a bit of fluid to make it nice an level, at the same time i'll take a closer look at it - color, metal shavings. taking on a transmission tear down is light years beyond me - i did that with VW mk3 manual and - well - after i opened it, lets just say that the VIN on the engine no longer matched the VIN on the gearbox

UPDATE: As you said the AT Fluid did have more dirt in it than i expected to see after 500 miles or so. ( no burnt smell as before ) about an hour of bolt on bolt off - and just over a quart of fluid now out of transmission, not very precise method, + i did it on a cold car by cold measure marks of the dip stick. it is still a bit more than normal level, but i decided its better to have a bit more Fluid, than it is to have a bit less.

5 minute test drive

- Improvements: too early to talk about shift flares - but noticed that it goes into gear much faster than before when the leaver is moved ( about 0.4 of a second delay vs about 1 second delay) - that in my personal understanding is about right. Also shifts are faster by themselves. will know more after a proper test drive

[dera]

As a safety precaution, I would remove the transmission endplate and check the condition of the bearing pressed to the endplate (the one where the main input shaft drum connects to). These are a known problem with that gearbox, and is easy to check and can prevent bigger issues in the future.

[yevgeniy]

Thanks - will do as time allows

[TurboZutek]

While fluid colour can be a good guide to a fluids state, it's not always the case that clean fluid is good fluid. ATF can have some water emulsified into it (enough to kill the box eventually) and still look nice and clean, for instance.

And, as you say there could be any number of odd additives or wrong fluid in there too... Only way to be sure with that is to send a bit off for oil analysis.

I personally find the dipstick (especially the COLD side) to be mostly useless, so I try and get the level right and then measure with a graduated container the exact amount out and replace with the same amount back in.

Originally Posted by dera

As a safety precaution, I would remove the transmission endplate and check the condition of the bearing pressed to the endplate (the one where the main input shaft drum connects to).

Tell us more about that?

Chris...

[yevgeniy]

UPDATE: drove it to work just now, took the longer rout, stop and go traffic. Had a small shift flare of about 200rpms, wouldnt even feel it if i wasnt looking at the rev counter. And a "harsh" downshift from 2nd gear, and even that was noticed only because the radio was off and i could hear it. other than that it was perfect as compared to what it was when i got it. Still, lower torque mount and another flush is coming up within the next few weeks

[Axionknight]

Suffering the night shift too? I feel your pain mate!

[dera]

Originally Posted by TurboZutek

Tell us more about that?

Chris...

I dont have my AW manuals here, I've been a software guy for 10 years so my terms might be a bit inaccurate.

The main input shaft of the gearbox (about 30cm long, has splines in the end that go to the oil pump) has a drum (I think its used as a clutch actually, I dont think it was a brake) in the other end of it.

That drum is held in place by the transmission back plate (the plate that has 10 or so bolts, that you can see on the back of the transmission), which has a bearing. This bearing lets go and usually breaks the welding between the shaft and the drum. This prevents the clutch to have enough oil pressure to operate correctly(oil escapes through this crack in the weld), and since the gearbox is continuously adapting, it usually starts to show signs of wear as harsh gearshifts (gearbox adaptation for gearchange pressure maxes out, meaning a slow, but harsh gear change).

I can take a picture late next week when I get back to my old workshop. I have about 15 of AW50/55 gearboxes in parts there. Its easier to show in a picture than to explain here.

[TurboZutek]

Originally Posted by dera

I can take a picture late next week when I get back to my old workshop. I have about 15 of AW50/55 gearboxes in parts there. Its easier to show in a picture than to explain here.

That would be great matey, the more information on autos on here the better I reckon!

Chris...