How much vacuum?

[gazby]

Hoping to be able to help an old mate out here, I was wondering if anyone can put a figure on how much vacuum is required to operate the power brake booster on a 1985 LR County. The booster was replaced 18 months ago and has been working ok for the past 50,000Klm but just recently he has noticed the assistance is not quite what it had been, removal of the hose from the vac pump shows the pump is sucking, there is some vacuum, but it would be nice to measure if it is up to specs. The County is fitted with a VM diesel ex an '88 Range rover and has what appears to be a "rotary" type pump. any help appreciated.

[roverrescue]

gaz,
Check the booster where it bolts to the master with Dick standing on the anchors
Even a newish booster will be prone to crack at this weak point.

I grafted two cracked plates into one booster and thickened up the lip just last weekend before swinging the motor in. Sick of them failing in the pressed tin.

The crack opens with pedal pressure and lets out the vacuum.

S

[gazby]

Thanks for the lead S, I doubt it will be easy to hear a vacuum leak over the clatter and din of the "mighty VM".
I keep forgetting that you're constantly working through ALL the problems as they occur, you should write a text book on "The joys of owning a.........", or alternatively "Landrover, not just a 4x4 but an occupation"
I will check that today as we are taking the "County" up to the Loco workshop to fit new springs, shocks and replace those flogged uni's.

[Gerokent]

A quick check would be to pump the brakes (with engine off), until pedal goes hard (10 or so pumps). Keep foot on brake and start engine, pedal should go down as vacuum builds up (very noticible). If pedal doesn't go down, booster or vacuum pump no good.

[roverrescue]

gaz,
you dont need to hear a vac leak.
The bloody booster will have a crack in it that will open up like a californian quake.
Even old blokes without their glasses will see the leak!

Unfortunately i dont have any other boosters to cut up and use the front plate off to make a doubler from?

S

[gazby]

Hey S, had that check today as suggested, no noticeable distortion of booster body or vacuum leak apparent around the master cylinder joint, the pedal goes fairly well down on the first pump (adjustment of rear drum brakes ?), but will pump up with a few applications. I cannot vouch for the braking effectiveness on the road as we ran out of time after doing uni joints and rear springs/shocks.
Will try the suggested pump up and start engine method as soon as can be done, that will at least prove the booster/vac pump combo.

[roverrescue]

i assume you would have seen fluid leaks at wheel cylinders / calipers?
How worn are the front pads?
"JC " justin cooper in hobart has written a post some place here with the booster pressure specs.

And i just found it. ? ? The land rover master speaks. Jc says vacuum should be 12 - 15 inHG and smooth suction.

Chuck a gauge on the vac and see what you have?

S