Need some brake master cylinder info
Thread Starter
Suckin' gas, haulin' ass.
Joined: Apr 2010
Posts: 1,100
Likes: 8
From: Newport News Virginia
Need some brake master cylinder info
Working on my 1989 and I'm looking to upgrade the master cylinder. I'm looking for a master cylinder that will bolt up with relatively few to no modifications that does not have an internal proportioning valve. Right now I don't have enough rear brake bias and it's causing the rear to dance a bit under hard braking such as the back straight at Road Atlanta and both straights at VIR.
I'm also considering going with Wilwood fron 13" brakes down the road as well. I'll also be adding a manual external proportioning valve.
Also, just FYI, I have the DRM spring installed currently. I'm just at the point where I can use more rear brake and also more brakes, but that's another thread.
I'm also considering going with Wilwood fron 13" brakes down the road as well. I'll also be adding a manual external proportioning valve.
Also, just FYI, I have the DRM spring installed currently. I'm just at the point where I can use more rear brake and also more brakes, but that's another thread.
Thread Starter
Suckin' gas, haulin' ass.
Joined: Apr 2010
Posts: 1,100
Likes: 8
From: Newport News Virginia
Not a whole lot of info on this apparently.
Does anyone have the flange dimensions for the stock master cylinder? I'm thinking an aftermarket one would possibly bolt up, maybe with a spacer.
Does anyone have the flange dimensions for the stock master cylinder? I'm thinking an aftermarket one would possibly bolt up, maybe with a spacer.
Pro
Joined: Jan 2003
Posts: 664
Likes: 119
From: Albany OR
When I changed the brakes on my 1985 track car to Wilwood GNIII 6 piston fronts and Wilwood FSL4 4 piston rears I changed the stock master out for a 4th gen Camaro master cylinder. It has a lager 1" bore so the brake pedal travel works out just right with these larger brakes. The Camaro master cylinder does not have a integral proportioning valve so I added a Wilwood one like what you are wanting to do. If you send me a pm with your email I can send you a document I put together detailing the system and various adapters I used to work the swap. I think I posted something on this swap a couple of years ago but I can't find it right now.
Brian
Brian
Team Owner
Joined: Sep 2003
Posts: 25,393
Likes: 2,741
A couple snapshots of "VanSteel" M/C install:
https://www.corvetteforum.com/forums...post1581179895
https://www.corvetteforum.com/forums...track-car.html
OP
If you could use the pedal/steering column support bracket assembly and pedals from a '92+ car you could increase the pedal ratio to 4:1. How difficult to accomplish I have no idea but it would be interesting to maybe have both parts side by side to check the feasibility of the effort.
https://www.corvetteforum.com/forums...post1581179895
https://www.corvetteforum.com/forums...track-car.html
OP
If you could use the pedal/steering column support bracket assembly and pedals from a '92+ car you could increase the pedal ratio to 4:1. How difficult to accomplish I have no idea but it would be interesting to maybe have both parts side by side to check the feasibility of the effort.
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
Quick fix for a track car without an adjustable prop valve.
Remove the rear pads. Working the top edge grind each pad down about 1/4 inch across the top radius to reduce the size of the pad.
This will reduce the swept area = less rear brake. Its a trial & error thing to dial it in.
Still have the ABS on board? Suggest the circle file for that
conglomeration.
Suggest waiting to purchase a MC until you know what replacement calipers will be used then compute what MC bore size will be required.
For power brakes shoot for a 14 to 1 front hydraulic ratio.
For manual brakes 18 to 1 hydraulic ratio + the brake pedal ratio needs to be 6 to 1.
Remove the rear pads. Working the top edge grind each pad down about 1/4 inch across the top radius to reduce the size of the pad.
This will reduce the swept area = less rear brake. Its a trial & error thing to dial it in.
Still have the ABS on board? Suggest the circle file for that
conglomeration.
Suggest waiting to purchase a MC until you know what replacement calipers will be used then compute what MC bore size will be required.
For power brakes shoot for a 14 to 1 front hydraulic ratio.
For manual brakes 18 to 1 hydraulic ratio + the brake pedal ratio needs to be 6 to 1.
Instructor
Joined: Oct 2008
Posts: 117
Likes: 0
From: Townsend TN
Wilwoods installed
Working on my 1989 and I'm looking to upgrade the master cylinder. I'm looking for a master cylinder that will bolt up with relatively few to no modifications that does not have an internal proportioning valve. Right now I don't have enough rear brake bias and it's causing the rear to dance a bit under hard braking such as the back straight at Road Atlanta and both straights at VIR.
I'm also considering going with Wilwood fron 13" brakes down the road as well. I'll also be adding a manual external proportioning valve.
Also, just FYI, I have the DRM spring installed currently. I'm just at the point where I can use more rear brake and also more brakes, but that's another thread.
I'm also considering going with Wilwood fron 13" brakes down the road as well. I'll also be adding a manual external proportioning valve.
Also, just FYI, I have the DRM spring installed currently. I'm just at the point where I can use more rear brake and also more brakes, but that's another thread.
