Servo Gone! (single or dual line?)

Z

zebedee37

New Member
Had the wonderful experience today of losing my brakes!! All the brake fluid had dissapeared and no sign of a leak - I refilled the reservoir and with a good deal of pumping the pedal - got slight braking to enable me to move car.

Repair kits seem to be few and far between for the 3500S. The standard 3500S - does that have a single line or dual line servo?
 
I wouldn't use a repair kit, the one that went on mine after dismantling looked like it had a kit fitted. The bore on the slave cyclinder was pitted near where the control valve fits, apparently they are prone to it. My new one is sleeved with a chrome bore, which seems to be the thing to do.
 
Hi Fenton

Did you manage to get a video of the event? Quite looking forward to the expression of terror!!!

I am 99% sure that new servos for the V8 are unobtainable - although you can still get servos for the 4 cyl cars. General consensus seems to be that you really ought to get the bores sleeved, and it's pretty clear that the white plastic air valves are a potential problem (although yours sounds rather more funadamental!). I strongly suggest getting a master cylinder while you're at it. Even if it wasn't the cause, you are going to have the system empty of fluid (as opposed to just having an extremeity open to do a caliper or brake hose) and bleeding from that state is a real pain, so best get all the possibles in that general area out of the way at once!

A previous topic recommended a recon from Wynn's which sounded like it had been done properly, otherwise you're into sending it away for a refurb to someone like The Quality Factor epbranch@thequalityfactor.co.uk , 0151 356 2125 or Past Parts, Unit 4 Chase Road,
Northern Way Industrial Estate, Bury St Edmunds, Suffolk IP32 6NT, 01284 750729
restore@pastparts.co.uk

Chris
 
What I have done three times very successfully is to buy a brand new Lockheed remote servo - the hydraulic part is identical to the original - even down to the numbers cast onto the body.

Then you unbolt the tank & throw this away - fit the existing tank from the defective servo (check that the rubber diaphram is sound - if not fit a new one, check the piston rod is unmarked where this penetrates into the bore) and fit this to the hydraulic cylinder. You will need to swop the securing bolts over as the latest seem to be metric - this is the only difference I can detect - all the other parts - bore diameter & stroke - are the same.

You will have a brand new servo for less than a re-sleeved bore, very simple to do - the only difficulty is getting the new Lockheed servo in the first place - I believe that they manufacture in batches, so not necessarily a constant supply.

As I say, I have done this three times (got the tip from a Rover P5B owner) and this is the best & quickest solution (the work can be done in a few hours) and you've got the closest to having a brand new servo.

Good luck!

Gary
 
A very handy tip, but would be of far more use with the Lockheed part number of the donor servo.
 
So - do I understand correctly - it doesnt matter what car the servo is made for?

eg would this be worth going for and then using the internals?

ebay 180187539512



Edited By zebedee37 on 1196972508
 
zebedee37 said:
So - do I understand correctly - it doesnt matter what car the servo is made for?

eg would this be worth going for and then using the internals?

ebay 180187539512
Click to expand...
That actually looks very similar to the P6 2000/2200 servo, I wonder if the diameter is the same.

I would assume the cylinder to be the same, certainly looks like it.
 
zebedee37 said:
So - do I understand correctly - it doesnt matter what car the servo is made for?

eg would this be worth going for and then using the internals?

ebay 180187539512
Click to expand...
Its the ratio that's important, that much I do know. I got conflicting information on what that ratio is. Most people say its the amount your peddle effort is multiplied by, which sounds correct to me. But I've read a few articles that say its the ratio between the bore of the slave cylinder and the bore of the breaks its working on. This is odd, and possible that I miss understood. But at the end of the day its the ratio that is important. All depends which part of the servo creates the ratio. Gary's solution sounds good as its tried and tested, i'm sure if he did it once and found the breaks were poor he would have not done it again. When I was looking to do the same I found a recon servo for my 4 pot at about the same cost so took the lazzy man option. :;): Also looks like mine had the wrong servo on it away so was the best option for me.
 
It is the remote servo - from memory - it is the size of tank that differentiates what is suitable for each car - as the tank is not needed it doesn't matter.

The one shown on e-bay looks similar to those fitted on the P6, and it would need to be compared like for like to be sure.

When I bought mine, it was about 5 years ago for the first, I took the old along and compared this visually to what was offered (externally identical) and the subsequent ones I bought I just asked for a Lockheed remote servo, and these were all identical.

The very first time, I checked all the vital internal bore dimensions - they were identical - except for the fixing bolts, which were metric rather than imperial.

I do not have any packaging left, so I don't know the actual part number, but I can't image that they have that many servos of this type still in production, but like I said, it is the tank size that defines the application.

I hope that is of some use - best to approach a proper motor factors rather than Halfords, I used Cliffords in Hove and also Speedy Spares, also in Hove/Portslade on the Sussex Coast.

Good luck.

Gary
 
The one on ebay looks right - and is a very good price, I paid about £110.00 for the ones I bought.

I have always had really good brakes on my P6's - I always renew all the parts as soon as I get the car - the car with the least reliable brakes is my current early 2000 (1965) and the problems related to the master cylinder, which was re-sleeved - had to scrap it in the end & fitted a brand new m/c for the later cars - much better.

The re-sleeved servo has been fine - this is quite different to the later cars, so I couldn't do my usual trick!

Gary
 
That's fascinating! I had assumed the bores would be different from servo to servo. Perhaps it's just the master cylinder bore that varies then? The one on Ebay has the white plastic air valve as well, so that's a double win. Don't forget to renew the master cylinder as well, it would be a terrible shame to get all the bleeding done only to have to have a second bite at it for the master cylinder!

If you go down this route, please report back and we'll all be doing it!!!

Chris



Edited By chrisyork on 1197037948
 
AFAIK the bore of the cylinder on the servo has no effect on the actual mechanical advantage in the system, that is obtained by the ratio of the m/cyl bore and caliper bores. All the cylinder on the servo does is allow a point at which the vacuum can be applied into the system to give the assistance.

The only way the servo bore could affect things is if there was a variation in the bore between where the fluid enters and where it exits the servo.
 
The price of the one on ebay is so seductive - can't see you can go wrong - not sure how good the Wins one will be - their operation is essentially a scrap yard speciallising P6's.

I would suggest that it would be very sensible to obtain full test results following reconditioning to verify a range of input pressures gives satisfactory output pressures - not an unreasonable request that I feel sure a reputable reconditioner would be happy to oblige.

If it were me I would take a chance on the price of the one on ebay - if it was found to be unsuitable it can easily be sold on, might loose some money, but if it was correct - a significant gain!

Good luck.

Gary
 
A brake servo boost ratio refers to the tank and membrane diameter. The membrane is what pushes the piston through vacuum underpressure and creates the brake boost i.e. takes the effort out of you. So, there is no reason to have different bores in the servo cylinder, it would make no effect really. But the size of the membrane makes all the difference. The 4 cyl cars have a 7 inch servo i.e. the membrane diameter should be 7 inches. The V8 models have bigger 8 inch servo, because they need the added boost of the bigger membrane. I presume this is to compensate for greater brake pad area that need more pressure in comparison with the 4 cyl cars.
 
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