Automatic Trans Trouble Shooting.

[Jeff Collins]

I have read some of the post on the forum on checking thr k4c-025 trans,and was looking for some info on where to hook up the pressure/vacume guages and for some pressure references so I can trouble shoot my trans.I have changed filter cleaned the valve body,& retorqued.checked contacts,and all of the 3 way valve operations,inside of trans looks brand new.I just dont seem to have any initial pressure when car is put in gear,I can give it throttle and car will move a little but need some more info to reach some sort of conclusion.

68 250 sl auto/ac
86 944 Porsche
96 K35 t/d 4w
99 ultramax
2000 fatboy pro

[ja17]

Hello Jeff,
Sometimes the ears on the torque converter or the corresponding slots in the front pump are sheared off from improper installation or wear. So when the engine is running the front pump is not turning.

What is the history on your problem?


Joe Alexander
Blacklick, Ohio

[Jeff Collins]

I bought the car after the motor was rebuilt and installed.I have checked the majority of the work that was performed and it seems that everything was done by a competant mechanic.I Cleaned out fuel tank,lines,inj pump etc, car runs pretty well.Other than what I posted in the above that is about all the history there is.Car appears to have a fluid coupling instead of a torque converter.I kinda feel that it may be in the pump like you mentiond but would like to find the problem before I remove tranny for a rebuild when it could be somthing simple(overlooked)

68 250 sl auto/ac
86 944 Porsche
96 K35 t/d 4w
99 ultramax
2000 fatboy pro

[ja17]

Hello Jeff,
The front pump (primary pump) supplies hydraulic pressure for lower speeds (up to around 18mph). I would still be suspicious of a damaged front pump. I have seen these pumps ruined during installation of transmissions or engines.

Of coarse a stuck hydraulic valve or bad band piston can also cause this kind of problem also.

There are seven or eight test plugs where different pressures can be checked. However you may want to loosen the transmission hose going into your radiator. If you do not have good pressure at idle you may have a primary pump problem.

If the people who installed the engine did not have the torque converter lined up correctly with the front pump, then the pump would have been damaged when the engine and tranmission were bolted up.

Joe Alexander
Blacklick, Ohio

[rwmastel]

quote:Originally posted by Jeff Collins

Car appears to have a fluid coupling instead of a torque converter.

You might want to elaborate on this point.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[lurtch]

Hello Jeff,
      Just recently I had good success fine tuning the modulator pressure on my transmission.  The attachments illustrate the fitting you will have to come up with to tap into the external pressure measurement ports down on the trans. I through-drilled the bolts and silver soldered a fitting on. There are at least three tap-offs but I found I only need to monitor two of them, the modulator pressure and the so-called "shift pressure". Be sure to do your road tests with the vacuum line disconnected ( and plugged-off ) or you will get incorrect pressure readings. The modulator pressure should be set to read right around 40 psi after the shifts have occured. Mine was incorrectly set at 33 and I was experiencing slip-shifts and torque induced break away. I think it was two turns "IN" on the small shaft with two flats, and I had the fix. All seems to be fine now. Good Luck,  Larry In CA

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[Jeff Collins]

I finally recieved my BBB off of ebay checked out the trans section and figured out I need another book.Its funny that they  spend 1/4 of the book on brakes but only about 5 pages on the auto trans.

68 250 sl auto/ac
86 944 Porsche
96 K35 t/d 4w
99 ultramax
2000 fatboy pro