1972 GMC Jimmy not shifting no reverse

FATBOYMAFIA72

MEMBER
1972 GMC JIMMY

Transmission problem
1972 GMC Jimmy V8 Four Wheel Drive Automatic

hello I recently purchased a 1972 gmc jimmy with a 5.7 350, th350 tranny with 203 t-case. Now when I purchased it. The owner told me that the tranny had been rebuilt. When I took ownership of the vehicle, I shifted it into reverse, (b&m ratchet shifter) it did not move, I put it in drive and it grabs, although does not shift out of 1st, my cousin tells me its the modulator, although it doesnt seem to have one where it should be, it just has a plate over it, please any and all help would be greatly appreciated with this issue. Thank you josh, with the no go 72'

2 Replies

HMAC300

MECHANIC
48,601 POSTS

The B&M shifter is justa shifter it has nothing to do with the transmission other than putting it in gear. The vacuum modulator assist in shifting up and down and not much more. I would suspect that this trans has been modified as there is no reason to block off the modulator. If it doesn't shift out of 1st gear I would suspect the govenor at first. If that operates ok then it will shift. It has a plastic gear on the end which often breaks or tears the gear and it won't turn so you don't get a shift. However it hasn't much to do with reverse. I would suspect that there is a valve body problem as well as even if it's been "rebuilt" doesn't mean it was done correctly, even if it were modified. Unfortunatley you'll have to take it to a trans pro and see if he can see what's wrong with it. There is what is called a sprag and low/reverse clutch which both or one of them could be bad.