Hydraulic Power Booster

Hi All,
Vince is having trouble with his brake pedal not returning fast or not at all and on occasion his brakes have locked on.
He has all new calipers and disks, lines and rebuilt master cylinder so the only thing left is the Booster.
Has anyone had trouble before?
Can anyone tell me the brand and model so he can get a new one if that is the problem.
Martyn

Mort I'm away at the moment so don't have part numbers etc but from memory the hydroboost is off a Chev/Holden Suburban, something Chev anyway.
I had one play up on a previous vehicle and they aren't really repairable and most mechanics here in Oz run a mile as they aren't common. Heaps of vehicles in the US use them from sportscars through to trucks so they are pretty common over there and much cheaper than here even after paying GST and shipping. They come in two basic types, one with the nitrogen cylinder and one without which is what gives you a couple of brake applications with the engine off..
Have you tried flushing and replacing the power steering fluid as if it is dirty it will affect the brakes.
Also check the clearance on the pushrod out of the hydroboost, there must be a very small bit of freeplay or the master cylinder can't return completely and the brakes will stay on, sometimes you might need a washer between the hydroboost and the master cylinder to get the right freeplay as the pushrod isn't adjustable.
But if the pedal is slow to return then that might indicate that the hydroboost is faulty.

How would one know it is the booster and not the MC sticking?

Really the only way is if the brakes stay on after say a dozen jabs of the brake pedal and then separating the hydroboost from the master cylinder which in the Oka is a mission as there isn't a lot of room without complete removal of the dash.
If the brake release as soon as the hydroboost is loosened then that is the problem.
There was a thread a couple of years ago about problems between the two when fitting a new master cylinder and the solution was to insert packing between them or minutely shorten the pushrod.
might have been Pete Fox that first had the problem, I know when I changed mine I measured everything before and after and yes the freeplay had decreased but was still ok but some aren't

Peter and Sandra OKA 374 wrote: Really the only way is if the brakes stay on after say a dozen jabs of the brake pedal and then separating the hydroboost from the master cylinder which in the Oka is a mission as there isn't a lot of room without complete removal of the dash.
...

A 32-mm hole saw can poke holes inline with the bolts.
The door hauraulic deal has to be unbolted and a drill with a 90-degree joint is helpful.
A lot of swearing...
And some 1" webbing and some dowel wedged between the metal and curlicue pipes may be helpful to get them in alignment.
More swearing.
Then 32-mm cover (s) from the sparkle shop can cover the holes.

Holmz you will find that it isn't actually that hard to remove the dash, take the drivers seat out, unplug the wiring plugs to the steering column, undo the 4 bolts holding the steering column and lay it against the floor , flip the upper dash up and use rope or wire to hold it up there, pull the ducting off the dash vents, undo the bolts holding the lower dash in place, two near the A pillar near the door and two on the tunnel, then you can lift the lower dash out and everything is "relatively" easy to get to. I might have missed a step or forgotten something else that ahs to be disconnected but it is basically how I did it when replacing my master cylinder and removing the clutch pedal apparatus.

Peter and Sandra OKA 374 wrote: Holmz you will find that it isn't actually that hard to remove the dash, take the drivers seat out, unplug the wiring plugs to the steering column, undo the 4 bolts holding the steering column and lay it against the floor , flip the upper dash up and use rope or wire to hold it up there, pull the ducting off the dash vents, undo the bolts holding the lower dash in place, two near the A pillar near the door and two on the tunnel, then you can lift the lower dash out and everything is "relatively" easy to get to. I might have missed a step or forgotten something else that ahs to be disconnected but it is basically how I did it when replacing my master cylinder and removing the clutch pedal apparatus.

^Fantastic info^
Ta

Don't waste any more money, you either have the wrong master cylinder or the set up is wrong and that is why the lock up
Cheers,Joe

Dropping the steering column and removing the lower dash panel only works on an LT, XT dash is continuous across to the LHS

Peter thank you a part number would be good as there is a few that could fit but the right one is better, no hurry for the next week or so as Vince has ordered a master rebuild kit so we will see how that goes before replacing the whole thing if needed.

Hi Holmz, again Peter is right it is so easy to remove the lower dash ON an LT and Frank is right for an XT. I was told a few years ago by oka parts that if one needs to get to the master cylinder that it is easier to cut a hole out on the side facing the door and then screwing on a cover plate which I have seen done and it is very neet. On Vince's the previous owner took to the front with tin snips and maybe just a hammer and chisel for how bad a job when there was no need for it but all good as Vince has patched and painted to look like new.
Martyn

Hi Joe,
Vince had all the calipers replaced as new when he had the Diff's rebuilt and also brake lines that was 12 mts ago with no problems since that also included the hydrulic pump and steering box.
A few weeks ago he was driving down Roe Hwy and stopped at the lights at Kalamunda Rd all good until he tried to proceed but brakes locked on he rang me to help but by the time I could ring back maybe 1/2 hr the brakes had released on their own, since then the brake pedal while engine off return freely after being depressed but if engine on they either dont return or are very slow to return.
Vince has now had his own master cylinder rebuilt and proprioning valve but the brakes have not changed.
I was around his place on saturday and there is a hissing noise coming from his booster when engine on and brakes depressed which I am guessing is a good indication that the booster is faulty and as Vince doesnt want to spend any more money than is necessary if you know of any thing else please let me know.
The Master cylinder is the same one as always and the same one that was on there when this started it has now been reconditioned by a brake specialist and the problem is still there and it has been reinstalled the same way it came out.
Martyn

Mort it sounds like the hydroboost is crook, the one on my previous vehicle did similar, started hissing and pedal slow to return. I can't help with a part number, maybe Joe has one, it would be from a Suburban or Chev ute of a similar vintage to the Oka.

Check out this post I put up a few years back, it may be your problem

www.oka4wd.com/forum/oka-maintenance/1039-brakes-not-releasing

Thanks Pete, was trying to find it and the site didn't cooperate, from that thread the MC is a Dorman M39309 which cross references to a few others, truth be know they are all probably the same.

Thanks Peter Fox for finding that past posting. I have read all comments and just goes to confirm what I had suspected that it is the booster because Vince had not touched the master when the problem started and continued after he had his own master rebuilt.
Martyn

Peter it is good to see that some one else had a similar problem as it appears to be rare.
On a side note wasnt there going to be a parts/parts number list which I would think it is a good thing as postings get lost in the system as time goes by and that is not to say you should do anything I am just thinking aloud or in writting.
Martyn