[Murf]

No, not like that! ��

Some of you may remember me posting questions about carb & ignition tuning, as I was having low speed drivability issues. The car was tugging & bucking, kinda like it was in too high of gear for the speed of the car. I’ve done a lot of messing with carb and timing adjustments to no avail.

I decided to see if it could be driveline related. One shop told me, “ there’s no way you can tell, unless you check backlash with a dial indicator. Which I don’t have & they weren’t interested in checking it out for me. Anyway I slid under it & tried to check it out. Looks excessive to me but I don’t know anything anyway. Gonna try & post a video. Please tell me what you think.

[Murf]

Of course, it won’t let me attach the video. I’ll keep working on it.

It’pretty hard to get a measurement but it moves about 5/32-1/4 inch at the chalk mark. I also have a clunk when backing out of a diagonal parking space when I start to go forward. The steering wheel is always turned slightly left so I had been looking at the front suspension. Could the rear be clunking? Maybe I’m grasping at the straws?

[Half-Inch Stud]

Get some side shims to move the Diff and ring gear closer to the pinion. And a new cover gasket.

[steve25]

While that is the not the best I have had a bad U joint cause exactly what your talking about .
Amazingly the joint did not feel too bad with the wheels on the ground when just rocking the driveshaft back n forth, but when I dropped it down I could not believe it just had not ripped out on me .

There where no needle bearings left in one cap.

It was making a noise at speeds below 25 though.

[mysticmissle]

Probably can just shuffle what you have from side to side to
Make
It right

[Gach]

Looking at that picture That U-joint cap is pretty beat up, that could be causing your caulking noise. More then the play your seeing. Either way that’s not gonna stop your lugging issue. Which more then likely is a timing issue either timing Advance isn’t working so its not getting the timing it needs, its real hard to tell unless your there in person to check every thing out.

[Gach]

One thing you can do it put a timing light on it and see if its advancing bring motor up to about 2500 watching see what timing is doing. Making sure its not advancing past that point. See if timing mark is Bouncing all over the place. From what your saying definitely sounds like a timing issue. But you can at least illuminate that possibility.

[Sirrotica]

Seeing the picture, it's a lot of play, but unless someone has been in the axle, and set it up wrong, there is likely something worn out, bearings or gears would be my guess. Plenty of reasons to get excessive backlash other than not shimming the ring gear deep enough. This may, or may not, be the noise you're experiencing at low speeds.

No matter, excessive backlash isn't going to cause any problems that translate into poor drivability. If you don't have the necessary tools to set up a rear axle, I would suggest farming the operation out to someone that does, and is totally familiar with setting up rear axles.

Pontiac cars have always been geared really low numerically to get decent fuel mileage (2.41, 2.56, 2.73) ratios are fairly common, so unless you have a fairly radical cam in your engine, the rear axle ratio isn't something that's a consideration in a drivability problem at low engine speeds. Most engines can pull smoothly under 1500 RPM without bucking, and jerking.

Thing is no one here that can lay hands on your car, so trying to do internet diagnostics is just shooting in the dark, basically guessing. In the past people have posted videos of noises here, but just hearing the noise on a video isn't going to help much without actually hearing it in person, then trying to find where it actually is originating (stethoscope, long rod, hose held to the ear). Much easier to do diagnostics where the car is.

Hopefully you can find someone locally that can give you a hand sorting all this out.

[steve25]

And don’t rule out a bad motor or tranny mount.

[Murf]

Thanks everybody.
I have checked the ignition timing repeatedly and to the best I can tell it is functioning properly.

I have checked motor mounts, transmission mounts and crossmember mounts. They all seem OK

The u-joint is not “beat up”. I’m unsure what you’re seeing.

To try & clear up what the issue is. It’s not “noise”. There are no noises at anytime. Car is smooth on the highway always & around town mostly.

