wheel cylinders too big??

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stumpofj40

stumpofj40

10 Year 15 Year
Joined
May 8, 2007
Threads
15
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203
Location
Brisbane, OZ
Well I ordered 4 new rear wheel cylinders the other day and they were the wrong size (larger bore size) but decided I would try them out anyway. Now my brakes feel like I need to pump the hell out of them to get them to work.
Am I right in thinking that the MC just can't provide enough pressure for the larger cylinders????

Am running a hj60 MC with the smaller 22mm bore size (instead of the original which I think had close to a 27mm bore?) and have 60 series discs with 4 runner calipers on the front. Rear end is also a FF from a 78 pig.

Would fitting an earlier model MC with a larger bore fix my problem?
Thanks...
Dan
 
possibly, but are you certain they're adjusted right? it takes more than you'd seem to think. a little tight is ok at first as they will wear in to just right, you just don't want to have to use a wrench to turn the tire...
 
Yeah I'm pretty certain they're adjusted just right, I re-did it about 3 times because I wanted to be sure, but I pretty much adjusted them until I could hardly spin the wheel and then backed them off slightly...can just hear the pads touching the drums...
 
stumpofj40 said:
.can just hear the pads touching the drums...
Click to expand...

Try tightening the drums another click or two. also, do you still have the residual valve for the rear circuit in the MC?
 
LAMBCRUSHER said:
possibly, but are you certain they're adjusted right? it takes more than you'd seem to think. a little tight is ok at first as they will wear in to just right, you just don't want to have to use a wrench to turn the tire...
Click to expand...

stumpofj40 said:
Yeah I'm pretty certain they're adjusted just right, I re-did it about 3 times because I wanted to be sure, but I pretty much adjusted them until I could hardly spin the wheel and then backed them off slightly...can just hear the pads touching the drums...
Click to expand...

Pighead said:
Try tightening the drums another click or two. also, do you still have the residual valve for the rear circuit in the MC?
Click to expand...

yaw, tighter than you might think at first- the shoes will center as you drive them in and they will also wear into their new homes fairly quickly and become much looser than you had thought that they were. it is ok to have resistance while turning the wheel- just not breaker bar resistance. click a couple more clicks on all 4 cylinders- as PIGHEAD mentioned, the residual valve needs to be in the rear circuit as well- these things have been passed around a bit over time and you don't know what you've got sometimes till you find out for yourself. someone may have removed the residual valve at one point thinking they were doing a disk conversion- or it's an aftermarket replacement that was never fed the valve...
 
Thanks for the reply guys,
Tried tightening the drums more to a point where the wheels were REAL hard to turn and it made no difference...
Not sure about the residual valve Pighead, I just have the factory proportioning valve set up that bolts to the bottom of the MC...doesn't mean its not been tampered with though... I have a earlier model MC laying about, would it be worth trying it and seeing if it does make a difference???
 
Not sure which way a stock HJ60 proportioning valve proportions...I've never owned one.
I'd put the early MC in and see if that helps.
 
Bigger wheel cylinder bore needs to be matched by a bigger master cylinder bore. Been through it on many rigs, try to find what the wheel cylinders are off of and then find the corresponding master cylinder. Bigger is better when it comes to master cylinders (to a point) especially when mixed with larger tires. 22mm to 27mm is a fairly significant jump in size.
If you have brake lines laying around you could also try bypassing the proportioning valve just to see if your brake problems are resolved. The proportioning valve limits the fluid to your rear brakes, removing it would give full pressure to them which if you were hellbent on keeping your current master cylinder then that would at least tell you if you are flowing enough fluid to run the bigger wheel cylinders. On rear disc conversions many times the proportioning valve is left out altogether in order to run enough fluid for calipers.
 
jamister1 said:
Bigger wheel cylinder bore needs to be matched by a bigger master cylinder bore. Been through it on many rigs, try to find what the wheel cylinders are off of and then find the corresponding master cylinder. Bigger is better when it comes to master cylinders (to a point) especially when mixed with larger tires. 22mm to 27mm is a fairly significant jump in size.
If you have brake lines laying around you could also try bypassing the proportioning valve just to see if your brake problems are resolved. The proportioning valve limits the fluid to your rear brakes, removing it would give full pressure to them which if you were hellbent on keeping your current master cylinder then that would at least tell you if you are flowing enough fluid to run the bigger wheel cylinders. On rear disc conversions many times the proportioning valve is left out altogether in order to run enough fluid for calipers.
Click to expand...

Ok well today I did exactly that, put in my bigger bore MC to match the bigger wheel cylinders and it made a very noticeable difference however I had to pump the petal once or twice to get it firm
I adjusted the rear wheel cylinders out a fair bit to a point where it almost made the 2H feel even more sluggish....and it did make a difference but the first stroke on the pedal just feels too soft...

could it be that because the front discs now have the residual valve removed from the circuit that the softness in the pedal is the "slop\ between the pads and the disc??
also I can lock the brakes up if I pump them...
thanks,
Dan
 
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