Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 20 of 236 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
feeling of being bumped when stopped

has anyone ever experience the feeling of being bumped from behind only to look in your review mirror and no one hit you? occasionally when at a stop sign/light i get a jolt like someone bumped my vehicle from behind which of course didn't happen ...any ideas why??/


Lisa
 

·
Registered
Joined
·
12 Posts
Discussion Starter #3
lol....yessssssssss, and i just realized I posted on the trailBlazer instead of the Envoy to make matters worse. But I am serious about the question it really does happen.:(
 

·
Registered
2003 gmc envoy_sle
Joined
·
1,504 Posts
March said:
has anyone ever experience the feeling of being bumped from behind only to look in your review mirror and no one hit you? occasionally when at a stop sign/light i get a jolt like someone bumped my vehicle from behind which of course didn't happen ...any ideas why??/
Actually it did happen to me i think twice. My wife thought somebody hit us from behind. It happened right after stopping about a second later. It's kinda strange and I have no idea what must have caused it.:confused:
 

·
Registered
Joined
·
72 Posts
Yes, everytime I stop a little hard I feel that small bump right after the TB stops. Maybe something with the breaks? (I hope not)

-Gaspar
 

·
Registered
Joined
·
12 Posts
Discussion Starter #6
i just had the envoy in because of 4w drive problems and they replaced the transfer switch. When I picked it up the cashier asked if they took care of the bump.....I assumed they did so she asked the service guy and he said with a confused face "oh ya that was related to the 4w drive problem" I really think he forgot to look at it and was passing if off as part of the problem with the switch. The bump happen again tonight so they didn't fix it.

Lisa

ps thats what the hubby said maybe the breaks.
 

·
Registered
Joined
·
3,390 Posts
Moved to the correct forum.
 

·
Registered
Joined
·
2,024 Posts
I havent been under my 2005 TB much yet, but a driveline thump or bump upon a stop or take-off on a 4x4/AWD is usually a dry slip yoke on the font or rear driveshaft. The driveshafts need to 'telescope' in/out to absorb chassis/drivetrain movement. A nice layer of (thick/sticky) grease in the 'telescoping' slip yoke is needed. If it drys up, the movement becomes abrubt and jerky, giving the *bump* feeling. Not sure if the envoy has grease fittings or not on the driveshafts (look for rubber boots on the driveshafts), but most require the driveshafts to be dropped, boot clamps cut, driveshaft serperated, splines cleaned, regreased and the hole thing reassembled and reinstalled with new boot clamps. The driveshafts are typically flanged & bolted at both ends for easy removal. You also need to mark the driveshaft halves anytime you seperate it @ the splines so you reassemble it the same way for proper balancing. Slip yokes are one of those 4x4 maintenance items that never seem to get listed anywhere.:duh:

G/luck
Joel
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
5,267 Posts
Ive also experienced a small bump- under 2 scanarios...
1- I have slowed down suddenly and right before I stop completely, i feel a light bump/jerk, and I attribute that to the driveshaft/gears "letting go" is the best I can describe it... or shifting into the lowest gear........
Ive felt it in my 70 Monte carlo too... so thats what I think my case is....
the other case is when im on a road or highway and my side of the road or lane has come to a stop and the opposite side of the road has vehicles traveling at fast speeds... as a vehicle drives by it creates a wave of air or a small vacuum and I can feel the trailblazer move... sometimes its enough movement that I think the vehicle behind me has tapped my bumper.. and I look and the car is at a safe distance behind me.
Semis will cause this if im slowly moving. trucks, suvs cause it more, and some passenger cars will do it also if theyre traveling fast enough in the opposite lane....
But i feel this alsmost everyday when im stuck in traffic in Loas Angeles in morning rush hour and im in the carpool lane and the oopsite side of the freeway has a car zoom by at 75 mph... , i can feel the TB really move.
 

·
Registered
Joined
·
108 Posts
i had the same prob. and every few times it did it the oil pressure gage would drop and the driver info display said oil pressure low. apparently my truck was leaking oil, and enough to make a noticable difference. moreover, when you come to a stop, the pressure drops (which is normal), but if your low on oil, the pressure gets too low, and the engine begins to stall. mine died on me several times after this happend. pay attention to if your truck is leaking oil. at first the dealer couldn't find a problem, then i noticed it leaking oil and took it in for that, and they had to put die in my oil to find my leak. once the leak was fixed, no more problems since
 

·
Registered
2003 chevy trailblazer_lt
Joined
·
92 Posts
Bump

I have experience this when starting from a stop. The first time it happened I almost got out to see if there was any damage... I think this has to do with the rear brakes releasing. They appear to let go after the front and it gives you the bumping sensation.
 

·
Registered
2005 gmc envoy_denali
Joined
·
9,380 Posts
March said:
has anyone ever experience the feeling of being bumped from behind only to look in your review mirror and no one hit you? occasionally when at a stop sign/light i get a jolt like someone bumped my vehicle from behind which of course didn't happen ...any ideas why??/


Lisa
Do you by any chance have the rear air suspension on your Envoy?
 

