Discussion in 'The whoa and the sway.' started by 1969RIVI, May 21, 2020.
Just use it and don't sweat worrying yet.
Why you driving yourself nuts with this combination/proportioning valve thing.
Get a metering valve/block from Speedway Motors & be done with it.
Much less plumbing needs done & NO need to center anything to properly bleed the brakes.
All the proportioning valve does is hold off the application of the front disc brakes until there is 300lbs. of pressure on on the rears & then it allows fluid to the front disc brakes.
Same thing basically on Larry's car.
I don't care what I use as long as both back and front brakes work. I want this to be as simple as possible I just know I can't swap to front disc without adding something either a proportion valve or metering block. Where does the metering block get installed, up at the master or in the lines going to the back drums?
Go back to post #15
Oh for crying out loud, use a modern COMBINATION valve. You can mount it anywhere you like, below the master, or anywhere convenient on the frame. You are going to have to make some new lines if you want to do it right. A hold off valve and proportioning valve are two different functions. The warning light section is important for safety reasons. The COMBINATION valve combines all 3 functions. Watch the video.
The metering/hold-off valve measures 2x3x1. Much smaller & MUCH easier installation. Most times you can reuse the two brake lines going to the front discs so basically all you have to do is make one line from the master.
Just remember to put a "curl" in it.
For me, The only thing I did was bolt up the brackets on the spindles along with all the other components (calipers etc). I did nothing to the MC (all drum), F/R distro block, hard lines etc. After 5+ years, this year, I did replace the MC with a OEM disc unit because my original started leaking at the rear. With the original MC I just had to be mindful about the fluid level because the calipers have a larger capacity.
While there is information floating everywhere about conversion, many are opinion based. Somewhere, I had read it was technically unnecessary to add, change or mess with a proportioning valve on a big buick. I wished I had kept a link to that information. So far so good with my setup.
You might get by without a proportioning valve or hold-off valve in a big car since they are a fair bit heavier. I know with a lighter GS/Skylark, a panic stop without a proportioning/hold-off valve will result in locked rears. The front noses over, the rear gets light just about the time the rears self-energize and you are sliding sideways if you don't back off. Ask me how I know? Going four wheel discs doesn't need a hold-off valve due to no need to delay the fronts while the rear drums catch up.
A panic stop in an original disc brake optioned 1970 GS car can lock the rears. I know. So, to me, the argument about a proportion valve is simply about preference and opinion. Nothing wrong with it, just disagree. A factory configuration is sufficient for braking in normal circumstance. If you own a car like these you should know how the car behaves in all situation with in reason. Racing is an entirely different matter.
In good conscience I cannot recommend anyone mix brake types and NOT use a valve that deals with the speed and pressure differences. It is not merely a preference.
I own a 70 power 4-wheel disc conversion GS from factory front discs and a 71 4-speed power front disc conversion from 4-wheel drums without the prop/hold-off valve. Lastly, my buddy has a 71 Skylark with factory power front disc car with a combination valve.
The 70 was stock power front discs with a front hold-off and a distribution block for the first 30 years I owned it. Yes, I could lock the rears but it took a really hard panic stab at the brake pedal to make it happen and it rarely happened. It stopped as well as a non-ABS car could be expected to stop. When converted to rear discs, a 100% panic stop results in the ever so slight tire chirps. I would bet money it stops within a foot or two of a similarly weighted ABS-equipped car.
My buddy with the factory front discs will also lock the rears at 100% panic stop but again it is rare. It is also like what you'd expect a non-ABS car to stop like.
My 71 conversion from standard 4-wheel drums without anything but a 4-wheel drum distribution block will lock the rear tires at the least little bit of extra braking. I have slid in my own driveway when I forgot to leave something in the garage from 5MPH and I have scared numerous people around me and myself when I forget I'm not in the 4-wheel disc car and stab the brakes slightly harder than a gentle, driving-Miss-Daisy stop. It really isn't safe as it is and I'm only waiting until I make up my mind to go 4-wheel disc or just put a 71-type combo valve where the distribution block is now.
The way it is set up now, I won't let anyone drive it alone unless I'm going with them to remind them the brakes are overly sensitive to rear lock.
To be very clear, for the Big car it is about preference. Whats-more, I remembered why, the Rivera front hard lines are smaller in diameter equalizing the rate, because even drum out front on the big cars stopped better than the 4 wheel drum A Bodies. So yes, on the Big cars it is an opinion because the design does suitably compensate.
Disc brakes - regardless of vehicle size as discussed in this thread - require movement (back and forth) of much more brake fluid than drum brakes do. So, if there are/were originally front drums, that may be the reason for smaller diameter lines.
Yes, there is much more fluid behind the piston(s) of disc brake calipers, BUT, the actual movement is much less, very little in fact. That is what makes disc brakes so instant acting as opposed to drum brakes that require overcoming of spring force, operate with clearance, and have the self energizing design. The difference is why a hold off valve was used in the disc/ drum systems.
Not only is the caliper filled with fluid, but as the disc brake friction material wears (from new material and with the caliper holding its min amount of fluid), the disc circuit also needs more fluid to fill the increasingly largr area in the caliper and must draw from the larger resevoir/lines holding fluid.
Well, the hold off valve is designed to allow engagement of the rear brakes first so the rearend will more predictably follow the front end while braking - that's a stability issue - same as the reason why you don't just rely on front brakes riding a bike or a motorcycle as steering dynamics change radically.
