I need hydroboost help!

Jmansjeep

New Member
I have a 84 GN that I have put a ls engine into. All four brakes are now Wilwood disc, stainless steel lines, distribution block removed, wilwood proportioning valve, and a Wilwood 1 1/8” master cylinder. This setup worked good for several months and then one day driving home the brakes self applied and wouldn’t release. Got home loosened the MC from the HB and the brakes released. I have put a new power steering pump in, had the HB rebuilt, and replaced the pressure lines.
My problem is the brake pedal has maybe 1” of travel total. I barely touch it and the brakes apply. Power steering seems to work as normal. I have no idea what's chanced any why it’s so different. The pedal is the same wether the motor is running or not, very high and no travel.
Can anyone help me with this?
 

TexasT

Texas, Where are you from
Is this a stock hb unit? What power steering pump are you using? I'm guessing some kind of LS unit that a 6L truck might have. Who did the rebuild on the hb unit?
Being you were able to take the mc off and have the brakes release I would be looking at the hb or pump. The hb is pretty simple but if it is leaking internally i guess it could apply the brakes.
 

Chuck Leeper

Toxic old bastard
Staff member
Brakes are locked because the mc piston has not fully retracted. This blocks the fluid coming back from the calipers. You released it, when you loosened the mc.
The HB may be at fault, as could the mc.
 

Jmansjeep

New Member
It’s a stock HB for the GN. I had it rebuilt by Cardone and have heard there are sometimes problems with rebuilt units, so I got a rebuilt unit from Autozone and put it in, same problem. The pump is a stock pump for a 4.8 ls that had hydroboost brakes also.
 

TexasT

Texas, Where are you from
If you think the hb unit is functioning I would take a look at the mc. I had one that didn't allow the brakes to apply. Ended up bending the snap ring that held the guts in the mc. Yours might be hanging up on the mc in there. Pull that mc and look in the bore and see about the actuator from the hb unit will fit past the gut retainer in the mc.
 

Jmansjeep

New Member
It clears, but just barely. When I first installed the MC the HB actuator drug on the snap ring and wouldn’t let the pedal return, that’s fine now. I put a clamp on the MC piston and got not quite 1/2” of travel, Wilwood says that’s within spec.
 

TexasT

Texas, Where are you from
Above my pay grade then. I've just used stock type mc. Wilwood is a fancy brand so I guess they know what they are talking about.
 

TexasT

Texas, Where are you from
Can't see that a filter is a prob unless it gets to where it is restricting flow. But if it was I would think the pump would make enough noise to know it was happening. Sounds like to me the hb plunger got caught up in the mc.
 

1984 t-type

Murphy's Law
Sounds like the plunger may be too long and need to be ground down. You would think this would be an issue from day 1 tho. When I did my conversion last year mines drove fine and had no drag even at idle, but when I went to get an alignment one day they couldn’t get my car to roll forward on the lift all of a sudden. Worth a try I suppose
 
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