·
Registered
Joined
·
2,024 Posts
So much for the dry driveshaft slip-yolk idea (that was the cause on isuzu rodeos & my old chevy truck). It looks like TB's dont even have them.:duh: I got a good look underneath my 2005 LS 4x4 to notice this. The only unfamiliar thing I noticed was a funky flex coupling type thing at the transfer case end of the front driveshaft? :confused: Never saw anything like it. Instead of a slip-yolk and u-joint at that end, there's only cylinder/barrel shaped coupling thingy on the xfer case end?! What the heck do u call them?

Thanks
Joel
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
MTPockets said:
The only unfamiliar thing I noticed was a funky flex coupling type thing at the transfer case end of the front driveshaft?
CV (Constant Velocity) joint. Less rotationally erratic than U-joints.

 

·
Registered
Joined
·
2,024 Posts
the roadie said:
CV (Constant Velocity) joint. Less rotationally erratic than U-joints.
Cool pic! :hail: The joint I'm referring to is at the transfer case output, on the drivshaft that goes to the front diff. It's got a metallic collar on it. Also wassup with the ball joints? They look like they are integral with that cast steering knuckle?

Joel
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
MTPockets said:
Cool pic! :hail: The joint I'm referring to is at the transfer case output, on the drivshaft that goes to the front diff. It's got a metallic collar on it. Also wassup with the ball joints? They look like they are integral with that cast steering knuckle?
Sorry.:eek: I should have figured you knew what front driveshaft CV joints were. The manual calls the shaft from the transfer case to the front differential a prop shaft.

Anyway, that's an excellent question. The shop manual, page 4-5 calls out the front u-joint spider assembly and the shaft itself, but is silent on the function of the collared item. No cross section or replacable parts shown.

On page 4-17, the theory of operation says the front prop shaft consists of a shaft tube, u-joint, flange yoke, and a CV joint. So I'd guess the mystery collar is hiding a CV joint. Why, I don't know.

The manual has a LOT more details about how the CV joints in the front drive shafts can be rebuilt, with many drawings. But the front prop shaft is not documented 1/10 as well.

Oh, and the ball joints? The upper control arm has what they call a pinch bolt and nut that clamps the top end of the upper ball joint. Once you remove the pinch bolt, you can pry the upper control arm up off the cast steering knuckle. The ball joint is retained by a circlip that's normally hidden since it's between the control arm and the steering knuckle. Once the circlip is off, you can press out the ball joint.

The lower ball joint is retained by a flared flange! You have to chisel off the old one before you press out the old joint, and the installation instructions refer to a special GM flare tool. The designers of this suspension were especially evil.
 

·
Registered
Joined
·
2,024 Posts
Great info roadie. Thanks. That does make sense that the item on the front prop shaft is a type of CV joint as something has got to have some 'give' in this system (move axially). The rear prop shaft appears solid (not allowed to move axially) which seems very odd for a 4x4. Man... I would never have figured out the circlip/flange thing for the upper/lower BJ's!! I thought the 3 rivet deal on the older GM's was very rude of the suspension designers.:hissy:

Joel
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
MTPockets said:
The rear prop shaft appears solid (not allowed to move axially) which seems very odd for a 4x4.
The shaft is solid, but there is a traditional slip spline section where it connects to the transfer case. The transfer case rear output has a longish "snout" to accommodate the slip spline, and the seal is at the rearmost part of the snout, so you can pry it out with a screwdriver when the prop shaft is removed.

The front prop shaft out of the transfer case doesn't need a dynamic slip spline because the geometry is fixed. The transfer case is hard bolted to the rear of the transmission, and the front differential is bolted to the oil pan, so there's no relative motion for the shaft to accommodate.

If somebody ever does a SAS (solid axle swap), the front prop shaft would have to have some slip spline section and much more serious joints. Maybe in 5-6 years when my daily driver might be a full electric vehicle, I can take the Envoy down for a few months and put in a pair of Dana 60's. :rotfl:
 

·
Registered
Joined
·
154 Posts
driveshaft slip-yolk

Both my 96 and 2000 Tahoes did the same thing here in Florida. When they got real dry. it would clunk almost every time you took off from a stop. Sitting in traffic after a hard stop the thing would let go with a bump and a clunk.
Grease'er up and that will go away.
 

·
Registered
2005 gmc envoy_denali
Joined
·
9,380 Posts
CopyGuard said:
Both my 96 and 2000 Tahoes did the same thing here in Florida. When they got real dry. it would clunk almost every time you took off from a stop. Sitting in traffic after a hard stop the thing would let go with a bump and a clunk.
Grease'er up and that will go away.
Your bump different than thread starter. Origional poster stated felt a bump while sitting still.
 
1 - 20 of 236 Posts
Top