brake master cylinders

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john vanlandingham

Quote
Eric Ewert
The fact that I can lock the fronts waaaaayyy too early. Its like the rear brakes are hardly there. They will lock with enough effort, but not till the fronts are long since locked up. fresh pads/ rotors all around and bed in. Rear calipers have the benefit of being refurbished and fresh too.

Conclusion: fawking weird.

Wait! I think those gwddam things have stepped bore masters! Double check that...

How do you tell if its stepped bore? I know the front is a 5/8th and the rear is 7/8th bore size. From what I recall reading through a few group A manuals (e30 m3, sierra cosworth... couldn't find a volvo one) the typical setup is a 5/8th front and a 3/4 rear bore size. Makes me think the rear is oversized. I realize that at least the e30 m3 used a 4x36mm piston caliper on the back but im not convinced thats necessary for my skillset or rather lack of! Plenty of quick folks on the other side of the pond using the standard calipers.

Quote
Eric Ewert

Quote
john vanlandingham

Quote
Eric Ewert
The fact that I can lock the fronts waaaaayyy too early. Its like the rear brakes are hardly there. They will lock with enough effort, but not till the fronts are long since locked up. fresh pads/ rotors all around and bed in. Rear calipers have the benefit of being refurbished and fresh too.

Conclusion: fawking weird.

Wait! I think those gwddam things have stepped bore masters! Double check that...

How do you tell if its stepped bore? I know the front is a 5/8th and the rear is 7/8th bore size. From what I recall reading through a few group A manuals (e30 m3, sierra cosworth... couldn't find a volvo one) the typical setup is a 5/8th front and a 3/4 rear bore size. Makes me think the rear is oversized. I realize that at least the e30 m3 used a 4x36mm piston caliper on the back but im not convinced thats necessary for my skillset or rather lack of! Plenty of quick folks on the other side of the pond using the standard calipers.

Vince and I just talked (ya know telephone?) and he reminded me that we had already looked on Rock Otter and yeah its some fucked up stepped bore thang..Fucking weird.

Look again or harder, the typical front in all the set-up sheets I've seen is 0.7" front and .75 rear
As for Grope Eh E30 M3 goes I cannot imagine they have 4x36 in back..Not when evverybody elses uses 4 x 1.25 or 31.75mm
But that's unimportant now..
We've used Volvos 4 x 38 fronts and 2 x 38 rears on a number of cars and they worked...
But those cars did have either dual masters or single bore

So sounds like their stepped bore thing is the culprit...
The nice step-by-step piccies of what was done on Håkansainalainens 240 which Sean Medcroft now has have all been sent down the truth-hole cause they were on hus UW student account..fawkin internet and fawkin dead links.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Quote
john vanlandingham
Vince and I just talked (ya know telephone?) and he reminded me that we had already looked on Rock Otter and yeah its some fucked up stepped bore thang..Fucking weird.

Just to clarify, I said I was 99% sure we came to that conclusion and started chatting about something totally different.

But yeah, someone would need to take one apart and stare at the thing with an intense puzzled stare to make it to a 100%.

---

Ask for work.
If they don't give you work, ask for bread.
If they do not give you work or bread, then take bread.

- Emma Goldman



Edited 1 time(s). Last edit at 12/20/2017 07:02PM by Vincent Gagnon.

Quote
Vincent Gagnon

Quote
john vanlandingham
Vince and I just talked (ya know telephone?) and he reminded me that we had already looked on Rock Otter and yeah its some fucked up stepped bore thang..Fucking weird.

Just to clarify, I said I was 99% sure we came to that conclusion and started chatting about something totally different.

But yeah, someone would need to take one apart and stare at the thing with an intense puzzled stare to make it to a 100%.

Yeah we better look at a real one or a book...I just read some well known place that says they're 22mm or 0.866 and we know that's close to 7/8" which is 0.875

But I want to see Greenbook saying they're straight size.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

John, just went back and looked at that e30 grupp A manual and for once in my life my memory actually worked... 42x2 and 38x2 front pistons, 36x4 rear. .625 front and .75 rear master cylinders. Maybe this was for the track/ tarmac spec? Not that the piston sizes are important as we both know the standard 240 calipers can be used effectively... but like you said what seems common to them working well is some sort of master cylinder change. Can't help but to notice the master cylinder sizing on the e30 though. Seems to be a common combo offered on aftermarket pedal boxes which would make me think its a good starting point?

