Hey fellas, Im new to the blazer game. Today I went out and got the truck dirty for the first time. I didnt think I was pushing it to hard, but I hit a good rut and bounced around a little. After which I went into a field and got slightly stuck. I worked my way out and realized that my truck doesnt shift on it own anymore. I have to put it L1, then shift it up as I accelerate. Sucks, still drives and works but now I have to shift it manually. Does anyone have any idea what would cause this?? I checked the tranny fluid aswell afterwards and it seems like its a little over full. would that cause to much pressure and cause issues? Thanks for any help you guys can give me. Im also looking for a front drive shaft. The slip yoke is broke on the one I got with the truck, came that way. So I need a new slip yoke for a 77 blazer, with a 350. Its got 16 blue splines, and is roughly 7 1/2" long from middle of u joint to end, and about 2" in diameter. Does anyone know where I can get one? thanks again for any help provided!








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do you see any water in the trans fluid, white blotches on the dipstick? im not 100% on this (someone else will chime in) but thereshould bea vent on the top of the transmission, if any water got into the valve body it may not shift properly. If so I would change the fluid and filter, thats just me.Also is there any damage to the trans pan? Or shifter linkage?

Always check Ebay and local junk yards for driveline stuff

 

thanks for the tips, there isnt any water in the tranny fluid, it just seemed a little above the line when I checked it. It happened right after I hit a big bump, and then I lost momentum going into the field and then I had to start shifting it manually. Its not leaking, and there is no damage to anything underneath the truck. I was only in a muddy field, nothing deep at all. The truck just stop shifting on its own so I lost momentum and got stuck for a bit, until I figured out that I had to put in first until it got up to speed to shift into 2nd, and then into regular drive. Still drives fine, I just have to move it up the gears on the steering column rather than just letting it shift itself while in drive. So something is keeping it from shifting on its own. Anyone else have any ideas? thanks

 

yeah man, im stumped on that one, someoneshould know, one thing you can check, there should be a steel line coming out of the back of the intake manifoild by the distributor going to the trans, I believe that is the vaccume line for the shift solenoid, if that got jard hard enough and devloped a crack or leak that would probably stop your trans from shifting, it would also give you a rough running idle though

 

ill check that, Ive noticed some other loose fittings aswell. thanks, Ill look into that line being loose or cracked. any other suggestions?

 

well I looked but didnt find that tube to be loose. I did find a "t" fitting that connects that tube to the manifold, and on of the "t" opening was just open, and sucking in air. I plugged it with my finger, but nothing tranny wise changed. When I put it in drive, it feels like it wants to go, but just isnt getting any grip, at least not enough to move, the same all the way down until I get to 1st, then it goes it great. Then when I get going I can shift into second but I have to be in the second gear range, and the same for 3rd once Im going fast enough. So I have to shift it like a manual. Its like the something wont let it shift on its on, it can only go into gear if I place it the right gear manually. Anyone have any other ideas? I appreciate the help!!

 

get under the passenger side of the truck and look for your vacuum modulator. its going to be towards the rear of the transmission. should have a vacuum line attatched to it, if not thats one possibilty of why its not shifting. also check it for vacuum. could have sucked some garbage up in the line.

 

how do I check it for vacuum, just pull it loose and feel if its sucking. Could you describe where it goes a little better. Is that the tube that runs from the intake manifold all the to the back of the tranny? Cause its still there and seems to be working ok. Describe it a little more and Ill run out and check it. thanks

 

ok I checked that line, i think its the one you described. And no leaks. But I checked the tranny fluid while the truck was running and it was right at the cold line. So does that mean I am low on tranny fluid. And if so what fluid do I use to fill it back up with? thanks.

 

If you have a vacuum tee on the manifold with one open port, then it probably should have a line going from the tee to the modulator valve on the transmission.
What transmission do you have?