In Gear Surge

[79brent]

Hello guys. So yesterday i was sitting with my truck in drive and it jumped two times when i had my foot on my brake? Ive been pulling a trailer with it lately so it couldve broke somthing maybe. Also it clunks when I let off the gas and hit the gas again, sounds like it is coming from the transmission maybe the tc, however it is not the u joints because they are new.
Any help would be appreciated, Thankyou
Oh its a 79 c10 350/350 2.76ratio 12 bolt

[Captkaos]

Have you inspected the motor mounts, transmission mount, rear axle yoke?  What does the transmission fluid look like?
Did this just start?

[79brent]

motor mounts have maybe 15-20k on em, tranny mount is brand new, the rear axle yoke does seem to leak a lot, but is tight. The fluid in the transmission has about 6k on it and yes it has only done that 2 times that I have felt, within 15 sec of eachother. Thankyou for the quick response! I need to get to the bottom of this even though I hate using my baby as a work truck  . But gotta make some extra money to fix this kinda stuff lol.

[79brent]

The clunk has been going on for awhile though.

[Captkaos]

What the torque converter replaced/checked when the trans was rebuilt?

[79brent]

It was rebuilt years ago and sat in a truck with a blown motor and i swapped the tc and tranny into my truck prolly 7 months ago. Im thinking it is the tc but i wasnt sure about it. Also my truck just died yesterday on the freeway going 80 mph cruising, all the guages were where they should have been. tried to start it and it wanted to start but would backfire out of the tailpipe as soon as you let off, now its not getting spark to the plugs. No fried wires from what I seen. The coil is almost new as is the cap rotor and module as well as the spark plug wires. Sounds to me like the distributor, its going to the shop monday but I just wanna get a roundabout on what it is. Also I dont think its a link because everything else in the truck works ex-radio, lights, gauges etc.

[bd]

...my truck just died yesterday on the freeway going 80 mph cruising, all the guages were where they should have been. tried to start it and it wanted to start but would backfire out of the tailpipe as soon as you let off, now its not getting spark to the plugs. No fried wires from what I seen. The coil is almost new as is the cap rotor and module as well as the spark plug wires. Sounds to me like the distributor, its going to the shop monday but I just wanna get a roundabout on what it is. Also I dont think its a link because everything else in the truck works ex-radio, lights, gauges etc.

Make sure the distributor isn't loose and just spun around.  If you have 12 volts to the B+ terminal on the distributor and no spark, one possibility is the pick-up coil (since e/g else has been replaced), or the module died.  It's also possible it blew a pinhole through the rotor.

[79brent]

It did not come lose, I checked that already. Not sure how to do any of those other things you suggested and I do not have an ohm tester currently. Thats the only thing I think it could be. I remember when my uncle and I put in my motor the gear at the bottom of the distributor that runs the oil pump had some play in it so maybe it broke and its not letting the rotor spin in the cap. Thats my theory lol. Thanks for helping me out, this forum is cool.

[79brent]

So would the torque converter cause that clunk?

[84burb]

Did you have the clunk before you changed the trans, mounts, and u-joints?
Is it the same now as before?

It is possible the clunk is a loose TC or even the flex-plate (flywheel), tho those will usually cause a vibration also, especially under load. You can check the TC bolts easy enough by dropping the inspection cover. Checking the flex-plate is more involved and requires some dis-assembly.  We'll save that as a last resort. It could also be the trans is loose at the engine. That easy enough to check both visually and by checking the bolts.

Assuming the mounts and u-joints are okay...
Put the rear axle up on some solid jack stands on a level slab. (It wouldn't hurt to put the front up also)
Now for the visual inspection.
No cracked/broken springs or loose u-bolts allowing the rear-end to move.
Look to see if there are signs of the leaves moving forward and back at the rearend spring pad indicating a broken center bolt.
Are the spring bushings okay.
Check for play in the pinion.
Does the flange move up and down or in and out.
Grab the drive-line and twist it back and forth. Is there any movement of the pinion before you feel it make contact inside the rear-end. Ideally, there would be minimum movement when you twist the drive-line. This is usually the source of a drive-train clunk. Then it becomes a matter of how much play is too much.
Worn slip yoke splines can also cause a clunk.

[79brent]

I will go in and check all of that asap. Thankyou burb.