I have an 82 C70 Chevy 10 wheeler dumptruck. I did some brake work on the rear axle, driver's side. Rebuilt a wheel cylinder and put in a new hard line. Bled that brake using a Mity Vac until there was no air, pulled about 2 cups of brake fluid through it after no air just to make sure. Pedal felt fine, everything checked out ok. Went to drive it from my house to the farm last night and about got into a wreck. Hit the brakes at the stop sign to get on the 55mph highway (from a 25mph side road) and the pedal went right to the floor I tried to pump it but it stuck to the floor and wouldn't come up. I ended up being able to pull along the shoulder not wreck. Just pissed off a few people passing by and ran over a speed limit sign... oh and a pair of undies, pants and seat cover. (before you mention the parking brake, my truck just has a "mico-lok" which runs off the hydraulic brakes) Anyhow, after I got calmed down, I was able to pump the brakes and get some pressure. Brought the truck back home, bled with the Mity Vac, ran almost a gallon of brake fluid through. We bled ALL the wheels. Pedal was still soft. Decided to do it the manual way with one person on the pedal and one opening the bleeder and now my brakes are ok, had a bunch of air in it somehow? It seemed like a big air pocket up by the master cylinder. I don't understand that though, I didn't let it go dry. I just am really shaken from what happened, luckily I was able to think quick and going slow enough that I was ok, but it could have been much worse if I had been loaded or traveling at highway speeds! Is there anything in the system that won't allow to just vacuum bleed the brakes? I've worked on cars and heavy equipment for years, but this is the first hydrovac setup I've worked on. I understand the basics on how they work, we had a section on them when I went to school and I even dug out my old books and re-read recently (before working on the brakes)
When you say Hydrovac, are you referring to that GM thang that uses the power steering pump or the booster with the big vacuum diaphragm? I think the maybe the pump one is hydro-boost? Any way, the one with the diaphragm has another master cylinder that is operated by vacuum, or by hydraulic pressure if the vacuum isn't there. I use a pressure bleeder on big trucks, but I have used the mity vacs too. What I do is bleed the wheel cylinders, then manually bleed the fitting on the Hydrovac unit. I think this resets the unit, rather than getting air out of it, but I can't swear to it. I know the brakes don't work well until you manually bleed a little bit. Now for the snide comment: I bet you'll never again drive off after working on brakes without thorough testing. I won't tell you I learned that by backing into the shop years ago. Btw, you mentioned in another thread about single axle C70s, actually tandem ones are rare.
Did you start bleeding the brakes from the further wheel from the master cylinder? Did you bleed the hydro-vac? The hydro-vac could have a blown diaphram. Take a long pipe cleaner and take the check valve off and stick the the pipe cleaner down and see if there is fluid down on the vac side. If so, the diaphram is blown. Did you noticed that the brake fluid was low after the accident? This will tell you that the diaphram could be blown. These are difficult to bleed without a power bleeder. What I done without a power bleeder is to just crack the rear bleeders for an hour and let gravity go to work (be sure to keep checking the master cylinder for fluid). Then repeat on the front brakes.
Those things can pull a lot of air past the wheel cylinder lips. I like to pressure bleed. For my vehicles I would make or buy a reservoir cover with an air chuck nipple in the top. Top off the reservoir and attach 10-20psi regulated air. Open the bleeder valves until clear. Make sure it doesn't go dry.
Hydrovac, not hydroboost. Hydrovac runs off engine vacuum, more or less like a regular power assisted brake setup on a car, just larger. Hydroboost uses power steering pump (usually) to power them. I just bled the side I did work on, I hadn't touched anything else. I guess that was my mistake. I did test the brakes while pulling down the driveway and they were fine. Not sure why they just decided to give up a mile down the road! I have a friend with 4 of these C70s (all parts trucks) and those are all tandem and I've seen 5-6 on the road still... all tandems. I've never seen a single rear axle one actually. I thought that was what made it a 70 vs a 60 or 65. Huh, learn something everyday.
