Automatic Transmission... Lurch?

turbozutek · Post by **turbozutek** » 06 Sep 2011, 06:00

Hey everyone!

Ok, I'm having a couple of small issues with my 1995 850GLE 2.0 Auto;

1. It's an auto, AW50-42... Not much I can do about that though.

2. When changing up and down gears there is an odd 'surge' when the next gear engages. If you've ever driven too quickly over a hump in the road and had that 'heart in the throat feeling'; it's almost exactly like that. If I wanted to re-create the problem in a manual, I'd drop the clutch, change up a gear and then revs the tits off it as I let the clutch back up.

Clearly, something is a bit wrong here. The car has 124K and there's no record of any transmission problems before in the PO's documentation.

Here's what I've done to try and alleviate:

1. Swapped the auto transmission fluid for fresh COMMA Dex3. What came out was quite dark, but not foul smelling or burnt in any way really. Why Volvo didn't specify a fluid replacement schedule I'll never know; these boxes should not be 'sealed for life'!!

2. Repaired and cleaned the PNP switch (there was a code set for bad input and the reverse lights were intermittent. This fixed the lights and no codes since, but changes still a bit jerky.

3. Added some Lucas STOP SLIP, amazing stuff which I've seen perform minor miracles in the past. This seemed to help a little, but not much.

So, other than that, I'm not really sure what else I should be looking at / for?

I've NOT done the following:

1. Checked electrical impedance (resistance) of the solenoids.
2. Cleaned the VSS (no codes for this mind and the speedo is fine).

Does anyone have any ideas or further things I should be looking at? Currently it's more of an annoyance than anything else, but I don't fancy the box throwing in the towel any time soon!

Chris...

Post by **jblackburn** » 06 Sep 2011, 10:22

A couple more questions for you...not really any solutions here just yet:

How much fluid did you change out? 12+ qts? It may be worth waiting a bit and repeating a flush on it.

No flashing arrows/codes?

Check port A1 for any stored codes and clear them all.
http://www.volvospeed.com/CheckEngine.php

Pre-1996 (mostly 94-early 95) transmissions used different solenoids that tend to crap out. However, I'm not so sure your issue is a shift solenoid so much as a line pressure problem, though.

turbozutek · Post by **turbozutek** » 06 Sep 2011, 14:03

Hi jblackburn, thanks for reading!

I changed out 11 litres of fluid, which I think is around 11.6 qrts US. Initially when I'd done that, the fluid on the dipstick was almost impossible to see (it was so clean it made checking the level quite difficult) but now its settled to a darker red. Not as dark as it was by any means, but nowhere near as clean as the fresh fluid going in was.

There are no flashing arrows at all and no entering into limp mode. I checked for codes last week and got one for PNP switch input error; but I'm sure it's an old one and it hasn't recurred since the PNP rebuild. I then ran the diagnostic test function of the auto trans, which completed without setting any additional codes.

While I know next to nothing about auto trans (other than knowing I wouldn't be having this problem with a manual trans) I do tend to agree that it feels like a line pressure problem... I know the pressure solenoid is supposed to reduce the pressure in the circuit as the box shifts gear, but it feels like it's not or it's not reducing it enough? As soon as those clutches come back together again it feels like a few milliseconds of warp drive! :-S

So if it's the case that the solenoid is lazy or sticky, should I check it for impedance? If that's good, would it be an idea to hook up a pulse driver and 'exercise' it? Do you think a few thousand actuations on / off would help un-stick it?

Chris...

Post by **jblackburn** » 06 Sep 2011, 18:36

Do you have the service manual that details running those tests? That may help, because I know you can get it to test and activate the solenoids in some sort of test.

If you don't have the document I'm referring to, shoot me a PM to remind me, as I've got the link bookmarked on my other computer.

The pressure solenoid is located inside the transmission itself, and not accessible. Do the RPMs surge a bit when it upshifts before it "grabs" the next gear?

turbozutek · Post by **turbozutek** » 07 Sep 2011, 04:03

Yeah, I got the service manual which instructed me to press the diag (A1) button three times to implement the test. The transmission did a few clicks and the idle speed went up and down for a little while and then it ended the test with 111.

I learnt about that function from here:

Volvo Club UK Auto Trans Diag

The RPMs do not surge in the least as the car up-shifts; looking at the rev counter, everything is as smooth as silk!

As for the solenoid, isn't this it in the middle (the big fat one):

If so, I should be able to get to that in the same way as swapping the S1/2 solenoids? Or am I looking at the wrong thing?

I've never performed any kind of surgery on an Auto Trans before, but looking at this it should be do-able? IF that's my problem of course, lol.

Chris...

Post by **jblackburn** » 07 Sep 2011, 08:11

Good, that is the one I was going to point you to.

Getting that cover off the transmission is a real beyotch and I had to drop the subframe and deal with a ton of stubborn bolts. If you can avoid going that far in, I'd try as many other things as possible first. It took me about 8 hrs over the span of a few days to get in there and put it back together again.

