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#25192 08/27/2003 4:47 PM | Joined: Jan 2002 Posts: 175 Member | | Member Joined: Jan 2002 Posts: 175 | working on new brakes for a 49 1/2 ton. As I read the shop manual it seems to indicate that all brake lines were 1/4 in dia tubing. I ordered a preformed set from Jim Carter and the tube that would connect the rear cylinders is a smaller dia than the rest of the lines. Is this correct? Does it make a difference in braking efficiency? Any body jump in that has a thought. Thanks. | | |
#25193 08/27/2003 5:35 PM | Joined: Feb 2001 Posts: 198 Shop Shark | | Shop Shark Joined: Feb 2001 Posts: 198 | If I remember correctly it was an early and simple attempt at brake equalization. Smaller line moves smaller amount of fluid, less braking at the rear than at the front. Someone here will probably confirm or deny this theory. 
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#25194 08/27/2003 6:30 PM | Joined: May 2003 Posts: 224 Wrench Fetcher | | Wrench Fetcher Joined: May 2003 Posts: 224 | | | |
#25195 08/27/2003 9:23 PM | Joined: Jul 2000 Posts: 504 Member | | Member Joined: Jul 2000 Posts: 504 | The lines that connect to 1/2 ton wheel cylinders are 3/16. As for the carrying lines from the master to the blocks , I think they are 1/4 inch..
Bill M
53 GMC Hydra-Matic
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#25196 08/27/2003 10:36 PM | Joined: Apr 2003 Posts: 140 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2003 Posts: 140 | In any hydraulic system, pressure is equal throughout the system, regardless of line size.
So when you step on the brake, fluid is gonna move through tubes and push the shoes out. Until the shoes hit the drums, there's not much resistance and the pressure is low.
Once the shoes meet resistance, pressure goes up rapidly and remains equal throughout the system.
A smaller tube would introduce a *very* slight pressure drop during the initial take-up show movement, but that wouldn't matter since the shoes aren't touching yet.
Once the shoes touch, the amount of actual fluid flow is small, and so the very small pressure drop through the tube is not significant comapred to the severla hundred PSI operating pressure.
I'd use whatever tubes, etc fit the fittings.
Cheers!
George | | |
#25197 08/27/2003 11:00 PM | Joined: Jan 2001 Posts: 428 Shop Shark | | Shop Shark Joined: Jan 2001 Posts: 428 | If I remember right,when I redid my 50 with the Huck brakes all the lines were 1/4". On my 51 with the Bendix brakes the line from the master to the frame block was 1/4". All other lines to wheel cylinders were 3/16". | | |
#25198 08/28/2003 1:36 PM | Joined: Jan 2002 Posts: 175 Member | | Member Joined: Jan 2002 Posts: 175 | Thanks for the input. I talked to Bob Adler about this and he indicated that the 3/16 connectors would not even fit in the brass junction blocks in the wheel cylinders if they were original 49s. I checked this out and he is correct. All lines on the 49 1/2 ton were 1/4 inch. Jim Carter is exchanging the 3/16 that they sent for 1/4". | | |
#25199 08/29/2003 3:58 AM | Joined: Aug 2000 Posts: 197 Member | | Member Joined: Aug 2000 Posts: 197 | You can get adapters from your local parts house to fix this.
Jason
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