Guys,
All my current braking problems have been traced to seized rear brake cylinders ... both sides.
Now, I know what you are all thinking, " what kind of idiot doesn't check his rear brakes before putting 1000 miles on a 28 year old car?"
Well, you are right. I bled everything but didn't bother checking front/rear bias. I am an idiot!
Anyway, as a temporary fix, I will replace the rear cylinders, and am looking for advice on what size bores to chose. I have a stock lockheed master cylinder and the original Sprite front discs. My old cylinders are 5/8" bore. What I've found in the spridget catalogs are 3/4" and 7/8" bore. Recommendations on sizing appreciated.
It's no wonder stopping distances were not good, front lock-up was so easily achieved, and the car pushed a bit when braking into a corner (trail braking). Jan and I had a couple of long conversations about front/rear bias with dual MC's, etc, but all that may not be necessary once I get the existing system sorted out.
The brakes locked up on my because when I jammed the pedal down for an emergency braking situation, it moved the seized cylinders out just enough to lock up the rears.
Yes, I will replace every single wear item in the braking system over the winter.
John
Rear brake cylinder sizing
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xkfeng7
- Posts: 31
- Joined: Mon Aug 13, 2012 3:33 am
- Location: Boston, MA
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Rear brake cylinder sizing
1275 rear cylinders are usually 3/4", at least that's what I have, and the size I used for replacement. This, with the 3/4" master cylinder should fix your rear brake problems.
Usually, one adds a proportioning valve to the rear brakes to limit the pressure to the rear so that the rear brakes don't lock. If the rear brakes have too much authority, you get oversteer, usually the snap variety, which is really hard to catch. also, you will lose directional stability during hard braking.
Properly set up the W11 will rotate fine on its own... You don't need the brakes to do it. I would not really want to put the prop valve on the front brakes, as this may serve only to lengthen the stopping distance. If you convert to a tandem master cylinder, a prop valve might be advised. If you decide to fabricate a new pedal quadrant, with twin master cylinders, use .7 or .75, depending on how much mechanical advantage you have in the long pedals (pedal length will be critical). With a bias bar, no prop valve will be needed.
The rear brakes don't do too much on the 11, and the braking performance is pretty much late 50s, with decent modulation and feel once the system is sorted. It is not anything like contemporary brakes, but then neither are the tires, especially if you are running the narrow 4.50X15. It is not bad, when you take into consideration what the car really is. I imagine that fade could be a problem, but I don't use the brakes that hard, and have never experienced it, even at the track, during an extended lapping session. I just don't depend on them that much to go fast. I am thinking about momentum, and carrying it, not suppressing it.
You can get more accurate front braking through alignment, taper wheel bearings, and perhaps new calipers to match your new wheel cylinders and master cylinder.
I had lots of problems with the braking on my car, and I finally got a handle on it when I installed the taper front wheel bearings, followed by a brand new master cylinder to replace my old, rebuilt one. My calipers were not in bad shape on my LHD car, and I am still running the originals that I had honed and replaced the seals. On my dual master cylinder RHD car, I replaced EVERYTHING from the donor, including the calipers, wheel cylinders, springs shoes and drums. Only the hand brake expanders and the adjuster/wedges were retained.
If you are looking to take a little under steer out of the chassis, mess around with the setup. 5.5" front and 7" rear ride height is a good place to star. Front camber from -.5º (bias ply race tires) to -1.5º or more on radials). If you have the right springs, and the right dampers, a single click of compression damping on the rear should be immediately felt in the balance when cornering, or when testing on the skid pad. My LHD car is easily biased to the rear for cornering and rotation by just making a small damper change. It took a while to find the sweet spot, but I did finally find it, and the response to changes in the dampers is very satisfying. I now run the rear dampers (AVO) at the softest setting, going up one click for autoX or if I want the car to have a bit more bias to the rear. WhEEEE!
Usually, one adds a proportioning valve to the rear brakes to limit the pressure to the rear so that the rear brakes don't lock. If the rear brakes have too much authority, you get oversteer, usually the snap variety, which is really hard to catch. also, you will lose directional stability during hard braking.
Properly set up the W11 will rotate fine on its own... You don't need the brakes to do it. I would not really want to put the prop valve on the front brakes, as this may serve only to lengthen the stopping distance. If you convert to a tandem master cylinder, a prop valve might be advised. If you decide to fabricate a new pedal quadrant, with twin master cylinders, use .7 or .75, depending on how much mechanical advantage you have in the long pedals (pedal length will be critical). With a bias bar, no prop valve will be needed.
The rear brakes don't do too much on the 11, and the braking performance is pretty much late 50s, with decent modulation and feel once the system is sorted. It is not anything like contemporary brakes, but then neither are the tires, especially if you are running the narrow 4.50X15. It is not bad, when you take into consideration what the car really is. I imagine that fade could be a problem, but I don't use the brakes that hard, and have never experienced it, even at the track, during an extended lapping session. I just don't depend on them that much to go fast. I am thinking about momentum, and carrying it, not suppressing it.
You can get more accurate front braking through alignment, taper wheel bearings, and perhaps new calipers to match your new wheel cylinders and master cylinder.
