Brake servo/slave cylinder replacement

I’m replacing the original brake master cylinder and servo/slave brake cylinder on my 72 S3. The servo/slave unit is a close fit with nearby chassis tubular braces running from the upper firewall to the lower front end. The shop manual says only to “maneuver” the servo/slave out of the car after detaching it from the firewall. I managed to get the old servo/slave unit out after several efforts at “maneuvering” around the chassis tubing obstruction. The new unit, obtained from Barrett, looks identical to the old one—-same dimensions. I took pictures as I extracted the old unit, but despite that I haven’t been able to successfully “maneuver” the new one around the obstructions into position against the lower firewall. Advice from any who have done this project would be much appreciated.

I have a 1969 Series 2 and did this identical task a few weeks ago. I don’t know enough about the differences between our two cars, but in my case, I ended up taking the battery, the battery tray, and the rock shield floor from under the servo out and inserting the servo from under the car.

I know it sounds like a lot of extra work, but it maybe added an hour on taking those parts out and an hour putting them back it, but it sure made the task of getting that large servo into place easier.

I pulled the battery also in mine for the same work a couple of years ago. The access was fine. The tricky part for me was connecting the line between the servo and the MC. I might have said a few choice words and consumed an extra beverage in the process. When you get to the bleeding part try doing it with syringes. This worked great for me and others in the forum have also done it. No helper is needed.

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Is that the hands :rofl:


The small bracket that the nose of the slave bolts to can be moved. That helps when it’s going back in. There’s a very small bolt and nut that clamps it to the frame rail. I only discovered that after cleaning off years of grime.

Worth noting that these connections are easier (but not easy) if done before the mounting nuts & bolts are tightened up - some wiggling of the cylinders helps the connections to line up & threads to get started.

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You may want to consider checking your vacuum tank for brake fluid when replacing your servo. Mine was half full of old fluid due to a failed slave (replaced a few months ago) I’ve had my 69 S2 for 26 years and dont remember having to add brake fluid to the resevoir. Certainly not 16 ounces!

Many thanks to all for the very helpful ideas. I should have noted in my request that my car is OTS, LHD. So my battery is on the R (passenger) side firewall. But there may be some movable flooring under the servo/slave which I will check. Any other thoughts or ideas are welcome.

Hello highleymd,
As far as the Slave/Servo system and battery locations are concerned, they’re all the same, LHD/RHD, OTS/2+2.

There is a removable mud shield directly below the Slave/Servo system.



Thank you for the helpful info. Do you know for certain if the slave/servo will fit thru the space into position on the lower left firewall if this mud shield is removed?

I have never knowingly sent any computer generated emails.

If your battery and tray are mounted at the right (passenger) firewall and the slave/servo is on the left (driver) side, how does battery removal help get the servo in? Pardon my ignorance, I have a lot to learn about E-types!

They are not. I have a left hand drive Series 2 FHC, which means the battery, battery tray, servo, master cylinder, and clutch master are on the left hand side of the car. I removed the rock shield on the left hand side to make installing the servo a bit easier. I was also installing new brake lines and I needed to get to the rear brake line that transitions to a “T” for the brake switch and then onward to the master/servo.

Me too (mine is also a Series 2). I just removed everything that could be removed including sliding that bracket on the front of the servo forward out of the way:

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Highleymd’s car is an S3. The battery is on the opposite side to S2 cars.

Frank, you must be a magician if you removed the servo from the top without removing the mud shield. Or perhaps the S3 has a lot more room between frame tubes. Going in from the bottom should make things easier for you.

Yes, I’ve only ever worked on an S3 but I suspect there’s more room between the chassis tubes above the slave/servo than in the shorter S1/S2 cars. I was just following the S3 shop manual instructions. But it’s still a very close fit. I suspect the slave/servo is the same size in all series. Thanks. Frank

Looking at the photo in a prior post of the slave/servo as viewed from below in an S2 car, I don’t think the S3 has nearly as much room to pass a slave/servo thru the chassis tubing from below as the S2, unfortunately. That’s partly because the left front torsion bar passes thru that area on the S3. I would be very grateful for any comments from anyone who has done this job on an S3 car. Thanks to all for your help. Frank

I was unable to find a clear description of getting a new brake slave/servo into an S3 car, but I managed to get it done. (I saw no way to do it from below because to the left front torsion bar position in the S3.) It looked as if the servo needed to be vertical and as close to the firewall as possible because that’s where the most clearance is around the chassis tubular struts which obstruct the area. But the key turned out to be moving the slave/servo assembly slightly forward, away from the firewall. In my car, that could not initially be done because the end of the slave cylinder is obstructed by the thin sheet metal partition separating the left front wheel well from the servo/slave compartment. However, there is a row of 3 nuts on bolts holding this partition in place. I removed those so the end of the slave cylinder could push the partition forward less than one inch. When I did that, the servo dropped into its
normal position against the lower firewall! Reinstalling the 3 nuts & bolts was easy. I would not try this without removing the PDWA unit from a nearby strut, but I did not need to remove the bracket which holds the end of the slave cylinder. Overall, a happy ending to this part of the job.

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Glad to hear you got it in. Now to bleed the system.:worried: Just did mine yesterday after replacing the mc and servo. I got a solid pedal using a MityVac, but plan to do a final bleed when my ‘assistant’ is available.