4n71b post mortem

[HowlerMonkey]

This is an autopsy of the L4n71b from my 1984 maxima with 277,000 miles (50,000 miles after turbocharging).

 

One day out of the blue, the car was reluctant to shift to 2nd gear but it did shift a bit delayed on the way home from work.

 

A few miles later, I was putting down power while turning pretty hard (sticky comp T/As 225/50-15) and lost drive when the inside tire broke loose causing the car to from 1st to 2nd to 3rd in quick succession.

 

This was followed by loss of drive in 3rd and a ringing type grinding noise that lasted for 2 seconds and no more noise........but no 3rd gear either.

 

I drove the last two miles home with 1st and 2nd gear only.

 

The car also had no reverse.

 

Upon disassembly, I found this.

 

Parts are as they are in tranny.....left to right is front to rear.

 

No trouble here from convertor to rear of overdrive unit.

 

 

There it is...........just behind the drum support that centers the overdrive unit on the front face and the drum that contains the front clutches and front planetary set.

 

I usually don't see this failure on this type of tranny.

 

Look where the "drums" meet and you will see they no longer have "teeth" with which to mesh like the assembly above or the one behind it.

 

 

Looks like the non-metal thrust washer split and fell out allowing the front drum to rub on the back of the drum support......which would be the back of the front pump if it didn't have an overdrive unit sandwiched between the bellhousing and the rest of the tranny.

 

I placed half of the washer where it belongs but all both halves were in the pan when I opened it up.

 

The added play allowed the drum that contains the front and rear clutches as well as planetaries to not fully mesh the "connecting shell" which is really just another drum that doesn't have a band acting on the outside of it.

 

You can see where the lack of thrust washer allowed the drum to rub the support in the center as well as on that bright spot at the top of the pic.

 

 

It's usually a planet seizing in one of the planetary gear sets that I find or burning.........and then a planet seizing...........after one is overheated to the point that the non-metal thrust washers compress or break up causing tolerance trouble and possibly low pressure system wide.

 

Different damage and causation in my case than most I've seen but it always seems to be the non-metal thrust washers that start the cascade of failures.

 

Since I found zero wear or damage to any of the gearsets or anywhere else, I fully believe these would last forever if .......

 

1. Fluid is replaced any time tranny has gotten hot to restore some sort of film to keep metal to metal contact from happening.

 

2. Non-metallic thrust washers were replaced with some sort of metal thrust washers that don't melt when tranny does get hot.

 

Now that I think of it, this is the first 4n71b failure I've seen without burning or contamination causing undue wear since only large chunks came off and fell down rather than smaller debris being sent throughout the tranny to grind it to death.

 

Time to go back outside and rescue the innards for future use.

 

I think I might see just how far I can build up a 4n71b using 300zx turbo parts since I now have a bellhousing with which to mount the stronger Z31 box to a L series engine.

[Bernardd]

I have the specs for a 600hp 4n/3n if you want them. It's not much extra work to make it hold a lot more power and if you want to make it a full manual shift that's easily done along with the shift kit mods. Can you tell me if the planetary in that trans has 4 gears or 3 gears? I am looking for a 4 gear set to get the rated power of my trans to match the next setup for my car.

[HowlerMonkey]

All of the gearsets have 3 planets.

 

Now, I am curious. Are there 4n71b with 4 planet gearsets?

 

The output shaft is larger diameter like the 3n71b found in the 280zx turbo rather than the thinner one found in the N/A models but I've heard the first generation maxima iteration is weak compared to the 300zx version but maybe that's down to the number of friction plates and clutch plates.......not sure.

 

As far as mods go, they sound like the mods I did in 1981 to the 3n71b that came in my RX-2 which are along the lines of the B&M shift kit available at the time.

 

I guess they now call them "level 10 mods".

 

Since this is a L4n71b and not a E4n71b, should I be keeping the cases as well?

 

I was wondering if the hydraulic 4n71b is more desirable for a high hp build.

[Bernardd]

All of the gearsets have 3 planets.

 

Now, I am curious. Are there 4n71b with 4 planet gearsets?

 

The output shaft is larger diameter like the 3n71b found in the 280zx turbo rather than the thinner one found in the N/A models but I've heard the first generation maxima iteration is weak compared to the 300zx version but maybe that's down to the number of friction plates and clutch plates.......not sure.

 

As far as mods go, they sound like the mods I did in 1981 to the 3n71b that came in my RX-2 which are along the lines of the B&M shift kit available at the time.

 

I guess they now call them "level 10 mods".

 

Since this is a L4n71b and not a E4n71b, should I be keeping the cases as well?

 

I was wondering if the hydraulic 4n71b is more desirable for a high hp build.

 

As far I know the turbo 4n's have 4 gear planetary's. You are correct in that the holding power of the various tranny's is tied to the clutch's and valving. And I would also say that the hydraulic version would be easiest to work with.

[HowlerMonkey]

Cool.........I'll save all the cases/housings, valve body, and shafts while looking for the best application for a starting point.

 

These transmissions are stronger than people know as I had a stocker 100,000 mile, 10 year old 3n71b last 1 year behind a bridgeported 13b that I shifted at 8500 rpms many times a day.

