47-55.1 rear brake line routing

[nvrdone]

I need to re route the rear brake line on my '49 3100. so far I plan on running the line from the m/c down the left frame rail. im not sure where to end it & how to route the hose to the rear axle. the axle is a 12 bolt out of a c10 & the lines to the drums come up to a connection at the top of the diff. should I end the line on the frame even with the center line of the axle & use a hose over to the diff? or should I route the line across the center of the rear crossmember & run a hose in a loop to the diff?
any ideas & pictures would be appreciated
thanks

[mr48chev]

If you have a crossmember for the shocks to mount to i'd run the line to the center of the crossmember and put Brake hose mounting tab there for the end of the hose to be secured on. You can buy the tabs new (just google brake hose mounting tab) or scavenge one from a donor rig or even make one. I think that O'Reilly's and Autozone usually have the clips in the "Help" section.

You want the hose long enough so that it isn't stressed when the axle hangs all the way down like when the truck might be raised on a two post hoist at a shop.

[nvrdone]

mr 48 chevy: what you describe is exactly the way my rear brake line is routed now.
the problem is that when the engine is running my pedal goes right to the floor and the rear wheels can be turned by hand. with the engine off, the pedal is hard - goes down about 2" - and the wheels can not be turned by hand. I disconnected the flex line to the rear axle and plugged it. with the engine running or not the pedal is hard & drops the same 2".
Ive bled the system by having my wife push the pedal, used a vaccume suction bleeder, and reverse bled the system. no change any way I bleed it. I think there is air trapped in the flex hose that I cant get out. ive also replaced the m/c 3 times. im about ready to give up and go back to the stock single chamber m/c

[dsraven]

I would start by checking the brake booster to see if, when the engine is running, the pushrod to the master cyl is being moved into the master cylinder or if the brake pedal moves towards the floor when the engine starts. this can happen with a faulty booster when vacuum is applied but with no vacuum the brakes would operate like normal. you could do a simple check by having a friend start the truck while you use some sort of stationary object, like a short stick, placed next to the pedal to check if the pedal moves when the engine starts. then try loosening the mounting bolts/nuts that hold the master cylinder onto the booster, just enough to allow some slack but not enough to allow the master cylinder to fall off or anything like that. then step on the brake and see if the rear brakes now operate like they should. another thing to check is the amount of free play there is between the master cylinder piston and the pushrod from the booster, the brake pedal linkages for play/binding and a return spring to ensure the pedal is returning all the way. since there are normal brakes without the engine running I would say look closely at the booster, pushrod adjustment etc.

[nvrdone]

dsraven - thanks for the suggestion. this has been an on going issue for about 2 years & I think I did what you recommend, but it doesn't hurt to re check.

[dsraven]

first off, what do you have for a brake set up? disc front/drum rear, disc/disc, master on the frame or master on the firewall? what style of master cylinder do you have-full open top or partially closed top with a small cap?
have you looked closely at the pedal and linkage to the booster rod? if the booster rod is pushed into the booster at all, due to a poor or missing pedal return spring or a sticking pedal pivot bushing or linkage which the return spring cannot overcome or some other reason, then this will have an affect on the valve operations inside the booster. the booster rod needs to be able to easily return all the way back after every brake application. is it possible for you to remove the pin from the pedal to the booster pushrod, pull back slightly on the booster rod to see if it is seated all the way back? then start the engine and see if the booster pushrod moves into the booster when the engine is started? (indicating a valve issue in the booster which allows a pressure differential between the 2 sides of the booster diaphragm which in turn draws the pushrod into the booster)
if the valves inside the booster are not seated properly, like if the pedal isn't free moving and adjusted properly to allow the booster pushrod to return all the way, then the pedal can be drawn down some which can have an affect on the brake system operation. it would be like the master cylinder never gets to return all the way to a "brakes released" scenario when the engine is running because the engine vacuum draws the pedal down, partially applying the brakes.
if you have a master cylinder with a large lid (as asked above) that you can see down into, remove the lid and (with safety glasses on) watch the fluid inside the reservoir while a buddy slowly steps on the brake pedal. there should be 2 distinct little "fountains" of fluid rise up for a second in the fluid then all should be calm. this is a test to see if the master cylinder is returning all the way when the pedal is released. if it is then you will see the fountains which is simply the fluid displaced as the piston travels down the bore, the fluid comes up through the 2 holes that feed fluid to the bore. when the piston goes past the holes the fountain stops and fluid will be displaced out of the master cylinder into the brake lines until the brake components bottom out against the rotors and/or drums at which point pressure will build in the system depending on how much pedal pressure is applied. if you step lightly on the pedal and no fountain appears then you possibly have a pedal that is not fully returning so the piston in the master doesn't get to return past those fluid feeder holes in the reservoir bottom-no fountain then because the piston hasn't returned past the holes. another test to do would be to hold a brake application for an extended period to see if the pedal slowly drops to the floor. this would indicate internal leakage inside the master cylinder. do this with the engine running because when the engine is off it takes more leg pressure to get the same amount of brake pressure. there would be no vacuum assist without the engine running.
here are a couple of links to booster operation and testing that may help. if you have a good hard pedal without the engine running then it sorta points to a booster or adjustment issue. pedal height with engine off should equal pedal height with engine on. this is with brakes not applied. check all the linkages, pivot points, return springs and rubber pedal bumpers to ensure the system is functioning properly before you start and you have a pedal that returns to exactly the same height each time, engine off, and there is also some free play in the pushrods both at the pedal and also at the master cylinder. hope that didn't confuse you.

https://m.roadkillcustoms.com/unders...rake-boosters/

https://axleaddict.com/auto-repair/B...-Booster-Check

[dsraven]

if you have a good hard pedal on the first pedal application (no pumping required)with the engine off and it will hold the same pedal height with the same pressure applied for a couple of minutes, then you probably don't have air in the system and your master cylinder is probably fine. more likely a booster issue, a linkage binding or being "held up" with carpet or grommets etc, a return spring issue or a pushrod adjustment issue either at the pedal attachment or at the booster to master cylinder. have you tried pulling the pedal backwards towards the seat to see if there is something binding or stopping the pedal travel? poor rubber bumper for the pedal so the pedal isn't always stopping at the same height? worn pedal pivot bushings so the pedal has some side to side play allowing the pedal to miss the bumper stop or bind with the booster pushrod? if you pull the pin from the pedal to booster link and move the pedal through a full stroke it should be very easy to move and should return all the way back up. a master cylinder under the floor can complicate this simply due to linkage pivots and cab movement affecting linkage etc. plus the pedal does have seals/grommets where it goes through the floor. disconnect at the booster and check to see if the booster pushrod "returns" at all. if it does then maybe the pedal return spring is too weak.

[dsraven]

does the booster hold a vacuum? if you started the vehicle, let it run for a minute or 2 , then shut it off and allowed to sit for a couple of minutes before pulling the vacuum valve out of the booster, would you hear a pretty good vacuum leak when you pull the valve out? do you hear any air leakage from the booster pushrod area when the engine is running?
if you have access to a vacuum pump, even a hand held one, pull a vacuum of 20in on the booster and see if it will hold for a couple of minutes.

http://www.agcoauto.com/content/news/p2_articleid/129