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CardinalFJ60
05-18-2009, 11:12 AM
I replaced the vac hose and I checked the "check valve" which seems to work fine, and all the forums tests point toward needing a new booster for the 77 fj40. (pedal pressure normal to about halfway down, then hard as a rock and tough to get the thing to stop)

My question is whether I should replace the M/C at the same time? much like the idea of replacing both clutch slave and master at the same time. Should I consider just 'baselining' it or just hope the M/C has more life in it?

thanks!

subzali
05-18-2009, 04:25 PM
they have different failure mechanisms, so in my opinion just replace the booster for now. But while you have the master off you can check and see if it's pitted and would need to be replaced...

CardinalFJ60
05-18-2009, 04:36 PM
Perfect. thanks matt!

Air Randy
05-18-2009, 05:39 PM
Remember, the booster only makes it easier to press the pedal. The brake system should still work fine without any booster assist, just like a manual non-power system. My point is, if your pedal is really hard to press AND its hard to get the vehicle stopped, you may have some other problem going on.

You may want to perform more diagnosis before replacing the booster.

Jacket
05-18-2009, 09:02 PM
Having recently replaced my BMC in the 40, I can attest that it is a pretty simple job and you wouldn't gain much by doing both at the same time (except having to bleed the brakes twice....).

nuclearlemon
05-18-2009, 09:09 PM
i wouldn't replace the master, just rebuild. run a hone through it to clean the sides, new pistons and seals and you're done.

Rzeppa
05-18-2009, 09:51 PM
I agree with Matt, if the booster is faulty, replace it. If the Master is faulty, replace it. But there is little to be gained by proactively replacing the M/C at the same time. It's not like a rear main seal that is a huge amount of work to get to when you are replacing the clutch.

Air Randy
05-19-2009, 07:34 AM
I agree with Matt, if the booster is faulty, replace it. If the Master is faulty, replace it. But there is little to be gained by proactively replacing the M/C at the same time. It's not like a rear main seal that is a huge amount of work to get to when you are replacing the clutch.

Agreed, but I think we need to address his real issue :

"pedal pressure normal to about halfway down, then hard as a rock and tough to get the thing to stop".

That sounds to me like the pedal is bottoming out the MC without applying enough hydraulic pressure to fully activate the wheel cylinders. Which could mean the booster is fine but the MC is bad.

Do you have disk front/drum rear or drum front/drum rear? Dumb question but have you checked the pads/linings and adjusted the drum brakes? Are there any signs of leaks anywhere on the brake lines from the MC to each wheel?

subzali
05-19-2009, 08:31 AM
I think he has a '77 so disc front/drum rear.

Cardinal - have you verified for sure that it's not your master cylinder? I think Randy has a good point.

EWheeler
05-19-2009, 08:39 AM
My experience:

When my truck ('80 40) was running & I depressed the brake pedal, I would hear a loud hissing noise. Quick search on MUD pointed to booster. Everyone said that if your master starts leaking brake fluid into the booster, it will eat away the seals and the booster will leak. Sure enough, pulled the master from the booster and it has been leaking for some time, the booster had a bunch of brake fluid in it. A tell tale sign of a master that has been leaking is a trail of paint that has been eaten away by brake fluid underneath the master cylinder, down the front of the booster, & even down onto the fire wall sometimes (underneath the booster). Im sure that the diaphragms and seals in the booster can fail over time, but from all that I read on MUD, most of the failures were due to leaky master cylinders. Give yours a look over.

My solution was to run to the auto recycler and pick up a booster and master pair off of a '92 4runner for $75. The booster bolted right to my firewall, and I only had to trim about a 1/2" off of the booster push rod that connects to the brake pedal to be back on the road. Hope that helps,

Evan

CardinalFJ60
05-19-2009, 09:24 AM
It's a 77 so disc front, drum rear.

Here's a little clarification, but tonight, I'll go through the stuff I checked out and take notes to report back. This is new territory for me, so I'll be asking lots of questions.

more info:
- MT wrote: "That sounds to me like the pedal is bottoming out the MC without applying enough hydraulic pressure to fully activate the wheel cylinders. Which could mean the booster is fine but the MC is bad."
-- the pedal doesn't bottom out, it's more like it gets rock hard about halfway down and for a weakling desk-jockey like me, it would take quite a bit of pressure to slow down quickly. If I put some decent ummmpfff behind, she'll stop. :D
- I don't recall any hissing noises, but will re-check.

- when I pulled the check valve, there were no obvious signs of fluid leaking in there, again - I will double check.

- M/C info: no obvious signs of leaking. I topped off one of the reservoirs about 6months ago, and the level hasn't changed. the outside of it is rusty, but that's about it.

- drum brakes have not been adjusted.

- what should I look for on the pads and linings? just thinkness? or material quality.


Should I just drain/re-fill the fluid as a first step? I haven't done the "basics" yet.

thanks everyone.

nakman
05-19-2009, 09:41 AM
Should I just drain/re-fill the fluid as a first step? I haven't done the "basics" yet.

thanks everyone.

You know that's where I'd start, I'd remove one of the bleeders from one of the the back wheel cylinders and just see if I could squirt a bunch of fluid through there. With the bleeder off you should have an easy time depressing that brake pedal all the way down, right? Maybe there's a little piece of crap in the line that you can flush out... then work your way up to "proving" that each of the 4 brakes is actually working, then start messing with the booster & MC.

Air Randy
05-19-2009, 11:50 AM
I would suggest something even simpler: Adjust your rear drum brakes before you do anything else. It sounds like your pedal is soft the first half of it's travel because the rear drums are out of adjustment. Once you know those are adjusted right, then consider bleeding the fronts and rears just to be certain you have all of the air out of the system. Then test drive it again and see if there is much improvement.

Once you have the brakes stopping you good with a firm pedal near the top, then you can investigate whether the booster is working.

Doing all of this above shouldnt take more than 1 hour if you have someone to help you pump the pedal while doing the bleeding and will cost you nothing more than a few ounces of brake fluid.