Let's talk master cylinder braces
08-09-11, 09:05 AM
#1
Full Member
Thread Starter
Let's talk master cylinder braces
I am wondering who on here has built their own master cylinder brace (or bought a commercially available one if such a thing exists)?
I have found the one thread on here where somebody discusses building their own but there is only a quick "it made things better" type of post with no dimensions or detailed pictures of the assembly.
The brake pedal in my rx-7 is firm and nice and high where it should be (new master cylinder, serviced calipers, single fronts), however at the end of its travel it feels springy and soft. When I am auto-x'ing I have times when I cannot build enough vacuum before having to brake and so sometimes I am braking with only partial assist so I have to press quite hard on the brake pedal. When I do this I find this springy feeling to be quite disconcerting and I am wondering what is available for master cylinder braces and whether they will be enough to fix this problem?
To throw a little bit of science at this problem I borrowed a deflection gauge and took some quick measurements of the displacement of the master cylinder:
At rest:
Under hard braking:
Master cylinder attachment height:
Brake pedal arm length:
I can see that the master cylinder itself displaces approximately 0.040", and with about a 4:1 ratio between the length of the arm to the attachment point relative to the length of the arm to the end of the brake pedal that translates to about 0.160" of motion. Of course this isn't absolute, my dial indicator was not aligned perfectly along the axis of the master cylinder, and I probably wasn't braking as hard as I possibly could have been, but it gives a decent idea of how far things move.
Watching the brake booster I can see that the outer face of the booster is where the movement occurs, the firewall does not appear to flex, but the outer side of the brake booster does.
I have found the one thread on here where somebody discusses building their own but there is only a quick "it made things better" type of post with no dimensions or detailed pictures of the assembly.
The brake pedal in my rx-7 is firm and nice and high where it should be (new master cylinder, serviced calipers, single fronts), however at the end of its travel it feels springy and soft. When I am auto-x'ing I have times when I cannot build enough vacuum before having to brake and so sometimes I am braking with only partial assist so I have to press quite hard on the brake pedal. When I do this I find this springy feeling to be quite disconcerting and I am wondering what is available for master cylinder braces and whether they will be enough to fix this problem?
To throw a little bit of science at this problem I borrowed a deflection gauge and took some quick measurements of the displacement of the master cylinder:
At rest:
Under hard braking:
Master cylinder attachment height:
Brake pedal arm length:
I can see that the master cylinder itself displaces approximately 0.040", and with about a 4:1 ratio between the length of the arm to the attachment point relative to the length of the arm to the end of the brake pedal that translates to about 0.160" of motion. Of course this isn't absolute, my dial indicator was not aligned perfectly along the axis of the master cylinder, and I probably wasn't braking as hard as I possibly could have been, but it gives a decent idea of how far things move.
Watching the brake booster I can see that the outer face of the booster is where the movement occurs, the firewall does not appear to flex, but the outer side of the brake booster does.
08-09-11, 09:22 AM
#2
Interesting, but this hasn't been enough of a problem (it moves very little, just over 1/8" according to your measurements) worthy of a fix. Not sure about the racing world.
I believe the thread you're referring to was a guy trying out different master cylinders - maybe that's why the bracing was needed? Not sure.
About your lack of vacuum assist. Are you sure the one way valve is working ok? No sig. or info in the thread...is this a TII?
I believe the thread you're referring to was a guy trying out different master cylinders - maybe that's why the bracing was needed? Not sure.
About your lack of vacuum assist. Are you sure the one way valve is working ok? No sig. or info in the thread...is this a TII?
08-09-11, 09:43 AM
#4
The bracing is not necessary. It's a band-aid fix for a problem with the stock system. Have you done the vacuum tests on the brake booster which are outlined in the FSM? Maybe the one way valve isn't working 100% or the brake booster has a leak. Do all 4 brake calipers float freely? Sometimes the pins on which the calipers slide become rusty. If you were driving at 35mph and hit the brakes as hard as you could, would all 4 wheels lock up? Would the fronts lock up first?
Dam that's a clean MC.
Dam that's a clean MC.
08-09-11, 12:32 PM
#5
Full Member
Thread Starter
Sorry, I didn't expect this thread to be so much about my car personally or I would have provided more information initially.
I do have a minor vacuum problem with the brake booster on my car, there is a small leak before the one-way valve so it takes the brake booster longer to see full vacuum and the engine runs as if it has a small vacuum leak (because it does...). I do plan on addressing this problem before the next event since it does result in greatly increased braking pressure, but it does not cause the springy feeling.
The car in question is not a TII, just a boring NA (GX), and the master cylinder is nice and clean because it is essentially brand new, the old one had a severe internal leak so I replaced it when I serviced the calipers 2 months (and 210km) ago. The blue tinge was because I finished up a can of ATE super blue when I started bleeding the brakes, and the dye is so strong that even nearly 1L of brake fluid later there is a visible blue tinge still. In my car all 4 calipers float freely, I went through them all very carefully and brake heating is very even side to side and as predicted front to back (cooler in the back).
