Started with a mid-70's C4 trans that only had reverse - no forward gears.

I tear down the trans and the intermediate (front) band and the clutch pack that it wraps around have obviously been way too hot. The rear band and it's clutch pack look alright. I rebuild it completley with new frictions, steels, seals, etc. I tear the valvebody down completely and clean it. No sticky spools - just usual residue. I check the governor - spools are free and all looks well. I disaasemble, inspect and clean, then reassemble the front pump. I flush the convertor, the lines, the cooler and put it all back together with great confidence. Then I make a horrible mistake. I accidentally mate up the convertor and the flexplate so that the drain plug on the convertor does not line up with a clearance hole in the flexplate. I had 3 out of 4 chances to get that right and randomly picked the only bad combination. Trust that I will never make that mistake again the rest of my days.

It made a few odd noises when started, but they went away. Moved it through all gears as we filled it with fluid, backed it out of the shop to drive down the road and verify it shifts out okay - no shifting no matter what. Reverse and first are fine - no second or third - regardless of rpm or shifter position. Less than a mile into trying to diagnose why - I lose everything. No forward or backward motion.

Drag it back to the shop, pull a cooler line from the radiator and start it. No flow. Pull the transmission back out and verify that the front pump gears are toast (inner one broken) from being in a bind due to the misallignment. The fluid that I drained was clean and the pan was clean, so I rebuilt the pump with fresh gears, reinstalled everything and tried again - making sure to line up the convertor drain plug with a hole in the flexplate. Fired it up, topped it off, good engagment in reverse and forward. Test drive - won't shift. Reverse and first only.

Figured the pump going bad got trash in the valvebody. Drained it and pulled the valvebody and there were some sticky spools that were perfectly free before. Disassembled the valve body, cleaned everything thoroughly and reassembled. Verified all spools were perfectly free. Reinstalled valve body and topped off the fluid. Test drive: first and reverse only - no shift.

Pulled the modulator valve and rod - all looked well. Verified proper vacuum at the modulator valve with engine running. Tested modulator valve on the bench with a vacuum pump - good. Removed tail housing and pulled governor - all good. Spools were as free as can be but I tore it down and cleaned it all again anyway. Since reverse and first work, but nothing else, I assumed maybe something with the intermediate band. I had verified that the anchor and apply struts were in position while the valvebody was out. The bands were adjusted properly when installed. I removed the intermediate band servo and all looked normal. Air-checked it through the hole in the shaft and it applied as it should.

I'm at a loss. I left it as is - tail shaft off, governor and intermediate servo piston on the bench. I guess I will go down and pull the valvebody again and look for something unusual? All 3 check ***** are in proper position, the valve and spring are installed under the filter tab, gasket is installed correctly. Maybe I should swap valve bodies? I have access to another one.

Having reverse tells me that the high-reverse clutch is engaging. Having first tells me that the forward clutch is engaging. Am I missing something here guys? Any help or suggestions would be MUCH appreciated....

 

With the governor off and the valve body on you can blow air into the hole that's under the governor, this will cause the 1-2 and 2-3 shift valve to move. You might have to have to pan off to hear them.

With the valve body off you also can air check the band and air check the 1-2 and 2-3 shift valves again to see them move.

This will help you narrow it down.

 

Think I found it - sticky spools in the valvebody again. The 1-2 and 2-3 spools were stuck in their bores again due to tiny particles that I assume came from the pump failing originally. Second time I have had it off and these particular valves have been stuck. I clean it meticulously and they are sticking again before I can get it out to drive it.

So.....is there any way to get the trash out of the system before these spools stick again? I have a Wix in-line trans filter I can installl in one of the cooler lines. It is a 25 micron and also magnetic. Should I install this, partially refill with fresh fluid, and let it run for a while before cycling through the gears and topping it off? Any other suggestions?

Also, which line on the body of the trans sends fluid to the cooler and which is the return?

 

Front line on the trans is fluid out of the trans to the cooler, rear line is return to the trans. Hot ATF is the best cleaner for the cooler, it is probably clean from the last time you had it all together. I would still blow air through it just because you can.

When you are done with the valve body before you install it back into the trans blow air into (I think) the bigger hole on the plate at the bottom. This should cause both shift valves to move.