Ilovemountains

The brake booster in my 1988, 3.0 4x4 Auto is going bad, I just rebled the system, I get 100% rock solid pedal until I start the engine and then you can put it into the carpet. I’ve checked Autozone & Advance Auto, Advance has one on their site for $150 after the core swap but are telling me the vendor is out and they may not be able to get them, Autozone has the same PN only $180 after the core, same story they told me the best they could do is call me Tuesday with an answer. So, that said will a booster from a 90+ fit, it calls for a different PN but they are the same system if Im not mistaken.

My truck calls for a 53-2775 and a 93 V6 auto, 4x4 calls for a 53-2776, which they have in stock. Does anyone know the difference? My master is less than 6 months old but I would be willing to replace it too if I had to with a 93 unit if the later booster would be a direct swap. Let me know! ~Matt

corax

I've never heard of a brake booster failing by giving too much assist . . . have you adjusted the rear drum shoes? When you say the pedal is hard, is that after pumping it up?

Ilovemountains

The rear shoes and drums are new and adjusted, the front calipers are new, the pads have about 2500 miles on them and so do the rotors & the master might have 6000 miles on it!!! I’ve been chasing this issue for a long time. I’ve bled them by the book a few times including the LSPV, the booster isnt really assisting at this point, you can get up to about 30mph and mash it to the carpet and cant lock a wheel. With the truck off I get full hard pedal after 1 or 2 pumps of the pedal. I’ve been reading over on Pirate that a booster for a 97 T100 4x4 non ABS might be an upgrade to my problem and the local Autozone has one in stock. What are your thoughts?? I just don’t know what else it can be, I’ve not replaced the rear wheel cylinders, they are not leaking and when I put the new shoes in I gave them a good test without the drums on and they expand all the way out. Im at a loss unless the LSPV is bad, I just don’t know why I get a rock solid pedal with the engine off....

xxxtreme22r

pedal to the carpet is the brake mater cyl not the booster. If it were the booster you would have a rock hard pedal both running and non running.

Ilovemountains

What is inside of the booster? If the master was bad wouldnt it leak or not hold pressure when the engine is off either? I can stand on the pedal and its rock hard. The booster does move in and out quite a bit when you step on the brakes with the engine running, meaning the whold master moves in and out like the metal is actually springing! I bench bled the new master and have since rebled the whole system a few times, its very frustrating! I dont know exactly what is inside the booster or if something in there has broken off, it is an 88 with almost 190k on the stock booster... Im tempted to drop the $230 for a T100 booster and swap it in just to see, its really about the last thing on the system that I havent swapped out!

Ilovemountains

Im going to borrow my buddies professional power bleeder and pull a few more cans of fluid through to make sure I dont have any hidden air, Ill tap on the new calipers and see what happens before I swap in a new booster and master, its just getting really irritating!!!

corax

The booster uses engine vacuum to pull on a diaphragm inside the booster. Normally there's vacuum on both sides of the diaphragm, so it doesn't move either way. As soon as you step on the pedal a seal closes off the vacuum port to the backside (right side in the diagram), and simultaneously opens the backside up to atmospheric pressure. With vacuum on one side and atmo. on the other, the diaphragm tries to move towards the master cylinder. Since the MC pushrod is connected to the diaphragm, this reduces the amount of force you have to apply to the brake pedal




The best method to determine if the brake booster is functioning properly is the following:
-With the engine turned off, press and release the brake several times to assure there is no vacuum remaining in the booster
-Using a fairly firm foot, hold down the brake pedal and turn on the engine
-When the brake booster is functioning as it should, you will feel a slight give underfoot as the engine turns over.
-If the pedal doesn't gets "softer" then the booster isn't working

The T100 booster has dual diaphragms and will provide MORE assist than a single diaphragm (but not more brake pressure), so that's probably not the way you want to go. Do you have the stock calipers, or did you upgrade to V6 or T100 calipers? The stock MC has a weak pedal as is, so if you upgraded calipers it'll be even worse. If that's the case (or even if it's not), I would suggest the 1" MC.