That was my point, The reason is to slow fluid flow to prevent the original front drum from locking up, though it is still possible. Though exactly opposite of the complaint about the ABody folks where the rears lock up easily in a disc conversion w/o the proportion valve. The conversion to disc in big cars, to be very precise - cars with smaller diameter front hard line that had bigger drum brakes (big cars had bigger brakes than A Bodies and were not much heavier) that could lock up are in fact a suitable candidate for disc conversion up front w/o the valve because the rate of brake engagement is actually moderated by the fluid in the smaller lines trying to rush to fill the piston of a disc brake set up, meanwhile the rears are engaged. The assumption being yes, the system has been properly bleed and primed, esp the calipers. So, to the discuss of the original post, we are talking about a big car not an ABody. The proportion valve has already been discussed and the reason for it. I was trying to shed more light on the 'why' for Big Car all drum set up the valve isn't as crucial. In fact, if a valve is used then the front lines should be replaced.
Now for full disclosure, I am not impressed by the disc brake set up, the only benefit has been no brake fade. Stopping has been just as good as all drum. Some day I may actually install new, bigger hard lines up front and a proportioning valve. fwiw I am not the only Riv owner who has done this type conversion and not be impressed. We can lock up the front brakes when driving in reverse and we can lock up the rear brakes in drive just like if the system was all original drum.
Brake line size beyond the absolute minimum to get the job done has little or nothing to do with the issue. If you think it does, I respectfully suggest you don't understand pressure and volume in fluids. We aren't talking 40 gallons per minute at 6PSI. We are talking about the movement of less than an ounce of fluid at very high relative pressure once the system is full and bled.
If you are not impressed with the disc brake conversion, there is something wrong. Discs are inherently less prone to lockup due to the lack of self-energizing effects. They are brutally simple and significantly more reliable. Drum brakes are a Rube Goldberg device that somehow manages to get the job done despite itself.
A properly set up front disc (or all-wheel disc) brake system will put you through the windshield well before panic stop levels. The difference between an A-body and a B-body is one of scale, specifically heavier and longer. The laws of physics do not change for 750lb extra pounds and 2 extra feet.
I respectfully disagree. Prove me wrong by doing the math or placing smaller diameter hard lines on a car and measuring reaction time, braking distance etc. Ignoring the smaller diameter hard lines that must fill a piston to engage the braking surface (disc) is a bit of a stretch.
Two cars can have a disc/drum brake setup and not be impressive because there are other factors to consider like brake pads.
"I am not impressed," but I am not the only riviera owner not impressed, because maybe the drum brake setup was just that good.
My Riviera drum/drum & disc/drum set up is night and day better than the all drum setup on my 71 Gs Convertible.
Likewise it would be foolish to ignore the hard lines while adding any valve.
The laws of physics were never claimed to be different with 750lb and 2 feet, but forces and weight distribution do matter.
I'm not going to argue with you and this is my last post on the subject. You can have the last word.
The line and caliper are already filled. That's why you bleed brakes. How much fluid comes out with each press of the pedal when bleeding all the way to the floor? Not very much and that is at least 3 times more than what is needed to panic stop a car. It is the pressure that does the job, not the volume.
The act of applying the brakes moves less than one ounce of fluid for both front discs to actuate. Liquids are not compressible and act instantly. The size of the line is more than sufficient to allow free movement of less than an ounce of fluid at 800-2,000 PSI. Brakes need pressure, not volume. That's why you don't use compression fittings on brake lines and must use double flared ends. Smaller diameter tubing will take more pressure than larger tubing.
I stand by my statement that if your disc brakes aren't impressive, there is something wrong with the implementation. Either the master, rotor or caliper is not sized properly. There is no case where drums would be superior to disc. They are better in every way, simpler, quicker response, more resistant to fade and less likely to lock up. That's why almost every car made now has 4-wheel disc brakes and nobody puts drums on the front of any vehicle made in the last 40 years or more. Be it a Mini Cooper or a 6-ton Suburban, they all use discs to stop.
In short, I should be clear. Ignoring the full implementation is not good. Which you finally pointed out and acknowledged. I am not disputing compression of fluid. I am disputing the rate at which the small front diameter hard lines limit the rate to move even 1 oz of fluid, it does affect pressure and clamping force. That can not be ignored. Moving 1oz through 1/16" ID is going to take longer and more pressure than 1/4" ID. The force applied to the pedal to move that fluid to achieve the needed clamping for across the pad is moderating the whole system.
A simple experiment with a faucet can prove my point. Use your palm and turn the faucet on slightly to barely achieve a dribble, maybe just a constant dripping. You will be able to hold back the water, turn up the faucet, " make the line bigger" you will likely not be able to hold back the water. The same pressure exists pre-faucet valve. If you turned the water on slightly and are able to hold back, continue turning the valve and notice the delay to when you can hold water back. That is the sweet spot that the engineers of the Riviera brake system likely calculated and it works.
My Riviera stops fine, it isn't " new car throw you through the windshield" but enough to get the car stopped even in a panic. Are there more conventional ways to implementing a braking system yes. To assert aluminum 12" drum brakes can stop extremely well isn't a stretch and I'm not ignoring the short falls when the drums are wet.
We in the roundy-round cars back in the day, 60's-70's, most ALL of us used the Buick aluminum drum brakes. Some, like I, used the Buick shoes also because they were self energizing & were 12" x 2 1/4" as opposed to the Ford brakes, but they were a fixed shoe & some were only 12" x 1 3/4" wide.
The Buick brakes handled better because they were LIGHTER than the Disc's available at the time. Less UN sprung weight = a better handling car.
Of course we were kinda out of the norm because we didn't use a Ford Flathead or some other engine.
IT HAD TO BE A STRAIGHT 8 BUICK. We held the track record for 3 years after the switch to the SBC over head 4bbl. V-eights that most, many used at the start of the '73 season. AND, we were only allowed a 2 bbl. carb.