Automatic transmission diagnosis

[Randalla]

I'll eventually be swapping in a manual, but wondering if there's anything I can do, short of a rebuild of my stock automatic, to buy some time. The car is a 72 510 4-door with 54,000 original miles. I bought the car last Fall and drove it home across the country (2,400 miles). The trans worked fine all the way home. Yeah it was slushy but working as well as they do. Last week I began noticing a very slow up-shift that seems to be getting worse. Wondering what might be easily serviceable. The fluid is topped off, not discolored or burnt smelling. Do these things have a vacuume modulator? Can the bands be adjusted like an American auto trans. Can you drop the pan and replace the filter? Is there anything else to try to improve the up-shift?

[kevins750]

There is a modulator, left side about middle of tranny body...metal hose going into it...I have a auto also, I am no expert but if oil is clean I would try the modulator...My trans slipped badly, oil was black and burnt and pan was full of clutches fragments..You can pick them up at local stores, at least I did...

[datzenmike]

Two things...

 

With engine off slowly depress the gas pedal. You should hear a definite click at almost full throttle. This is the electric switch for the kickdown. If badly adjusted the transmission may think you are passing another car and have floored the accelerator. This will delay the up shift to increase the performance.

 

Check the hoses on any part of the shift modulator valve circuit mentioned in the other post. If leaking vacuum, the transmission will be fooled into thinking the gas peddle is more floored than it is and producing low intake vacuum. This will also delay the up shift. Maybe check your intake vacuum. Should be 15-18 in. Hg. Overly tight valve lash is the usual cause. Remember that poor engine performance will affect the shift points greatly.... get a tune up.

 

54K miles is not nearly close to needing maintenance like modulator replacement and clutch adjustments but time may have deteriorated the ATF. I would start with easily done things that you can do, like replacing the fluid. To drain you have to remove the pan so get and replace the filter and the pan gasket. For ATF use a DEXRON formula about 6 liters.

[Randalla]

Great advice guys. Thanks! I have not changed the fluid in the short time I've had the car and don't know for sure how long it's been so I'll begin there and change the filter. Will also look into vacuum modulator. If I can find one, and it's cheap, I'll probably just swap a new one in.

[ggzilla]

> The fluid is topped off, not discolored or burnt smelling.

 

Then do not change the fluid or filter. It can last the lifetime of the car.

 

Instead, inspect the modulator which has a direct effect on the crispness of shifts.

[datzenmike]

31931-H0101 is the Nissan part number for the 3N71B.

 

Remember that poor engine performance will affect the shift points greatly.... get a tune up.

[MaxEmiliano]

I'll eventually be swapping in a manual, but wondering if there's anything I can do, short of a rebuild of my stock automatic, to buy some time. The car is a 72 510 4-door with 54,000 original miles. I bought the car last Fall and drove it home across the country (2,400 miles). The trans worked fine all the way home. Yeah it was slushy but working as well as they do. Last week I began noticing a very slow up-shift that seems to be getting worse. Wondering what might be easily serviceable. The fluid is topped off, not discolored or burnt smelling. Do these things have a vacuume modulator? Can the bands be adjusted like an American auto trans. Can you drop the pan and replace the filter? Is there anything else to try to improve the up-shift?

[MaxEmiliano]

Randalla I'm having the same problem did you ever find out what the problem was?

[datzenmike]

Prolonged or slow up shift to next gear is most likely the modulator valve not getting a sufficient vacuum signal from the intake. This is likely a vacuum leak from a split hose. The line from the intake to the valve is metal but there are two short pieces of rubber hose at each end.

 

 

Upper left. Small rubber hose connecting to a hard line looping down under throttle linkage and down over transmission bell housing.

 

 

 

This is the other rubber hose end.

 

 

 

 

Remember that poor engine performance will affect the shift points greatly.... get a tune up.

 

Poorly adjusted valves can reduce intake manifold vacuum too. Low vacuum signal tricks the automatic into thinking you are holding the gas peddle down farther than you are, as in accelerating up a hill. This will delay the up-shift to increase performance.

[danfiveten]

Max what year.  The borg warner autos in my book are pieces of crap lol, the jatco ones are usually bulletproof, have a feeling as dmike said above. Mine has 136k, stock survivor show car with automatic, and i just went to jccs last year, 16 hours one way, doing 80 most of the time, 90 to pass asshats that were driving like idiots or possibly drunk, and no issues on hills.  I love when people complain about autos saying they are worthless, yet i love my auto just as much :)  

 

tell us some more info, year, and we will try to help you figure out whats going on . 

[datzenmike]

Yes I assumed same problem was same transmission. Up to April '71 were BorgWarner of some type. Some had a manual kick down cable from the throttle that could be adjusted wrong or as above the engine lacks power and the throttle is being pushed down farther to compensate.

 

I have an auto L18 and the only problem is... it's a bit boring. Calling them autotragic or slush boxes is just sour grapes. My L18 has done upwards of 90 MPH on an incline too.

[MaxEmiliano]

I have the jatco auto transmission and 1st gear revs high then finally when it kicks into second it only goes half way through the gear And back to first reving really high? I'm going to check all the hoses and linkage today

[datzenmike]

Check fluid level.

Check for vacuum leak between the intake and the modulator valve.