Broken stud on brake booster

Well, I was installing my freshly rebuilt brake booster and I broke one of the studs off (mounting side, not master cylinder side). It was that one that’s a pita to tighten on the bottom fender side.

I have a feeling I know the answer to this already, but can I run this with just three studs holding it in place?

Well, how…?! But I’d say yes it’ll work.

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I was using a new nyloc but and I thought it was giving me extra friction. I guess between thinking I was trying to overcome that, plus the weird angle and limited range of motion In bent the stud and a couple more turns twisted it off.

It will of course function, Jay - until it breaks lose…:slight_smile:

… which is very unlikely…

xj6 85 Sov Europe (UK/NZ)

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Different answer than I expected. I was expecting the worst; welding on a new stud or a whole new booster. I was going to take note of any abnormalities while bleeding the brakes. If none, then run it as is for the time being.

Got to get the new xjs in the garage for examination…

When it’s all together, sit in the driver’s seat and push on the brake pedal with all you’ve got. If nothing snaps, you’re good to go. You don’t want it to snap during a panic stop, though.

I’ve been trying to visualize where the force is being applied during hard braking.

Is it pushing the booster towards or away from the firewall?

Are here any threads left?
Even a couple would suffice, get a long extension nut and a threaded rod.
You might have to enlarge the hole on the firewall.


It’s rotating around the brake pedal pivot, isn’t it? So up and away…

The pedal rod pushes directly on the master cylinder piston, Jay - not involving the booster housing. The boost likewise applies pressure on the piston, proportionate to the engine vacuum to ambient air pressure - which pushes the booster body backwards, towards the firewall.

Nominally, the maximum ‘backward’ pressure from a 10" booster is in the region of 800 pounds (23" Hg overrun vacuum) - pedal pressure does not affect booster body.

xj6 85 Sov Europe (UK/NZ)

Oops, yes. We‘re talking about the booster and that is pushed away from the alloy casting isn’t it…