Having a problem with my baby. Been having it all along but it never really bothered me much until I started driving my blazer as my DD. I have an 89 iroc z, 305, 5 speed. 5 speed was replaced with a t-5 worldclass after the previous owner blew the **** out of it, rear was also replaced with a 3.08 posi with drum brakes. Computer/prom was also mucked with by this idiot but then the original was supposedly replaced, so I'm thinking I'm working with the original ECM/prom (as best as i can tell.)

Problem I am having is that in gear, I cannot get to low rpms /speeds without it bucking. In my blazer and in most manual cars I have driven, once you're in gear, especially in like 2nd, you can get down to roughly near idle without it bogging down. May not sound like it's having fun, but theres no jerking back and forth or and it's a smooth drive even if gutless. Can pretty much do this in almost any gear. In my camaro on the other hand, once I get down to low idle in gear the car starts bucking like mad, and I have to press the clutch pedal down and either just for example take my turn then give some gas and let up the clutch or downshift. Happens in almost any gear, even first but I have to be near stopped in first for it to do it.

It's highly annoying, and the way it bucks to me feels like a misfire. Out of gear and with the clutch pedal depressed it runs smoothly and doesn't seem to misfire, and at high speeds runs beautifully.

I'm at a loss of what to check. I cant imagine it's missing because it's in gear vs not in gear....

I have no codes showing as best as I can tell (no SES light at the least), so I r confused. :P

Thanks,
Bez

 

have you checked for play in the driveline? incorrect mesh or excessive play in the axles, ring and pinion, and u joints can cause the driveline to bind and unload at low rpms, which will fool the ecm into thinking it wants to stall and will open the iac, thus creating even more of a buck. also, the springs in the clutch assembly could be worn if they are of cheap quality, and that will cause the same binding/unloading issue. i put a cheap ebay clutch into my geo and it does the same thing you desribed. i just learned to push the clutch in when turning, or just drop down a gear and rev it higher

 

No I have not checked for play in the drive line, but it does totally make sense. I've also learned to just push the clutch in when turning, but it's frustrating compared to my truck. :P

 

Bit of an update of info: Drove around a bit more with it and it seems the jerking back and forth only comes when I put my foot on the gas again. Obviously if I get it too low it starts to buck again as well, but where I've noticed it is the following:

If I'm driving and let my foot off the gas, car slowly decelerates until a point where the gears REALLY start to grab and the car noticeably slows even more. At that point if I just give it more gas again it tends to buck a little. If i'm low RPM on that it really goes crazy.

Mostly happens in 1st 2nd and third, 4th and 5th don't seem to be too prone.

 

sounds more like the springs in the clutch are soft, possibly some difference in driving technique that the car doesnt like either. ive driven a few different manual cars; some will come off idle in second gear without any sort of problems, others will jerk and rock up to about 2k and smooth out. others wont even go anywhere in a gear unless above 3k. it all depends on the car, condition that its in, and driving technique.

 

Hrm, entirely possible. My friend's been telling me "these old cars just do that", but my pops old 70 chevelle didn't do this so it's just frustrating. First 5 speed third gen I've owned, so I have nothing else to really compare it to other than my 01 blazer.

Not too big of a deal just a bit frustrating but it's comforting to hear other people have cars that do that.

 

I have a 91 z28 305 with the world class T-5, and it will do the same thing. I thought it was because the differential fluid was getting low, since there was a slow leak out of the pinion yoke seal. I have since then replaced the dif cover gasket and pinion yoke seal and put new fluid in the differential. It smoothed out quite a bit, but every now and then I will get a pretty decent bucking at around 1100, mainly in second gear. So the only thing I can think of, since the motor is rebuilt, every sensor replaced, and the tranny fluid level checked, is there is excessive play in the rear end. And on that point, does anyone know the difficulty and price involved in rebuilding a rear end?

 

depends on the extent of the rebuild, if it was needed. complete gears, seals, bearings, and consumables, look up to $1000. you could just have it checked for the correct backlash and wear pattern, and have the axles inspected, for about an hour of shop labor. that would give you the info needed as to if the rear is worn out or not

 

Check the EGR. They are an ornery little part that can give you a world of grief!