MadaboutKitcars

Dual Servo



Hi Nigel

As you are doubtless aware several adopters of this servo had problems with sticking brakes, and it took us a long time to work out why - and I hope the answer will help with your question.

We found that the servo pulled the brakes on by itself over a period of driving. The final conclusion was that we should have been advised to fit a reasonably strong pedal return spring - the Landrover one advertised on ebay for £2.38 a pair is ideal.
And this brings me to an answer to your issue.

The dual servo must create a seal to atmospheric pressure when the pedal is at rest - if there is a leak it will effectively suck the brakes on and lead to binding and severely over heated brakes. I suspect the experience you are feeling is the 'stickiness' of that seal: it will have an internal spring to help close it off. I do not think you have a problem.

If you have not fitted the master cylinder, have you changed the adjustable screw in the output rod end? The supplied adjuster is not quite long enough to engage with the Sierra master cylinder: it must be change for a longer dome headed screw. This can be difficult, as there is a lock nut to be loosened before it will unscrew, and access in the deep recess is difficult. The best solution is to depress the input shaft in a wide vice with wooden jaws (a B&D Workmate is ideal) - this keeps the output shaft and nut easily accessible.

You will be amazed at how it transforms your Sportster: you can drive it harder, with much more confidence.

Goodluck, and let us know what you think when you have it up and running.

Mike

Servo issues

Mike
thanks for the prompt reply. Yes i have had a special adjustment screw machined up and tested in place with the M/C. Also took the precaution of fitting Goose's Land Rover spring mod.

Hope your'e right about the sticking issue. Just having the brake pipe plumbing done by a local garage and they are going refill and bleed the system this week.

Fingers crossed. Note of warning to anybody having to order a dual servo make sure you emphasise that what you want in large bold text in your email, they got it wrong and with duty and shipping and everything i ended up nearly £ 200 out of pocket.( anybody want an 8" servo!)

Nigel

As I will be helping Happy Dave fit a dual servo soon to his newly acquired Hunter (currently has the Metro one) I have been re-reading all through the earlier posts for this epic project to refresh my memory.

Regarding the pedal pull off spring I have checked and none is fitted to mine. That said I have never had any tendency for the brakes to pull on by themselves. There is quite a positive spring action for the pedal return so that must come from within the servo itself?

Peter.

Mike. Can you please tell me where you obtained your rose joint for the end of the push rod and what the thread is? I will buy two as I want to replace my own original clevis sometime for peace of mind. Peter.

Rose Joint

Peter
excuse for jumping in on this, but i got mine from from ABC (Anglia bearing Company) part no. MP061F39 (male only available).However when i contacted them i had the last one, i tried to get an additional back up but it seems like they were manufactured specially (was it for Mike ?) as a job lot . I phoned round about 5 other specialist companies and basically the answer seemed to be that no one did a 3/8 UNF male thread and a 10mm rose joint hole.

Mike may have better answers. I had to have a collar machined up anyway to join the male joint to the servo push rod thread. I found in my Marlin i had to shorten both the rose joint thread and pushrod thread length slightly to get them to fit and still have a decent amount of thread in the collar. So there is no reason the collar could have different threads at each end 3/8 facing the servo and 10mm to meet the male 10mm rose joint.

Nigel

Hi Nigel.
No problem and many thanks for this info. I had intended to use a female rose joint to replace my existing female clevis so maybe one of those in 3/8" UNF will be easier to source. Peter.

There is an interesting back story here which may prove useful to know......

My rose joint solution was to source a 10mm female rose joint and weld a 3/8" x 20mm long collar collar to it.

See post 653 in this thread. Whilst I am 100% confident of its structure (it operates only in compression), I felt others may want an off the shelf solution, - hence the Anglia Bearing 3/8" male threaded 10mm rose joint and a 3/8" collar, which all simply screws together.

If this is no longer available off the shelf, I would be happy to get a 10mm rose joint professionally welded to a 3/8" collar, as per my own arrangement, for anyone wanting to go down this route. Send me a PM.
Mike

Hi Mike.
Yes I would be interested in two please. Have sent you a couple of PMs, but on the other forum hwell: Peter.

Binding brakes - hard pedal- my theory

So having fitted my servo and having servere problem with pedal getting rock hard and brakes binding on. All was well for the first 250 miles so the basic set up must have been correct. I did all the recommended things ( return spring on the pedal and rose joint between the pedal and servo input rod).

Everybody here with this problem is thinking it related to alignment but i'm beginning to suspect its not. Having watched at some length a detailed video on how these servo's actually work it seems to me that the problem is related to the atmospheric valve failing to reseat properly when the pedal is released or pressure on it reduced. Its admits too much air in.

Why is the happening maybe related to one thing all BMW engined Sportster's have ( i don't know about other non E series engines ) but the exhaust manifold sits in very close proximity to the exhaust servo.

So these servo's get a big dose of exhaust heat. In addition the heat is not even. My servo gets very hot underneath as its exposed heat rising ( esp in traffic ) from the exhaust manifold collector pipes ( i have 2 on my M3 Evo engine) . Also my bonnet has no venting on it which may make it worse.

So my theory is that given these servo's are fabricated out of pressed steel, uneven heating can lead to it getting distorted and either the atmospheric valve does not seat tightly or the whole chamber is leaking.

Would appreciate anybodies comments /thoughts on my ideas.

I'm in communication with Pirate Jack ( where i brought them from) and waiting to see what they say.

Hi Nigel

I have had exactly the same brake servo problem this weekend, despite fitting the rose joint and a Landrover return spring. But I did find how to solve the problem...............

