Auto Trans Oil Change?

[ramsesosirus]

I hear lots of contradicting info about this,

but my stock 76 has a stock 3 spd automatic transmission.  The odometer shows 85,000 and is likely accurate, judging by the rest of the car, but it could theoretically be 185,000.  The car is 40 some years old.  The service records never indicated a transmission fluid change.

I know I would NOT want to flush it, but would dropping the pan and changing the filter/refilling be a good idea?  (I've done this job on other vehicles, got the transmission oil bath...)

I'm not having any problems, it is shifting great.  Also, what would be a good fluid to use to refill?  I assume it hasn't been using synthetic.  

The color isn't black, but it's not a nice red/pink either.  And filling transmissions to the proper level is kind of tricky I've noticed.  It doesn't say on the dipstick how to check, but a lot of cars say to check it: warm and in neutral.

Honestly I'd probably rebuild the auto if it ever did go out, even though I have a later 6 spd in the garage.

The auto is much better for cruising, which is all this car is for.

Thanks

[Stanley]

I'm using synthetic. Dropping the pan and cleaning or replacing the screen is not a big deal. I  put my car's front wheels on the ramps to do it. You need to get the fluid out of the torque converter first. Disconnect the trans cooler hoses and direct the out hose into a container. Run the engine about 30 seconds in park until the fluid stops coming out. Then pull the pan being careful about the oil bath. Do the screen and clean the pan. You can adjust the bands per Chilton manual or Datsun auto trans manual, it's easy. Refill per FSM. The car will need to idle for about 30 seconds to refill the torque converter before you can drive.  Then recheck the fluid level and add fluid as required.

[ramsesosirus]

Thanks for the reply, good advice.  

I'm more concerned about whether or not I should even do this, since I've heard that if you wait too long (or if it hasn't been changed in a while) that the detergents/etc... in the new fluid might help the trans to fail.  

Surely it's been changed once in it's life?  Could trans oil last 40 years and still allow the unit to perform well?  Mine shifts great, just wanting to stay on things. 

[Chickenman]

^ Old Internet Wives tales. Change the oil and Filter.  It's one of the first things I do when I buy any used car with an Automatic Transmission. Two things Auto Trans missions like. Clean oil and cool oil. Auto trans oil is no different than engine oil. Auto trans oil cannot last 40 years and still be good. BTW, I'd go for a complete flush and replace the Filter and out in a good Synthetic fluid.  Amsoil Dexron ATF has saved me two Automatic transmissions that were incorrectly assembled by so called " Experts". .

 

Edited October 3, 2017 by Chickenman

[ramsesosirus]

Is it ok to use synthetic after using the regular for all these years?  I've read that you don't want to switch to synthetic engine oil on an engine that has been using standard for years.  

Now, if I were to ever rebuild either, I'd definitely go with the best synthetic I could get.

[Chickenman]

IMHO, there should be no issues at all switching to a full synthetic after years of regular petroleum oil. . Again, most of this was old wives tales from way back . When Synthetics first started appearing in the early to mid 70's, they did have some issues with seal leakage. Mainly because of lack of  normal petroleum products that would cause the seals to swell. 40 years later and that is no longer a real issue. Synthetic formulations have changed and now include seal swellers.

 

Even the seal technology has changed so it is more compatible with Synthetics. . If you are buying new seals ( O-rings whatever ) from the aftermarket or even Nissan, the materials are different. If you have 40 year old seals in the engine... or Transmission... well it might be an idea to pull it apart and freshen it up. Auto tannies can take a lot of abuse. But once they start eating them selves alive, it a very fast downward spiral of destruction.  

If you are really concerned about old brittle seals. Throw in 1 bottle of non-synthetic Tranny fluid to mix with the Synthetic. That should provide more than enough Seal swelling agents. Although as I mentioned,  New synthetic formulations have had over 40 years to solve that problem.

Personally,  I've used full synthetics ( Amsoil, Red line, Motul, Shell Rotella T6, Mobile 1  ) in a variety of Vintage cars for over 35 years,  and have never has any leakage issue or any other problems at all. That's with engines, manual transmissions, Auto Transmissions ( Amsoil ATF ) . Power Steering and Diffs. Have I left anything out? I used Amsoil products pretty much exclusively until the Mid 2000's when I started to use Rotella T6 on some of my Turbo cars. Amsoil was just getting a bit too pricey. 

 

[Chickenman]

There is some truth in the Tale of not switching to Synthetics in an old engine that has had regular oil in it for decades. And that is when people abuse the engine and do not perform regular oil changes. Then you get horrible amounts of sludge building up Modern oils ( Synthetic or Dino ) have pretty powerful detergents. Often these detergents will dissolve this old sludge and it can end up clogging the oil pickup. Or with oil pan gaskets, the only thing holding the brittle old gaskets together is the sludge. But if your engine is all sludged up like that... well what type of oils you use is the least of your problems. 

