L4N71B transmission issues - advice needed

#1

Hi all,

I'm starting to have a few transmission issues on my '86 Nissan Laurel. I took a look to the gearbox and I saw that I have an 4N71B transmission ( the "L" letter is not there, but I suppose it's a L4N71B)

It just started to slip especially in 3rd, when pushing hard, and it also slips betwen 2nd and 3rd, I mean between gear changes. I'm not very familiar with automatics, please excuse me if I'm not very clear. The gear change from 3rd to OD is smooth, no problem with that.

Also, when cold, with OD off, it goes into D pretty hard, I have to push the gas pedal a bit.

I don't know if the transmission was ever flushed, I own the car for 6 month. I don't even think that the transmission filter was ever changed (btw, the 4N71B has a real filter? because I read that the 3N71B don't) One month ago I did a drain&fill, so I replaced about 3 liters of ATF. It is still brownish, though...

My question is: how bad do you think the sitiuation is? I don't know how much the transmission can last in this condition...

Since automatics are extremely rare in my country, finding a good and trustable repair shop is quite hard.

Do you think it worth is to try to repair the gearbox? I don't even have an estimation about the cost of such an operation.

My last solution would be to try a conversion to manual if the box will fail...
I have another Laurel, a C31 from '84 with the same LD28 engine but with a 5 speed manual. I Checked the wheelbase of my C32 and is the same with my older Laurel's, so maybe is possible.

If you have any advices/thoughts regarding my problem, please let me know.

Thank you.

#2

I'm not the expert, but here are a few generic comments based on my own experience.

- Of course, make sure the fluid is at the correct level; you probably have done that, but JIC... Check while hot after normal city driving; I have seen some comment that highway driving gets it rather hotter than city driving and thus if checking immediately after highway driving it will read higher than normal. Put the car into each gear for a moment before checking, then put in PARK and check the dipstick (car perfectly level).

- Using the car to pump fluid out while idling (shut down immediately it stops coming out) from the ATF hose connection at the radiator will allow you to do the job quickly which in turn will allow you to do it several times (after refilling with new fluid in approximately the amount you pump out) until the stuff coming out is pristine pink. Check the thread here about changing tranny fluid. It will take 2 or 3 times the amount of fluid normally required, but it will get the job done completely.

- Lucas transmission additive is the favorite around here for "fixing" little problems like yours. Some people seem to mostly just fill their tranny from the Lucas bottle.... But it would make more sense to simply run the car on the clean ATF for a bit and see if anything has changed before spending for the Lucas juice. I believe it works by swelling some of the seals in the tranny and no point in using it if you don't have to.

- Sometimes the "bands" can be readjusted tighter to help with slow shifts, revs flaring up between shifts and slipping. You might find some mention if it here or I'm sure Al or one of the more experienced members would comment.

Best luck.

Rufus

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#3

Well. it seems that the problems got worse, before I could do anything.

I just noticed this morning that it wouldn't shift into 2nd, unless I manualy put it into second, and after that it would normally shift into 2nd only randomly...
Also, during a highway drive I noticed that it sometimes shifts into OD earlier that it should, at about 70 km/h ( normally it does it at 80 km/h)

Another thing is that it sometimes gets stuck into 2nd when stopping at a red light and if pushed hard, it just jumps out of gear then goes back into second....

I don't know what to do, maybe I'll try a Lucas fix as a last resort...or maybe is time to park the car?....

#4

Forgot to mention that (I think - haven't deal w/my tranny for a while) some of the tranny control depends on good vacuum. If your vacuum is bad (pump bad or big leak) then strange things may happen; however, strange things would normally _also_ happen to the power brakes if you had no vacuum at all. In my Ford van what happens w/no tranny vacuum is that it won't shift until you top out the revs, like if you were getting on the highway and had the peddle to the floor - only all the time. Haven't had occasion to find out what vacuum loss would do to the Nissan shifting, but there is probably a comment here somewhere.

Good luck. Rufus

#5

Thanks for the tips:)
I was thinking about a vacuum problem, but as you said, it should affect the brakes too, which are perfect in my case.
However, I will get under the car and check out the vacuum lines, who knows, maybe there is a crack somewhere....

Is pretty strange to me how fast the gearbox has begun to have problems...when I bought the car six month ago it was perfect, no shift/slip problems at all....

#6

If I had to guess, I'd remove the transmission pan and inspect the "filter". The "filter" is a brass-like screen. If the torque converter's lockup clutch is dying, it will shed debris and begin to plug the screen. Hydraulic pressure is reduced, and all kinds of shifting ills begin.

