Pirate 4x4 banner

Really Odd Brakes

904 views 7 replies 8 participants last post by  Bob Garrett 
#1 · (Edited)
Okay, so here's the deal. I'll be driving around, come up to say, a yellow light, push in the clutch and casually apply the brakes. Nothing extreme, just touch the brake pedal. Rear wheels lock up completly. If I leave the clutch engaged, you can feel the truck brake HARD, but won't lock up since I have a lockright in the back.

On quick inspection, it could be the LSPV since I have the arm tied up to max.

BUT, this only happens every so often. Especially when it rains. Must be the moisture.

It rained this morning and dried up during the day and was able to lock up my rear wheels on dry pavement. Pretty impressive for some crappy drum brakes to lock up 35s. I literally pushed the brake pedal in like half an inch. As soon as I felt and heard the wheels lock up a let off and touched the pedal and locked up again. Basically, as soon as the pedal got through the freeplay, the wheels locked up.


My truck: 1983 Pickup, with 35x12.50 tires and a rear Lockright.

My brake system consists of:
1" master off a 4runner
Stock 83 booster (brakes are harder to apply than stock because of the large master)
Front calipers are off a V6 truck and have the large 4 pistons.
Vented rotors off a FJ40
LSPV with arm cut and tied to max (started leaking so I cut it and moved it up, arm didnt reach with the lift anyways)
Stock rear brake drums, probobly packed with mud, newish shoes, probobly toast by now.

I have a few theories:

The rear LSPV was leaking, so it could be plugged for most of the time. Becomes unplugged and the wheels lock up. Possible due too the moisture.

Front calipers could be plugged, too hard to move the pistons. Fluid takes the path of least resistance and locks up the rear. I got these calipers used for 50 bucks off a early 90s runner. They work great. My pedal was spongy with the stock master, so I upgraded to a 1".

Master cylinder might be plugged alowing more pressure to the rear brakes. But it has done this with the old master as well.

Gremlins?

Anyways, this whole thing makes NO sence. My brakes should be hard to use with the stock booster and 1" master. Usually they are hard to use.

Sorry for the loooong post, just wanted to get it all in there.
 
See less See more
#4 ·
my 85 does that exact same thing..allways has... i thought when i went to 35s it would stop. it certainly doesnt do it as bad as it did with the 31s but the rear is still very touchy sometimes. i thought it did it worse in the rain because of less traction. i assumed it was the lspv acting up. my rod is still attached, but flexed out to the max with the 3" lift. my brakes are stock.

now for the first week or two after lifting the truck(still had 31s on it) i had a spongy pedal and almost no brakes. i thought there was some air in the lines, but it firmed back up all on its own and is hard as a rock now like it allways has been.

everytime someone slams on the brakes in front of me my arse puckers up wondering if this time the rears will immediately lock or not.. its no fun when they lock because the truck goes sideways and trys its damnedest to spin in circles which is not the thing i want it to do on the highway in rush hour traffic when that M5 BMW or whatever is braking at its best in front of me.
 
#7 ·
I had the same problem at one time. Turned out adhesive failure between the pad and metal shoe. The pad was just flopping in the drum and would catch in there all funny. Only thing to do was replace the shoes. Hope this helps.
 
#8 ·
Stock rear brake drums, probobly packed with mud, newish shoes, probobly toast by now.

I have a few theories:
So do I, but I'd start with pulling the rear drums and cleanin' them up. :shaking:

Check the wheel cylinders for any leakage and while you're there check the bell cranks on the parking brake and make sure they aren't rusted and frozen. Get rid of the LSPV valve. Installing a Summit proportioning valve as shown by crawlininspector is a good idea as well, but I would correct the problem you having first. (I have the same setup as you with the exception of the 4Runner master and it works fine). Flush the brake fluid. In addition to getting the old fluid out, it will help determine if the fluid can flow easily to the calipers and wheel cylinders.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top