[SOLVED] Brakes get really stiff after accelerating

Hello!
I bought my Mazdaspeed 3 about 3 weeks ago now and I've been loving it, however have just been noticing an unusual problem. Its a 2008 gen 1 model, completely stock, and treated quite well by previous owners.

Often after I accelerate quite fast and hit the brakes they feel really stiff, and I can't press it very far. After about a second it goes back to normal and I can actually brake.

It only happens after I've just accelerated, not so much if I'm just driving fast. It also happens more when I brake harder as opposed to slowly braking.

Other than this the brakes are great and have no problems when driving normally.

I've had a bit of a look around for any similar problems but I don't know a great deal about cars at the moment.
This person had the same issue it seems, but I don't really understand what their solution was (I know nothing about check valves) :
https://forums.nicoclub.com/brake-pedal-hard-to-press-when-engine-is-under-acceleration-t563281.html

Thanks in advance for any advice you can give!

 

Ok so here is a few questions that anyone who will respond to your questions are going to need. Stock means exactly that. So if you have a high mileage model (miles currently?) what is past service history...Or lack of the past is needed. Did this problem exist since the beginning of your ownership. A better description of troubles, braking has different modes. I will use a example...60 mph...clutch in, full brakes to 20 mph. Repeat 3 times. All three times same braking distance, time to reduced speed? Fading ? Acceleration mode...full throttle ? Gear? Speed?
Important is your mechanical skill set too. The check valve inquiry makes me wonder if you understand what a vacuum brake booster does.
If you want a picture of my brake booster/hose/check valve or others. Best is a picture of yours to let us see what maybe wrong or missing.
Not trying to a pain, just the problem vs description is very vague.

 

Understood! Thanks for a quick response.
90% sure it's completely stock, did all the checks I could find from Youtube.
80,000kms on it at the moment.
Unfortunately no service history.
Pretty sure problem existed in my entire ownership, but can't know for certain as for the first week or so as I didn't drive particularly fast.
Problem happens when I switch quickly from throttle to brake, clutch is never touched.
I've noticed it happens most in 4th and 5th gear.
Happens at speeds between 60+ km//h but only just after accelerating (will do some testing in the morning).
I have no idea what a vacuum brake booster does - just did some research now though.
I tried to take some photos but I actually couldn't find the brake booster so you might need to point me in the right direction haha

Sorry I realise I'm not being very useful but I reaaaally appreciate any help at all so thanks a tonne.

If you need anything from me ask away I'll do my best!

 

I've just done some more testing and it actually happens at pretty much any speed, as long as switch from throttle to brake quite fast, and so long as I'd just been accelerating quite quickly.
It happens in every gear (couldn't properly test first or sixth).
It's worse* the faster I'm accelerating, and the faster I switch. It's not actually worse at higher speeds.
*by "worse" I mean it stays stiff for longer. When it is stiff there is virtually no braking.
If I pause a second between taking my foot of the gas and hitting the brakes it's completely normal.
It's worth noting that when the braking does eventually happen, its really quite strong, more than usual I'd say.
I tried braking with and without the clutch pressed in, it didn't make any difference.

I would include specific numbers but I didn't take any distance measurements, was mainly looking at the amount of acceleration. However taking into account specific landmarks I could at least identify the trend.

 

There is a check valve in the brake booster line. Yours has failed. On the stock hose you cannot see it it is integrated into the hose.
When you accelerate boost is getting past the check valve and taking away the vacuum assist to the power brakes

 

This is most likely what your issue is. I had the brake booster vacuum line on my Turbo 300ZX burst while at the drag strip. Try having to stop a car at 100+ MPH without power brakes is scary. Literally was standing on the pedal to get the car to stop

 

https://www.jimellismazdaparts.com/showAssembly.aspx?ukey_assembly=2258210&ukey_product=1824716#4
The hose is Part # 4 on link.

I point out the hose on the 07 with no TMIC cover, the 08 is the other. Sadly Mazda thought of how to make as hard as possible to replace.
The area you need to access and hose to replace is behind that bracket support towards firewall. Mazda Manual would be your best friend here!

 

Guys thank you so much!
Just woke up to all this support, I was really worried last night.

This is so helpful, I'll give it my best shot.
Thanks again I'll let you know how it goes.

 

Hello everyone!
Sorry for such a late update, hopefully someone's still interested!

