Some may recall some posts I've made over the last ~18 months about what I interpreted as sub par braking performance, and after some research myself and finally getting a shop to also notice.... extensive testing has identified what I already suspected, which is that the vacuum booster (servo) is not holding vacuum.

Normally this wouldn't be a huge deal, as typical new OEM boosters are usually only a few hundred dollars and remanufactured units may be well under $200, sometimes under $100. After all, it isn't a complicated part.

Well, not so for our X300s ...and with that, I think I've finally found one of the examples of where our Jags do have a premium parts price tag.

For some unobtanium reason, the booster for our X300s comes in two flavors, one listing for about $600-700 (2 hole mount?), the other for $700-850 (3 hole mount) And of course, mine is the latter.

One can also get a remanufactured unit, but those still are $250-350 ....and the booster that failed in mine IS a reman, so that doesn't build confidence.

Now, I also could get a used unit for less than $100 all day long, but there's a risk there too obviously, but it's mostly in the time invested in my labor and any unknown about the longevity (or if it even works) of the used unit.

So that begs the question; what is the typical failure rate of an original OEM booster? Rare? I know I've never had to replace a booster in ANY car I've owned for decades, so it seems like a rare failure overall. So maybe if it is rare, the risk of installing a used booster may be minimal if it hasn't been flooded with brake fluid?


So thoughts on the alternatives?

Brakes are certainly of paramount importance and something not to go cheap on, but approaching the better half of $1000 for a booster is pushing the limit. After all, I've been driving it with limited boost for nigh 18 months and really have gotten used to it honestly ....so it's not like the MC is failing or something catastrophic, so perhaps there is a reasonable alternative to a new $800 booster?

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Oh, and for those interested in the symptoms, all was noted as abnormal:

• Initial harder pedal effort than normally expected, much like an old non-power brake car
• Brake pedal will occasionally push down very low when stopping
• Brake pedal will rise back up forcefully when engine is cut off
• Vacuum will go to 0 in booster often after one brake press after engine off, compared to other XJs it takes on average 3 presses to exhaust vacuum

The symptom of the brake pedal sinking is normally a classic indication of a master cylinder failing, but additional investigation of my scenario by the dealer indicated everything else (pads, rotors, calipers, vacuum supply and check valve and MC) were OK. The additional observations indicated that the booster was not holding vacuum.

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I would check out a current issue of Hemmings magazine. You might find a rebuilding service that could rebuild your existing unit for a fair price.

 

I've had good luck with this outfit:

Booster Dewey Power Brake Booster Exchange Inc.


Cheers
DD

 

What a great idea!

And with a little Googling, here ya go:

Power brake booster rebuild - Technical - Antique Automobile Club of America - Discussion Forums


Doing some research, it looks like that Ed Strain ( Ed Strain, Incorporated - Power Brake Booster Rebuild ) fellow mentioned in the thread above is well respected for vintage booster rebuilds, but unfortunately he only rebuilds boosters from the 1950s through early 60s. But I may give him a call or email to see if he recommends anyone else for modern applications.



Some others after a quick Google:

Booster Dewey Power Brake Booster Exchange Inc.

BrakeBoosters.com

Power Brake Exchange

karps power brake rebuild boosters power brake rebuilding, Karps Power Brake Service Upland, ca Upland, CA Home

Power Brake X-Change Inc.


From Hemmings:

https://applehydraulicsonline.com/

Brake Cylinder Solutions


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I'm facing the same dilemma. My problems are intermittent and I'm 90% sure it's from a small split in the diaphragm which seals up with heat. I brake in an odd way, tending to feather the pedal to stop smoothly, and it's been getting harder to do that because half the time, the pedal feels like it has an exercise ball under it. Sometimes it just fails completely and the brakes lag for a whole second. I was thinking the check valve but I couldn't remove the vacuum line from the engine at all.

I'm probably just going to get a secondhand one. Worst case, you'll be stuck with useable parts from both units and you can attempt a rebuild (unsure if this is possible). Do let me know if you find a good solution!

 

Also for reference, the X300 boosters are:

To VIN (748414) JLM12078
From VIN (748415) (3 hole fixing) JLM12188

My VIN is 795... so that makes mine a JLM12188 variety apparently.

I'm not sure if the JLM12078 is a 2 hole, 4 hole or other than 3 hole since the JLM12188 is specified as a 3 hole?


Also the JLM12188 was used on the XK8 through VIN 038099, any idea what model year XK8 that ran through?


If I go the rebuild route, I'll probably buy a cheap used one for $25-50 and have it rebuilt so I can keep driving. So any help narrowing down which year XJ and XK8 have the 12188 is helpful, either by model year coverage or if there is some visually distinguishing characteristic.

