Can parking on an incline leave the auto trans starved for fluid?

[Jonathan]

My garage floor is not very level. The front of the car is higher than the rear by 3 full inches when it's parked. 3" over the 8' distance between wheels equates to a "grade" of about 2.8%. The driveway incline is a bit steeper and then my street, in the direction I usually drive away in, is also at an incline.

The reason I'm mentioning this is the transmission seems like it is starved for fluid when I first head out for a drive. It doesn't persist and it doesn't happen again at any other time during the drive. I start the car up, let it idle for a half minute maybe as I get the lights on, radio on, windows down, etc. I put it in reverse, back out of the garage and then driveway and then go on my way. As I put it into Drive though, it will slip like there's no power. If I baby it a little, it gradually gets going and then once I'm over the crest of the little hill I live on, it's fine. It drives fine at that point and the engine isn't hot by then either.

This has me thinking that somehow when it's parked on that incline overnight or for a few days, the auto trans fluid is either getting trapped on the wrong side of some internal baffle or perhaps is causing the filter to briefly get plugged. Or starved or something along those lines. Closest thing I ever had was a few years ago when my original filter was definitely plugged up and the car had no forward power and would only rev up but not go anywhere. If I shut the car off, the fluid seemed to settle and then when I started it again, it would drive okay for a few blocks until it repeated. I got home that night and then got a new filter to replace the old one and it was fine from there on after.

This is a little different feeling in that it doesn't rev really it just doesn't do anything. Like I said, it feels like it's slipping and there isn't power there and because of not wanting to go hard on the transmission and risk damaging something, I baby it a little until I feel it "catch" sort of and then it's fine after that.

I don't believe my fluid level is flat out low as I have checked the dipstick level when hot and it seems to be where it needs to be. I could be wrong though or maybe it is something else? That's why I was wondering about the incline thing, as it only does it in that circumstance and no where else. Everything else on the car checks out ok. I haven't checked the final drive oil level this season though admittedly.

Anyone with auto trans experience got any ideas for what might be going on? Or if this incline parking thing is a possibility or is that just me thinking it could be it instead of something else?

[DMCMW Dave]

When the engine isn't running, the fluid level is WAY over the normal full level. Check the fluid level cold and with the engine off, and it will seem to be halfway (exaggerating) up the dipstick. But way over full. So it would be difficult to be low enough to starve, yet still move the car at all. As soon as you start the engine, the pump pulls fluid into the main area of the trans and the level drops to normal. The fluid actually starts out bit low and comes up as it warms up, (which is why you have to check the level hot and engine running).

More likely the fluid pressure is set low, vacuum modulator is failing (extremely rare), or you better start saving for a trans.

But - "Not revving" sounds weird. If the clutch packs are failing, the engine should flare (i.e. trans slipping). Are you sure it's not an engine problem, i.e. a lack of power for some other reason?

[Jonathan]

Thanks Dave. Good explanation on the fluid level. Agreed it likely isn't actually low. Not low enough to starve things anyway like you said.

For the vacuum modulator, are there any external signs or adjustments or tests to know it's working correctly? What does it do exactly btw? I can get under there and look it over easily enough. I'm familiar with the routing of the short rubber hose on the end of it and then the tube that runs the length of the trans and back up to the engine. If that vacuum hose connection was pinched or obstructed in some way, would you still be able to drive the car normally?

The car drives well and has ample power when I'm out. I can floor it and the full throttle switch engages and it goes like stink. Well, lol, it goes as quick as you'd expect our little 130 hp cars to go. If there was an issue with the engine and not the trans affecting power, I'd be inclined to think it was something related to temperature and before the car warms up because it seems good all the time except right when I leave the house.

Air, fuel, spark? I can check the usual suspects like a sticky idle speed motor or the air plate perhaps? My tach needle is still fluttering from time to time. It doesn't correspond to the engine RPMs actually bouncing up and down, just the gauge. Or so it seems. That was one of the reasons I redid my ground braid on the engine mount. That's the only other symptom I can think of for poor performance or something else weird.

I might not have explained the no revving correctly. It might flare up like it was slipping, but since I'm aware of the possibility, I don't give it that chance by staying on the gas. Does that make sense?

For the fluid pressure setting... this is something I'd like to look at closer. I've never done this and I don't know what mine is set to (or how to measure it or adjust it). Special gauges needed I assume? Procedure in the workshop manual?

[David T]

If you think there is a problem with fluid or pressure the best way to tell is with a line pressure gauge. I agree with the previous poster that it sounds more like an engine problem than a transmission problem. When you start out cold the engine isn't running it's best even if perfectly tuned. Vacuum leaks or a CPR that is not working right can make the motor run badly when cold too. It is also possible the shift computer is not working right when cold and you are starting in 3rd gear. That can be verified with a light box.

[Jonathan]

Thanks for the ideas. I read up on checking the fluid pressure in the workshop manual and that will have to wait until a time I can get the car on a lift. Not going to go through that procedure by myself using jack stands.

Having said that, I did look things over in the engine bay some more. Electrical connections look ok. Took each accessible connector off and reclipped it in place. Some of them are not what I would refer to as snug... the plastic holder seems to be doing more of the grabbing than the metal tabs. I may gently push some of those tabs closer together to get them to bite more than they are right now.