If you have sludge ( engine ) or varnish ( Auto trans )  build up , really the proper way to fix the problem is to disassemble and clean everything properly. Otherwise you are sitting on a Ticking time bomb.

Those early Jatco 3 speed Auto's are also fairly easy to rebuild. Simpler than an engine IMHO.  

 

[Bernardd]

IMHO the best oil to run is jd hydraulic fluid.  I was pushing over 400whp thru a jatco and it was the only oil that wouldn't slip.  Ever.  In fact it lowered the stall from 3k to 2400  because it was so grabby. I bent the tangs on the input shaft but it didn't slip.  A low power application would last forever assuming seals and such aren't leaking.  I would run at least 1qrt/ltr of standard oil because it makes it easier to see the fill level.  YMMV.

[ramsesosirus]

On 10/14/2017 at 9:11 PM, Chickenman said:

There is some truth in the Tale of not switching to Synthetics in an old engine that has had regular oil in it for decades. And that is when people abuse the engine and do not perform regular oil changes. Then you get horrible amounts of sludge building up Modern oils ( Synthetic or Dino ) have pretty powerful detergents. Often these detergents will dissolve this old sludge and it can end up clogging the oil pickup. Or with oil pan gaskets, the only thing holding the brittle old gaskets together is the sludge. But if your engine is all sludged up like that... well what type of oils you use is the least of your problems. 

If you have sludge ( engine ) or varnish ( Auto trans )  build up , really the proper way to fix the problem is to disassemble and clean everything properly. Otherwise you are sitting on a Ticking time bomb.

Those early Jatco 3 speed Auto's are also fairly easy to rebuild. Simpler than an engine IMHO.  

 

That's what I've heard (for both engines and trans.), is that the synthetics "knock" the sludge/deposits loose, causing problems.  I change my oil regularly, but you never know about the POs.  This is a used transplant engine to replace the blown stock one, and I've changed the oil 3 times in about 1000 miles just because, it probably sat unused for a long time.

Good to hear the Jatco's are easy to rebuild.  I've never rebuilt an engine, but I did take about a Chevy TH350c just to see how they work.  Is there any way to "beef up" these auto trans for more power during a rebuild?  Or anything else I should know about these trans? 

I know I'll prob get some flack for saying this, but I really prefer auto transmissions.  My left leg doesn't get sore, cruising is fun, no clutch to go out, etc..   And, if they're built right, you don't lose a heck of a lot of power, at least when you're not a professional/and/or racing for money, something like that.

[Chickenman]

Funny thing with Auto's. I ran modified Camaro's in Autocross for years. In what would be equivalent to SCCA  Prepared clas ( Really soft Goodyear slicks ) .  I originally ran am Auto then switched to an 4 speed stick. Car was faster with the Auto. Geared to run 60 MPH in first gear ( 3.3 rear end Ratio and 7,000 RPM )  . Auto trans was modified extensively with many parts from Trans-Go including full manual shifting at any speed and RPM. 3,000 RPM Stall. Torque convertor. Torque convertor gave better Torque multiplication out of corners and was smoother to drive. Only put in the 4 speed when I started doing Hillclimbs and track day events. 

As far as HD parts go. Look for online Auto Matic Parts suppliers such as ATS.  send them an E-Mail. You may even have some suppliers available locally. There are normally HD parts available for all types of transmissions. HD clutch plates and bands made out of vbetter material should be fairly easy to get. Shift kits may be available or you can make modifications on your own if you have the knowledge. Most shift kits involve raising pressures with internal springs and changing shift points with the governor. Band apply pressure can be adjusted with springs or by increasing Accumulator piston Apply area with special pistons. 

TransGo is a really good supplier for modified parts. They may have something for Jatco's. You will probably have to call them by phone though. Jatco parts may not be listed in their catalogs.

 I'm pretty sure there is a publication by ATSG Technical or HP  Books on how to rebuild and modify Jatco transmissions. I've seen it at a local speed shop. I'll try and find some links for you later, but I've got to run tight now. 

Edited October 17, 2017 by Chickenman

[Chickenman]

You can also upgrade to a locking convertor model in either 3 speed or 4 speed. ( L3N71B and L4N71B )  Bear in mind that for high HP drag racing use, the non-locking 3N71B may be a better choice. Lock up convertors can be more troublesome on high HP  Turbo applications. The  clutch plates in the convertor usually doesn't have enough surface area. ( You don't want to be Boosting 10 lbs or more  with the stock convertor locked ) .  And they are more complicated.  

http://community.ratsun.net/topic/36901-automatic-transmission-upgrade/

[Chickenman]

Australia is a big source for Jatco 3N71B racing parts. Ozzy's luv rotaries and the 3N71B  from the first Gen RX7 is very populra in Drag Rcaing. 

http://www.keas.com.au/products.php

 

You could also contact RB30X at Australian Z Car. I belive that he has developed some kits.

http://www.viczcar.com/forum/topic/5097-shift-kits-for-auto-zeds/