Brakes locking up after driving a few minutes

screech · 07-12-2009, 01:29 PM

So I got a 86 4runner a few weeks ago. I was driving it around the neighborhood today and the brakes locked up after a few minutes of driving.
I searched and found a few people that say the brake lines internally failed. So I had the brakes lock up again and cracked the lines, fluid was coming out of the flex lines so I know it couldnt be that.
I replaced the vaccum booster a few days ago and that is when I noticed the trouble began. I lined up the brake pedal rod with the previous booster so it shouldnt be the rod length.
master cylinder was replaced last year, so it shouldnt be the master cylinder. replaced the front pads....
anyone have a suggestion as to what I should do next?
should I swap back in the old vaccum booster? reason why I changed it was because the pedal would fall nearly to the floor but have pressure half way down.
I also rebuilt the calipers because one piston was leaking when I swapped pads.
Seriously stumped.... and I am ASE certified in brakes!!! so I feel like a total tard.

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screech · 07-12-2009, 01:33 PM

One more thing- they locked up yesterday. When I tried it today fully cold they were working fine.

Justinvd · 07-12-2009, 01:47 PM

The brake lines swell and create a kinda 1 way valve. They let brake fluid go to the caliper but not back. Another thing ive seen cause brake lock up was the push rod coming out of the booster not being in correct spot. It was kinda off to the side and it created the same problem. Wouldnt release all the way. Hopefully someone who knows more about brakes chimes in.

854x4 · 07-12-2009, 01:50 PM

Which brakes are locking up the front or back? Also which side left or right or both? Does it just happen or does it happen when you press the brake.

screech · 07-12-2009, 01:57 PM

The front brakes lock up. Going back out in a second to jack up the truck see what side.
was both yesterday though. Its the front though that is definatley locking up.

854x4 · 07-12-2009, 02:02 PM

Does it only do it when you touch the brakes or does it do it for no reason?

screech · 07-12-2009, 02:37 PM

only does it after a few good test drives. Went back outside... it started pouring, but got the booster loose, and only put the nuts in a little bit to compensate for a mal adjusted booster. I think its my booster internally leaking because it wants to stall on me whenever the brakes are applied. but no locking brakes at this moment, to wet to get the brake fluid up to temp right now.

854x4 · 07-12-2009, 02:51 PM

Did you replace the booster with a new or used one?

screech · 07-12-2009, 03:18 PM

replaced it with a used one. 30 day warranty.

Justinlhc · 07-12-2009, 03:40 PM

Ummm....master cylinder. Had the same problem. Barely made it home one day, had the front brakes smokin hot. Replaced the master cylinder and haven't had a problem since.

854x4 · 07-12-2009, 03:40 PM

If you didnt have any problems with the brakes before you switched the booster then I'm going to say its the booster, it could be bad or misadjusted. If both front brakes are locking up then its probably not the front lines unless both of them are bad. I dont think one bad line will cause both brakes to lock up. Could also be the master cylinder but make sure you have the booster adjusted before you switch that.

Flash319 · 07-13-2009, 04:55 PM

I had the same problem. Was the Master not leaking back to the reservoir causing the bouncing of the pads to pump up the lines. I would go about 3 miles and wow.....

Easy test, just pull the line for the fronts off the master and the oil should just keep dripping out. If not then it is NG.

Kiroshu · 07-13-2009, 04:59 PM

Your problem with brake lock up is 95% chance faulty master cylinder replace it. If your engine dies down when you hit the brakes at all your booster is leaking and or the vac line going to the booster is leaking, and also needs replaced with a new one or a reman.

screech · 07-14-2009, 03:14 PM

So it ended up being the push rod adjustment. actually the entire push rod, and diaphram. I pulled the booster, and the pushrod fell out. tried lining it back up see if could get it back in place for fun. Didnt happen actually the seal in the front was split. I put the old booster in and worked perfect.
thanks for input everyone, I appreciate it.

07-12-2009, 01:33 PM	#2 (permalink)
screech Registered User Join Date: Jan 2009 Location: Hampton Roads, VA Posts: 58	One more thing- they locked up yesterday. When I tried it today fully cold they were working fine. __________________ evo, turbo 4runner, f150, cobra, n/a 4runner, 69 stang. "I am not a slacker, I am a deligater."

07-12-2009, 01:47 PM	#3 (permalink)
Justinvd Registered User Join Date: Oct 2007 Location: B.C Posts: 737	The brake lines swell and create a kinda 1 way valve. They let brake fluid go to the caliper but not back. Another thing ive seen cause brake lock up was the push rod coming out of the booster not being in correct spot. It was kinda off to the side and it created the same problem. Wouldnt release all the way. Hopefully someone who knows more about brakes chimes in. __________________ 1988 4runner- 22R-E 1986 P/U 22R-E T urning O ver after Y ears O f T rail A buse

07-12-2009, 01:57 PM	#5 (permalink)
screech Registered User Join Date: Jan 2009 Location: Hampton Roads, VA Posts: 58	The front brakes lock up. Going back out in a second to jack up the truck see what side. was both yesterday though. Its the front though that is definatley locking up. __________________ evo, turbo 4runner, f150, cobra, n/a 4runner, 69 stang. "I am not a slacker, I am a deligater."