For example on the XK8 after VIN 038099 it went to a 4 hole fixing, so that one's easy. Not sure what might be distinctive about the earlier XJ 12078 booster?



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I'm not aware of it being a common failure point. Perhaps try a used one if you can pick it up cheap?

I assume the vacuum pipe and associated check valve have been checked and are good?

 

I tend to agree with Jagboi64 , boosters do fail , but are not a common failure

Given that you have replaced the booster once before , I would , (if you haven't) have the engine vacuum checked .

If you have less than 18 inches of vacuum at idle , the booster won't be your problem .
You need around 26 inches for the booster to work continuously .

Most boosters are a SINGLE TYPE DIAPHRAGM , you will find that yours will be a TWIN TYPE DIAPHRAGM , and yes they are a lot dearer .

These boosters are very complex , but you don't need to buy another booster , they are easily repaired , parts are still available and if you do have an internal leak you may only need to replace the rubber diaphragms .

I believe part number JLM12188 was fitted to the XK8 from 1997 through till 2004 .

 

Al,
I sympathise regarding the price of a new replacement booster, and would be inclined to agree with jagboi that a used replacement would be worth a try. I would also check your vacuum hose to the engine.
On a cautionary note, if you loose all assistance on that car, braking will be highly unsatisfactory, and nothing like an "old non power braked car". I have never heard of total loss of power assistance on an X300, but they, like the rest of us, are getting older every day....! I would be inclined to prioritise getting to the bottom of this one.

 

Al,
I'd go for a used one from a breaker, install, then ship your original off or repair yourself as needed. You may find the used replacement more than adequate and reliable. If not, you've got your original for refurbishment.

 

Thanks, yes the vacuum supply hose and check valve were both tested and verified by the mechanic.

Notes from Jag mechanic:

"Sometimes pedal goes very low on stops. Difficult to stop quickly or get ABS to activate. Measured rotor temp, all equal. Checked for brake drag, none. All calipers appear to function normally. Noticed with foot on the brake pedal when engine shut off, pedal would rise. Checked vacuum supply to booster, 18" at idle. Tested check valve, working normally. Tested vacuum held in booster, 18" when brake applied, goes to 0. Compared to another car. Pedal does not rise when shut off and takes several pedal applications for vacuum to go to 0. Booster appears to be leaking when applied. Recommend replace booster."

I'm going to make some calls to some rebuilders tomorrow to see if they rebuild our Ate booster, and at what cost.

BTW, I bought the car with the remanufactured booster already installed, so I don't know its history.

My plan is to potentially get a cheap used unit and have it sent off for rebuild. I don't want to install an unknown quantity used unit, to just have to uninstall it again to install the rebuilt unit...

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That may be the problem right there, who knows how well it was rebuilt? I have seen a few X300's at the wreckers here and they do appear to have the original booster, surprised it would need replacing.

 

Yep, that's always been the original thought, which I now feel better about being confirmed.

That's why I'm hesitant to invest in another reman unit or have my reman unit rebuilt, so it's either new OEM, used OEM, or getting a used "un-reman'd" OEM rebuilt.

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Just chatted with Dewey at the shop above, and unfortunately he doesn't rebuild our boosters. But he gave me three other places to try. I'll post what I find out.

I checked out all the others in my list above and for various reasons they cannot either, except for "Power Brake X-Change".

So out of three that Dewey provided, "Power Brake of Metro Denver, 303-428-2209" was the only one that said they could rebuild our late model, dual diaphram, "sealed" Ate booster. He seemed very knowledgeable without much prompting from me and described the particular booster from memory. Price is about $150 (which seems consistent for other re-builders of other types of boosters), and along with the rebuild they bead blast and repaint it black like factory.

Power Brake X-Change ( http://www.powerbrakex-change.com/ ) which I found via Google, is the other shop that says they can rebuild the unit. Their price is about $250 for a similar service that rebuilds and refinishes the booster. His recommendation was also that unless the master cylinder had recently been replaced this is a good time to do so as any future leak from the back of the MC would ruin a new/rebuilt booster. This is of course true, but these OEM Ate MCs are pretty reliable and long lived units if the fluid has been kept up, but then again if original mine is 20 years old, soooo..... something to think about. A remanufactured MC is about $170, but new is $800. That BTW is not unique to our Jags. My Buick Riviera's Ate MC is a similar cost new versus reman. Remanufactured MCs used to give me pause as they had such bad reputations, but I've installed two over the years, one as recently as a couple years ago on the Riviera and have been pleasantly surprised. So maybe they've improved.


Unfortunately I can't find any substantial reviews of either company online. The Power Brake X-Change at least has a web presence, and the Denver place has one positive and one bad review online, but neither having a web-page nor one or two online reviews necessarily means much these days.

So I'll have to sleep on choosing which, as this isn't just about cost and a mere $100 difference isn't the sole consideration.



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