Spark plug wires seem snug. Injectors look fine as well. Air filter housing was removed and inspected and reinstalled and it seems ok. No rips or tears in any of the vacuum hoses up top. I am going to crawl under the car at some point and inspect the small right angled vacuum hose that connects the end of the vacuum modulator to the metal tubing. I know I had moved that around a couple times earlier in the season working on other things and it's not out of the question that the hose has a small split in it.

It's raining out tonight so will need to wait to take the car for a drive and test things out. I don't have one of those auto trans diagnostic light boxes made up so can't test that theory of it starting off in third. I suppose that is still possible so I won't rule it out. I'll look closer at the fuses and whatnot and other things electrical to see if I spot something out of sorts.

[DMCMW Dave]

What's the history on the computer governor? Could it be that the car is actually starting out (cold) in second gear? That would feel really sluggish, and no engine flair. There are a couple of failure modes on the governor and this would be one. When the OE versions fail, they tend to get better as they warm up. . . . . Until they don't.

When David T mentioned "shift computer" and "light box" he's referring to a home-made tool that can tell you what gear the governor "thinks" its in. It's simply monitoring the two shift solenoids with a simple LED circuit. You have two LEDs, one across each solenoid. If both are on, the governor is in first gear. If one is on, second gear. None of them on, third gear. This is why pulling the fuse from the governor just drops the car into third. It can be connected to the transmission at the connector block in the firewall under the ignition resistors.

I'm guessing that you've had the governor replaced/rebuilt at least once (only because I know you've had the car a long time!), and if not I'd start there. Even if you have, it's important to know whether it was a rebuilt original or a replacement/upgrade. A rebuild original is still kind of a POS, and a now 40+ year old piece of 1970s electronics. Failure rate on the upgrade version (talking about the DMCH version here, not sure about any others) has been extremely low (but not zero - nothing is!).

If this is likely, don't drive it much like this because it is very hard on the clutch packs in the trans. It will also get worse over time (with age) and eventually the car will only start in second gear.

[DeloreanJapan]

What's the history on the computer governor? Could it be that the car is actually starting out (cold) in second gear? That would feel really sluggish, and no engine flair. There are a couple of failure modes on the governor and this would be one. When the OE versions fail, they tend to get better as they warm up. . . . . Until they don't.

When David T mentioned "shift computer" and "light box" he's referring to a home-made tool that can tell you what gear the governor "thinks" its in. It's simply monitoring the two shift solenoids with a simple LED circuit. You have two LEDs, one across each solenoid. If both are on, the governor is in first gear. If one is on, second gear. None of them on, third gear. This is why pulling the fuse from the governor just drops the car into third. It can be connected to the transmission at the connector block in the firewall under the ignition resistors.

I'm guessing that you've had the governor replaced/rebuilt at least once (only because I know you've had the car a long time!), and if not I'd start there. Even if you have, it's important to know whether it was a rebuilt original or a replacement/upgrade. A rebuild original is still kind of a POS, and a now 40+ year old piece of 1970s electronics. Failure rate on the upgrade version (talking about the DMCH version here, not sure about any others) has been extremely low (but not zero - nothing is!).

If this is likely, don't drive it much like this because it is very hard on the clutch packs in the trans. It will also get worse over time (with age) and eventually the car will only start in second gear.

Mr. David . How can you tell the AT governor is rebuild or not ? from outside visually ? or from shift feeling ?
I have a 81 AT , imported from US to Japan , Shifting is so far so good,
I did replaced the AT filter once in the past 3 years ,and add some additives to make the shift shocking more less .

[David T]

If you do a search there is a lot of info on how to construct the light box and how to use it. It will tell you what gear the shift computer, aka governor, is commanding the transmission what gear to be in. You should not have to add any modifiers to the transmission fluid. Verify the shift computer and the transmission are starting out in 1st and shifting properly through the gears. Once you can verify that, if the problem still persists, you can figure out what's going on with the motor. Start with making sure the fluid level is correct and you have the proper line pressure. These procedures are in the Workshop Manual.

[Ron]

If you do a search there is a lot of info on how to construct the light box and how to use it. It will tell you what gear the shift computer, aka governor, is commanding the transmission what gear to be in. You should not have to add any modifiers to the transmission fluid. Verify the shift computer and the transmission are starting out in 1st and shifting properly through the gears. Once you can verify that, if the problem still persists, you can figure out what's going on with the motor. Start with making sure the fluid level is correct and you have the proper line pressure. These procedures are in the Workshop Manual.

+1 on all this, especially WRT modifiers.

[DMCMW Dave]

Mr. David . How can you tell the AT governor is rebuild or not ? from outside visually ? or from shift feeling ?
.

The only way to tell for sure is to remove the small aluminum cover and look inside. There is a very visible difference between the original and the replacement. The most obvious thing you can see is that the wiring is soldered on the old one but connected via screw terminals on the new one. Another obvious difference is the color of the circuit boards. The originals appear tan, and almost like paper. The newer ones are modern fiberglass boards, usually green.

Also, if you have the test lights, watch the lights as you turn on the ignition without starting the car. With the original boards, both lights will come on as soon as power is applied. With the replacement boards, the lights will come on one at a time as the microcomputer boots up.

Original Boards:

OE Board.jpg


Newer Boards:
replacement board.jpg