Hello all....it seems that my '95 Runner just wants to give up and quit! ( dead#4 cylinder, weird vibration noise @ 4Wd shifter auto) and now the brakes! I was driving earlier and noticed that the pedal was going all the way to the floor, at first I could pump up pressure but if I kept my foot on the pedal it would de-pressure and go to the floor. Now it will not pump up any pressure and goes all the way to the floor. Is this the master cylinder or the brake booster? There is no loss of fluid...BTW. Any help?

Merry Christmas to you too
Maybe the booster if you see no fluid loss

If your pedal goes to the floor, the problem is not your brake booster. The problem lies either in your master cylinder, brake lines or one of the calipers. My bet is on your master cylinder. However, bleed your brakes and be sure you don't have any air in the system. Make sure your reservoir is topped off and you're not short on fluid.

betcha one of your brake line is rusted out, prob the front calipers.

Check the MC for fluid level drop....then check for fluid around the calipers, and or drums...then check line integrity...last but noe least (Chevrolet's are famous for this one) behind the MC into the booster for fluid leaks. It doesn't happen much, but fluid/pressure will leak at the "O" rings behind the cylinder.
A drop in fluid level will let you know someting is leaking, someplace.

This is why I think booster but other wise I would say the master unless you see a visible leak at a line, caliper, or wheel cylinder.

If it was the booster then the pedal wouldn't go to the floor. The brakes would still work but there just wouldn't be any assist, the brakes would be very firm.

If the pedal goes to the floor then the problem is past the booster. It is either in the MC, lines, or the calipers. Since he doesn't have any fluid loss I'm betting he has a shot master cylinder or a lot of air in his lines from a bad caliper or something.

OP: If you want to test your booster just to rule it out then do the following:

1) With the 4runner turned off, pump the brake pedal until you feel it get firm.
2) Keeping your foot on the brake pedal turn the truck on.
3) If the pedal goes to the floor then the booster is doing its job. If the pedal doesn't move or doesn't move much then your booster is bad.

The function of the booster is to provide vacuum assist to the master cylinder for power assisted brakes.

The master cylinder takes that assist and pushes an internal plunger to provide pressure through the lines and to the calipers.

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Okay, a little background may help. I have been noticing for a while that sometimes the brakes went to the floor but, if I would pump them they would stiffen up and act right. The other night I was pumping them while sitting @ idle and all of the sudden they just go straight to the floor. It seems like the rear brakes are not working at all if I mash to the floor the front locks up(no rear ABS). Also as a side note when sitting at idle and tapping the brake pedal there is a clicking sound coming from the shifter(auto). Any suggestions? There is no fluid loss, no blown fuse . Something electronic/vaccum? Help! Thank you in advance

That ticking sound that you're hearing when tapping the brakes is an electronic lock release for the auto shifter. It prevents the transmission from being shifted into gear when the brakes are not applied.

There is no electronics on the brake system, and the only vacuum on the brakes is on the brake booster.

If you're certain that there is no fluid loss I would look towards the master cylinder. If the rear brakes aren't working and the front are working as they should then you have a bad lspv (load sensing proportioning valve). The LSPV is a valve that senses the load on the rear axle with the help of a rod that connects to the rear axle. When the rear is loaded with cargo the rear suspension will compress. When that happens the rod on the rear axle will push on a plunger in the LSPV and allow more fluid to go to the rear brakes. If your rear brakes aren't working at all then I would check into replacing your LSPV.

I removed my LSPV completely because I have oversized tires and I don't really carry a lot of cargo. I also have a slightly modified suspension

Thanx bro, I am changing out the Master cylinder today, hopefully that will solve it. Do you have any suggestions on the best way to bench bleed it before installation? Also how do I get rid of the LSPV? My truck always has a load in the rear ( I do carpentry) and until I can get springs,shocks etc. I don't want to run the risk of this valve malfunctioning, if it is not needed....off it goes!

Master Cylinder Bleeding - How To Bench Bleed Your Master Cylinder - Remove Air Bubbles

That is a pretty good article on how to bench bleed a MC.

As for the LSPV, as long as you either have over sized tired or always have a load in the 4runner then you're fine deleting the LSPV. If not you'll need to get a manual proportioning valve that you will put inline with the rear brakes. The idea behind reducing the amount of fluid to the rear is to avoid locking up the rear brakes when the rear end is light, as you put more weight in the LSPV will give more fluid to the rear brakes.

To delete the LSPV you'll have to do the following:

The LSPV has 2 lines going in, and one going out. The two lines going in are from the "T" fittings on the front right of the frame near the front right wheel. The forward most "T" fitting will have a line going all the way back to the LSPV. Remove that line all together, you will not be needing that one anymore. Now the LSPV will have two lines in it, just splice those lines together and now you have just bypassed the LSPV. You can either remove the LSPV and throw it away or keep it... Just make sure that you plug the forward most "T" fitting so you don't have fluid loss, you kinda need that stuff

Thank you! I replaced the master cylinder and that seems to have fixed it You are a full of great info., so let me ask you about something that perplexes me. I have a vibration/spinning? noise coming from the console shifter area(if I place my hand on the shifter it feels as though it is right below) I have replaced all universal joints and also the front right cv(busted boot, knocking when turn). If I push the 4WD shifter forward the noise seems to disipate but not completely go away. Also it is more pronounced if accelerate or coast? This has been a major issue, it seems worse at 70. Thank you in advance YOU and people like you are why I have joined this group and I plan on helping just like you.....once I am capable

do you have manual hubs or add

If you are asking if I have to lock the hubs-no it is an auto-lock I think.

Crawl under your runner and wiggle your transmission. You may have a rubber transmission mount that is starting to go bad. Does it do this only while driving and in gear? Try this, get up to speed and put your 4runner in neutral. Does the vibration go away? The drive shaft will still spin and in turn, turn the transmission. But it will do so under no load so the vibration of a bad transmission cross brace mount should either lessen dramatically or go away.