Sti Master Brake cylinder swap Qs

I got the STI brake booster hose yesterday and cut out the check valve. It is approximately 3/4" long and tightly fits into the hose. There is a rounded top like a bullet that points towards the intake manifold and a flat base which points towards the brake booster. I could not get the check valve to slide into my old hose so I put it back in part of the STI hose and got a 3/8" x 3/8" barb connector (nylon) and tied the two sections together. I used Silicone spray and heated up the old hose, but still couldn't get in there. I would rec. just cutting the old and new hoses and splicing them together to avoid a lot of headaches trying to get that damn valve in there without destroying it (it is thin plastic.)

 

On an aside, I bled the two brake lines that come out of the MC. However, I didn't bleed the bleeders on the 4 calipers, anyone think this would be necessary too?? Seems fine without bleeding them but perhaps someone else knows something I don't know. I also cycled the ABS a few times, pedal remains firm throughout.

Edited April 2, 2011 by Burock

I wonder what the height of the STi reservoir is compared to stock. If it's lower, it'll better clear an aftermarket TMIC.

 

Good question, I was wondering that myself! Can anyone comment on this yet?

The height is essentially the same with the STI reservoir. It is so far over to the right that it makes no difference with an aftermarket TMIC. I have an AVO TMIC and there is no problem with clearance issues.

Final impressions on the STI BB/MC Swap: Pedal is much firmer, modulation remains linear but requires a tad bit more foot pressure than previously, stopping distance is most likely the same. For those of you plagued by the "parachute effect" and marked pedal input necessary with the stock setup, it will solve this issue for under 5% of the cost of a BBK kit. In fact, it makes expenditure on a full BBK kit unnecessary except for those tracking their car weekly. Granted, the bling factor of this swap is non-existant vs the BBK kit. It also makes the prospect of the upcoming GrimmSpeed MC brace less necessary, and in all likelihood, useless.

I got the STI brake booster hose yesterday and cut out the check valve. It is approximately 3/4" long and tightly fits into the hose. There is a rounded top like a bullet that points towards the intake manifold and a flat base which points towards the brake booster. I could not get the check valve to slide into my old hose so I put it back in part of the STI hose and got a 3/8" x 3/8" barb connector (nylon) and tied the two sections together. I used Silicone spray and heated up the old hose, but still couldn't get in there. I would rec. just cutting the old and new hoses and splicing them together to avoid a lot of headaches trying to get that damn valve in there without destroying it (it is thin plastic.)

 

On an aside, I bled the two brake lines that come out of the MC. However, I didn't bleed the bleeders on the 4 calipers, anyone think this would be necessary too?? Seems fine without bleeding them but perhaps someone else knows something I don't know. I also cycled the ABS a few times, pedal remains firm throughout.

 

Yeah, I used a very small socket driver so I was only pushing on the outside of the check valve. It took me about 5 minutes but I got it in past the first 90 degree on the hose closest to the booster. I didnt feel like going to the store to buy the barbs so that is the only reason why I pushed mine through the hose instead of just cutting and splicing.

I have had some MAJOR problems following my STI MC/ BB swap. After running the car for a while, the brakes are locking up in all four corners to the point that I am running at 3000 rpm just to go 10mph and all four corners were smoking hot. After the brakes cool down, all is good again until the next time I travel, happens after about 5 miles or so. Unfortunately it happened on I-95 in downtown Providence last week and the car became essentially uncontrollable. I've bled all four corners and the MC but I suspect it is a problem with the MC. Perhaps it is because I am using an STI manual transmission MC with an AT Legacy. I'm hoping I can remedy my problem with a brand new WRX automatic transmission MC. Anyone have any ideas why all four brakes are locking up now when hot?? Would an ineffectively bled MC cause this?

I dont see why an auto or manual MBC would cause this problem? The MBC just moves fluid and it is mechanically controlled by the pedal. Are you sure you bled the entire system after you replaced everything? Do you have the check valve going the right direction?

do you have the check valve going the right direction?

 

+1

Also, did you kink any of the hard lines during the swap?

I dont see why an auto or manual MBC would cause this problem? The MBC just moves fluid and it is mechanically controlled by the pedal. Are you sure you bled the entire system after you replaced everything? Do you have the check valve going the right direction?

 

I second the above. Maybe, a vacuum bleed of the brake system is needed. Was the MC used and full of fluid before you started. Most new and refurbished MC call to be bench bled before installed and then each wheel bled after install. Some say that you never want to let the ABS modules (or VDC for the matter) run dry, as you may never get all the air out. Dealers have to hook their diagnostic testers to the car and cycle the ABS and still vacuum bleed.

The check valve installed direction could be it too! How did you determine the bullet shaped in went toward the intake? Integroid should be to confirm this since he installed the same MC/BB/CV combo.

Sorry, but I am glad I held off buying any parts to swap mine.

