Manual trans bouncing in gear

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shift5

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Not an issue i've encountered before and so i'm not sure where to look. Only thing I can think of is U-joints.

Essentially while driving in higher gears (I think 3rd gear and up, maybe second gear too), when I let off the throttle and it starts engine braking, the truck jerks and bucks badly for a few seconds back and forth, like there's too much slop in the drivetrain. I also can hear a slight banging noise, that might be normal though. It bucks back and forth probably 5 or 8 times depending, before settling down and engine braking normally.

It's kind of like if I were barely getting on and off the throttle repeatedly. It's not nearly as bad though. It's enough to notice and confuse you but probably liveable.

Since I know people will ask, the engine is NOT surging. Engine is not the issue, just seems like there's too much slop somewhere and it's causing the clutch springs to play ping pong.
 

454cid

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Interesting. I had a Jeep Comanche that I couldn't shift through the lower gears without it bucking... my dad said he had no issue with it, Though. I never did figure it out. Sorry, I can't offer any real help. I haven't had a stick for a long time.
 

shift5

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I can shift them fine without bucking, it's just when I'm driving normally in town holding speed. Giving very little throttle and getting off throttle is the problem. It's totally fine when moderately accelerating or when banging gears.
 

sewlow

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Check all the suspension mounting & pivot points.
These trucks are bad for the U-bolts & the lower plates rusting out. (axle>spring mounts)
-Spring eye bushings, Shackle bolts.
-Pinion/axle bearings.
-Universals.
-Engine/Transmission mounts.
-Lug nuts tight?
Open diff? When was the fluid last changed? Might as well. ...and while you have the cover off, inspect the teeth on the crown & pinion along with the spider gears. Check for any excessive play/slack between the C-n-P. Look at the cross shaft for wear too.
Posi? My condolences. They're called 'Gov-bombs' for a reason.
How many miles on the trans? Probably an NV3500. Input shaft bearing? Big job just to check. Even just a fluid change may help.

Could end up being just a cheap simple fix or a weekend of busted knuckles, cursing & an empty wallet.
 
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JackE

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I had a Subaru that did something like this, it ended up being a crossfire in the distributor cap. New cap and rotor fixed the problem.
 

shift5

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Check all the suspension mounting & pivot points.
These trucks are bad for the U-bolts & the lower plates rusting out. (axle>spring mounts)
-Spring eye bushings, Shackle bolts.
-Pinion/axle bearings.
-Universals.
-Engine/Transmission mounts.
-Lug nuts tight?
Open diff? When was the fluid last changed? Might as well. ...and while you have the cover off, inspect the teeth on the crown & pinion along with the spider gears. Check for any excessive play/slack between the C-n-P. Look at the cross shaft for wear too.
Posi? My condolences. They're called 'Gov-bombs' for a reason.
How many miles on the trans? Probably an NV3500. Input shaft bearing? Big job just to check. Even just a fluid change may help.

Could end up being just a cheap simple fix or a weekend of busted knuckles, cursing & an empty wallet.

-U-bolts & lower plates: Great,will check
-Spring eye bushings, shackle bolts - will check
-Universals - my first guess. Never done this, how do I check them?
-Engine/trans mounts - are those a common thing on these? Owned GMs my whole life and my dad had a few GMT400s over the years and never had a mount issue. I'm sure its possible though, especially on a manual with the additional shocks from gearchanges
-Lug nuts - yes, tight
-Open diff, fluid changed...2 weeks ago :)
-NV3500, 145k miles. Do not have history. I've got a few quarts of Synchromesh in the shop waiting to go in once I get the racecar off the hoist to get the truck on.

I'm gonna be honest here, i'm doing a partial restoration on the truck and have no problem throwing parts at it. This is not my primary car, or my secondary car. I bought it as a toy. My point is, if there's common issues that are easy replacements, I'm happy to just spend the money and do them. Parts for this thing are dirt cheap.

I had a Subaru that did something like this, it ended up being a crossfire in the distributor cap. New cap and rotor fixed the problem.
Cap and rotor are brand new.
 

sewlow

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Grab the driveshaft & twist it back & forth while looking for any play where the stubs of the universal fit into the cups.
 

Ironjet

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I have a 95 that i was/ am experiencing something similar. I changed my coolant temp sensor, MAP sensor and my TPS , and it has cleared up quite a bit, but it’s still there. My next step is to change the fuel filter
Right after I cleaned my k&n air filter I started having this issue , probably coincidence though.
Also , I just finished the 5 speed swap so May have a different issue
 

shift5

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So update to this - i did solve the issue. It was the IAC valve, and i just took it out and gave it a good cleaning with some carb cleaner. I know I said it wasn't engine related, but I was wrong. It wasn't a problem at idle! I guess it was just sticking and interfering when it shouldn't have been. Been driving for a couple months now and absolutely no issue.
 
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