TH400 Transmission shifting problem

[arctic cat]

I have a 1986 Chevrolet G30 HI CUBE, 6.2 Diesel, paired with TH400.   While driving today the shifting became a little harder but it did shifted.    I stopped at O,Reillys and the transmission either don't shift pass second or if I step on the accelerator I do a very forceful shifting.   I believe the Vacuum Modulator may be faulty or vacuums leak somewhere.  I have a vacuum meter so I will be testing the vacuum tomorrow and the same time replacing the modulator.    The other thing that may be wrong is a faulty kickdown solenoid or switch.  Any input from some of you guys.

 

[AngryVanMan]

When was the last filter change? I had a truck with a TH400 that I got for salvage price due to not shifting up past second, they had it flushed and thought it would need a rebuild. Got it home, dropped the pan and installed a new filter and oil, shifted perfect the rest of the time I had it. Pretty stout transmission overall, just missed not having overdrive.

 

[highdesertranger]

x2 on the service if it's been awhile. what does the fluid look like? definitely check the vacuum. if your blend doors for the heater and AC work then your pump is ok but you might have a leak. what type of vacuum pump do you have? I have a cam driven one that I am not using if you are interested. highdesertranger

 

[arctic cat]

x2 on the service if it's been awhile.  what does the fluid look like?  definitely check the vacuum.  if your blend doors for the heater and AC work then your pump is ok but you might have a leak.  what type of vacuum pump do you have?  I have a cam driven one that I am not using if you are interested.  highdesertranger

The Van was an old military van.   All the fluids were drained and the fluid were red put back in October for testing and down again about two months ago and replace with new filter about 2 months ago.   The fluid is not burned and smell good and pink.    Don't know the type but I look down there and it have been a while since is a rusty one,  took the vacuum line off to see if there was any fluid leaking but no leak.

 

[highdesertranger]

6.2's use 2 types of vacuum pumps. I can't recall the year they split right now. the older ones used a cam driven pump. it's in the back of the engine where the distributer sits on chevy v-8's, it is driven just like a distributer. the later ones use a belt driven pump. it is of course driven off the serpentine belt. highdesertranger

 

[arctic cat]

6.2's use 2 types of vacuum pumps.  I can't recall the year they split right now.  the older ones used a cam driven pump.  it's in the back of the engine where the distributer sits on chevy v-8's,  it is driven just like a distributer.  the later ones use a belt driven pump.  it is of course driven off the serpentine belt.  highdesertranger

Imine have no serpentine belt.  It must be an older one.  I would check the location  it also have no ac just heat from factory

 

[arctic cat]

well check the vacuum and it was working. The gauge show a little high but I believe on diesels in run higher than petro engines. Replace the AT modulator on the TH400 and took for a very short drive and it shifted normal. Would like to take it for a longer drive to perform a longer test under regular driving condition. I believe as a preventive measure I may replaced the kickdown switch or solenoid as that van is 30 year old and I don't know what kind of maintenance it received while in the service

 

[highdesertranger]

good to hear, hope it works out. highdesertranger

 

[speedhighway46]

A.C.

Hats off to you for your analytic ability and perceiverance! Great job of taking care of a major problem without someone emptying your wallet!

 

[arctic cat]

A.C.

Hats off to you for your analytic ability and perceiverance!  Great job of taking care of a major problem without someone emptying your wallet!

Yep, $11.24 and about 15 minutes of actual wrenching.  I took it for a longer drive and it work well.

 

[rvpopeye]

Well done Mr Shade Tree !!!!!

 

[arctic cat]

Well done Mr Shade Tree !!!!!

Actually I do have a Master Mechanic Certification with formal schooling somewhere. I worked in Alaska for a brief period of time as a mechanic but is one of those things that is not just in your heart.   I have my own personal shop but is for my own equipment.       I do take a full set of tools with me when travelling

 

[arctic cat]

But yes it was under a shade tree that I did this one, so I guess I'm a shade tree mechanic