I had lots of problems with the braking on my car, and I finally got a handle on it when I installed the taper front wheel bearings, followed by a brand new master cylinder to replace my old, rebuilt one. My calipers were not in bad shape on my LHD car, and I am still running the originals that I had honed and replaced the seals. On my dual master cylinder RHD car, I replaced EVERYTHING from the donor, including the calipers, wheel cylinders, springs shoes and drums. Only the hand brake expanders and the adjuster/wedges were retained.
If you are looking to take a little under steer out of the chassis, mess around with the setup. 5.5" front and 7" rear ride height is a good place to star. Front camber from -.5º (bias ply race tires) to -1.5º or more on radials). If you have the right springs, and the right dampers, a single click of compression damping on the rear should be immediately felt in the balance when cornering, or when testing on the skid pad. My LHD car is easily biased to the rear for cornering and rotation by just making a small damper change. It took a while to find the sweet spot, but I did finally find it, and the response to changes in the dampers is very satisfying. I now run the rear dampers (AVO) at the softest setting, going up one click for autoX or if I want the car to have a bit more bias to the rear. WhEEEE!
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xkfeng7
- Posts: 31
- Joined: Mon Aug 13, 2012 3:33 am
- Location: Boston, MA
Re: Rear brake cylinder sizing
Stock rear cylinders on the later Spridgets was 5.8" (IIRC).
But, I've heard many people go with 0.75" as a replacement. Not sure why unless they've also changed the front brake spec.
I decided to stick with 5/8 for now, but these parts are so cheap that I'll worry about sizing it right after I rebuild the rest of the car.
But, I've heard many people go with 0.75" as a replacement. Not sure why unless they've also changed the front brake spec.
I decided to stick with 5/8 for now, but these parts are so cheap that I'll worry about sizing it right after I rebuild the rest of the car.
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adamwilkinson
- Posts: 187
- Joined: Wed Jun 29, 2011 12:17 pm
Re: Rear brake cylinder sizing
It helps with lowering the brake fluid pressure to the rear brakes especially if you dont run a bias bar.
Dont forget your taper wheel bearings during your rebuild!!
Everyone knows you cant get a firm pedal without them... oh hold on i must be mistaken as our brake pedal is very firm and we dont have them...
Dont forget your taper wheel bearings during your rebuild!!
Everyone knows you cant get a firm pedal without them... oh hold on i must be mistaken as our brake pedal is very firm and we dont have them...
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erictharg
- Posts: 680
- Joined: Thu Jan 29, 2009 7:50 pm
Re: Rear brake cylinder sizing
Got to love those angular contact front wheel bearings! Just keep rolling on... for some of us anyway!
2 1/2 seasons racing on my fronts (from Peter May - so correct face located) and still tight as ...( insert suitable metaphor).
I run whatever the stock rear cylinders are. And apart from wearing shoes out when racing they seem to behave.
But I've never locked a wheel except in the wet.
I know - not trying hard enough!
Or maybe trying just hard enough...??
2 1/2 seasons racing on my fronts (from Peter May - so correct face located) and still tight as ...( insert suitable metaphor).
I run whatever the stock rear cylinders are. And apart from wearing shoes out when racing they seem to behave.
But I've never locked a wheel except in the wet.
I know - not trying hard enough!
Or maybe trying just hard enough...??
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Westfield 129
- Posts: 867
- Joined: Sat Jun 04, 2011 4:20 am
Re: Rear brake cylinder sizing
Go with the 3/4" size and the rear brakes will work better, with a bit more authority and precision when using the single master cylinder. Also, clean, unoiled and brake fluid free shoes will help as well.
Note that the type of master cylinder will make a difference in the rear wheel cylinder size on some cars. All the local cars here run 3/4", and rear brake authority is actually quite good.
One thing that you don't want is locked rear brakes. Once that happens, you lose all directional control. That said, I have not had the problem running the 3/4" master cylinder and 3/4" rear wheel cylinders.
Don't try any other combination until you have driven my car. The brakes are pretty good, and I have already spent the better part of a decade sorting them. Short of fabricating a new pedal quadrant for twin master cylinders, it's not bad. You can also run a tandem master cylinder, but you might end up with different front calipers as well.
Firm pedal is easy. PRECISION is the hard part. I was able to get a firm pedal with the ball bearings. However, the firm pedal had different pedal travel for each application... "Two pump brakes". If you really want precision, install the taper wheel bearings. The difference is amazing.
Our Timken sets available in the US feature the proper shims for installation and pre load. The price has actually dropped 20% for the identical parts over the last year as well. Contact Speedwell Engineering, USA
Note that the type of master cylinder will make a difference in the rear wheel cylinder size on some cars. All the local cars here run 3/4", and rear brake authority is actually quite good.
One thing that you don't want is locked rear brakes. Once that happens, you lose all directional control. That said, I have not had the problem running the 3/4" master cylinder and 3/4" rear wheel cylinders.
Don't try any other combination until you have driven my car. The brakes are pretty good, and I have already spent the better part of a decade sorting them. Short of fabricating a new pedal quadrant for twin master cylinders, it's not bad. You can also run a tandem master cylinder, but you might end up with different front calipers as well.
Firm pedal is easy. PRECISION is the hard part. I was able to get a firm pedal with the ball bearings. However, the firm pedal had different pedal travel for each application... "Two pump brakes". If you really want precision, install the taper wheel bearings. The difference is amazing.
Our Timken sets available in the US feature the proper shims for installation and pre load. The price has actually dropped 20% for the identical parts over the last year as well. Contact Speedwell Engineering, USA