Hot Rods Oh no not another brake questio

I have a Chevy pickup master cylinder as pictured firewall mounted it was 1 1/8" on both bores which gave me a very heavy clutch and brake pedal. I have had it sleeved down to 15/16" on the brake side and 7/8"" on the clutch.I now have great clutch control and great brakes (rear drums front discs). When I refitted it I decided to put a 2lb residual valve the front brake line (also have a 10lb one in the rear line) I have noticed a bit of drag on the front brakes, can push the car but not as easy as before. Thinking about removing the 2lb valve?

 

Your MC is below the front caliper level? What style front calipers?

 

The valve is used when the master cylinder is lower than brakes.
Terry aka dirt t

 

My cylinder is on the firewall way above the brakes.

 

No residuals required as fluid cannot flow back into the reservoirs as would be the case under the floor.

 

Are you sure it's not the calipers hanging up.

On almost every GM D-52 caliper I worked on, I had to take the sleeves that the ride on and run all four of them on the grinding wheel until it slid through the caliper O-rings easier. I think it was el-Pollock-o suggested I use the black brake grease with the.
Another benefit in doing this was when the light turns green and I let off the brake pedal, the brakes release faster.

 

The calipers were fine when just using the 1 1/8" cylinder with no valve. Calipers only started to drag when using the smaller bore cylinder and the valve.

 

That might be so, but after you refitted the bores, you added the residual valves. Do you drive it without the residual valves beforehand?

Edit: I meant had them sleeved, drove it, then added the residuals.

 

I fitted the sleeved cylinder and valve at the same time.

 

After reading the replies above, have you thought of taking the valves out?

 

I sure would try that first.

 

Think I will take the valve out. I tell other people only change one thing at a time.

 

You don't need those valves.

 

IMO, that is a maybe. If the rear wheel cylinders have metal cup expanders, then none needed there. But if it has no expanders the RPV will help prevent air from entering when the shoes retract.

Front, none needed.

 

Eventho my MC is above the rear drums, the manufacturer recommended the use of a residual valve in the rear when I installed a disc/drum system and it works great. When not using a vacuum power assist, a smaller bore MC and proper pedal ratio works as original manufacturers intended giving a good pedal feel. Many miss this.

 

Remove the FRONT 2lb valve, make sure the push-rod clearance is correct and the calipers (you didn't say what style you are using) are free in movement (sliding-floating).

Keep the rear drum RPV (#10).

 

I’m no brake expert (just ask Kult above) but do you really think 2 lbs of pressure in the front system is going to keep you from pushing the car?

 

Or the fact that a 2lb valve is no problem if the master is below the floor but suddenly causes a brake drag if the master is moved up. Regardless I doubt that is the problem. The pads should be lightly dragging on the rotors and since disk brakes are not self energizing they rely one hundred percent on clamping force to apply, the 2 lbs likely is not doing anything…. Is the pedal pushrod adjusted properly?

@alchemy I generally stay out of brake threads now as well.

 

Just for fun, what size are the caliper pistons in the front?

 

Unknown as you won't state what brake style you are using on the front axle. Will that residual brake pressure cause the caliper piston not to return to rest properly? I would say yes.

The OP stated the car was more difficult to push w/ the valve. I guess so.

The FIRST THING YOU DO is to remove that valve from the circuit and go from there. Whether it will or will not cause pad drag is not the question. It has no business being there.

 

Interesting, I've never used residual valves in anything unless the master was below the bleeders.

Might try this. Jack up the car so you can spin the wheels. Pump the brakes a few times, then disconnect the brake pedal from the master to take that out of the equation. Check each wheel for resistance. The wheel(s) that resist the most, crack the bleeder for a split second to remove the slight pressure contained from the residual valve and see if that helps. If so, you may have found the problem. If the wheels seem to have normal resistance, reattach the pedal to the master, pump the brakes and repeat the above wheel test. It's also possible the pedal rod is adjusted too far into the master. Also check for full pedal travel and ensure that the master bottoms out before the pedal does.

I'd try that real quick before you take anything apart.

If the rear drums don't drag with the valves installed after initial brake adjustment, I might check them after a few short trips just to ensure they don't cause things to "tighten" up. One would think that the valves would hold the 10psi as soon as the pedal is pushed and the brakes are actuated, but it could take a couple of cycles. Just a thought.

 

The FRONT CIRCUIT #2 VALVE has to be removed before going through diagnostics. It is not the OP's fault as these so-called brake conversion sellers don't present needed information correctly.

The residual pressure valve will not cause drum brakes to drag. If one does, it has very weak shoe return springs.

It's design is to prevent outside air ingestion around the cups on sudden brake release. If air is ingested or has fluid leakage, air will enter the complete system and cause a soft pedal.

 

Being a smaller bore now means a little more pedal travel required. Let's ignore the residual valve for a moment and look at your return pedal travel. Is there there free play in the push rod now that there is a different brake piston in there now?

 

Why? We don't know if that's the problem.

If the rear brakes are adjusted and then bled, I can see a situation where they could very well cause drag.

Every explanation I can find online is that the residual pressure valves are used when the master cylinder is mounted below the bleeder valves to retain minimal brake line pressure to eliminate excessive brake pedal travel, IE spongy pedal. While they may help what you're describing, I've seen many drum brake designs that do not have a residual pressure valve installed. Is it a specific style brake cylinder that require these, if so, this should be pointed out so the OP can determine whether or not he needs one. I have two vehicles with rear drums and neither have residual valves in the rear brake line.

Where's the residual valve in this master?:

 

^^^^^ 2178

 

yup 2178

 

Where's the residual valve in this master?

[/QUOTE]
Yep,
2178

I don't remember ever seeing a master from a HAMB era car without that part. And that includes all the early 50-60s with cylinders on the firewall.

 

Another thought. Did sleeved cly. receive an internal residual valve and you don't know it?

 

No we don't, but I can guarantee it is part of the problem. It has no business being there, period.

Kindly explain to me how residual line pressure @ 10lbs is going to overcome a brake shoe return spring tension (even if fatigued and never replaced)?

The RPV was replaced (not all systems) by WHEEL CYLINDER EXPANSION CUPS. Now this mostly done with a diagonal brake system that will have DISC and DRUM ON ONE CIRCUIT.

​

You're being serious?

 

^^^^^ In today's world one can not assume that wheel cylinders will have cup expanders. Buy a new replacement for an older vehicle and see what you get.