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Brake Cylinders

gli77

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Looking for some info on brake cylinders on a PA-18-150 with 8.00 tires. Was looking at the direct univair replacement but see Dakota cub has a high pressure version. Would this be too much pressure for the smaller wheels? Any other solutions to look at?
 
Looking for some info on brake cylinders on a PA-18-150 with 8.00 tires. Was looking at the direct univair replacement but see Dakota cub has a high pressure version. Would this be too much pressure for the smaller wheels? Any other solutions to look at?

If you pump them up and get rid of the airgap the stock brakes work fine with 8.00 tires

Glenn
 
Looking for some info on brake cylinders on a PA-18-150 with 8.00 tires. Was looking at the direct univair replacement but see Dakota cub has a high pressure version. Would this be too much pressure for the smaller wheels? Any other solutions to look at?


also make sure your rubber diaphragm is new and not deformed...
 
I always carried a spare, and 8-32 socket heads except behind the hose. Changing a diaphragm became a 15 minute exercise. They tear if you let the fluid get low.

As for $36 diaphragms - I use truck inner tube or Buna N sheet. Cost is pennies; service life is literally years using either Dot 3 or Dot 5.

Moot for me - I hold field approvals for both types of Grove master cylinders. Flawless operation daily, check fluid at 25 hr. service intervals.
 
Looking for some info on brake cylinders on a PA-18-150 with 8.00 tires. Was looking at the direct univair replacement but see Dakota cub has a high pressure version. Would this be too much pressure for the smaller wheels? Any other solutions to look at?

Are your current brakes not working? Can you explain a bit more why you are looking to replace them?
 
We're doing a rebuild and need to replace the existing brakes cylinders. I see Steves also has a brake set. Was wondering if these are more meant for the larger bushwheels and would have too much pressure for 8.00s? I started out thinking I'd just order the replacements from Univair but now see there are some other options.
 
The only part that needs replaced for those small tires is the diaphragm.


Sent from my iPhone using SuperCub.Org
 
gli77
The amount pressure is controlled by the pilot, so it is pretty hard to have too much brake. Things that will make most any set of brakes work better. Take a good look at the brake lines. Replace any old lines and make sure they do not have bends or loops in them that can trap air bubbles. You see this a lot when the lines come out the belly go several inches down then back to the top of the gear leg. Mount the calipers at ten or two o'clock position, may need to change for ski issues. If the bleed nipple is down put a 45 not a 90 degree fitting coming out of the top of the caliper. This will avoid air bubble at that spot. If you have uncovered legs mount calipers with nipple down. Make sure you have a flex line to the caliper not hard line. I know, it will work with a hard copper line but it is a rebuild so do it right. So just make one line that go's from the brake up to bulkhead fitting on the fuselage, I have mine coming out the side above the front gear fitting (need tab on frame). Then a short line to master. That way all the lines and fittings are exposed so it is very easy to work on. The brakes seem to work if you do none of the above, but, it will help prevent a lot of headaches and money trying to fix a "soft" brake down the road.
DENNY
 
also make sure your FRONT brake pedals are not TWISTED, that will limit travel..very common... face of pedal where foot pushes should be in line with hole in arm that rod going to master cylinder goes through
 
The one on the left after straightening. The right one before.
955C3226-6279-48EA-83C2-D4BCC07A936D.jpeg


also make sure your FRONT brake pedals are not TWISTED, that will limit travel..very common... face of pedal where foot pushes should be in line with hole in arm that rod going to master cylinder goes through
 

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We're doing a rebuild and need to replace the existing brakes cylinders. I see Steves also has a brake set. Was wondering if these are more meant for the larger bushwheels and would have too much pressure for 8.00s? I started out thinking I'd just order the replacements from Univair but now see there are some other options.
What exactly are you thinking about? The master cylinders must be matched to the wheel cylinders. Which brake cylinders are you asking about? The masters or the wheels? Since you mention 8:00 tires I can assume that you still have the original expander tube wheel brakes? Those are matched to the master cylinders to which mike and Bob are referring. This system utilizes low pressure (350 psi max) and relatively high volume. The diaphragm needs to be maintained. Whereas all of the available modified or replacement master cylinders are intended for disc type wheel cylinders. These require higher pressure (aprox three times as much) and lower volume for proper operation. Grove does have a disc modification for the original 4" wheels which have the expander tubes type of drum brake. They are the only ones that have a direct conversion for both units.
 
Diaphrams work well with small tires. They do require adding fluid from time to time because it is a closed system. Dakota Cub and Steve's are vented and only require you check the reservoir at annual and that is about it. Steve's use your existing brake frames and pedals with a new piston, reservoir bolted to it. Inspect for cracks around the arms that hold the pedals. Dakota's are a complete new unit, nothing used from the old Scott system except the parking brake valves. If you search this thread you will find a lot more info on this subject.
 
Thanks Steve. I saw the Steves version yesterday. I have to order a gascolator from them anyways so I'll ask about their brakes. We need to order a set of master cylinders so just looking at what the best option is, Univair, Dakota, or Steves. We have the Cleveland wheel & brake STC and plan on going 8.00 tires.
 
No. So I am going with something and just deciding if it should be the original design or another version. Asking price on those?
 
I got sticker shock looking at Univair, they show just over $1000 each. I have a couple of sets of used ones. Make me an offer.
 
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