07-12-2009, 02:37 PM	#7 (permalink)
screech Registered User Join Date: Jan 2009 Location: Hampton Roads, VA Posts: 58	only does it after a few good test drives. Went back outside... it started pouring, but got the booster loose, and only put the nuts in a little bit to compensate for a mal adjusted booster. I think its my booster internally leaking because it wants to stall on me whenever the brakes are applied. but no locking brakes at this moment, to wet to get the brake fluid up to temp right now. __________________ evo, turbo 4runner, f150, cobra, n/a 4runner, 69 stang. "I am not a slacker, I am a deligater."

07-12-2009, 03:18 PM	#9 (permalink)
screech Registered User Join Date: Jan 2009 Location: Hampton Roads, VA Posts: 58	replaced it with a used one. 30 day warranty. __________________ evo, turbo 4runner, f150, cobra, n/a 4runner, 69 stang. "I am not a slacker, I am a deligater."

07-12-2009, 01:50 PM	#4 (permalink)
854x4 Registered User Join Date: Jul 2004 Posts: 197	Which brakes are locking up the front or back? Also which side left or right or both? Does it just happen or does it happen when you press the brake.

07-12-2009, 02:02 PM	#6 (permalink)
854x4 Registered User Join Date: Jul 2004 Posts: 197	Does it only do it when you touch the brakes or does it do it for no reason?

07-12-2009, 02:51 PM	#8 (permalink)
854x4 Registered User Join Date: Jul 2004 Posts: 197	Did you replace the booster with a new or used one?

07-12-2009, 03:40 PM	#10 (permalink)
Justinlhc Registered User Join Date: Feb 2009 Posts: 646	Ummm....master cylinder. Had the same problem. Barely made it home one day, had the front brakes smokin hot. Replaced the master cylinder and haven't had a problem since. __________________ 1993 4Runner SR5 3.oh 5speed 232k+ miles. Mostly for the trails and beach. Mods so far: Thorley headers, 4.30 gears, Rancho 5way shocks, AISIN hubs, LockRight rear locker, no sway bars.....32x11.50 BFG M/T's on 15x8 Cragar Soft8's.

07-12-2009, 03:40 PM	#11 (permalink)
854x4 Registered User Join Date: Jul 2004 Posts: 197	If you didnt have any problems with the brakes before you switched the booster then I'm going to say its the booster, it could be bad or misadjusted. If both front brakes are locking up then its probably not the front lines unless both of them are bad. I dont think one bad line will cause both brakes to lock up. Could also be the master cylinder but make sure you have the booster adjusted before you switch that.

07-13-2009, 04:55 PM	#12 (permalink)
Flash319 Registered User Join Date: Feb 2006 Location: Barrie, Ontario CANADA Posts: 1,356	I had the same problem. Was the Master not leaking back to the reservoir causing the bouncing of the pads to pump up the lines. I would go about 3 miles and wow..... Easy test, just pull the line for the fronts off the master and the oil should just keep dripping out. If not then it is NG. __________________ BRAKE LINE NUTS $1 each !!!!!!!(min 10) PLASTIC COATED BRAKE LINE $1.50/foot Coated Front brake lines with nuts $10 each 95 22re extra cab, custom box, 4:56, 31inch tires, electric fan, Flat black paint, 4 runner buckets and mirrors WANTED: aussie or lockright in CANADA!!!

07-13-2009, 04:59 PM	#13 (permalink)
Kiroshu Registered User Join Date: Oct 2007 Location: wade, NC Posts: 1,342	Your problem with brake lock up is 95% chance faulty master cylinder replace it. If your engine dies down when you hit the brakes at all your booster is leaking and or the vac line going to the booster is leaking, and also needs replaced with a new one or a reman. __________________ My current: 1986 Toyota 4runner SR5 EFI 4cyl 2.4L 22RE 5-Speed 242,000 Miles 95% Stock __________________ (Still working on restoring her) My old: 1988 Toyota 4runner SR5 EFI V6 3.0L 3VZ-E 5-Speed 302,000 Miles All stock (sold)______________ (Was my fastest truck i miss her...) My old: 1989 Toyota 4runner Non-SR5 EFI 4cyl 2.4L 22RE Automatic 231,000 Miles (sold)______________ (was my quietest and slowest yota.)

07-14-2009, 03:14 PM	#14 (permalink)
screech Registered User Join Date: Jan 2009 Location: Hampton Roads, VA Posts: 58	So it ended up being the push rod adjustment. actually the entire push rod, and diaphram. I pulled the booster, and the pushrod fell out. tried lining it back up see if could get it back in place for fun. Didnt happen actually the seal in the front was split. I put the old booster in and worked perfect. thanks for input everyone, I appreciate it. __________________ evo, turbo 4runner, f150, cobra, n/a 4runner, 69 stang. "I am not a slacker, I am a deligater."

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