Lost first gear in my 904 today

[Sublime/Sixpack]

Fired up the '68 today for a drive and found that I had lost first gear in the 904 trans. Second and third are okay but no first. Does anyone know the most likely cause of the loss of first? (It's the original trans. with 80 thousand miles on it).

Should have had it rebuilt last year when I had it out for the engine swap.

[John_Kunkel]

If you lost 1st how did you get to 2nd and 3rd? Are you saying it takes off in 2nd and shifts OK to 3rd?

[Sublime/Sixpack]

Yes it starts out in second and shifts to third.

Here's what happened, I hadn't driven it for 3 weeks, then today when I fired it up, put it in Drive to move the car out front and noticed it seemed odd but I didn't think much about it at that moment. Turned the engine off for a few minutes while I took care of a few things before leaving home, fired the engine up and took off. All seemed good. Drove car about 20 miles getting on it several times WOT like I often do, then stopped at a red light and when taking off I realized the trans. hadn't shifted down to first, it was starting out in second. Slowed down, dropped the lever to first and floored it, no first. Stopped, started out again and no first. Just second and third.

[John_Kunkel]

If it won't start out in 1st from a dead stop with the shifter in 1, either the governor is faulty or the 1-2 shift valve in the valve body is stuck. Only way to isolate the problem is to hook a test gauge up to the governor test port in the tailhousing....anything over 2 psi in drive with the wheels stopped is a governor problem, if governor pressure is OK it's the valve body.

[Sublime/Sixpack]

Thanks John, you're a wealth of knowledge!
Since my work on automatic transmissions is limited to changing filters, front and rear seals etc. I'll have to think through the process you've suggested. Would you point me in the right direction as to what type gauge I need to check the pressure?

[John_Kunkel]

The test port threads are 1/8" NPT so any 0-50 psi gauge would work.

[Sublime/Sixpack]

Thanks for the information John.

FWIW
Today I decided to take the car down the road and back just out of curiosity, and found that when I started out all I had was 3rd (Drive) even when shifting the lever manually down into 2nd and 1st. Then after stopping and starting out again I had first, but basically no 2nd or 3rd (just slippage).  Then after a while it was back to no 1st, but had 2nd and 3rd.  On the highway in Drive when floored there was no passing gear (auto shift down), would only drop down into 2nd manually.  Then more of the same. I parked it.
Time to drop the trans. for a rebuild wouldn't you say.