I might try running test mode #3 or #4 and activating that solenoid specifically a few times. That's on page 16/17 of that document.

It seems strange to me that you're getting that feeling without ever seeing the RPM needle jump up. Hmmmm...

turbozutek · Post by **turbozutek** » 07 Sep 2011, 09:21

I think if I ever did this job (the swapping of solenoids that is) it would be as an epic last resort! I agree with you, I will try everything and anything else first before contemplating it, not least because the solenoids themselves are a bit tricky and expensive to source in the UK (As a country we dislike automatics, because of threads like this).

My "Simple" options right now as I see them are this:

* Try as you suggest and individually test that solenoid a few times to see if it'll free up any.

* Flush out the ATF (again) and replace with fresh stuff (I could also drop in a flushing agent prior to this if you think it might help?).

* Open the connector on the transmission and hook up a DC power source to the LP solenoid - pulse the power source on for a half second every few seconds for 20 minutes or so. This should excite the solenoid through the entire range at least 200 times, hopefully cleaning off any gunk and crud from around it. I've seen this trick used on electro-hydraulics in the past and it's worked well for freeing off lazy components. Never heard or seen it used on an auto trans, though I think the principle should be the same?

* Something else I've not considered?

As for the needle not jumping up, I'll have a long and careful look tonight and maybe get a video of the fault happening.

Chris...

Post by **jblackburn** » 07 Sep 2011, 09:32

I strongly dislike *most* automatics. The Volvo's is actually halfway decent, but I'd still rather have a manual. Many cars over here are EXTREMELY hard to find in manuals - even new. On new cars I'm looking at, you can't even get a manual in the upper trim levels. Jerks. /end rant

Yeah, I think you've got a perfect list there of things to try. Maybe switch up 2 and 3 in order. If you do re-do the ATF flush, yank the drain plug from the bottom of the transmission - and I wouldn't use any kind of additives or anything. I have had a very good experience with synthetic ATF in my own car to take care of some hard shifting/dropping out of gear issues (turned out to be a shift solenoid later on down the road), but I'm not sure if that would be worth your money or not.

turbozutek · Post by **turbozutek** » 07 Sep 2011, 10:02

Mate, I'm moving to Canada in a short while and I find the EXACT same problem; North American cars with manual are mostly hateful base models. That's why I intend to import a 15 year old Volvo or Merc of some type, should save me having to put up with the low power engines and the horrid autos you got there.

Anyway, back on topic!

Right, I think I'll swap those two items and give them a go some time next week. I think before I play around with the solenoids I'll check their electrical resistance quite carefully and if it's clear they are shot I won't even try powering them up from an external source.

I have to say when I did the flush last time I did NOT pull the drain plug - it just seemed like a bit of a ball ache to do and instead did it with the cooler pipes only. This time around I will pull the plug and clean it though if I go to swapping ATF. I don't know if too much crud got left behind last time by doing it the way I did maybe.

I think if I do replace the fluid I'll also skip the LUCAS Stop Slip as well - it didn't really seem to help so much last time around and it was a major pain to actually get into the filler!

Of course I'll report back here with what I find!

Chris...

turbozutek · Post by **turbozutek** » 20 Sep 2011, 07:59

Ok I've been mental busy but I did get a little look at this today and did a few basics:

: TCM Ver 3.3; Auto Trans TCM.jpg (113.94 KiB) Viewed 7168 times

I have TCM Version 3.3; most of the cars I've seen in the scrappy around here have a higher version (5 something) in this slot. Anyone know the differences?

Anyways, I removed the unit to get at the connectors below and couldn't help but notice how simple it would be to open up and inspect... Almost like the designers wrote an invitation on the box!

Inside I found the capacitors to be in good condition visually, though I did find this:

: Diode with dry joints.; Auto Trans TCM PCB - Diode.jpg (106.43 KiB) Viewed 7168 times

It may or may not be relevant to the problem, but these solder joints on this diode didn't look too clever and ready to cause all sorts of intermittent nastiness, if not now then soon! I scraped away the conformal coating with a fibreglass pencil and re-flowed both these joints with lead solder and flux.

Other than that, I could see no faults with the TCM itself - all the caps looked OK and the switching transistors were all within spec.

That out the way, I resumed the trouble shooting on the car side of the problem.

My solenoid resistances are as follows (I got these from the connector under the TCM, to give a better picture of any cable faults which might exist):

LPR Solenoid = 7.2 Ohm
S1 and S2 Solenoids = 15 ~ 16.8 Ohm (the fluctuation here is probably just my meter and the way the probe sits in the connector)
LCK Solenoid = 15 ~ 16.3 Ohm (as above for the fluctuation)

I measured all of these to the car chassis ground, except the LPR which has its own ground pin (I guess this is a PWM solenoid?).

So, do these values seems healthy or out of spec do we think? I recall reading that the factory spec of the solenoid should be about 15 Ohms for the S1 and 2 units but I can't find values for the others. At a guess I'd say they are probably all OK electrically?

Chris...