vrracing

iTrader: (1)

A few years ago when we did the Tii swap into the vert we replaced all of the rubber lines with silicone. We didnt realize the brake booster line had an embedded checkvalve.

I now understand the checkvalve allows air to be sucked out of the brake booster creating a 'vacuum' which provides the braking assist and it retains that vacuum even if the RPMs of the engine arent conducive to maintaining the vacuum. It also prevents said booster from getting pressurized when producing boost.

So for a few years now we've been pressurizing the booster. Any experience on what if any damage we could have caused?

We don't have consistent or overt vacuum issues beyond a bouncing idle that may last for 20 seconds with no obvious pattern and AFRs at idle that are about 16.5.

Thanks

Galaxysi

other then the inconvenience of presurizing the system, probably nothing. have you changed it back???

vrracing

iTrader: (1)

No, just realized it today. But the kid hasnt been happy with the braking because they are "inconsistent" and seems to require a lot of effort.

I check Atkins and Mazdatrix and neither carries the booster to hardline hose with the checkvalve in it, only the hardline to manifold which suggests it is no longer available.

Grainger has a 3/8" (10mm) viton check valve that I may pick up.

vrracing

iTrader: (1)

I was wondering specifically about the boost. That system would have been designed to flex in a relatively small vacuum but we've been pressurizing it at 12psi of boost. So probably more than the diaphram was designed for an in the wrong direction.

Galaxysi

12psi does sound a little much. i hope someone else chims in here with more info. any local junkyards you could hit up to find a replacement for the time being?

bumpstart

the hot turbo air will eventually kill the vac booster ,, the one way valve prevents the hot air making the diagphragm ,, and traps a vacuum on the other side that will be ready to assist when you hit the brakes ,, even when in boost

having added turbos to many oldschools-
,, leaving out the one way will amount to a dead vac booster within 12 months

vrracing

iTrader: (1)

Hmmm... I ordered a check valve from Grainger today.


Spring Check Valve, 3/8 In, Barb, Grey PVC
Spring Check Valve, Ball Cone Design, Material of Construction Gray PVC, Size 3/8 In, Barb Connection, Length 3.53 In, Width 1.00 In, Overall Height 1.00 In, Rated For 125 PSI, Cracking Pressure 1 PSI, Max Temp 140 F, Seat Material Gray PVC, Spring Material Stainless Steel, Seal Viton, Hex Size 1.00 In

3/8" == 10mm which is the diameter of the hardline. The Viton seal will survive the crankcase vented phlegm. If we see 125psi of boost the engine will be shards of steel and aluminum on the road. I'm just hoping the 1psi of crack pressure will be ok.

Thanks for the info. Makes sense.

vrracing

iTrader: (1)

To convert inHG to PSI you multiply the inHG by 0.4912. Target vacuum at idle should be 19.7inHG per FSM page P-30 which is about 10PSI. So that should easily open the 1psi rated check valve.