How do I know if the transmission is slipping or if I just need to replace gear shaft

More information is needed to be able to know if it is automatic , standard transmission . Also the make model of the vehicle.

And, No. The drive shaft is the part that turns when the clutch is engaged. It could be a bad or slippery clutch plate if it is not an automatic tranny.

Usually a transmission slipping isn't due to the drive shaft, but the transmission itself. I know this might sound a like a crazy question, but have you checked the transmission fluid levels, could be a leak, if not full would cause slippage.

When any gear is slipping in an automatic transmission , that is a sign that the transmission is worn out, and needs to be rebuilt or replaced.

Transmission gear assembly and transmission needs inspection. Also check the transmission fluid level. Also is the fluid getting leaked or its low.

There are few very helpful links with solutions to troubleshoot this problem.

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I suggest you to refer these links.

Click the link below:-----

2000 Toyota Camry: Transmission slipping and Stuck up?

http://whatisbyme.blogspot.in/2012/05/2000-toyota-camry-transmission-slipping.html

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Transmission Slips out of 2nd gear?

http://repairhelpcenter.blogspot.in/2012/02/transmission-slips-out-of-2nd-gear.html

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Car engine Overheats and transmission starts slipping?

http://schematicsdiagram.blogspot.com/2011/12/car-engine-overheats-and-transmission.html

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2006 Ford Explorer: Engine Vibrates and gears slipping?

http://whatisbyme.blogspot.in/2012/06/2006ford-explorer-engine-vibrates-and.html

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Clutch slipping problem?

http://howtobyme.blogspot.in/2012/03/clutch-slipping-problem.html

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Dodge Anti slip System is not operating?

http://whatisbyme.blogspot.in/2012/07/dodge-anti-slip-system-is-not-operating.html

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OD light flashing and transmission fluid leaking?

http://repairhelpcenter.blogspot.in/2012/02/od-light-flashing-and-transmission.html

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Transmission fluid leaks near radiator on ford windstar?

http://repairhelpcenter.blogspot.in/2012/02/transmission-fluid-leaks-near-radiator.html

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Ford Windstar transmission fluid leaking?

http://technoanswers.blogspot.in/2012/02/ford-windstar-transmission-fluid.html

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TRANSMISSION REPLACING AND TROUBLESHOOTING

http://alltypesofpartsreplacing.blogspot.com/2012/12/transmission-replacing-and.html

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These details will help.

Thanks.

your transmission lock -up - converter valve is loosing pressure and it may be causing this problem that you have. it is in the transmission pan area on the valve body. they sell a replacement valve for this

Engine Light ON (or Service Engine Soon Warning Light)
- Incorrect transmission shifting Possible causes - Low transmission fluid level
- Dirty transmission fluid
- Shift solenoids
- Transmission mechanical problems
- Transmission hydraulic control circuit Tech notes Start by inspecting the transmission fluid level and condition, and change fluid if necessary. When is the code detected? P0734 is detected when A/T cannot be shifted to the 4th gear position even if electrical circuit is good. P0734 NISSAN Description This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by Transmission Control Module (TCM) as follows:

Torque converter slip ratio = A x C/B

A: Output shaft revolution signal from revolution sensor
B: Engine speed signal from Engine Control Module (ECM)
C: Gear ratio determined as gear position which TCM supposes

If the actual gear position is higher than the position (4th) supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.

this means the trans is slipping as measured by the input and output shaft speed sensors.

Sometimes the axel shaft backs out of the transmission on front wheel drives when not seated correctly. This usually occures in new transmission or engine swaps. I would take a look at the driver side shaft for fluid residue and shaft placement.

you need your transmission rebuilt the clutches are slipping

First,a teardown is in order to determine exactly what is damaged.Inspection is another term.If the 1st gear on the countershaft is damaged,the entire counter shaft would have to be replaced.There are two shafts inside the trans,that mainshaft which has mounted onto it,the input shaft,and all the speed gears,synchros and forks that integrate with the main shaft.The countershaft also has speed gears,but they are actually made into the counter,and not replaceable individually.If any one of the speed gears on the countershaft is damaged,the entire countershaft has to be replaced.As far as manuals,i don't know of any for manual transmissions.Try contacting some places on the internet that specialize in manual transmissions,as they might know some sources for manuals.There are many,many things not covered in manuals that can only be learned with time,experience,and apprenticeship.Like unit endplays,how to determine good and bad parts.etc.