But then I dug up the sierra rally prep manual. Didn't see any piston sizes listed but meh... the master cylinders were and were what you said... .7 front .75 rear. Hmmm.. what to buy? Probably a good chance that either combo will work? Might come down to what's easily available.

For the standard master cylinder, can't say I have taken it apart and measured but heres a copy and pasted info thing off rock auto.
RAYBESTOS MC39298 {#2539298, M39298} Professional Grade; New; Bore Size= 5/8 "& 7/8" Info
Previous Image

Next Image
CAD$46.87 CAD$0.00 CAD$46.87
Add to Cart

Had a look in my haynes manual, no go on master cylinder bore sizes to confirm but it shows a cutaway... yup looks like a stepped bore.

Shame Kevin's pics of the setup you two did are gone but really shouldn't be too big of a deal to build something to bolt in place of the old booster. Sure its a few bucks but it isn't that bad and as an added bonus will clear up space for itbs or a 16v down the road if wanted.

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Eric Ewert
[...] a 16v down the road if wanted.

---

Ask for work.
If they don't give you work, ask for bread.
If they do not give you work or bread, then take bread.

- Emma Goldman

Quote
Eric Ewert
John, just went back and looked at that e30 grupp A manual and for once in my life my memory actually worked... 42x2 and 38x2 front pistons, 36x4 rear. .625 front and .75 rear master cylinders. Maybe this was for the track/ tarmac spec? Not that the piston sizes are important as we both know the standard 240 calipers can be used effectively... but like you said what seems common to them working well is some sort of master cylinder change. Can't help but to notice the master cylinder sizing on the e30 though. Seems to be a common combo offered on aftermarket pedal boxes which would make me think its a good starting point?

But then I dug up the sierra rally prep manual. Didn't see any piston sizes listed but meh... the master cylinders were and were what you said... .7 front .75 rear. Hmmm.. what to buy? Probably a good chance that either combo will work? Might come down to what's easily available.

For the standard master cylinder, can't say I have taken it apart and measured but heres a copy and pasted info thing off rock auto.
RAYBESTOS MC39298 {#2539298, M39298} Professional Grade; New; Bore Size= 5/8 "& 7/8" Info
Previous Image

Next Image
CAD$46.87 CAD$0.00 CAD$46.87
Add to Cart

Had a look in my haynes manual, no go on master cylinder bore sizes to confirm but it shows a cutaway... yup looks like a stepped bore.

Shame Kevin's pics of the setup you two did are gone but really shouldn't be too big of a deal to build something to bolt in place of the old booster. Sure its a few bucks but it isn't that bad and as an added bonus will clear up space for itbs or a 16v down the road if wanted.

Ok jumpy around..EVERYBODY always lists every size master ever made in Homologation forms and in ALL the homologation forms I've looked at they show all kinds of crazzy ass calipers and its mind-boggling..
That's why Fords actual "Build sheets" for the various events are valuable cause that shows what at that very eearly stage what they were using..
Then we can sit and ruminate about what from that is applicable to our or your conditions.

As you see in this issue but about braking--From each according to..."


The Sierras on gravel, even very fast --Finland--type, the closest to your condition--nearly always used thos progressive 2x 1.5+ 2 x 1.625 fronts..Everybody with cars this size and weight did as well as FWD Golves, Saabs, Opels, Citroens, Renaults, Pugs, Fords...

As I said, I cannot imagine a use of 4 x 36 in the back...that would be enormous and flat weird balance--unless it was limited down all to fuck.
(But generally BMW had some weird ass ideas--I've seen some flat strange valving numbers on a bunch of their shit that is exactly same both ways...Huh? But you know Germans--they get some theoretical idea and can't bend)
So whatever, forget about it, its an outlier...

