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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #681  
Old 21st August 2016, 12:55
Nigbo Nigbo is offline
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Default 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.
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  #682  
Old 22nd August 2016, 11:49
Mike Mike is offline
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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
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  #683  
Old 8th August 2017, 23:53
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Grey V8 Pete Grey V8 Pete is offline
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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.
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  #684  
Old 9th August 2017, 11:27
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peterux peterux is online now
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Wild guess maybe Ford transit. Try eBay item
371901589550
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  #685  
Old 9th August 2017, 11:57
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Grey V8 Pete Grey V8 Pete is offline
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Quote:
Originally Posted by peterux View Post
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.
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  #686  
Old 11th August 2017, 09:27
Mike Mike is offline
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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-Sierr...sAAOSwiA9ZaSrb

Mike
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  #687  
Old 11th August 2017, 12:22
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Grey V8 Pete Grey V8 Pete is offline
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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.
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  #688  
Old 11th August 2017, 16:45
Mike Mike is offline
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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.
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  #689  
Old 11th August 2017, 18:56
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Grey V8 Pete Grey V8 Pete is offline
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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.

Last edited by Grey V8 Pete; 12th August 2017 at 22:47.. Reason: 22mm added
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