Servos and MCs
Discussion
Here's a teaser for someone.
My 1990 S3 used the Saab servo and MC, with remote reservoir. You will see from the pic below that I need to replace them, and I got a new Saab servo (courtesy of RayTVR - cheers mate) last year. This was closely followed by a Saab MC donated by a pal who said "maybe this will fit!".
As you can see, the it looks the same and the bore is 22mm.
The only problem is that the MC is in a box marked 'Taxi' and has different numbers on the plastic tag to those on the original.
Does anybody here know if this will work or not?
ALSO, will the Saab setup be OK with brakes upgraded to rear discs, and larger fronts, as per the Griff 500??
[PS. No comments about charging payment to passengers from Glen please
Thanks for any help.
Tony
My 1990 S3 used the Saab servo and MC, with remote reservoir. You will see from the pic below that I need to replace them, and I got a new Saab servo (courtesy of RayTVR - cheers mate) last year. This was closely followed by a Saab MC donated by a pal who said "maybe this will fit!".
As you can see, the it looks the same and the bore is 22mm.
The only problem is that the MC is in a box marked 'Taxi' and has different numbers on the plastic tag to those on the original.
Does anybody here know if this will work or not?
ALSO, will the Saab setup be OK with brakes upgraded to rear discs, and larger fronts, as per the Griff 500??
[PS. No comments about charging payment to passengers from Glen please
Thanks for any help.
Tony
Hi Tony, I have the Delphi parts specifications available and I can have a look later tonight to see how that mastercylinder compares to the original. I am assuming you have confirmed the servo is correct?
I should be able to tell you if they are compatible and will give the same performance as the original.
I cannot however tell you if they will work OK with your modified system. You have changed the volume displacement necessary to operate all the brake pistons and inevitably that means it would be a miracle if the master cylinder will still match your system. You really need to calculate, and it isnt easy, the new displacement required and work out how much it has changed. This, with respect, is why there are lots of different systems and cylinders out there. Putting on bigger brakes does not mean better brake control unless the hydraulics, and the mechanical operation of those hydraulics, matches.
I should be able to tell you if they are compatible and will give the same performance as the original.
I cannot however tell you if they will work OK with your modified system. You have changed the volume displacement necessary to operate all the brake pistons and inevitably that means it would be a miracle if the master cylinder will still match your system. You really need to calculate, and it isnt easy, the new displacement required and work out how much it has changed. This, with respect, is why there are lots of different systems and cylinders out there. Putting on bigger brakes does not mean better brake control unless the hydraulics, and the mechanical operation of those hydraulics, matches.
Many thanks. It would be great if you can check compatibility from your Delphi specs.
I take your point about the upgrade, and am resigned to possibly getting a Griff servo and MC to match the other parts. (I'm hoping the brake balance and performance cannot be too far out since the Griff and S are reasonably similar size/weight - but only some testing around Blyton Park will confirm, I suspect!)
I take your point about the upgrade, and am resigned to possibly getting a Griff servo and MC to match the other parts. (I'm hoping the brake balance and performance cannot be too far out since the Griff and S are reasonably similar size/weight - but only some testing around Blyton Park will confirm, I suspect!)
Taxi! ;DThat great Steppenwolf number springs to mind Tony:
" Getcher meter runnin', head out on the high street.... Lookin' for a good fare.... trying to make ends meet.... " etc. I won't mention a single word about "Joe le taxi", because his Avensis is not a true taxi, it's a minicab!
Edited by glenrobbo on Wednesday 9th March 20:33
I am afraid the box isnt going to help. That reference is for a clutch master cylinder for a RHD SAAB 9000 2ltr! Not what you have at all. Does the plastic tag round the cylinder have any clear references?
Incidentally, just to illustrate the point that there are a lot of different hydraulic system combinations out there, the Delphi catalogue for brake and clutch hydraulics for cars only is 1328 pages long! And that is just Delphi (Lockheed).
Another word of warning. Fitting bigger brakes doesnt necessarily mean increasing the hydraulic displacement needed but in many cases the slave cylinders/caliper pistons will increase in size, which requires a bigger fluid displacement. That may well be achieveable from the original master cylinder if the travel of the cylinder increases. The problem with that is that it reduces the factor of safety. Cylinders are designed to work over a certain swept volume, place a greater demand on it and the piston will go further down the cylinder. Fine if everything else is perfect but if the fluid is hot or has absorbed more than a certain degree of water (or of course if there is any fluid loss anywhere)the margin of safety goes and the piston could run out of travel when you really dont want it to. Study the operation of a tandem master cylinder carefully and you will see there isnt much margin. Each particular master cyclinder has a specific bore and stroke for a reason!
If you want to play at redesigning the brakes then you do so very much at your own risk!!
Incidentally, just to illustrate the point that there are a lot of different hydraulic system combinations out there, the Delphi catalogue for brake and clutch hydraulics for cars only is 1328 pages long! And that is just Delphi (Lockheed).
Another word of warning. Fitting bigger brakes doesnt necessarily mean increasing the hydraulic displacement needed but in many cases the slave cylinders/caliper pistons will increase in size, which requires a bigger fluid displacement. That may well be achieveable from the original master cylinder if the travel of the cylinder increases. The problem with that is that it reduces the factor of safety. Cylinders are designed to work over a certain swept volume, place a greater demand on it and the piston will go further down the cylinder. Fine if everything else is perfect but if the fluid is hot or has absorbed more than a certain degree of water (or of course if there is any fluid loss anywhere)the margin of safety goes and the piston could run out of travel when you really dont want it to. Study the operation of a tandem master cylinder carefully and you will see there isnt much margin. Each particular master cyclinder has a specific bore and stroke for a reason!
If you want to play at redesigning the brakes then you do so very much at your own risk!!
Thanks for checking. It explains the strange results I got from my own Google research! I meant to include the tag info in my original post:
Old MC tag: 6519 06/13B
New MC tag: 6814/ as-as-22 dk
They are certainly quite different.
I have a ford servo now as well, and so I'm likely to go for the Griff MC on this set up, and will check the pedal lever/pivot dims as well. After that I suppose it's just a case of doing what TVR did - try it out!
Thanks again.
Tony
Old MC tag: 6519 06/13B
New MC tag: 6814/ as-as-22 dk
They are certainly quite different.
I have a ford servo now as well, and so I'm likely to go for the Griff MC on this set up, and will check the pedal lever/pivot dims as well. After that I suppose it's just a case of doing what TVR did - try it out!
Thanks again.
Tony
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