Brake Servo/Booster Replacement

toopy

Club Member
This obviously concerns my 260z 2+2 servo, but apart from the servo size difference on other cars, it's pretty much all relevant to 240z and probably 280z as well.

I recently replaced my failed brake servo with a re-manufactured unit, my car being a late 2+2 it has the larger 8" booster as standard, so I needed an early 280zx unit as a replacement, which I was reliably informed by MrF is a straight swap.

New and old for comparison.

BrakeBooster3.JPG

As bought, before i painted it.
New Booster1.JPG

I had previously replaced the master cylinder with a like for like 7/8 one (didn't see the need to go 15/16) as I had initially assumed this was the problem,
as after doing the Toyota 4 pot and vented disc upgrade, I couldn't seem to get the brakes to bleed properly.
In my case the pedal was soft, as if there was plenty of air trapped somewhere, but after renewing the MC
and still having the same issue, no amount of brake bleeding made the slightest difference.
I and as most people would rightly assume, when the servo fails or the non return valve plays up, the pedal will be harder to push, because there is minimal, if any servo assistance.
I searched for ages about servo/booster failures on classic and modern cars, and eventually came across a couple of forum posts in America of my exact same problem, and that it did indeed turn out to be servo failure.
It would appear, it is almost unheard of for them to fail in this way, but hey, i like to be different and apparently so did my servo! :confused:
Don't ask me exactly how it fails this way, as after looking at diagrams for hours, I'm still not entirely sure how they work normally!

So starting in the engine bay, remove the fusible link bracket as it stops the MC moving enough to get it off the servo,
if your car is a 240z, you don't have one to start with.
Remove/shift aside the washer bottle, it's impossible to remove/re-fit the servo with it there.
Unbolt the MC and pull it away from the servo and then push it towards the engine, the brake pipes will bend enough to allow this, you might have to be quite forceful, so don't be shy, but do be careful.

You might want to use a rag or old towel or something under the brake pipes, to stop them hitting and scratching the inner wing as you wrestle with the MC, I didn't consider that at first, and suffered the obvious! :eek:
IMG_0796.JPG
Unbolt and remove the aluminum spacer, at this point if you are in any doubt as to wether the servo has actually failed, and you may be refitting it, use an elastic band to hold the small central push rod in position. If you remove it or it accidentally falls out, there is a foam/rubber reaction disc inside that it acts on and holds in position, it's entirely possible for it to drop down into the servo housing, never to be retrieved.
This is especially important when the servo is out of the car, as it's all to easy to find yourself holding it in such a way that the rod can quietly, unnoticed, slip out!
IMG_0780.JPG

Inside the car, if your too big or have back issues that stop you laying across the sill with your head in the foot well..... stop now and, if your lucky and/or popular,
ring a friendly younger zedder to come give you a hand, and by that I mean, contorted and twisted and generally royally pissed off!! :cool:
On my car at least, there is a large electrical connector block, held in place by one bolt, detach it and remove all the plugs from the front, this gives much more
access to up and behind the brake and accelerator pedals, infact it's impossible to get to two of the bolts without doing this.
IMG_0786.JPG
Trying to unbolt the servo, I struggled with a selection of different tools for quite a while, hence the royally pissed off bit, in the end, the two pictured done the job,
a 1/4" extendable ratchet, with long reach socket and a flexible ended socket come spanner. Even so it's bloody fiddly and the ratchet barely moves a couple of clicks at a time, slow and steady it most definitely is.
IMG_0795.JPG
The main threaded push rod from the back of the servo connects to the brake pedal with a clevis pin, held in place by a spring clip.
Oh and get a really bright light, because although generally you can't actually see and work at the same time, it's mostly by touch in the end, the light really helps you see, before you can't see, if that makes sense!

Once the servo's out, and you've realigned your spine, and rubbed the mark off your forehead from the bottom of the steering wheel! compare old to new, take pictures and some measurements
for reference. I found the four smaller bolts on the rear were far to long, not sure if there length is correct for a 280zx but in this instance, they need to be 25mm. Also measure the total length of the larger rear push rod including the metal clevis on the end, mine was 149mm.

The bolts on the front/engine side were the same length, measure how far the smaller push rod protrudes past the servo case, as obviously you want the new one to be the same or ever so slightly shorter, but definitely not longer, and by ever so slightly shorter I mean approx 1mm to 2mm max.
It became plainly evident, as you'll read below, that the movement of the pedal is not remotely equal to the movement of either of the push rod's, so 1mm less on the small push rod length could mean around an inch extra travel at the pedal!