The transmission would probably have to be completely disassembled to fix this -- remove all clutch debris -- but at least you'd have a better idea about the problem.

Rufus, Nissan introduced a low-vacuum warning system on most of their diesel vehicles for 1983 (certainly, my 1983 Maximas & 1983 Sentra diesel have them), and die_stink's '86 Laurel should as well. But poor vacuum to the vacuum modulator (on the side of the transmission) would be a very good place to start diagnosis, yes.

(click on image for larger)

Take a look at these pictures of worn hard lines for the transmission vacuum.

And, for clarity, here's where to test for vacuum:

#7

Thanks for the confirm, Al.

That graph look familiar. Happily I haven't had need to look at it for a year more or less. <g>

Unfortunate possibility about the lock-up clutch. I re-read the post about early locking (70 v. 80 kph) - that seems a little high in any case because 70 kph is about 45mph (wag). The Maximas lock up about 37 mph. Maybe the Laurel is set differently.

The original problem was slipping in 3rd and revs flaring between 2nd and 3rd if I read the first post right. That sounds a whole lot like some kind of band/clutch problem - either low fluid, leaking seals (Lucas fix) or try tightening the bands. Kossak, are you sure you have a complete fill of ATF in the tranny? It sounds like your troubles started _after_ you changed the fluid.

I have heard that sometimes older trannys will barf when refilled w/new fluid. I'm not sure if this is good info, but I've seen it several places and so I suspect _something_ is going on. Before junking the car it would might be worth dropping the pan and looking for debris; then close it up and pump the fluid out a few times to get the old stuff in the convertor. Then run it "around the block" and if it has problems pump out some fluid (2 or 3 quarts - anyone?) and replace it w/Lucas juice and give it a few days and see if it works. After that if it's just slilpping then you could try tighteing the bands.

This stuff is a pain, but still pretty cheap and might get it running OK for a few years. Unless Al's picked the winner and then you're looking major trauma.

Rufus

#8

Thank you very much for your advices.

The shifting problems have begun almost at the same time the winter came here

We had terrible temperatures here ( about -10 celsius every morning) and that's when I started to have rought shifting problems. Of course, I always let the car to warm up a bit before driving it, but this was pretty hard because I noticed that I don't have a thermostat or it is locked in the open position.

So at the beginning it only started to slip in reverse in the mornings, that's why I did a drain&refill in a shop. For a few days the transmission felt more alive, I mean the car seemed to be stronger.
Then everything got back to normal.

After I had this problem with no shifting into 2nd, I bough a bottle of some Dura Lube transmission additive last week, and after a few miles it came back to normal. Now it shits nicely into 2nd.

So my guess is that it was a seal problem, since that Dura Lube thing solved the thing. Maybe the low temperatures from the winter had to do something with this...

Now I'm waiting for that Lucas bottle to be shipped to me (eh, only one Lucas dealer in Romania, so it takes some time)

#9

Glad to hear it's gotten better. You might want to put it into gear when you are warming up; I believe that in neutral the tranny fluid won't really get warm. Others might have a comment.

If it's working OK, it might be better not to pile on different chemicals. Set the Lucas stuff aside for use if you need it and as long as it runs good, don't put in more additives. Nobody promises what will happen when you mix additives from different manufacturers - who make a big point of never revealing whats in their can anyway. Probably fine, but if you don't need to, .. Besides, maybe Dura Lube works just as well and is cheaper? <g>

Check the engine temperature and see if the gauge works so you know what you know sorta speak. That thermostat is pretty important. Fix it if you can. See the threads about it on the forum here. In temps about 20 C. my engine warms up fully from cold in about 2-1/2 miles of light easy driving.

Rufus

#10

Hi again,

I coming with updates regarding my issue.

I did nothing yet to the transmission, I'm collecting information from now, hoping that I'll find out the real problem before even thinking to go to a repair shop.

So here's what I've noticed in the past few weeks.