So an issue I'm running into is mainly down to figuring out which part I actually need. I've done a little digging and felt very confident I knew the part I needed was the vacuum hose, as the check valve is integrated into it.
However after contacting and visiting a few parts dealers, I would always get quotes for just the check valve. I've attached a diagram they were going off:

On their systems, the part circled in red was labelled as the check valve, but to me it just looked like the hose connector. The main reason I'm concerned is that they use the rego* of the car to find the manuals, and are pretty confident it's accurate. I wonder if it's incorrectly labelled on their system?
My main question is whether or not I should go with the dealers part recommendation, or go off Cfcoldone's recommendation / what I've read in the manual I'd downloaded (for 2007 Mazdaspeed 3, as I can't seem to source the 2008 one).
A few clues I have -
1. The part for the vacuum hose is weirdly expensive, and the dealers say they're surprised a hose would cost that much, thereby suggesting it might not just be a hose (could have check valve as well) [the vacuum hose is $150NZD and the check valve is $81NZD]
2. On the diagram the dealers were going off (above) it says the year is 2006 at the top. (my car is definitely 2008 haha). Not sure if this is relevant.
3. Its a Japanese import (going off the Japanese chassis number as there's no VIN on the dash), and the manuals the dealerships were using were also in Japanese.

This is the diagram I was going off in the English manual :

as you can see the check valve is inside the vacuum hose.
This diagram is one I pulled from a US parts dealer (the same one they all use), I can't be certain this refers to my specific model though, its just the one in the description for the part I was looking at (BA6R43630).

I'm obviously not experienced with this sort of thing and I'm doing my best to research and find out as much as I can before I ask everyone here, but it's all getting a bit confusing now and I think I just need an outside opinion again.
I've gone in and located the part on the car itself and tried my best to get a half decent photo, which I've included below.

I might have a go at just pulling it all out and trying to eyeball whats what, just a little bit of a pain to do on this car (and I don't wanna fuck anything up).

THANKS SO MUCH FOR ANY INSIGHT!
I really appreciate it guys, I'm really trying my best, I know I'm not the most helpful.
Really enjoying learning so much so thanks again for any help you guys can give.
If anyone has the 2008 workshop manual that'd be invaluable, I don't know where to find it or whether it's even very different from the 07 one I have (can't imagine it would be).

*I've double checked my rego / car info

 

A left hand drive? If more people chime in all left drive the hose is pointing to the right. I have a 07 and 08 both are the same and match the drawing with arrow pointing to the part # 42-4360. Your picture if is oriented to show coming off vacuum booster "can" to the left is different than my 07,08. (They both go right) So I guess the picture and drawing with part# 43-770 is right hand drive. Reason I think that is the transition from 43-770 / hose / to metal pipe assembly is Not on mine. I have only rubber hose. Which makes sense in that right hand drive the distance is greater because must go all the way over engine. Left hand is much closer to were it connects to right angle then engine

 

Will they let you return the parts? Order both and check at the counter to see which one has the check valve.

The fitting should be easy to tell by looking at it the hose you would have to blow onto it from the engine end

 

OF COURSE
I feel like such an egg, my car is right hand drive.
I completely overlooked that, things make a lot more sense now.

I don't want to risk not being able to return the parts, so what I might do is just pull out the vacuum hose and the supposed check valve (#43-770), referring Japanese diagrams they supplied. The only issue is if the check valve is faulty I might not be able to tell where it is (in the pipe or the other piece; #43-770), worse case I'll take some photos and ask around (if not on this forum later haha).
Hopefully this time tomorrow I'll know which part I need and have it ordered.

Thank you guys so much, I'd literally have no idea what to do otherwise.
Will keep you posted

 

Hey guys, final update from me!
Had a chat to a few mechanics and got a part ordered just over a month ago. It just came in just the other day (there were none in New Zealand; typical), swapped out the old check valve today and the brakes feel normal.

Looks like the issue with finding the part was the slight difference between left hand and right hand drives. In the right hand drive (mine) the check valve isn't actually integrated into the vacuum hose, so I was able to order it separately.

Huge thanks for your help guys, I learned so much and I'm really grateful. It's a shame it took so long to get the part in and swap it out. Was really happy doing the first test drives today, brakes feel completely different (actually work now haha).

THANKS AGAIN
Much love

 

Thanks man have the same issue, in NZ as well. I have the part on the way, just to confirm it was Part number (FB44-43-770) right?