The thread I was referring to is indeed the one where another member went through some obscene number of master cylinder and booster combinations trying to improve pedal feel. In one of his concluding posts he mentioned that building a master cylinder brace made the single biggest improvement in pedal feel so I was curious if anybody else had done it and if so, what designs they had come up with.
I'm not much of an engineer so inventing things like this isn't really my strong suit, to be honest, I was hoping somebody else had done the hard work there, I just wanted to ask questions and help throw data at the problem since I felt this was a topic that has not been covered very extensively.
I think the total brake pedal travel is in the neighborhood of 2" with over 1" of that travel having almost no resistance, so although the deflection only causes 1/8" of travel, I still feel it is significant. I had a hard time measuring total travel with my big honkin' feet in the footwell (size 15.... they don't fit under the dashboard very well, let alone with my head and a tape measure down there) so I do not have an exact measurement for pedal travel, but I do also plan on adjusting the free play as specified in the FSM before this weekend.
I do have a minor vacuum problem with the brake booster on my car, there is a small leak before the one-way valve so it takes the brake booster longer to see full vacuum and the engine runs as if it has a small vacuum leak (because it does...). I do plan on addressing this problem before the next event since it does result in greatly increased braking pressure, but it does not cause the springy feeling.
The car in question is not a TII, just a boring NA (GX), and the master cylinder is nice and clean because it is essentially brand new, the old one had a severe internal leak so I replaced it when I serviced the calipers 2 months (and 210km) ago. The blue tinge was because I finished up a can of ATE super blue when I started bleeding the brakes, and the dye is so strong that even nearly 1L of brake fluid later there is a visible blue tinge still. In my car all 4 calipers float freely, I went through them all very carefully and brake heating is very even side to side and as predicted front to back (cooler in the back).
The thread I was referring to is indeed the one where another member went through some obscene number of master cylinder and booster combinations trying to improve pedal feel. In one of his concluding posts he mentioned that building a master cylinder brace made the single biggest improvement in pedal feel so I was curious if anybody else had done it and if so, what designs they had come up with.
I'm not much of an engineer so inventing things like this isn't really my strong suit, to be honest, I was hoping somebody else had done the hard work there, I just wanted to ask questions and help throw data at the problem since I felt this was a topic that has not been covered very extensively.
I think the total brake pedal travel is in the neighborhood of 2" with over 1" of that travel having almost no resistance, so although the deflection only causes 1/8" of travel, I still feel it is significant. I had a hard time measuring total travel with my big honkin' feet in the footwell (size 15.... they don't fit under the dashboard very well, let alone with my head and a tape measure down there) so I do not have an exact measurement for pedal travel, but I do also plan on adjusting the free play as specified in the FSM before this weekend.
08-09-11, 12:38 PM
#6
There is another thread you overlooked. I think it was called "DIY master cylinder brace".
IIRC it was a long bolt threaded through a bracket, mounted on the strut tower. Basically it kept the bolt jammed against the master cylinder, eliminating forward movement. A simple idea that looked like it worked well.
IIRC it was a long bolt threaded through a bracket, mounted on the strut tower. Basically it kept the bolt jammed against the master cylinder, eliminating forward movement. A simple idea that looked like it worked well.
08-09-11, 12:47 PM
#7
I would make sure everything is functioning as designed first. Next step is to make sure all the slop is adjusted out of the pedal assembly, be careful so you don't take out all the play you need to be sure the MC is still retracting all the way. Third, you might go with brake pads that have a higher friction coeffient.
The firewall in that area is double layer and fairly stiff. One issue is there is a rubber gasket between the firewall and booster and even tightening things down gorilla tight you are tightening down on spacers that fill the distance between the double firewall.
Brake pads will make a huge difference over anything, braided lines are nice for pedal feel if you don't have them yet. Less pedal effort needed for the better pads means less flex in the firewall.
The firewall in that area is double layer and fairly stiff. One issue is there is a rubber gasket between the firewall and booster and even tightening things down gorilla tight you are tightening down on spacers that fill the distance between the double firewall.
Brake pads will make a huge difference over anything, braided lines are nice for pedal feel if you don't have them yet. Less pedal effort needed for the better pads means less flex in the firewall.
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08-09-11, 02:34 PM
#8
Full Member
Thread Starter
I bet this is the thread referred to:
https://www.rx7club.com/showthread.p...cylinder+brace
I don't know how I missed that... some days I wonder about myself.
It would be nice to be able to install something that doesn't require drilling holes in the car but that is not a show stopper for me. Thanks for the tip
As mentioned above, I will be repairing the vacuum leak and doing the full free play adjustment, but I like to plan ahead so I wanted to start a discussion about master cylinder braces nice and early.
https://www.rx7club.com/showthread.p...cylinder+brace
I don't know how I missed that... some days I wonder about myself.
