Help! newbie brake problem (1 Viewer)

[TCinVA]

I wrecked my 93,000 mile 75 FJ40 in July. The guy who caused the accident's insurance company paid me 5 grand for the loss (I paid 400 for it 3 years ago). With the money, I bought a 72 with a 78 2f and 4 speed from a guy on this board (with plenty left over). The PO did a mini truck front disc conversion that I don't know any details about. When I brought the truck to the mechanic where I bring my diesel work trucks to be state inspected, they noticed (as did I) that it has a very hard brake pedal. It stops perfectly straight unlike my drum brake 75, but you really have to push HARD- like a power brake vehicle with the engine off. The mechanic checked all lines and bled the brakes- no change. He said I need a master cylinder and a booster and he couldn't find them through NAPA etc. locally. Before I spend big bucks on these parts, I want to make sure there isn't something else going on, maybe something with the conversion? Any help or suggestion would be GREATLY appreciated. Thanks- Tony

 

[Poser]

Master is likley fine if it is not leaking....booster sounds like it is not doing its job.

 

[mr_manny]

Do a search on boosters, I recently replaced mine and found a few helpful ones out there...

I would verify a few things:
The booster
The Brake Pedal adjustment
The booster rod adjustment
Bleed brakes

I recently replaced my booster on my 72 (donor vehicle was a 8x supra), and some fine tuning was necessary.

The trickiest probably the booster/MC rod...

If you remove the MC, you will notice a rod on the booster w/an adjustable end.
Pull this rod out 1/4 inch, and re-installed the MC to test (don't torque, as your going to repeat this step).
Once you've pulled your MC away from the booster, press the rod towards the booster...it should move.

I look for a good 1/8 inch...if you have more, it's time to grab some vice-grips and an 8mm wrench/socket.
Take your time extending the rod slightly and repeating the test mentioned above.

Jump in the cab and test the peddle...when your ready, take a test around the block.
If you find your brakes too responsive, you may have to re-adjust my brake-peddle (in cab).

Remember your brakes are the most important system in your truck, so please make sure everything is working properly.

hth,
manny

 

[Josie'sLandCruiser]

Hi All:

Both "Poseur" and "MrManny" have provided good solid info!

From my personal experience, it sounds like the booster on your '72 is dead. You can replace it with the brake booster from a Toyota 4wd mini-truck (do a search here on MUD and you'll find past threads on the correct years to look for and how to adjust them to work correctly.)

Good luck!

Alan

 

[ecodan]

Check your getting vacuum through the hose to your booster (pull it off at the booster end and stick your thumb over the end). I found mine sealed up with age and became so constricted the booster stopped working.

You can check your master cylinder by holding you foot on the pedal and waiting to see if it slowly sinks. If it sinks fluid is bypassing the piston and it must be replaced.

You can check your booster by putting your foot on the brake, starting the car and seeing if your foot drops slightly as the booster comes into operation (pedal should at this point become lighter to operate).

Hope this helps

I had enormous problems when i first replaced my master cylinder, turned out one of my hubs was badly adjusted and i just couldnt get the pedal up and air out till i got the adjustment right, so i would check the obvious before pulling off the master cylinder unless you can do it without disconnecting the brake lines.

 

[ecodan]

Just to clarify; according to my manual when you do the booster check the pedal is supposed to drop slightly when your foot is on the pedal as you start the car.

If it dosnt something is wrong with the booster, however when everything is running the pedal should not drop when you press and hold it firmly. If it does the master cylinder is bypassing fluid...
hope that is clearer

 

[73lndcrsr]

I will throw one more question at you.

Are your rotors vented or solid?

Your issue may be that the PO did a vented rotor/caliper upgrade as well.

Mine acted the same as you describe until I upgraded the MC.

 

[cruiser88]

dumb question how is the little check valve on the booster.does it rattle when you shake it.maybe not getting proper vac.maybe im way off.

 

[TCinVA]

Thanks, guys. That is some solid info . I should be able to figure it out now. This site rocks.

 

[yotawheeler]

i think all the mini truck rotors were solid wernt they? if you end up having to change the master you can get the stuff at 4wheelauto.com i have ordered some stuff from them and their pretty good....im told their prices are a little high though. i also think it sounds like a problem with your brake booster and not you MC though

 

[73lndcrsr]

The mini truck were solid, but there is a vented LC rotor and 4runner MC upgrade.


This gives you the better cooling of a vented rotor with 4 pot calipers for more stopping power. The stock MC will work okay, but not optimally.