No re master size F/R..I used the .7 and .75 and that was with flexy pedal box flexing all to fuck and it was flat scary..So bad I can't say if it was "right' cause the box flexed mad flexy.
The did homologate their swoot-frood cast magnesium pedal assembly and that had the 6 or 6+ to one pedal ratio that seems to be the shit...

As to modding a pedal box, that's phone call type stuff.. But you lazy fuck you haven't called in forever..Ya get done with school and poof! too busy to call.. I work my index fingers to the bone typing you thru all this and can you call on X-mas or the Solstice? Is it too much to ask?

Note one thing--the rear calipers on the escorts were 2 x 2.0" which is HUGE!!!!!! so they had to be limited down a shit ton..Maybe that is a way to go..overboard then limit down..

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Hmmm... it certainly is easier to take away some brake power rather than adding more. In the case of that massive 50.8mm x 2 escort caliper that is near as makes no difference the same as a front rx7 4x36mm caliper in terms of piston area... which could be easily made to clamp a volvo front rotor and mounted to the rear of the car. Seen a number of photos of euro volvos with front 240 calipers mounted to the rear and I assume limited right down. The front rx7 caliper would a be a bit more sensible.

Cost wise would probably be similar all said and done and simpler compared to installing a dual master setup. Would be nice to ditch the booster as it would eliminate one more thing to fail and make a bit more room for future fun items.

And yes been meaning to call, will have to do so in a few days as im working/ with the family for the next bit. Been very distracted with a few other things these past months... not a bad thing!

This is one of Vince's master cylinders.

Dafuq?

Then again this is also the same company that split the braking system across each front caliper.

Oh, wait! Is that a quick takeup type master? Then it makes more sense, the 7/8" bore pushes fluid past the lip seals in the rest of the master until pressure builds, then a popoff valve opens and the 5/8" bores actually put pressure to the calipers. It's a way to get a small bore master without a long pedal when using calipers with high-retraction seals. GM did that a lot in the 1980s before they realized that iron is cheap and 9" rotors don't make sense.

---

Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 12/25/2017 10:45AM by Pete.

Quote
Philippe Bellefleur
This is one of Vince's master cylinders.

A 240 master???
PN?

..Wanna bet a whole nickel if you punch the buttom and switch from metric to "some decimal based on the length of a mythological king's thumb" we'd see .875 and .625..

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.



Edited 1 time(s). Last edit at 12/25/2017 02:08PM by john vanlandingham.

Quote
Philippe Bellefleur
This is one of Vince's master cylinders.

First : LEAVE MY JUNK ALONE AND GO MEASURE YOUR OWN JUNK!

Second: Are you sure this is not from a 740/940/960?

Was it paired to a "skinny booster"?

Is there a part number of some sort?

Where was it exactly?

Happy celebration of the birth of a jewish agitator!

Quote
john vanlandingham
..Wanna bet a whole nickel if you punch the buttom and switch from metric to "some decimal based on the length of a mythological king's thumb" we'd see .875 and .625..

Why would anybody do that?
Fuck the king and fuck most of that island!


And yes it's 7/8 / 5/8.
What a stupid stupid stupid way of measuring stuff!

---

Ask for work.
If they don't give you work, ask for bread.
If they do not give you work or bread, then take bread.

- Emma Goldman



Edited 3 time(s). Last edit at 12/25/2017 03:37PM by Vincent Gagnon.

For part numbers this is all I can see.

If it was designed in fractional inches then it's easiest to say that, if it was designed in millimeters then it is easiest to say that. None of this 114.3mm bolt circle or 6.35mm chain pitch, those aren't nice round numbers because they're trying to hammerform a different language into a precise measurement. (Like 4.5" or 1/4" pitch, both dimensions of which are found on a late model Honda)

Anyway regardign the master cylinder, definitely not a quick takeup. That would have both line ports in the small section.

Deployment of dafuq is sustained.

---

Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 12/25/2017 07:14PM by Pete.

Looks identical to the master cylinder in my two four zero. If deployment of dafuq is sustained then deployment of disposal may be required.