As far as not being able to lock up the tires . . . anything bigger than a 31" tire is gonna start to get hard to lock up on dry roads. The tires exert leverage on the hubs which the brake system is trying to overcome. Bigger tires exert more leverage and the stock calipers/rotors/pads have a harder time overcoming the leverage to slow the tire rotation and stop the vehicle.

FWIW, most vehicles have at least a little bit of firewall flex where the booster is mounted.

Ilovemountains

Ill try that test tomorrow! I already have V6 calipers, I just replaced them with remanufactured from Advance Auto, same thing with the master, its just a stock replacement. I replaced it first thinking that was the problem but it made no difference on my pedal issue! My tires are 235/75-15 Revo 2's on stock alloy wheels, Ive had the truck for years and the brakes have never been this bad, I would tow or haul with it right now they are that weak! Thanks again for all the help, Matt

DJ99

I second this advice. BTW, a rebuilt MC is much cheaper than a new booster. Rockauto.com has a closeout for $18.39 plus shipping,

RustBucket

iTrader: (1)

I have had cheapie brake MC's go bad in a matter of months. The one you replaced it with may have been bad from the start?

c0ugar69

what size master cylinder is the stock unit, i put v6 calipers on mine and the pedal went down more than normal and it was hard to stop. the 90-95 v6 booster will fit, it is a double diaphram booster and has a larger master cylinder. I put these on my rig and it stops on a dime now. my old master had a round resevore and the new one has a rectangular one. just a thought!!

waskillywabbit

iTrader: (-1)

Tons of good brake tech in Pirate FAQ including brake booster swap compatibility.

:wabbit2:

myyota

A duel diaphragm brake booster from any 90-95 truck or 4Runner can be used on your truck. I have a duel diaphragm brake booster and master cylinder from a 92 4Runner on my 86 4Runner, its a direct swap and it makes a nice improvement in braking. I got my set up from pic n pull, so if you have one near you it would be a good place to look.

wrxnefx06

Scribed

xxxtreme22r

1" master with the 4cyl calipers and the single diaphragm booster will result in a harder pedal pressure.

I can only imagine that the reverse would be true using a 7/8 bore master and v6 calipers. Just like c0ugar69 mentioned.

That being said your issues might not be an issue at all and it's just a design flaw and driver error.

Ilovemountains

Today we rebled the entire system, drivers rear, pass rear, pass front, drivers front then LSV... We used the pro vac bleeder first, no luck then rebled the entire system again with the up down method, still mush. I adjusted the rear shoes to the point that they are dragging and still mush. I had the rear wheels on stands and started the truck, put it in gear to get the rear wheels turning and had to really really put some force on the pedal to even get the rear wheels to stop turning at idle. What position should the LSPV be in when there is no load in the truck? Im now thinking the POS AutoZone remanufactured master might have failed, probably from all of the pedal bleeding Ive done over the last week with the calipers, I don’t know. We did the booster test described above and unless the rod is bent inside the booster it seems OK. I’m going to try and find a larger bore master and try that next....

Ilovemountains

Are the Marlin 1" master cyls worth it? Are they rebuildable? Anyone using one? Im getting ready to buy one now but want to make sure its a good choice.

Ilovemountains

I’ve been comparing brake parts to the T-100. The 1/2 ton, non abs uses a 1" bore master that Ive read is a direct bolt on swap to my stock 88's. The 1 ton uses a 1 1/6" inch bore. Has anyone swapped one of these into an early truck or 4 runner? I can pick one up local at Autozone and install it tomorrow but was hoping for some input on pushrod compatibility etc. I was going to by a Marlin 1” but if its just a T-100 master that I can pick up locally Ill be set, they do look a lot alike! Any input would be great….

Ilovemountains

Confirmed!!

http://forum.ih8mud.com/60-series-wa...r-install.html

Im picking up a 1993 T-100 Master tomorrow. http://www.autozone.com/autozone/par...er=47201-3D020

ToyoTech559

did you bench bleed the mc before installing.