Also I noticed when i screwed the clevis onto the new rear push rod, that the rod/thread was also a bit longer, and protruded into the clevis by about 10 - 15mm, at first I thought it wouldn't matter, and left it,
but when i fitted the servo for the first time, it became apparent that, as the brake pedal shaft pivots, it hits the end of the rod/thread, thus the pedal can't move properly. Needles to say the servo came out again for thread length reduction!
IMG_0792.JPG

At this point you will probably of noticed, when the servo is the correct way up (the bolts are off set on the backside) that the vacuum connection is on the wrong side! unless you were fortunate enough to be sent a RHD one (Unlikely from the US)
In any case the vacuum pipework has plenty of give/flex to fit, although you probably wont be able to get it into the bulk head clip without stretching it unnecessarily.

With mine the new rubber dust cover on the rear push rod, was a bit loose and also a thinner gauge. I opted to reuse the old, thicker more resilient one, as it was obviously more than up to the job.
BrakeBooster5.JPG

Re-fitting is a simple reversal of removal, including of course, plenty of hot under the collar profanity! you may want to use some sealant or similar where the back of the servo is against the bulk head, there was no gasket on mine and none supplied, so safe to assume they weren't there as standard.
Mine did have some old sealant remnants, but no idea if that's factory or not, I didn't have any suitable sealant to hand so opted to use a bead of proper water proof grease. The only time i can imagine any water actually getting in behind a fitted servo is if the scuttle gutter above is rusted out, or your a Numpty with a hose at wash time if the bonnet still is open!
IMG_0790.JPG

Now, having got everything back in and bolted up, my enthusiasm for a job, awkwardly, but well done, quickly dissipated as I realised the pedal went far too low before the pads bite, it worked, but it was still shite! :banghead:
I removed the MC and spacer and had another measure of the little push rod, rough measurement showed it as about 4mm shorter. Now when i had measured them both for comparison on the bench, the new one did seem to be approx 2mm shorter, but trying to adjust it, while also not pulling the rod out of position in the front of the servo, is impossible.
They appear to be re-purposed old ones, and as such are seized pretty solid! whoever reconditions these things, can't be bothered to free them off, find a suitable replacement or re-manufacture them, so something to be aware of. It's not like you can use your old one of the correct length, because obviously you can't safely remove the new/old one from the new servo!!

I was hoping the 2mm difference wouldn't be significant..... Doh!

Anyway, how the difference got to be 4mm I'm not sure, maybe I didn't measure right, maybe the rod wasn't fully seated as supplied, I did think possibly the MC's were different, but measuring the depth of the hole in the end, they were identical.
So, I needed an extra couple of mm atleast on the end of my little rod!! the following bodge is certainly not recommended, but between a rock and hard place, I didn't have much choice.

I cut the end off a small plastic zip tie, which is approx 3mm, I put that in the end of the MC so the end of the rod once in position will bare on it.
Joy of joy, it works, the pedal is pretty much as it was before all the shenanigans started, the brakes aren't perfect, but the pads and discs are brand new so are yet to bed in at all, so hopefully in 50 or so miles, the feel will be as before, or very close to it.

Now your probably as uncomfortable with the bodge as I am, and the plastic zip tie head will be a temporary measure. ;)
An idea might be to pull the old rod out of the old servo, cut the required amount off the end, and use that piece instead of the zip tie, maybe Araldite it to the end of the existing rod.
Once something is in there and everything is in position, it's impossible for it to go anywhere, so I'm not worried about that, just something better shaped and more resilient than a plastic zip tie head!

Enjoy! :driving:

P.S. I will update the thread with whatever I decide to do to make the bodge, slightly less bodgy, and how things feel once the pads and discs have settled in. :p

IMG_0797.JPG
 
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Rob Gaskin

Treasurer
Staff member
Site Administrator
Wow what a write-up. Well done and I hope I never have to do it but if I do I know what to look out for.
 

tyroguru

Club Member
Yeah, thanks for the detailed write-up and the great photos. This kind of information and associated visuals are vital for me and one of the biggest strengths of this forum. I'm sure one day I'll be pouring over this page! Looking forward to hearing how things end up on the braking front.
 

moggy240

Insurance Valuations Officer
Staff member
Club Member
Could you make a smaller spacer between the servo and master cylinder to take up the slack of the shorter push rod or would make the bolt threads hit the brake reservoir.
 

toopy

Club Member
Could you make a smaller spacer between the servo and master cylinder to take up the slack of the shorter push rod or would make the bolt threads hit the brake reservoir.

Nice idea and yes, that would give the same effect, but also yes, the bolts would then be too long, they of course can also be cut down, but it's a faff for sure.
 

Zafraynn

New Forum User
Hi. I am in Malaysia. I also have a 1975 260Z 2+2. I now need to replace the brake master vac. Would you be able to tell me where you purchase yours please. Most sellers require a core exchange which I am not able to provide. Thank you.
Zaf.20191205_124408.jpg 20201026_124815vac.jpg
 
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