[jc052685]

I have done some searching lately for my auto tranny swap. Any info anyone has I would love to get. Well, info on building and gtting the tranny to hold some power

 

thanks

[HowlerMonkey]

Just finished my l28et/3n71b in a infiniti M30 and drove it about a mile and then no drive in any gear.

 

Coasted into parking lot and called wrecker.

 

Started car out of curiousity and had drive just fine for about 400 yards and then no drive again.

 

Turned it off and immediately restarted car and got drive for another 400 yards.

 

At that point I knew it was debris coming up to clog the filter and then sinking back down until sucked up again.

 

Opened up the tranny and found a mini-mountain of rear clutch particles in pan just under filter pickup hole.

 

Took out and apart tranny and, other than the clutch frictions drying out from 5 years storage (twice) everything else specs out ok.

 

It seems these trannies are bulletproof..........as long as you don't overheat them and end up with burnt fluid with abrasive chunks circulating to all the bearings.

 

If you have a jatco automatic, best thing to do is turn it off at the first sign of trouble and there should be very little damage.

 

The 280zx turbo tranny 3 speed 3n71b....... from front to back........has 4 clutch plates in the front (not the steels) 6 in the middle, and 7 in the rear (low/reverse clutch).....I think...will check later.

 

Time to do some valve body mods now that it's out.

[HowlerMonkey]

Here is a pic of what happened in 1 mile of driving with crispy clutch frictions.

 

You can see the galling that started when the low/reverse clutch lost the friction material and ended up metal to metal.

 

The car still moved fine (until filter clogs) and I encountered no slippage.

 

Had the chunks not blocked the filter causing a no-drive condition, this tranny would have died the horrible death that most 3n71b/4n71b die when driven afte they start slipping.

 

If I didn't know that most every single 3n71b and 4n71b in the junkyards had been burnt to the point of needing most every component replaced, I might have been inclined to rebuild these things for profit since they are cake to work on.

 

[Tony D]

My understanding is the Mistubishi Starions (turbo) of similar vintage have a beefier 4N than the standard Maxima Trannies (similar mods as done to Nissan 3N's for turbo service: more clutches, different line pressures, governor settings and valving, etc).

 

Bernard may be speaking of picking the 4Planet setup from later 4N's on other Nissan Models. The Starion stuff just has more clutches as far as I know. Change the bellhousing and maybe a U-Joint on the propshaft, and it's more durable than the N/A Maxima Setup at least.

 

Gotta love governmental guidance in Automotive Supply: "You will buy your autoboxes from this supplier, because it's our money supporting their consolidation"---and JATCO (Japan Automatic Transmission Company) was born! So Mitsu and Nissan had the same basic tranny module for years. Hell, so did Toyota, but they kept 2 speeds (Toyoglide) for waaay too long. INTO THE 70's!

[Diomedes]

I have the specs for a 600hp 4n/3n if you want them. It's not much extra work to make it hold a lot more power and if you want to make it a full manual shift that's easily done along with the shift kit mods. Can you tell me if the planetary in that trans has 4 gears or 3 gears? I am looking for a 4 gear set to get the rated power of my trans to match the next setup for my car.

 

 

I'd love some more info about this

 

Edit: Should have searched harder.

http://www.importperformancetrans.com/nissanauto.shtml#main

http://www.automatictransmission.com.au/release.asp?NewsId=8295

[HowlerMonkey]

Just put it back together and it runs like new.

 

I'm a little worried about driving a non-lockup 3n71b hard with only an auxiliary cooler running as the radiator was tainted by a failed later model tranny before I bought the car..

 

I flushed the tranny cooler portion of the radiator every day for about two weeks with all manner of chemicals and still had a random chunk come out when I blew air through so I guess a new radiator might be in the works if I my research on the magnefine filter doesn't give me confidence.

 

One thing.......the cover (nissan tech's call it the guillotine).

 

If you run the car without it on, you can hear the fluid hissing in the covertor or pump which makes you think something is wrong but......fitting the cover makes it disappear totally.

 

I forgot about that.

[Tony D]

I flushed the tranny cooler portion of the radiator every day for about two weeks with all manner of chemicals and still had a random chunk come out when I blew air through so I guess a new radiator might be in the works if I my research on the magnefine filter doesn't give me confidence.

 

I picked up a couple of remote filter assemblies from Autobacs when they were closing the store. Got em for about $30 each. Looks just like the standard automotive filter for oil, just made for Transmission Lines. Had some holes in the housing for thermo probes, etc...

 

That would kind of keep the stuff coming back and contaminating your new tranny from the old cooler/radiator. Olberg makes a nice filter that would work great for that as well...but it ain't $30!!!

[HowlerMonkey]

Good stuff.........I really want to use the radiator cooler since it is pretty good at dealing with tranny heat but I see people running what I have for years with no troubles........but I really want to moniter the heat of the tranny itself because I've already encountered (on a yacht) a temperature probe on a cooler line that read low because...................there was no flow....... and the bypass was in the transmission itself.

 

Those filter assemblies sound great.

 

I'll venture a bet they are 3.8 or 1/2 inch and used on diesel trucks?

 

Never thought of looking at truck parts but maybe it needs looking into.

 

Car is really peppy with the high stall speed and 3.9 but no top end to speak of so I may eventually build a 4n71b and go with 4.10 gears.

 

I'll bet that will haul ass down the strip.