Thunk
- Thread starter Hermit
- Start date
I don't think the lurching and thunking is a transmission problem since you say you have to down shift into 2nd going up a hill. Sounds more like the engine isn't making enough power. Did this happen all of a sudden or has it been getting slowly worse over time? Has the check engine light come on? .......Could be a lot of things. Clogged fuel filter, bad wires, fouled spark plug, vacuum leak etc.
It started happening recently, Max. After I drove up a hill that became very steep around the last few miles ..... but it didn't happen then, the trouble started the next day.
The spark plugs were changed out last year, and the engine has been quite strong in the lower gears ... I have to be careful about not going too fast from a stoplight.
Maybe the vacuum thing? .... don't know much about engine matters, but I did notice a distinct hesitation today before the thunk.
I've been adding engine cleaners to the gas, but with no effect.
The spark plugs were changed out last year, and the engine has been quite strong in the lower gears ... I have to be careful about not going too fast from a stoplight.
Maybe the vacuum thing? .... don't know much about engine matters, but I did notice a distinct hesitation today before the thunk.
I've been adding engine cleaners to the gas, but with no effect.
I had a similar problem with a buick -it was tuned up about a year or so ago but was losing power and just not acting right. Turned out one spark plug had built up a carbon bridge right across the electrode. I would start with the basics -plugs, wires, fuel filter, check air filter, look over the vacuum lines (make sure none came loose or are broken), check for loose or broken wires where the sensors plug in. Once you do these things if you still have the problem you at least will know for sure what is not causing the problem and can proceed from their. Also stop buy an auto zone or advance store and see if they can pull any trouble codes from the engine control module(ecm)l
I was thinking the same thing but he says he has to down shift going up a hill plus no complaint of clunking going from drive to reverse. But their could be a lot of things causing this problem
Not too clunky just now going in reverse and forward a few times.
Plenty of pickup except for the moment of hesitation before the thunk in third gear. Didn't have any problem when I floored it for a short time on a slight incline a few minutes ago, when it stayed in first and second. Not even any hesitation.
I don't have the tools or knowledge to fix this myself, but I wanted to get an idea of whether or not it was the transmission, which I'd definitely have to start saving my pennies for.
Plenty of pickup except for the moment of hesitation before the thunk in third gear. Didn't have any problem when I floored it for a short time on a slight incline a few minutes ago, when it stayed in first and second. Not even any hesitation.
I don't have the tools or knowledge to fix this myself, but I wanted to get an idea of whether or not it was the transmission, which I'd definitely have to start saving my pennies for.
If you have good strong power from first to second then clunk into third you may very well have a transmission problem. I always try everything I can before messing with the transmission. You should still check the vacuum lines and look for broken wiring. Jack up the car (use a safety stand and the jack) and crawl under and make sure everything connected to the transmission is secure. Is the transmission fluid red or is it brown and smell burned. Brown and burned is bad.
Mechanic
Inactive
I'm leaning towards the tranny. Fluid gone bad, internal flow messed up from dirt. I'd try changing the fluid and the tranny filter. Probably wouldn't hurt to do it anyway. 
Just to defer the suspicion of it being a u-joint, you would hear major clunking anytime there was a shift of gears.
Just to defer the suspicion of it being a u-joint, you would hear major clunking anytime there was a shift of gears.
2-3 months ago I did a T Tech transmission fluid exchange http://www.aatecusa.com/cloreautomotive/t-tech.htm
That doesn't change the filter though, just the fluid. Supposedly almost 100% of the fluid. Which was extremely dark after coming out (I didn't think to sniff it).
That doesn't change the filter though, just the fluid. Supposedly almost 100% of the fluid. Which was extremely dark after coming out (I didn't think to sniff it).
tech
Veteran Member
Don't forget that the coil, plugs, wires, dist cap and rotor all are subject to higher electrical loads when accelerating and could be the cause...lower gears may not put enough strain on the system to create the "thunk"
Worth checking out, and may not necessarily set any codes - depends on how often & how long it acts up.
Fuel pressure is critical on GM V8s also. below 9psi (TBI) or less than 50psi (PFI) and you can have drivability issues. A restricted filter, a weak pump, or the short length of hose inside the tank leaking are most common, followed (WAYYY back) by a bad pressure regulator.
Worth checking out, and may not necessarily set any codes - depends on how often & how long it acts up.
Fuel pressure is critical on GM V8s also. below 9psi (TBI) or less than 50psi (PFI) and you can have drivability issues. A restricted filter, a weak pump, or the short length of hose inside the tank leaking are most common, followed (WAYYY back) by a bad pressure regulator.