I've just rebuilt my Cabrio having had it painted. I wanted to take it on a 400 mile round trip to the Tatton Hall Classic car show, so wanted to make sure the electric fan worked. I parked it on the drive and left it idleing to build up engine temperature. When I came back to it I discovered the brake lights were on. These servos definitely suck them selves on!

I still went on the trip, and managed without problem - the solution was to pull the brake pedal back up with my toe every time I used the brakes - it did not make for a relaxing drive, but it passed off without sticking hot brakes. I now know for certain, with my servo at least, the issue is due to the inlet valve not seating. In my case I know a stronger return spring, or one mounted further down the pedal to gain more leverage is the solution.
Try this with yours - brake, and immediately pull the pedal back up with your toe ( and make sure your brake light switch does not prevent the pedal returning fully) - in my car there is definite movement to be felt. We drove non stop for 190 miles home without the brakes sticking on, so I know it worked for me.

Mike

Having enjoyed the benefits of the dual servo for some time I have found when bleeding the front brakes that a lot of black bits have come out in the collection jar. As that usually means wear in the master cylinder (at 40k miles) I have been looking for either a repair kit or preferably a replacement m/cyl unit. Mine is a Bendix m/cyl with three pipe connections (one rear and two front) and has a 23 on the raised boss but I can't find anyone who stocks one with a 23mm bore. Does anyone know which model Ford that would have originally been fitted to?

In the above dual servo posts there is talk of 22mm being the normal Sierra size. How does that perform as it is about 9% difference in surface area? I have 10" (Sapphire?) vented discs at the front and 10" solid discs (XR4i?) at the rear. Pedal travel with the 23mm m/cyl is fine so I don't want to increase that if possible.

I do have a s/hand 22mm sierra m/cyl, condition unknown, which may respond to a repair kit but would prefer to stick to the proven 23mm and a new unit if possible.

Feedback appreciated. Peter.

Wild guess maybe Ford transit. Try eBay item
371901589550

Thanks for the quick reply. It is close but the end boss is longer, it has an extra boss underneath and the mounting flange looks different. Will keep it in mind though. Also need to know other Cabrio/ Dual Servo users experience with the 22mm m/cylinder, especially pedal travel, as they are more easily obtainable and look externally identical to mine. The joys of kit cars eh! Peter.

Peter

There is a Sierra P100 master cylinder advertised for sale on ebay as being 23mm. Perhaps that is the original source for yours?

http://www.ebay.co.uk/itm/Ford-Sierra-p100-2-0-petrol-break-Master-cylinder-23-mm-3-pipe-/162591568315?hash=item25db3671bb:g:X3sAAOSwiA9ZaSrb

Mike

It seems that my 23mm Bendix master cylinder is for a Mondeo 2.0L 01- on.

However having trawled back through earlier posts I see that the 22mm Sierra master cylinder seems to be the more usual one fitted to the Cabrio and I am thinking of changing to that size if replacing it but don’t want to have excessive pedal travel.

So I have another question that wasn’t realy answered back then. What is the Cabrio pedal travel with a 22mm master cylinder and discs all round?

In my original post #220 I gave the following measurements:

With engine off. Pedal pumped several times (i.e. no vacuum /servo action).

Free pedal travel = 13mm

Total pedal travel with fairly hard push = 63mm.

With engine running at tickover.
Total pedal travel with fairly hard push = 90mm.

Handbrake when on works at 3-4 clicks but fully off for all above checks.

I have 10” (Sierra V6 / Sapphire?) vented discs at front and rear discs are solid 10” (Sierra 4x4 ?)

I would appreciate it if anyone with the same disc / disc setup as above could measure their pedal travel and let me know. Peter.

Hi Peter

I have the set up you describe - Cosworth 260mm front, and 2.0 GL rear discs.

I found my pedal travel increased when I fitted the Dual servo - there seems to be more free play in the actuator valve of this servo.

I have not measured the pedal travel, but I'll take a look this weekend and come back to you.

Regards

Mike

Beyond that I do not find the pedal travel excessive at all. Equally I do not recollect anyone fitting this set up and then complaining that the pedal travel was excessive.

Thanks Mike that's very encouraging.

I have looked at my spare old (like 20 years old) 22mm master cylinder which has plenty of black sludge in the reservoir so for safety I want to fit a complete new m/cylinder.

Kitspares do one for a Sierra for £87 and I have emaiiled them to confirm bore and flange sizes for compatibility with my Bendix one.

If your pedal checks at the weekend look ok and the Kitfit dimensions are correct I think that is what I will buy. Peter.

Still Sticking Servo

I have decided after a year and half of a sticking servo and trying various solutions to order a new one and hope its better than the last. Maybe I have just been unlucky and few others seem to have posted about the problem and have found solutions by installing a return spring. However I found I had to move the return spring (Landrover type) so far down the pedal to overcome the sticking servo that it frankly made the whole brake pedal action feel weird with so much spring pressure to overcome.

An expensive option given the cost of shipping.The only other option is to return to the metro servo unless anybody has any other suggestions

Nigbo

Presumably you mean it is sticking in the "on" position i.e. not releasing fully?

Do you have a rose joint between the pedal bolt and the servo input shaft? Sometimes those can seem quite stiff to me which may be part of your problem, although with the Land Rover return spring I would think it unlikely.

I have the original clevis set up, with one hole elongated a bit to allow for the offset angle issue, and have never had any sticking.

Do you have the correct clearance between the end of the plunger and the primary master cylinder piston? It should be only about .020" but there must be clearance there or the servo diaphragh and valve won't fully retract. Just clutching at straws here.

I would do anything to avoid going back to the Metro sevo as it is just not up to the job. Peter.