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Servo on front only or all round?


Waynebaby
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Hi All,

My Mk3 GT6 came with a factory fitted Girling Powerstop Servo, and apart from getting it refurbished to cure a brake-fluid drinking habit I've never thought much about it (the car stops safely if given sufficient notice) When looking through the "Guide to Originality" book by John Thomason however I spotted that my under bonnet brake pipe arrangement looks nothing like it should. From the wiggly state of the pipework it's obvious that the pipes have been changed at some stage, but the change seems to be more than just cosmetic.

As far as I can tell from looking at pipe runs in the the parts catalogue, the servo should be plumbed in such that the servo assistance only acts on the front brakes, with the rear circuit being acted on by pedal pressure alone from pipework on the "input" side of the servo. My car's brakes have been been plumbed in such a way however that the servo assistance acts on all four wheels.

Am I correct in thinking that the original design intent of Triumph was for the servo assistance to act on the front brakes only?

Given that the car stops, passes MOTs with good brake balance and the present arrangement seems to have served the car well enough for at least the last twenty years, can anybody think of a good reason why I should change the braking arrangement back to servo assistance on the front only? Will it stop any better?

Wayne

 

 

 

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Wayne,

Yours is the same as mine! 1973 Mimosa, non rotoflex. The Girling only worked on the front. My servo didn't work very well and then I started loosing fluid. The servo vacuum chamber was filling up with the stuff. I replaced it with a Lockheed. At first it didn't work, I tried all sorts, new return springs on the rear drum shoes, new rubbers in the cylinders, re-furbed the master cylinder. In desperation I plumbed it in to all 4 wheels. Nothing worked.  Finally I took the new servo apart and found it had been assembled by an 8 year old!

Anyway got it working, but the things I found out are these. Previously the servo could be fitted as an option and worked on all 4 wheels. But the Feb 73 up grade had the servo fitted as standard. Aditionally the rear drums were 1/4" wider and the cylinder bores increased in diameter. I think  beefing up the rear brakes unbalanced the braking and to compensate the servo was limited to the front only. 

I can confirm from my experience of fitting the servo to all 4, that on the front only, works best. Oh, and the Lockheed is MUCH better.

The bigger wheel cylinders are now hens teeth and Rimmers and the rest say fit the previous cylinders. I would ruminate that if you've had the big cylinders replaced by the smaller, braking at the back might not be so unbalanced for a 4 wheel servo.

 

Doug

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Doug,

Thanks for the reply. I still have the self-adjusters on the rear brakes so I suspect that back in the early 80s when the car had a major refurb' someone put the brake-pipes back together the way they thought made most sense. I'll leave the brake lay-out the way it is for the time being and try plumbing it in correctly as part of next winter's project work and see how that feels (It'll give me an excuse to change over to silicon brake fluid!)

Wayne

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Hi

Interesting read. I am considering the addition of a servo to the Herald, during refurb; Any Thoughts?. Bear in mind I am no longer in the "first flush of youth", so a bit of assist might be good?. Some Braking systems, I will have to check Mine, have a differential valve for the rear brakes, which limits the effort to "prevent" lock-up!. Cannot say I saw one on strip down?.

"Self" adjusters, on almost any vehicle are OK, at first, but largely because of their location, are prone to failure unless maintained! Now IF you are going to the trouble of "maintaining" them, Why do you need them?, it would be just a quick to make a manual adjustment and be done with it?.

Catch 22?

 

Pete

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The fits all kit servo sold by many is just that its not model specific, its just parts you make up to fit whatever

Look around prices vary wildly and its the same kit  

There are 2 different ratios to give greater or a bit lesser assistance.

On a herald or vitesse its fittedninnthe single line sytem to work front and the rear together

It just added to the circiut between the m cyl and the front /rear 3 way union

Various positions , across the clutch master, is normal, as theres no clues in the kits i moved the battery tray nearer n/s and 

Popped the servo next to the battery on my Vit6

Certainly takes the pedal load and Oh heck out of braking , i  also used mintex 1144 pads which make a very siimple braking improvement

Servos dont help braking they only help the drivers effort   but can uplift the feel of the braking 

So if sourcing look at all makes from jag to  mg  

The kit is just 'universal'  doesnt realy fit anything, you make it fit what you have

Youmget servo, bracket, length pipe , hose  and  no clues apart frommthe angle it should be mounted

Pete

 

 

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PeteH,

Not quite sure how you "maintain" GT6 self adjusters! :lol: The nature of them, the way they work, they just get bent and there's very little chance of getting them back to the right shape.  There is no external means of adjustment, unlike previous models so, it's wheel and hub off, tighten it up, try and get the hub back on, press the pedal to try and centralize the shoes. Put on the wheel, turn it, are the shoes rubbing? Yes/No? Do it all again, usually twice more. I would really like to retro fit the old system! Another job I'm unlikely to get around too. :(

The trouble I had with my new servo was probably down to the fact that it cost £80, £40 cheaper than the most expensive kit! I had to clean up the insides and fit a one way valve that actually worked.

Get a Lockheed style kit, much better than Girling. As Pete L says it can be a squeeze to get it in, make sure you fit the support arm for the slave cylinder. I've seen them without.  Without the hydraulic pipe will flex and eventually split. The support also ensures the servo slave cylinder is at the right angle. Not sure what car you have? Finding a source of vacuum might be an issue. Make sure the rubber vacuum pipe is long and dangles down to form a U trap, this prevent liquid getting into the servo.

Doug

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2 hours ago, dougbgt6 said:

PeteH,

Not quite sure how you "maintain" GT6 self adjusters! :lol: The nature of them, the way they work, they just get bent and there's very little chance of getting them back to the right shape. 

The clue's in the name. You adjust them yourself. On my Mk3, mine were so bad they released instead of tightening and I was sick of having to disassemble then adjust every so often, so removed them completely. 

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GT6 radiator is not very wide as it has to drop between the front chassis rails. It compensates by being tall and deep, if you follow me. Spitfire radiator on the other hand is very wide, not so tall and not nearly so deep.

gt6rad.jpg.ffbc0848fc9b93a44d2a45deeee9634d.jpgspitrad.jpg.f8acbf07eeda9bfa26bb28d5ea64a200.jpg

So I think it IS a GT6 radiator. But I don't know how it will cope with triple Webers and a stage 3 engine!

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17 minutes ago, Colin Lindsay said:

It's one of them there optical delusions, the way he's taken the photo distorts everything. I'm trying to work out what the brush shaft is for, that runs along the manifold side of the rocker...

Hello Colin

                   Its for the heater I did the same on Spitty

Roger

DSC03578.JPG

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