With OD on:

- the transmission is engaging immediately after puting in into D
- 1st to 2nd shift is ok, a little rough when cold, but is ok
- it shifts from 2nd to 3rd only if I move my foot from the gas pedal a little bit. For example, it shift from 1st to 2nd at about 1700-1800 rpm, then it pulls ok until ~2200 rpm, after that the rpm is going up and no gear change. ( I never let it pass 2500, to avoid slipping)
- if I start moving the car, and press the gas pedal gently, the shifts are ok, even from 2nd to 3rd, maybe a bit early, but is ok.
- when I need to quickly pass a car, and I'm doing like 30-40 km/h, then I floor the gas pedal, it almost always jumps out of gear then it goes back.
- downshift from 3rd to 2nd, when I push the gas pedal a bit harder is smooth
- shift to OD is smooth

With OD off:
- when the engine is cold ( and the transmission too, I think) and I put it in "D", it doesn't engage until I rev it up ( about 2000-2200) rpm.
- when it finally engages, if i push it a bit harder, i jumps out of gear ( from 2nd, that's what I noticed and it's for sure)
- if a come to a stop, it is going back to neutral.
- after the car is warmed up a bit, it is working OK, is engages immediately, no need to rev the engine.
- with OD off, of course, I have engine brake ( none with OD on) and I'm feeling that the car is pulling much better.

So I finally bought a thermostat to keep the engine hot and to warm up faster. Is not installed yet, but I'll do this asap.

Sorry to bother you with this things.

And one last thing: is the oil filter from the 4N71B replaceable? or it just needs cleaning? ( I found a new filter for about 100$, but I think is a bit too expensive)

How do I check the oil level from the transmission? with the engine running or turned off? I tried both, but with the engine running, I found no oil on the dipstick, but with the engine turned off I can read the level ( curently is a little above "High".

Thanks a lot, I really apreciate all your help.

#11

Hi,

can somebody please tell me how to check correctly the ATF level? I'm a bit worried because with the engine off, the level is pretty much above "High".

Sorry If this was discussed before, I searched the forum but I couldn't find anything.

Thanks.

#12

Start the car, drive it around until the fluid temperature is about 120 degrees F (warm to touch). Make sure you run it through all the speeds and reverse too. Stick it in park and leave the engine idling, the fluid level should be a somewhere between the low/cold and high/hot range.

I found with the L4n71b trans, the amount of fluid thatll take it from the low to high range is so little, that cold fluid that reads at the L would expand a little past the H if the fluid is hot. So, if its reading above the H line by under a 1/4" I wouldnt worry much.

But if you notice alot of bubbles in the fluid it may be a indication of overfilling or underfilling amongst other things

#13

Thanks for the answer!

I tried this and...suprize: with the engine running in "Park" the level was just a little below "Low" ! and I also noticed some bubbles at the bottom of the dipstick. I never thought that the level could be low, because I used to check it with the engine off and it was a little over "High" all the time.

The strange thing is that I never noticed any leaks, I always check for leaks when I move the car...

Maybe this could explain all the problems I have with the transmission, maybe even the problem with the slow engagement in D with OD off.

I will add oil and see what happens. Finger crossed

#14

It's been a year since my last post in this topic and since then I've observed what exactly is the problem.
The fluid level was low and I solved that, in fact I changed all the fluid.

So the real problem is the 3-2 downshift.
The gears are all working, shifting up through all of them pretty smooth.
But it's never downshifting to 2nd. When going to a complete stop it seems to somehow skip 2nd and shift directly to 1st. (really smooth, no jerking at all)

Here a scenario: let's say I'm approaching a hill in 3rd an I'm slowing down. I get to the hill and I push the gas pedal to accelerate. Then it should downshift to 2nd but instead it's jumping to neutral first ( revs are going up depending on how much the gas pedal is depressed) and then back to 2nd. All of this is taking about a second.

The same thing is happening if I just slow down to a speed somehow too low for 3rd gear. Pressing the gas a little harder = same behavior as I said earlier.

As I told you, everything else on the transmission is working correctly: lockup in 3d at about 30 mph, unlocking when accelerating harder, shift to overdrive and locking at 50. Kickdown also works great.

So far the vacuum hoses seem to be alright, I tried to drive with a vacuum hose disconnected from the vacuum pump and the gearbox changed as it should, higher. ( in fact for me it's nicer to drive it this way because it changing the gears higher).

I have this problem for almost one and a half year now and it didn't got worse.

My last guess would be to check the filter. Maybe cleaning it? As far as I understood from Al's topic on flushing the AT, it is brass like so there's no need to change it.

#15

2-1 is 15km/h

3-2 at light throttle is 15 km/h.
3-2 at half 15km/h
3-2 full throttle 65km/h
3-2 electrical kickdown 80km/h.

if speed signal pulse from speedo is bellow 20 ish kick down wont work.

sometimes if the 2nd gear band is loose or slow you miss 2nd down shift but the first gear you get is a freewheel type and feels like a neutral.

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L4N71B transmission issues - advice needed

L4N71B transmission issues - advice needed

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