Thanks for the responses so far. I actually swapped my Stock Legacy Gt MC/ BB back in last night until I can determine the problem. I bled the MC and all the lines and ABS worked fine after the STI swap. In fact, everything worked well for approximately one week then the pedal starting becoming progressively stiff, especially when warm, until finally they locked up. In regards to the Check valve, there was an arrow on the STI hose which indicated direction of flow of the check valve (bullet end towards --> Engine), which is what I did (towards manifold), and flat piece towards the booster. When I took out the valve last night, it was not clogged and was functioning properly. I did note that there was paint break down on the MC where it meets the BB, which may indicate a leak in the seals. I did not ruin any hard lines, b/c brakes function fine now w/ stock MC/BB.

 

The reason I brought up the AT vs MT MC is that is on the Subaru parts website, there are different part numbers for the WRX AT MC, WRX MT MC, and WRX STI MC. I suspect I got a bum MC from Ebay and will be asking for a swap. I may just buy a new STI MC for $162.

 

I am not too happy to be back the shi*ty brake feel of the stock MC/BB but at least its not locking up now.

Sh*ty brakes are better than brake lock up or little to know brakes. It does now sound like a bad part. My guess is a bad BB or check valve, but maybe not the MC.

 

Instead of typing all this I cheated and did a Google search for you. Here is what they say at http://www.aa1car.com/library/bfixes.htm

 

"HARD BRAKE PEDAL Lack of power assist may be due to low engine vacuum, a leaky vacuum hose to the brake booster, or a defective brake booster. The booster is located between the master brake cylinder and firewall in the engine compartment. Sometimes a faulty check valve will allow vacuum to bleed out of the booster causing a hard pedal when the brakes are applied. This condition can be diagnosed by starting the engine (to build vacuum), shutting it off, waiting four or five minutes, then trying the brakes to see if there is power assist. No assist means a new check valve is needed.

 

A quick way to check the vacuum booster is to pump the brake pedal several times with the engine off to bleed off any vacuum that may still be in the unit. Then hold your foot on the pedal and start the engine. If the booster is working, the amount of effort required to hold the pedal should drop and the pedal itself may depress slightly. If nothing happens and the vacuum connections to the booster unit are okay, a new booster is needed (the vacuum hose should be replaced, too).

 

On vehicles equipped with "Hydroboost" power brakes, a hard pedal can be caused by a loose power steering pump belt, a low fluid level, leaks in the power hoses, or leaks or faulty valves in the hydroboost unit itself (the latter call for rebuilding or replacing the booster).

 

On vehicles that use the ABS pump to generate brake boost, a problem with the ABS pump or high pressure accumulator can cause a loss of power assist. This will usually cause the ABS WARNING LIGHT to come on. The ABS system will also set a fault code that corresponds to the problem, which requires a scan tool to read."

 

Could there be more than one type (vacuum rating) of check valve, maybe from different years?

I have to agree on check valve and that would still answer your question if you swapped in the Legacy BB because the check valve is built in on the Legacy BB. Did you suck on the line to make sure you have it correctly? The end you can actually suck on is the end that needs to run to the manifold.

Check valve was properly placed per your description and was not clogged. THe only other thing I can think of was that I did not adjust the pushrod length when I received the MC/BB off Ebay. This could have been too short and could have needed adjustment to increase freeplay. However, before I put in the Check valve, I had no issues with the STI MC/BB gradually locking up and all was fine. Problems seemed to emerge after the check valve was placed in.

Looks like it is only $13.77 online at subarupartspro.com

 

I think I paid $18 for mine

 

As a side note, has anyone used subarupartspro.com to order things? I ordered the booster hose thru them almost 2 weeks ago now, and haven't received so much as an emailed order confirmation, and I've sent a couple email inquiries. Glad I didn't order rotors or anything....

I used them a long time ago but I actually called to place my order. Have you tried to call them?

 

http://www.trademotion.com/storefront/index.cfm?action=contactus&siteid=214725

I can't wait to go back to the STI MC/ BB setup. However, I plan to buy a new STI MC and adjust the freeplay on the push rod next time.

One of these days i'll get around to installing mine. I asked the seller to send me the STi hose along with it so it should be somewhat plug and play for me.

Just ordered mine... Let's see if the feeling of "I'm gonna die" during braking subsides after it's installed...

Just ordered mine... Let's see if the feeling of "I'm gonna die" during braking subsides after it's installed...

 

 

Drive around with the check valve out if you want that feeling back:)

How is this working out for those that did the swap? Still happy? I've got mc and booster sitting on my bench, but wanted to get some opinions from early adopters after the " new mod is awesome" glow has worn off a little.

 

 

Thanks

Still awesome:)

got mine on order , waiting for the konis and epics too, to get all installed at once , cant wait.

Has anyone done the STi BB/MC install on an 07+? Any issues?

 

I'm definitely going to need the larger MC for my potential brake setup.