Romthirty

Not exactly sure what to search for to get some answers for this, but basically my brakes on my FC feel very short and hard when I first drive the car. Almost feels like there's a brick under the pedal stopping it from a full stop. It makes it feel like the brakes aren't going to stop quick enough, like I have to put my whole weight on it to get it to come to a quick stop. I only ever notice it when I first drive the car for a few minutes, then it feels normal again.

I only drive the car a couple of times a week if that so it just sits in my parking lot most of the time. My thoughts are one of two things, they need to warm up to grip better? (none of my other cars have this issue - and I live in AZ), and my second thought is brake pressure of some sort? like it needs to build up pressure while I drive to fully function - if so, what would this mean? What needs to get checked/replaced? Brake pads and rotors are all good too.

Thanks.

docbong85

Vacuum to brake power booster, booster itself, sticking master cylinder, fluid level (ie air in the lines maybe)

docbong85

My 88 sat for 10 years, and I had the same problem when I started rebuilding with the clutch. It turned out to be a seized slave cylinder. I ended up replacing slave, and both brake/clutch master cylinders (as brakes wouldn't hold pressure, I found the master cylinder was pooched too)

Molotovman

iTrader: (49)

Check the vacuum hoses to the brake booster. The one a that is in a "S" bend above the exhaust manifold probably rotted through in one of the pits and it's preventing you from getting proper vacuum assist from the booster.

Romthirty

Thanks for the additional information. How quick do those components go out? It got a new master and slave cylinder back in 2012 (7 years ago).

Where I'm at with my testing:

Inspected all reservoirs for liquid levels and all are great.

So I started to poke around after reading your comment - both online and under the hood. My time on my car is limited because of work/son/wife so I only get a short burst of moments to actually go out there and mess with the car during the week so my testing hasn't gone far. So the very first thing I looked at was the check valve that I read about. I didn't see one at first, but later read that it's part of the hose that comes off of the brake booster. The hose looks bright still, and not crusty and dull so that was a good sign. I can see a slight bump where I assume the check valve is inside of it. My plan was to quickly remove it and blow/suck to make sure that portion is working as that would be the easiest and cheapest thing to replace. It was on there pretty tight so I wasn't able to quickly remove it so I'll try again on the weekend.

The next thing I tested was the pedal feel when the car is off. I pressed the pedal in and heard a loud HISS sound and the pedal went in just fine. I've read that this is a good thing as it's using the built in reserve pressure. After a day or so of driving and leaving it parked, I did this test again and didn't have the same results, the pedal kind of just stopped right away with no assist.

Next, I ran the car for a little bit, made sure the brakes had assisted pressure which it did, then held the brake pedal down and turned the car off. While holding the pedal down, I read that it should maintain in the down position with assist for at least 10 seconds? Well for me it started to slowly return to the up position right away after the car was turned off.

With the results of these tests so far, I'm leaning toward the Brake booster being the issue. I don't believe that has ever been replaced.

Romthirty

What I find odd is that it's very inconstant. Sometimes It feels great for the whole day, other times it feels like 0 assist for the first few minutes of driving. This causes me to brake extra early when driving because it feels like I may not be able to stop in time.

Romthirty

Oh wow, I didn't even think this could be an issue and had over looked that. I just ran out there to look at this hose again and yes, it looks old and crispy. It's even missing the lower clamp and I can see cracks in the lower end where the clamp is missing. I figured "it's a hose and its still in place. Should still be working" but didn't consider that it may be rotted and blocking pressure.

My other hose like my check valve hose looks nice and dark and fresh looking, but this S hose looks like it's been there for 30 years.

I'm pretty sure that hose will crack even more when I remove it so I won't remove it to check it, I'll just buy a replacement. But for my sanity, once I've removed it, will I be able to see a blockage in it visually? should I be able to blow through it freely? I suppose I can compare the new one with the old one.

Do you happen to know a part number for this?

Romthirty

I believe I found the part:
https://www.mazdatrix.com/product/ho...la-fc-nt-mani/
Can you confirm this for me, plz?

SKU: 43-8360-FB01
Manufacturer SKU: FB01-43-836

Which Mazdatrix no longer carries. But this gets me in the right direction!

EDIT:
Looks like Atkins carries it
https://www.atkinsrotary.com/store/8...-Manifold.html

Molotovman

iTrader: (49)

It's NLA at both places, Just pull it off and buy something at the auto parts store that is a close match and fit it. The hose won't be blocked, it will crack in the pits of the "S" bend and keep your booster from getting proper vacuum/manifold pressure.

Romthirty

Ah didn't notice it was NLA from atkins also.

Does the hose have to be any special type of hose? Do I just tell them it's for a vacuum line? I know some hoses have to be a special kind for certain applications.

Thanks for your intel.

Molotovman

iTrader: (49)

Just take the old hose off and bring it. It doesn't need to be anything special.

Romthirty

Sounds good, I'll try to get that done this weekend. They are going to look at my hose and say, "Sorry, we don't make any hoses made of stone like this one".

Thanks again for your help. I will report back in once I've replaced it to see if it's fixed my issue.

Romthirty

oh yeah. This guy was brittle as hell and has clear cracks on the bends. If I blow through one side and cover the other, air escapes from the cracks clearly.

What else could this have been affecting aside from the brake booster?

Romthirty

Quick update after installing new hose. So I havent driven the car with the new hose yet but I did a quick test while parked. I had the engine running, I stepped on the brakes and turned the car off. The pedal stayed down for about 12 seconds then started to come up slowly. Online it says a normal brake booster should hold for 30 seconds. Not sure if that should be the same I should expect on a small s4 (4 lug model) brake booster. Has anyone with my same specs done this test?

Molotovman

iTrader: (49)

Where are you finding this information? The FAQ sticky in this section has links to download the factory service manual for the car. it has been YEARS since I've looked at one for an FC but that is the correct place to find information about how the booster should behave. Take the car for a quick drive and see how they physically feel, that hose being rotted can make the car feel like there is no brake power assist at all.

Romthirty

Straight from the manual. It says it should hold for 30 seconds so I guess it's the same in all models of the brake booster. My hose with the check valve seems healthy (visually). It's nice and dark and doesn't feel old and dry, but I should still pull it off and test the valve to make sure it's operating properly. I'll also take it out for a drive today to see how it feels on the road.

Romthirty

Just another update (final update):

So I've driven the car a few times since I replaced that hose and it's 100% fixed my random hard pedal. Thanks again Molotovman! I finally feel confident coming up to a stop again!

Molotovman

iTrader: (49)

Excellent! I'm glad it was an easy fix.