Need help, shudder around 65 after rebuild
 

Hey y'all. I just got my '01 blazer back after having the tranny rebuilt and the intake gasket fixed. It runs good now, but around 65mph with just enough throttle to maintain speed, I notice a shudder in the pedal. I hate to say shudder, but that's the best I can explain it. It's not a hard buck or anything. The guy who rebuilt it seemed reputable, but seemed to take forever getting it done, cooler lines had busted and smoked the clutches. I received the truck with the tranny smoked, so I have no point of reference. I do have a few O2 codes, and I'm sure it could use a good time up.

It's my only vehicle, and I'm dreading bringing it back and having no ride so I'm wondering what y'all think it might be. If it sounds transmission related, I'll bite it and take it back. Also, my oil pressure seems to read low at idle, around 20. Goes to 40 when driving. Front end needs a bit of work as well. I'm a shade tree mechanic at best so I'm just looking for ideas here. TPS came to mind.

Thanks in advance

Could be any of the front end work that you say needs to be done.
Could possibly be the trans.
Could also be tires...inspect them visually and if you want, you could move the tires from front to back and see if it still happens.

Edit: Could probably be any where in the driveline...how are the U-Joints? CV axles?...maybe even transfer case

I haven't had it off the ground to check the front end, thing just rides like a lumber wagon and creaks like hell going down the road. It's only noticeable at that speed, seems to shudder once lightly and repeat every 15 seconds or so. Almost feels like a light shift, my rpms don't change during this.

is torque converter lockup working properly?

I'm not quite sure I understand the "shudder" description correctly...but your rear propeller shaft could be out of phase. Meaning whoever dropped the tranny did not use witness marks to hook the prop shaft back up to the rear differential the way it came off. Out of phase means basically "off balance". The prop shaft should always be hooked back up the way it came off.

shouldn't the drive shaft be balanced on its own?...Like a tire?

Well, no they aren't balanced on their own. Propeller shafts are balanced at the factory using little flat weights. But "Out of phase" means there is like a microscopic balance that is a combination of the propeller shaft with the output shaft of the the tranny, the u-joints and the differential. My assumption is that those parts "wear" together (for lack of a better term) that requires they all be put together the way they came apart. Or, the propeller shaft can be installed "out of phase".

EDIT: Maybe "tuned" would be a better way to look at the propeller shaft being installed "in-phase" as opposed to "balanced". The correct term however is "out of phase" if installed incorrectly.

How exactly do you tell if the torque converter is locking? My "butt dyno" isn't that well in tune to feel it. If it was constantly locking and unlocking wouldn't I have slight rpm spikes on the tach? I'm not sure how to describe it any better, my F150 had a shudder after adding a power programmer, but that was much worse. This just feels as if the tranny shifted, only not nearly as firm and as I said repetitive every 15 seconds or so. If I pull the shaft is there a way to tell where it should be set, a wear point maybe? I'm just a bit paranoid here, I try to avoid shops as much as possible, but automatic transmissions are beyond my skill level and I'd be screwed if I had to dump the same amount into it again.

Edit: I do appreciate the help so far gentlemen, forums like this are what helped me keep my Ford running with as little shop time as possible. I'm glad to be back in a Chevy again, she's damn near flawless interior and exterior wise and I saved her from the scrap yard. Just want her in line and hope she treats me better than my old vehicles have

^^^Looking at this post I don't think we are speaking about the same type of shudder. So I don't think its a driveshaft problem. Take a look at this link https://blazerforum.com/forum/tech-a...ilation-37689/ there might be something there that is helpful. At a minimum you will understand your auto trans better after reading it.