"Jolting" feeling while braking?

Question

2004 GMC Seirra pickup.
Sometimes while I am braking and turning at the same time, there is this wierd jumping feeling, it almost feels exsactly like if I had something very heavy in my truck bed, and it slid forward and banged against the back of the cab, or the back wheels bounced off the ground sideways (I know they didnt). It only happens if I have been driving at highway speeds, and I slow down a little faster than average. Not slamming on my brakes but just a quicker stop like if your about to miss a turn or something. Any ideas?

Answer 1

This is a late tranny lock-up solenoid disengaging. What I mean by late is this:

1. When driving, your tranny will eventually go into "Over Drive" and this means an electric solenoid has engage the torque convertor so that your engine to tranny ratio is 1:1. For every one turn of the crankshaft the transmission turns once, too.

2. When you take your foot off the gas, suddenly, the Over Drive is still engaged until you slow down to between 30-40 MPH.

3. If you tap the brake when you take your foot off the gas, this will open the switch to disengage the Over Drive electric solenoid inside the tranny. This allows a smoother stop than if you take your foot off and hit the brakes suddenly. The jerking for that split second is the tranny trying to slow the engine down with which it is engaged with at a 1:1 ratio and it can't down-shift normally until the electric Over Drive solenoid disengages.

So, hope this helps. Not much to worry about. I notice this in my old '85 Chevy with the old TH-350 lock-up torque convertor. It's just not that often you are doing everything a particular way at the same speeds. When I tap the brake right away I drop into 3rd gear without the torque convertor "locked" at a 1:1 ratio with the engine and there's no noticeable "jolt".

You might have them check out the vacuum switch that makes this happen faster so you don't notice it. My switch died a few years ago so the guy at the tranny shop showed me that I can just run a tiny piece of copper wire across the contacts so I get my Over Dirve and 15 miles per gallon.

Good Luck!

Answer 2

It's probably you rear ABS malfunctioning or your truck was not loaded and the rear ABS was activated when pressed the brakes hard.

Answer 3

sounds like a possible propotioning problem

like your rear brakes are not working

and all the load is going on the fronts...

if you have rear drums make sure they are adjusted properly

Paul

Answer 4

turn rotors gm had problem with rears