It would be nice to be able to install something that doesn't require drilling holes in the car but that is not a show stopper for me. Thanks for the tip
As mentioned above, I will be repairing the vacuum leak and doing the full free play adjustment, but I like to plan ahead so I wanted to start a discussion about master cylinder braces nice and early.
08-09-11, 05:15 PM
#9
This shows the brace I made for the FD, the one for the FC is almost identical:
Zero, my observations closely mirror your own.
On the FC, the most obvious movement is the brake booster, in the FD, the entire firewall flexes as well.
The brace will make an immediate and obvious difference to pedal feel.
Try it, you have nothing to lose.
Zero, my observations closely mirror your own.
On the FC, the most obvious movement is the brake booster, in the FD, the entire firewall flexes as well.
The brace will make an immediate and obvious difference to pedal feel.
Try it, you have nothing to lose.
08-09-11, 11:13 PM
#11
What's the point??
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But really, it feels so much better with manual brakes, especially if you're autocrossing and run out of vacuum assistance. Consistent pressure all the time.
But really, it feels so much better with manual brakes, especially if you're autocrossing and run out of vacuum assistance. Consistent pressure all the time.
08-10-11, 07:21 AM
#13
interesting about the vacuum assist, we were just talking about this last week.
On my big block car the cam I had in it did not produce alot of vacuum, I had a reserve canister AND a electric vacuum pump in that car because the brakes could get hairy in a emergency situation- wondering if vaccum is a problem for you track guys if a canister or pump would do the trick
but honestly I cant recall reading that many complaints about it over the years
On my big block car the cam I had in it did not produce alot of vacuum, I had a reserve canister AND a electric vacuum pump in that car because the brakes could get hairy in a emergency situation- wondering if vaccum is a problem for you track guys if a canister or pump would do the trick
but honestly I cant recall reading that many complaints about it over the years
08-11-11, 09:35 AM
#15
Full Member
Thread Starter
I checked vacuum at the booster and I am holding 18"Hg on a cold idle and 13-14"Hg on a warm idle, vacuum seems okay. I checked and bled the brakes again, got a super tiny air bubble out of the rear-right caliper but that was it. So far everything checks out. I just need to find where the one-way valve is supposed to be. I didn't see an in-line one, but the PO (or one of the PO's) had an aftermarket cruise control setup installed and they cut into the brake booster hose over on the passenger side to provide it with vacuum so who knows what they may have removed.
As for the topic at hand, I checked my strut tower over and there appear to be 2 holes with captive nuts in perfect alignment for mounting a master cylinder brace, either the square tube + bolt style, or the much more elegant thick metal plate style. It's almost like they designed it for exactly this. Thanks for all the advice, when I get a chance to hit up a local metal store (or scrap bin...) I'll be making one up. Unfortunately now that I know the details of how minor of an impact this has, it has been bumped pretty far down the priority list.
As for the topic at hand, I checked my strut tower over and there appear to be 2 holes with captive nuts in perfect alignment for mounting a master cylinder brace, either the square tube + bolt style, or the much more elegant thick metal plate style. It's almost like they designed it for exactly this. Thanks for all the advice, when I get a chance to hit up a local metal store (or scrap bin...) I'll be making one up. Unfortunately now that I know the details of how minor of an impact this has, it has been bumped pretty far down the priority list.
08-11-11, 03:16 PM
#17
Full Member
Thread Starter
Wagner thermoquiets, they don't specifically say what they are, just that they are OE composition.... I'd assume semi-metallic. I want to swap them for hawk HPS or HP+, but that may have to wait until next year when I have more money to throw at this car.
08-12-11, 12:32 PM
#22
Google knows everything.
http://www.rhdjapan.com/cusco-bcs-ki...c3c-fd3s-20070
http://www.nengun.com/cusco/brake-cylinder-stopper
These things say for RHD only though, can anyone verify that they work on LHD cars?
http://www.rhdjapan.com/cusco-bcs-ki...c3c-fd3s-20070
http://www.nengun.com/cusco/brake-cylinder-stopper
These things say for RHD only though, can anyone verify that they work on LHD cars?
08-12-11, 02:09 PM
#23
Full Member
Thread Starter
I don't use my rx-7 as a daily driver, I have something much newer (and more korean....) as a daily driver, the rx-7 was bought just for an auto-x toy, but I want it to be sellable at the end and tolerable for use so I have kept the A/C and am trying not to make any drastic changes to it.
I have checked out getting hawk HPS or HP+ pads from several online retailers and it looks like a set would be ~$140 shipped to me, so I am just checking with local stores to see what they can do before I decide whether new pads are in the budget for this year.
Thanks for posting the pics of existing braces, I'm going to try to fab something up in the next few weeks (before auto-x season ends...)
I have checked out getting hawk HPS or HP+ pads from several online retailers and it looks like a set would be ~$140 shipped to me, so I am just checking with local stores to see what they can do before I decide whether new pads are in the budget for this year.
Thanks for posting the pics of existing braces, I'm going to try to fab something up in the next few weeks (before auto-x season ends...)