I ordered the DRM spring, but it sounds like it may be insufficient - also, i read that having that and my wilwood brake bias proportioning valve (two bias items) is a bad idea. So it sounds like the camaro m/c may be an option. How about the lines, and hooking them up? the stock fronts are 10mm x 1.0 and rears are apparently 12mm x 1.x...not sure how to plumb that part. Brake woes are not a good thing to go to the track with!
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The purpose of a proportioning valve is to change the ratio of brake pedal pressure of the rear brakes in relation to the front brakes. The reason it's needed is because there is a weight transfer onto the front tires while braking. If the proportioning valve is not there then the rears (which get lighter during braking) tend to lock up. This is why rear rotors are usually smaller than front rotors. If the proportioning is perfect then the rears will not lock up before the fronts.
Supporting Vendor
Joined: Jun 2008
Posts: 2,199
Likes: 119
From: tempe Arizona
Locking up the fronts is not a sign of a problem. Just maximum tire adhesion.
Now..locking up the rears before the fronts would certainly be a problem. Sure...ideally they'd all lock at the same time. So many variables effect that and doing so on track vs on the street can have an effect as well as how fast you're going, what pads you run on each end etc.
Generally speaking one would look to run as much rear brake as possible. Until they lock up prematurely like the OP has issues with- then it's too much as the back end is "dance", which to me means they want to lock up. Too much rear brake, not too little.
The proportioning valve will do nothing for adding rear brake. They only LIMIT the amount of line pressure you allow the rears to receive. Relative to the total input pressure to the fronts and rears. Changing the adjustment or 'knee' point only changes the point of REDUCTION the valve kicks in. To be clear; you cannot add rear brake with such an item.
If one wants more rear brake then either larger rotors, more piston area or a higher Cf pad is needed. Put all that on there and you may then NEED that prop valve.
Now..locking up the rears before the fronts would certainly be a problem. Sure...ideally they'd all lock at the same time. So many variables effect that and doing so on track vs on the street can have an effect as well as how fast you're going, what pads you run on each end etc.
Generally speaking one would look to run as much rear brake as possible. Until they lock up prematurely like the OP has issues with- then it's too much as the back end is "dance", which to me means they want to lock up. Too much rear brake, not too little.
The proportioning valve will do nothing for adding rear brake. They only LIMIT the amount of line pressure you allow the rears to receive. Relative to the total input pressure to the fronts and rears. Changing the adjustment or 'knee' point only changes the point of REDUCTION the valve kicks in. To be clear; you cannot add rear brake with such an item.
If one wants more rear brake then either larger rotors, more piston area or a higher Cf pad is needed. Put all that on there and you may then NEED that prop valve.
Instructor
Joined: Oct 2008
Posts: 117
Likes: 0
From: Townsend TN
Locking up the fronts is not a sign of a problem. Just maximum tire adhesion.
Now..locking up the rears before the fronts would certainly be a problem. Sure...ideally they'd all lock at the same time. So many variables effect that and doing so on track vs on the street can have an effect as well as how fast you're going, what pads you run on each end etc.
Generally speaking one would look to run as much rear brake as possible. Until they lock up prematurely like the OP has issues with- then it's too much as the back end is "dance", which to me means they want to lock up. Too much rear brake, not too little.
The proportioning valve will do nothing for adding rear brake. They only LIMIT the amount of line pressure you allow the rears to receive. Relative to the total input pressure to the fronts and rears. Changing the adjustment or 'knee' point only changes the point of REDUCTION the valve kicks in. To be clear; you cannot add rear brake with such an item.
If one wants more rear brake then either larger rotors, more piston area or a higher Cf pad is needed. Put all that on there and you may then NEED that prop valve.
Now..locking up the rears before the fronts would certainly be a problem. Sure...ideally they'd all lock at the same time. So many variables effect that and doing so on track vs on the street can have an effect as well as how fast you're going, what pads you run on each end etc.
Generally speaking one would look to run as much rear brake as possible. Until they lock up prematurely like the OP has issues with- then it's too much as the back end is "dance", which to me means they want to lock up. Too much rear brake, not too little.
The proportioning valve will do nothing for adding rear brake. They only LIMIT the amount of line pressure you allow the rears to receive. Relative to the total input pressure to the fronts and rears. Changing the adjustment or 'knee' point only changes the point of REDUCTION the valve kicks in. To be clear; you cannot add rear brake with such an item.
If one wants more rear brake then either larger rotors, more piston area or a higher Cf pad is needed. Put all that on there and you may then NEED that prop valve.
Understood about the prop valve (and it is wide opened, allowing full press to rears) - only recently discovered should only have one proportioning valve in a system, and it may be that the whole prop system at the M/C needs to be removed...OR...switch to the camaro M/C setup, with the larger bore (also had questions about line sizes/adapters for that if anyone knows?). Hence my earlier post. Just trying to find balance in brakes, perhaps my description of locking the fronts was not descriptive enough. I do trail brake, er, rather want to at the track - so my ABS system is gone, which has sparked this whole issue for me. Thanks!
Last edited by TCurtner; Jan 15, 2015 at 07:53 AM.