At very light throttle , like slowing down & turning a corner without downshifting. The car will tug / buck for lack of a better description.
It’s about 9.25 to 1 , 230-236 cam, Quadrajet built by Quadrajet Power in Texas. DUI hei. 4 speed, 3:08 gear with 27 inch tall tires.
Car runs very smooth everywhere except low speed around town.
It wii tug at 20 mph steady state in 2nd gear.
Maybe I’m expecting too much but I kinda thought this combo would pull like diesel down low.

I guess I was kinda hoping the pat in the driveline might cause the tugging/ bucking sensation. I’m getting frustrated trying to figure it out.

Thanks for all the help!
Murf

[Gach]

Maybe its the quality of picture looks like has marks on it. You would know better picture vs seeing in person. My opinion being it’s a 4 speed and kind of doing it in second gear I’d say its the 308 gear. Probably not a big deal tho

[Murf]

Yeah, I know what you’re saying. I don’t have a tach in the car. I think I’m gonna try & rig up my diagnostic tach and get some idea of where the engine is at when it happens.

Thanks again for trying to help me out!
Murf

[steve25]

What do you have for a carb?
Does this condition only take place just above idle?

If so then the throttle blade idle setting may wrong in relation to the transition slots in the throttle plate .
This then makes for a lean stumble.

[Murf]

Steve, it’s a Quadrajet setup by Quadrajet Power. I sent it to them over the winter to see if they could find a problem. They did not.

Thanks for advice. I’m going to try & see if I can better identify what it’s do in my.

Thanks again!
Murf

[geeteeohguy]

Originally Posted by Gach

Maybe its the quality of picture looks like has marks on it. You would know better picture vs seeing in person. My opinion being it’s a 4 speed and kind of doing it in second gear I’d say its the 308 gear. Probably not a big deal tho

To me, the cap looks hammered and tapered and generally beat on as well. Not smooth sided like it should be. Could be an illusion.

[Schurkey]

Originally Posted by Murf

Thanks everybody.
I have checked the ignition timing repeatedly and to the best I can tell it is functioning properly.

Originally Posted by Murf

At very light throttle , like slowing down & turning a corner without downshifting. The car will tug / buck for lack of a better description...
...It wii tug at 20 mph steady state in 2nd gear.
Maybe I’m expecting too much but I kinda thought this combo would pull like diesel down low.

My first guess is too much (vacuum?) advance.
Second guess is too-lean fuel mix at idle/off-idle.

Distant third guess would be driveline lash. I have a motorcycle that has too damn much driveline lash, smooth operation at low speed is difficult, made worse by middle-'80s lean carb tuning at idle and low-speed.

Yeah, that differential has too much play, but it's impossible to know if that's from excess ring 'n' pinion backlash, or excess spider/side-gear backlash, or excess axle-spline to side-gear spline backlash, or worn bearings. Gonna have to come apart--or just be ignored.

I put a Truetrac differential into my '97 K2500. Backlash spec for ring 'n' pinion is .003--.012, .005--.008 preferred. Actual backlash was .013--.014 depending on where the ring gear was turned.

Bearing preload is two notches on the right-side adjuster collar for used bearings; actual was "zero" preload. The old differential worked fine--no noise, no problems, no unusual wear. I put it together with new bearings, same ring gear, same slightly-too-much backlash so I didn't change the wear pattern on the ring and pinion--but I did put proper bearing preload on the new bearings.

[gtospieg]

Just curious...have you ever messed with the advance springs in the distributor? If they are too light the vacuum advance could be overpowering the springs at low speed and cause a similar issue.

[Schurkey]

Originally Posted by gtospieg

Just curious...have you ever messed with the advance springs in the distributor? If they are too light the CENTRIFUGAL advance could be overpowering the springs at low speed and cause a similar issue.

FIFY.

[rohrt]

I wonder if the crush sleeve didn't get torqued properly.

[Formulas]

Does this happen in slow speed turns only? Or also in a dead straight line?

If turns only you could be feeling the posi working