Pulsing brake pedal

[914jaloppy]

I recently moved my First Gen. Moved it around the house to the side yard where it sat for a month while my moms kitchen got redone....I store it on her carport during Summer months so it looks like someone is there when she goes out(she got robbed in 2006).
It ran and drove fine.
I parked it near an Oak tree. I did some cosmetic work, not a lot, while it sat. Started it a couple times. Everything seemed fine.
Fast forward....I started it, warmed it up and made it back over to the carport.
When I applied the brakes, the pedal pulsed hard.
Only when the pedal is pushed do the brakes seem to pulse. While driving, no pulse.

What gives???
Newer tires. Recently had xfer case repaired(speedo broke). Ran fine after that.
Now this...I swear my deceased father is behind this..it was his truck!

Any replies will be appreciated!
Heidi

 

[Anime]

If by "pulsing" you mean it made an electronic noise and pushed back, that's the rear ABS activating. That can happen if you push the pedal hard enough, even just when backing up a bit.

If the pedal pulses every time the brake pedal is pushed, no matter how lightly, or how hard or soft the braking action is at any speed, then it might be an issue with the rear ABS sensor, which is located on the top center of the rear axle, on the differential.

There are other things that can cause ABS issues, including the ABS pump and the electronic controls, but the sensor is relatively inexpensive and easy to replace so that's usually the thing to check before either trying an expensive repair or disabling the ABS entirely.

You may also want to have the rear drum brakes and hardware all inspected to be sure they are working correctly, if not, the rear wheels can move more than they should when braking, which will make the ABS think the wheels are slipping and so activate and pulse the pedal during braking action.

 

[914jaloppy]

Thanks Anime.

I actually have the ABS sensor in a box rolling around under the rear seat...seems its been flashing on and off for some time,, maybe it just finally gave up. Rear Hardware was replaced in 2012, along with all the brakes lines from the back of the shields to the master cylinder.....
So, I'll start with that, should be easy--as long as I don't have to use a blow torch!

I'll keep you posted....thanks.

 

[92exp4x4]

My 92 sport does the same thing. I think its rust on the drums or rotors. It started doing it after the truck sat for about 9 months and was never moved. Since I have driven it maybe 100 miles. It still does it. I just havnt had time to pull the wheels off yet to find out for sure.

 

[gmanpaint]

Heads up... 94 has front & rear ABS. HCU (pump) has the rear brake pressure valve inside it. If this valve is stuck, it would think the rear brakes are locked up.

Other things to look into:

Front sensors are in the knuckles next to the spindle and the sensor head is visible behind the rotors.

There could be debris on them from sitting for so long. Animals could have been chewing on the sensor wires. The system could be blocked with junk in it somewhere. Rear pads could be froze on one side locking a wheel just enough to trigger the ABS pump. E-brakes can be a cause with either a bad cable, bad cable hanger, bad cable connection, bad shoes or broken springs.

I would check all the mechanical brake components front to back. Repair anything broken or out of place, then do a complete system fluid flush. If the problem still happens, consider the HCU for problems.

 

[WatchThis!!]

My 01 ST started with this same sort of problem not too long ago. I've had the brakes inspected and all(rotors, pads, drums, shoes) look fine; fluid was contaminated so I had it bled and filled but every now and then my wife(she does the driving) says it still feels like the pedal is pulsing back towards her foot and you can feel a grip/release. It only happens at low speeds when we're almost stopped. I was thinking the contaminated fluid might have done something inside the lines themselves, my wife thinks it's something with the pedal.
The parking brake has lost some of its spring when it's released; not sure if that has anything to do with it.
Any suggestion would be appreciated.

 

[2stroke]

I'm not exactly sure how much driving you did since 2006, but if its been just across the yard, its very possible the brake drums or the front rotors rusted, and are now uneven. Jack up the front and rear and spin the tires. If you hear an uneven swoosh swoosh swoosh as the tire spins, the rotor/drum is bad. The spring to release the e brake is inside the brake drum. Make sure you lube up the cable leading to it, and if you replace the drums, get new shoes, and the parts kit. If its not that, it would almost have to be something with the ABS. You can disable the ABS and see if that helps.