holding boost on line with vaccum brakes

[aufond]

I can't seem to be able to hold boost at the line with my brakes.

Vaccum conversion - check valve seems to be holding.
Gbody rear upgrade. (new)
Akebono front pads (new)

any recommendations on where to look next?

 

[gusszgs]

I was having the same issue. What I've done is added a stainless Russell flex brake hose kit along with S-10 wheel cylinders. And a new Husek 9.5" converter. Had the car out the other day play'n and could build boost to 5-7psi with MT DR's fairly easy. I'm sure the converter has had the biggest effect.
I'm running better rear shoes (forget the brand) but still retain one long and one short. May go with 2 long before year end.

 

[aufond]

have everything but a converter. thinking It's the next step!

 

[HyperV6]

I have never been able to hold boost like I could with the Power Master. I have all long shoes and S10 wheel cylinders. Some people are able to hold good boost with the vacuum system. Since I race my car every once in a while I'd prefer to have safe/good brakes with a little less holding power.

Craig

 

[tonka]

Converted my first car to vacuum when PM was getting weak. Pulled parts from the junkyard for the swap. Used the cheapest rear shoes (non riveted pads) the parts store could get, which they didn't even stock so had to have ordered in. Set up normal, one long one short each side with S10 cylinders. Replaced drums at the same time as they had noticeable grooving and didn't want to bother with having them turned. Go through a break in on the new shoes/drums. Give the car a couple neutral revs before staging to build extra vacuum in the brake booster, mine would hold 15 psi on the brakes. Make sure E brake cable is adjusted correctly as it affects rear brake operation also.

 

[JYLP]

I can't seem to be able to hold boost at the line with my brakes.

Vaccum conversion - check valve seems to be holding.
Gbody rear upgrade. (new)
Akebono front pads (new)

any recommendations on where to look next?

Get a little heat into the brakes, pump the brakes a few times and try that? Vacuum psi at idle? How much boost would you like to hold and so far, how much can you currently hold?

 

[huntsg]

Bailey's Two Step or the TR6 ignition module with Two Step. I've done the usual mods listed above, but with my TR6 I can build boost all day long.

 

[dank GN]

Pull up to the line put it in neutral rev it feel the brake pedal go down alil bit more hold it there and put back in drive and brake boost

 

[Nick Micale]

This has been beat to death for many years as holding boost on the line has nothing to do with the type of assist which is used for the master cylinder?

There are many factors that determine how good or bad the car can build boost.

Some of these mechanical items are the condition and state of contact with your rear brake shoes and drums, the torque converter match to the turbo, tires and road surface type and condition, and all these items come into play if you do not have a trans brake.

 

[aufond]

thanks guys,
I can probably only hold 3-4lbs right now before I push through.

 

[JimP]

Trans brake helps. If you have the extender chip you can also program what's called spool fuel, limits torque while building boost. I have vacuum brakes as well.

 

[Undercover87T]

If all else fails try using the ebrake. I've had to do that even with new large shoes, matched converter, and upgraded 4 piston front brakes and stainless lines. 7-8psi is max for me.

 

[aminga]

Bailey's Two Step or the TR6 ignition module with Two Step. I've done the usual mods listed above, but with my TR6 I can build boost all day long.

This. 2 Step set at 300 RPM above converter stall with 15 degrees of timing retard on the 2 step.

Even without the 2 steps a line lock helps.

 

[larrym]

Yes pulling the timing helps for sure. The extender chip also has launch assist which does the same thing.

 

[SCOOBY DOO]

I can hold 20 lbs of boost on the line with the foot brake and vacuum conversion. I don't see any mention of line lock.

 

[haywire4130]

This. 2 Step set at 300 RPM above converter stall with 15 degrees of timing retard on the 2 step.

Even without the 2 steps a line lock helps.

Do you have yours set on full cut or partial cut? I havent messed with mine much since initial setup. My car did a 1.53 60' with mine set like your recommendation minus the retard with a partial cut so i didnt mess with it hahaha. Is either full or partial better or worse as far as abuse to the engine/headers/turbo?

 

[Chuck Leeper]

I can't seem to be able to hold boost at the line with my brakes.

Vaccum conversion - check valve seems to be holding.
Gbody rear upgrade. (new)
Akebono front pads (new)

any recommendations on where to look next?

"Razor alky set up,"....You have the alky delay/relay set up? Or, do you have alky on set above launch boost?
Regardless, the idea of a converter is where I'd start..

 

[aminga]

Do you have yours set on full cut or partial cut? I havent messed with mine much since initial setup. My car did a 1.53 60' with mine set like your recommendation minus the retard with a partial cut so i didnt mess with it hahaha. Is either full or partial better or worse as far as abuse to the engine/headers/turbo?

I don't remember. I think it's a partial cut. Last time at the track though it was 1.47 60ft on 235 radials

 

[haywire4130]

I don't remember. I think it's a partial cut. Last time at the track though it was 1.47 60ft on 235 radials

Wow, guess im leaving a little on the table! Cant wait till next year to get a little more practice

 

[vboosted6]

I can't seem to be able to hold boost at the line with my brakes.

Vaccum conversion - check valve seems to be holding.
Gbody rear upgrade. (new)
Akebono front pads (new)

any recommendations on where to look next?