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I just purchased an 86 300zx. It's an automatic. Now the advice I need is to know where to look to fix two different problems. The first is that it shifts kinda late and a bit hard. The previous owner mentioned something about a valve that needs to be cleaned out or replaced. Replacement part should cost around $20 bucks, but I'm not quite sure of what it was anymore. The other thing.. does the spedometer on the digital dash equiped 300zx's significantly different than how a normal speedo on say.. a 1982 280zx stick shift? I've never messed with a system that wasn't a straight forward cable in the transmission system. He said it was related to the transmission issue. Any hints? Thanks!!

1986 300zx
Automatic Transmission
50,000 miles
Paid $500
What a steal!
 

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the trans. thing sounds like a modulator valve. it effects how you car shifts. mine cost 16 or 17 bucks i think. not to hard to do. on mine it was on the driver side of the trans. dont know about the oil pressure thing though.
 

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Check the vacuum at the modulator and and try to find a used or new Nissan part to replace it if needed...I tried an aftermarket adjustable one and ended up putting the old one back in.


Auto trans flush and mods:

Why to do it.....

If you have a trans that hasn't been totally flushed in 100K miles or so (these trans apparently run hot and the trans flushing mania is fairly new), it has a lot of clutch grit & metal particles in the fluid, which doesn't help bearing and gear wear. Also, and mainly, there is probably a lot of varnish & gum built up in & on the valves, passages, & surfaces inside.

Just draining the pan only removes about 3 qts, this flushing method (without pan off) exchanges around 6 qts of a total of about 7.3 qts in the trans.

This "manual" flushing method is probably easier on the trans and less likely to cause more problems than a commercial type flush. Maybe/maybe not.

Flushing and so forth might not cure serious problems, but might allow you to drive the car for awhile before real repairs are needed.

If you have a trans that has a few minor problems, you've got more of a chance and you could seriously extend it's life.

My trans actually functions better after around 43K more miles than it did before the flushing was done. (knock on wood as always)

*Don't forget to RECYCLE the ATF...try Advance AP? They will refine it and then sell it back to you.


Auto tranny flush:

1) Buy 13 qts of good quality Dextron III ATF & 6 qts Mobil 1 synth ATF
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2) Take the pan off and clean or replace the screen* (after running the car up on ramps) and clean the pan inside. Use a CLEAN rag and leave NO lint or particles in the pan. You might check to see that all visible bolts and screws are tight, but don't overdo anything. If you had no leaks at the pan gasket and it comes off intact, just bolt it back on. Don't overtighten these bolts or you WILL have leaks!

*If your filter has never been off, there is a stubborn bolt on the trans filter (basically a screen) that you can turn until the cows come home, but nothing will happen. This is might be Nissan's way of forcing you to get into the valve body, which only a fool (or an expert) would do.

Solution: Take all the bolts out except this one. Then take a pair of vice-grips, clamp down on it, and tear the filter off of this bolt. Remove any extra metal left under it. Buy a new filter, take a cold chisel and cut a V at this bolt hole towards the outside edge. You might want to put this area on a flat surface and hammer it flat. To install it, force the V cutout under the bolt (should be snug),then put the other bolts back in to specs.

3) Add 3 qts regular ATF (you'll want to put the pan back on first?), remove the passenger side trans oil hose at the back of the radiator, (after removing the splash shield) put the free end into a 5 G bucket and run the car in PARK and at IDLE ONLY until the flow starts to slow, then shut it off. Add 2 more qts ATF and run car again. Do this 1 more time until you've taken out 4 qts and added 4 qts, besides the first 3 to fill the pan. Around 7 total.

4) Put the hose back on and drive the car around 1000 miles. Drive as usual, but avoid a lot of fast driving, since you will be dissolving and loosening up MUCH varnish and so forth, and it might slip. Keep the ATF level where it should be.

5) Then, do all this again (except for taking the pan off) by adding and draining 6 qts; 2 quarts out and 2 qts in...3Xs. Drive for another 1000 miles or so.

*After the 1st flush using reg ATF, the trans might shift OK and then as the ATF loads up on the varnish left in the trans, it might be more like running a mix of molasses and ATF. You can use a clear bottle to compare the old ATF vs new ATF during each exchange.....when both look about the same, it's time for the synth ATF?

6) Do this one final time, draining /adding 6 qts Mobil 1 synth ATF (or Valvoline Maxlife ATF?) 2 qts at a time.

* Flush when the trans is hot. During all this, be sure you keep the ATF level where it is supposed to be....while driving the car. If you get too much slipping or sloppy shifts, you might go ahead and flush it again..but you need to keep the new ATF in the car long enough to dissolve out the varnish etc.


