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Girling Rear Wheel Cylinders
- Thread starter AlpineIan
- Start date
Ian, I think the rear cylinder size should be matched with the front brakes, not the master cylinder. If the car will have the larger front brakes, it should have the larger rear cylinder.
Bill
AlpineIan
SAOCA Founder
No, thats not right Bill... the difference has to do with the master and addition of the brake booster. Just got off the phone with Doug Jennings and here's the answer to my question:
7/8 rear cylinders - S1, S1 NO booster
3/4 rear cylinders - S3, SIV WITH booster
If you are not running a brake booster it's best to go with 7/8 rear and .070 master.
7/8 rear cylinders - S1, S1 NO booster
3/4 rear cylinders - S3, SIV WITH booster
If you are not running a brake booster it's best to go with 7/8 rear and .070 master.
Ian, changing rear cylinders because you eliminate the booster is total nonsense. I do not know which wheel cylinder was used on which Series, but brake line pressures front to rear do not change because of the addition or removal of a booster. If you remove the booster, going to the smaller master cylinder is correct in order to keep the pedal effort low, but changing rear cylinders will impact front to rear braking effort. Change rear cylinder sizes only if you are unhappy with your current front/rear brake performance.
Bill
AlpineIan
SAOCA Founder
Well then why would the factory change from a 7/8" cylinder to a 3/4" rear wheel cylinder when they added a brake booster in the S3?
I'm just trying to make sure that I'm setting this S3 up correctly for my customer. I just found out he is now running a booster and I want to ensure I'm putting the right parts on it for him. Just needed a reference as to which was which.
I'm just trying to make sure that I'm setting this S3 up correctly for my customer. I just found out he is now running a booster and I want to ensure I'm putting the right parts on it for him. Just needed a reference as to which was which.
65beam
Donation Time
rear wheel cyl
ian,
for what it's worth, all of my cars have the called for rear wheel cylinders with the 700 master . the series 4 & 5 do not have boosters and i have no brake problems . i do have a more solid pedal on jean's blue car than i do on the others ,but the rear brakes are adjusted a lot tighter than the 4 . the kid does drive the 4 a lot so the brakes never get adjusted .
ian,
for what it's worth, all of my cars have the called for rear wheel cylinders with the 700 master . the series 4 & 5 do not have boosters and i have no brake problems . i do have a more solid pedal on jean's blue car than i do on the others ,but the rear brakes are adjusted a lot tighter than the 4 . the kid does drive the 4 a lot so the brakes never get adjusted .
AlpineIan
SAOCA Founder
The brake disk changed from 9.5" on the SI ands SII to 9.85" on the S3 onwards. The brake caliper also changed at this time.
Bob I Bill... I'm not saying that the brakes won't work if the rear cylinders are not changed when removing the booster.... all I was trying to do was figure out which was which. I'm also going to add my finding to the site.
If I'm putting one together and I have the parts to choose from... I'm going to put it together right. Don't you guys get this?
Changing rear wheel cylinders will effect pedal and braking. In my conversation with Doug Jennings, he was telling me about how rear wheel cylinders had a huge effect based on the type of brake compounds they were using on the race car.
Bob I Bill... I'm not saying that the brakes won't work if the rear cylinders are not changed when removing the booster.... all I was trying to do was figure out which was which. I'm also going to add my finding to the site.
If I'm putting one together and I have the parts to choose from... I'm going to put it together right. Don't you guys get this?
Changing rear wheel cylinders will effect pedal and braking. In my conversation with Doug Jennings, he was telling me about how rear wheel cylinders had a huge effect based on the type of brake compounds they were using on the race car.
AlpineIan
SAOCA Founder
That is a very good question. I've not looked into this yet.
Ian, with all things being equal, when Rootes put the larger front brakes on the car, one would think they increased the wheel cylinder in order to maintain the front to rear braking balance. Never having measured the cylinders, I had always thought that is what they did. However, it appears they went the other way. There are a few things to be considered to possibly account for this.
You state the brake caliper also changed when they went to the larger disc. Did they change the cylinder size? That would impact the front to rear braking balance.
The rears wheels may have had a tendency to lock up under heavy braking with the old setup.
When the front wheel braking power is increased, there is more weight transfer to the front of the car in heavy braking. This can lead to premature rear wheel lockup and steering instability. This could be the reason.
If the suspension geometry, front or rear was changed, that could lead to different weight transfer numbers, influencing the decision.
They could have gone to a different, more aggressive brake shoe that necessitated a change in order to avoid rear lockup.
They could have adopted a different, less aggressive pad for the front to gain pad life. This would change the braking balance, requiring less rear brake effort.
Which should you use on your car? Let's assume the factory knew what it was doing and if the discs are small, use the large rear cylinder. If the discs are large, use the small cylinder. If you are unhappy with the current front to rear brake balance, change to the appropriate wheel cylinder. If there is no booster, use the small master cylinder.
Believe me, the brake booster has an impact only on the resulting pedal pressure, not wheel cylinder selection.
Bill
You state the brake caliper also changed when they went to the larger disc. Did they change the cylinder size? That would impact the front to rear braking balance.
The rears wheels may have had a tendency to lock up under heavy braking with the old setup.
When the front wheel braking power is increased, there is more weight transfer to the front of the car in heavy braking. This can lead to premature rear wheel lockup and steering instability. This could be the reason.
If the suspension geometry, front or rear was changed, that could lead to different weight transfer numbers, influencing the decision.
They could have gone to a different, more aggressive brake shoe that necessitated a change in order to avoid rear lockup.
They could have adopted a different, less aggressive pad for the front to gain pad life. This would change the braking balance, requiring less rear brake effort.
Which should you use on your car? Let's assume the factory knew what it was doing and if the discs are small, use the large rear cylinder. If the discs are large, use the small cylinder. If you are unhappy with the current front to rear brake balance, change to the appropriate wheel cylinder. If there is no booster, use the small master cylinder.
Believe me, the brake booster has an impact only on the resulting pedal pressure, not wheel cylinder selection.
Bill