I don't mean to jump on you but I must also add this is a really good reason to look for a better chassis. Hydraulic brakes are bad enough in a modern truck and in the old ones, they were really bad. Aditionally, parts are getting hard to find. It is hard to put a number on these things but I would say you will save money in the long run. Think of the $ lost with a wreck, or downtime if something in the master cylinder or boost unit conks out on you and you have to wait a week or two to fix it. Air brakes or hydraulic are a deal maker/breaker for most on this board looking to buy a truck, for good reasons....
Yeah, I wouldn't buy a truck with juice brakes anymore. When combined with your desire for diesel power, I know you could a newer truck, even a $3500 retired road tractor that you put your body on. I'm not jumping on you about the age of the truck, I have an 86 GMC 7500, 86 and 87 IH 2375s, 97 and 94 Macks, a 71 Chevy C90, all of which are diesels, and all air brakes except the GMC, which is hydraulic disk all around. I will replace it if the brakes become a problem. I bought it at a price that was a deal for the bed. I just know from experience that hydraulic drum brakes on a truck will nickel and dime you to death, and doing stuff like that engine swap is always more than you think. Stuff like that is usually done by enthusiasts who want to do it, not for practical reasons. I did however pay for a good used diesel replacement on the fuel savings alone when I parked my last gas burner. Good luck, Mitch
I have all the air brake parts for it, will swap it over this winter. The engine swap is certainly practical. I can't touch a similar sized truck in good shape with a diesel and air brakes for even twice what I'll have into this truck. With the engine and air brake swap I'll have about $6k into it. I've looked at a few that were 7-10k price and either they needed tires, brakes, engine work, had a million miles, body was bed to death, etc. Not to say this is my "forever" truck, but I'm just starting out and I can't afford a 30-40k dumptruck... not this year anyway, maybe in a few years. I've pumped over 100k into the company just this year alone. It's one of those... where the heck did the $$ go? But once you figure $1500ish each for saws, $35k for a processor, $25k for a skid steer, tools, parts, fuel, labor, PPE, etc... yeah... it ain't cheap!
I see it differently. I worked for Ryder Truck for quite a few years. The had a trade in cycle of 3-5 years. Just general maintenance was performed. They received a handsome trade vaule, excellent warranty recoveries and good manufactucter repore. But this cost was passed onto the customer and it costed some $$$. I then got hired on at UPS (Big Brown). They had the oppostite line of thinking. I went into repairing old, old, old equipment. GMC Astro's, Diamond Reo's, package cars that were made in the late 50's early 60's. These units were repaired from in frames, out of frames, glider kits, you name it. They had an excellent track record on break downs, cost and safety. What I am trying to point out is that it comes down to the maintenance of the units. From the operators, mechanics, management. The ROI (return on investment) and cents per mile. just my 2 cents (which two cents equates to 1/4 mile in my fleet)....................
FMD, you're not arguing with me, you're agreeing. If you look at my fleet I listed above, you'll see it runs from 1971 to 1996. I just found large truck hyd. brakes cost way more to maintain than air, and once they were old, they tended to have a lot of downtime. The gas vs diesel fuel economy speaks for itself. I guess the used truck market is different in Alaska, around here I could pick up a decent 10-15 y/o road tractor for $3500.
I would NEVER argue with you guys. You guys are too relaxed.........lol Someone mentioned purchasing older equipment is expense. This thought is my in differnace. New doesnt always equate to better, safer, faster et el. With the FMVSS regulations on stopping distance, the hydrualic brakes are the thing of the past of course. But honestly, if the hydraulic lines are replaced on a maintenance cycle and you have done some homework and find vendors still selling hydrovac, master clylinders, brake cylinders, the hydraulic brake system really isnt that more costly. We still struggle on certain winters with our air brakes and with 121 brake systems, it is getting more costly and difficult to diagnose the 121. Now a days you now need a computer to diagnose the ABS or pay big bucks to have someone to just hook up to the ALDL on post 1998 models.
All the brake stuff is available, nothing is really hard to get, Napa has most everything. The drums and shoes are $$, but they are the same ones the air brake units have, so... The other truck we use on the farm is a 1960s C50 so this C70 is light years better! haha. Sure I'd love to have a couple year old truck, but I don't have the $$. I've dumped about $100k into the company this year...