* Checking the ATF level:

CHECK with engine at idle and trans in Drive..........

ATF cold to lukewarm = L level = lower line

ATF hot after hard drive on hot day = H level = upper line

Approx 1 pint between lower & upper lines.


Keep those hose clamps tight. Also, check the condition of the hoses and if poor replace BOTH along with new clamps....being sure that they don't rub on anything....get the right high-pressure oil hose also.

Be careful with the small outlet "pipes" on the radiator, they can develop leaks and cracks at the solder joints and then you might have to remove the rad to have it resoldered...pull them straight off only or carefully cut them off, no sideways stuff.

*If you still have problems, try a bottle of LubeGard trans additive (in the red box..about $12 at NAPA) that is recommended by several car manufacturers like BMW, Saab, etc. (This has so far cured a "stuck governor" or valve problem with my trans where it would fail to downshift into 1st when cold and then would do this after a stop and starting out again..a SERIOUS CLUNK)


++ After this, replace the Mobil 1 synth ATF 1X per year or 15K miles, along with cleaning the pan & screen.

> Remove the pan & clean it....then replace it. The pan holds around 2 1/2 quarts.

> Add 3 quarts synth ATF to the trans. Flush about 2 1/2 quarts from the cooling hose.

> Add the remaining 3 quarts synth ATF to the trans...flush 3 1/2 to 4 more quarts from the cooling hose.

> Add 10 oz Lubegard.

The flushing process is simple to do (same hassle as an oil change) and you can probably do no harm, IF you get the hoses back on tight and keep the ATF level at the right place.

I've flushed my trans 4-5 times by now and am finding little or no brass or greyish sludge in the pan after 15K miles...just mostly a few black flakes of (maybe) old cooked on varnish? ATF is reddish brown when changed.

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>> Alternate method: Have a drain plug brazed into the bottom of the trans pan and then drain and refill with reg ATF at each oil change...this more or less changes the total ATF amount every 2 oil changes and drains some grit, varnish, and metal particles.

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Auto trans - simple mods and adjustments:

1) Adjust the kick-down switch to engage at about 1/8" to 1/4" from the totally floored position. This keeps you out of the kick-down area unless you really need it.

2) Check the vacuum at the vac modulator...make sure there are no vac leaks. Also, be sure you have an original Nissan vac modulator (this has NO adjustable screw in the vac opening for the hose, if it does, it is aftermarket). If it has been replaced by some aftermarket brand...at least try a used Nissan. This controls shifting and can be the source of many problems including slipping and poor shifts. Not too easy to get to, comes out by turning counterclockwise.

3) Adjust & test the Throttle position sensor...has a lot to do with shifting for an auto.

4) Disable the lockup clutches....this allows a reduced overall gear ratio in 3rd and 4th. In the top 2 gears, this results in an effective diff ratio of around 4.9 under WOT vs 3.9 when using the lockup clutches. How do you do this...don't know, my trans has always been this way.

5) Remove neg battery cable. Check the brain (black box) in the spare tire area. Remove conxs and bend in the split side of each conx using a very small flat screwdriver to improve contact. Use WD40 or di-electric grease to keep corrosion down. Work conxs back and forth several times to seat them real well. Might help.

Notes: This info is accurate according to my own experiences (one na auto trans), but each car and trans is different, and each has seen varying use / abuse. I think these trannys will last more than the typical 120K miles(?) or so, IF they aren't abused and are flushed & synth ATF used.

The Lubegard additive has some serious research & testing behind it. In my experience it works. It does not have a seal sweller in it.

Compared to the cost of a rebuild which might not be done right ($1200-1500?), $50 now and then $30 per year isn't a lot. If you have an auto trans...I'd say do it now...rather than later.
 

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I agree with amdz that the problem part sounds like a vacuum modulator on the auto tranny. Of course, we have to be suspicious as to why such a cheap fix was not done before the sale.

As for the speedo, the cable from the tranny drives a speed sensor. The sensor sends signals to the digi dash. The digi dash uses the signal, then fiddles with the signal and sends the new signal to the ECU, AT controller, ASCD and voice warning system.
The speed signal is modified to dumb it down a bit to make it compatible with the speed signals you would get from the analogue dash. This way, the ECU, AT controller ASCD and voice warning system can all be the same.
 

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Discussion Starter #6
Definately thought that as soon as I got it, but I really can't afford the swap right now! Thanks for all the advice, going to try it on my day off!
 
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