quick question...

[wardfoto]

just bought a 60 with rear disk conversion. very soft pedal, and i read that the way to fix it is with an 80 series master cylinder. do i also need the 80 series booster? the disks are using 83 monte carlo calipers, if that helps.
thanks,
-justin

 

[brokenparts]

did you try bleeding the brakes first?

 

[wardfoto]

nope, but the truck has had the brakes for 4 or 5 years now, i believe.
and they were done through a shop, so i'm looking at the m/c for a possible solution.
or adding the proportioning valve, but i've got a line on an 80 series m/c, just need to know
if i need the booster as well.

 

[brokenparts]

you are probably right in the direction you are going but bleeding the brakes cost you nothing except a hour of your time if that. I'd start there first?

 

[wardfoto]

true enough.
but if i want to switch the m/c, do i need the booster?

 

[cody c]

dont know if you need the booster, but i do have the monte carlo brakes and 4 runners in front and my brakes are not squishy. Although it may sound silly, i would suggest re-bleeding your brakes, and maybe trying to see if there are any high spots where air could sit and not be bled out, depending if the bleed valves are up high or brake lines could trap air somewhere.

 

[brokenparts]

true enough.
but if i want to switch the m/c, do i need the booster?

obviously it wouldnt hurt but I think you might be able to come up with some other solutions to try first that wouldnt require as much work. Cody C is on the right track for easy stuff first.

 

[IndianDoc]

MC info

I am no expert but have been considering the same. I understand based on reading several threads here that the 80 booster would not be needed but that you will need the non abs MC. If this is wrong then I am sorry and some of the brake guru's will chime in to correct me I hope. Just my .02 from my research so far into the same problem.

 

[wardfoto]

indiandoc-
thanks. i'll look that direction. good info, and sort of what i had found as well.
cody c- seems that if you convert to 4runner fronts, that also helps, but i've got stock 60's up front, and it seems that this often leads to squishy pedal. they work, just soft pedal. have you gotten the ebrake to work? if so, how? pm me, if that works better for you. thanks.

 

[boots4]

You'd really only need a proportioning valve if you had too much power going to the rear brakes. You don't want your rear brakes locking up first because that can cause the rear end to come around on your in a panic situation so a proportioning valve is used for that. A residual valve is different. It keeps a small amount of pressure on the brakes so you don't have to build all the pressure the next time you step on the pedal. Residual valves are typically used with disc/drum setups and in applications where the MC is not the highest part in the system.

Soft pedal can be caused by air in the system as stated before because air is a gas and is compressible thus requiring more pedal travel to actuate the brakes/calipers.

Your fluid could need to be changed out. This is something that is very often overlooked and I bet very few people actually do a brake fluid flush as often or ever as needed. Brake fluid is hydroscopic and can absorb water (DOT3, DOT4) causing rust in the system.

Your master cylinder bore is too small for the volumn needed. A too small cylinder will show up as a soft pedal with lots of travel and a too large cylinder will show up as a stiff pedel that takes a lot of effort to clamp on the brakes.

Figure out your bore size (7/8" according to napaonline.com) and go up from there. Making a 1/8" move larger can have a big affect so I'd look at a 1" bore for an MC. I believe T-100 MC and an 80 series MC both fit the bolt pattern on your booster. I've heard of both being used. Now the 80 series booster might be bigger and provide more assist, but I don't know if it is bigger or not but you don't "need" it if yours is still good.