| Author | Message | ||
| Scott Whitney (66.82.9.13) Rating: N/A |
Hi Folks, Lately it seems that my coach does not stop quite as quickly as it used to. Not sure if it is just my perception changing or maybe it is gaining some weight as the conversion progresses. Not wanting to take chances with things like brakes, I decided to investigate a bit. So, today I wanted to examine the brakes in action. With full air pressure of 120psi, I had a friend depress the pedal as I went around and underneath and watched each chamber activate the brake pads. All seemed to activate fine and release fine when he let up on the pedal. Adjustment seems fine too. After my friend left, just for the heck of it, I put my foot so hard on the pedal that it maxed out at the floor. Don't think I have ever done this while driving, so I wanted to see what it was like to really hit the brakes hard. I held it there solid and heard a slight hissing sounds. SO I wedged a bar onto the brake pedal to hold it a maximum application. I then went back under the bus and observed that both front brake cans release a slight bit of air from around the strap that holds the two halves together (as far as I could tell holding my hand up to them anyway) Is this normal? The rear don't leak a bit. (spring brakes in back) Both fronts do "leak". But they only leak with 100% full maximum pressure on the pedal. If I push it moderately hard, but maybe only 90%, they don't leak at all as far as I can tell. So I did an experiment. Starting at full 120 psi, I push down to maximum pressure on the pedal and hold. The pressure drops 10psi down to 110psi instantly with the initial application. Then, as I hold the pedal down hard, it continues to drop down to 90 psi over the course of one minute and 15 seconds. If I repeat the experiment, but don't totally max the pedal out, it still drops from 120psi to 110 psi on initial application, but will then sit there at 110psi until my leg gets too tired and I have to let up. Presumably, it would hold a long time this way. So...there seems to be some difference btwn a full-on pedal-to-the-floor application and a partial application. DO I have a problem? Or is this normal? Any thoughts appreciated. Scott P.S. All observations were done with chassis blocked up, spring brakes released, johnson bar set, and big rocks blocking wheels. Also, this is in my 1974 Flxible transit bus. I heard FF or someone say once that some transits had brake treddle valves that did not allow full pressure to the brakes - is this possibly what I am observing? If so, how hard it it to change to a system that does allow full line pressure to the brakes? Thx. | ||
| TWO DOGS (66.90.212.90) Rating: N/A |
I don't think you have a problem....don't get mad ,I don't know you, or know how much you know...sounds like the brakes need adjusting....VERY simple to do,if you want I will explain how... | ||
| Scott Whitney (66.82.9.24) Rating: N/A |
I do know how to adjust the brakes. Have done it multiple times before and did it again this evening just for good measure. My method of adjustment may not be perfect or ideal. I don't take the wheels off, spin them, and bang the drum with a hammer etc. I tighten them until the are locked against the drum and then back them off about a 1/4 - 1/2 turn. Don't think I could slip a piece of paper in btwn the shoe and drum. When brakes are applied, the adjusters looked vertical as far as I could estimate with my head stuck up in the wheel wells. Pretty sure they are in adjustment. But I suppose there is some flaw to my method and they are more out of adjustment than I know? Would being out of adjustment cause the air symptom I described? The first time they needed adjustment, I paid someone to do it for me. I watched everything he did from the sidelines. (I did not go under the bus, unblocked, like he did) From then on, I decided I would do it myself. Thanks, Scott | ||
| TWO DOGS (66.90.212.90) Rating: N/A |
yep...you are pretty close to right on the adj. no need to spin or bang or anything,,just as long as you did it with brakes released... | ||
| Geoff (Geoff) (66.238.120.116)
Rating: N/A |
Scott-- the air leaking around the strap that holds the "can" together means the diaphrams are leaking and need to be replaced. This is easy to do in the front, just take them apart. It is probably a good idea to replace the rear ones too, BUT in the rear, if you have "double cans" this means the parking brake side of the cans is spring loaded and you don't want to take that one apart without installing the threaded rod and nut. Here is where it may be wise to read up on what you are doing or have someone that knows what they are doing help you. Also, you should only have 1" of pushrod travel for a proper brake adjustment. | ||
| TWO DOGS (66.90.212.90) Rating: N/A |
one other thing you might want to do....get under there with a good lite and 'notice' how thick the brake lineing is....then...go look at a new one....truck and bus shoes are THICK | ||
| Bob (Bobb) (216.232.224.234)
Rating: N/A |
Here is a link to an overview of what is required in BC for air brake pretrips and adjustments.. I'm sure most of you already know this, but it may help someone. http://www.icbc.com/Licensing/lic_utility_resman_commercial.html | ||
| Scott Whitney (66.82.9.37) Rating: N/A |
Ah, ok. I'll probably rebuild the front cans then. Sounds like it is not too big of a project. The rear ones are fine, I think. I had spring brakes installed a couple years ago. Half of my can is the new spring brake chamber, the other half is my old brake can. Reason is my bus had extra long rods and the truck shop that did the spring brake upgrade didn't have a part source for new cans with such long rods. So they cobbled the two cans (new and old) together. Don't know if I would have ended up with new service diaphrams from that or not? The mechanic who put the spring brakes in, did notice oil in the chambers when he took them off. So subsequently to that, I replaced the compressor. Maybe that oil did some damage to the front diaphrams too. I'll probably dissassemble the fronts tomorrow and seek replacement diaphrams on Mon. Will post a foll-up here. Regarding brake linings. . .I am getting close to the replacement line in some spots. What is left is over half inch thick or more. But I am afraid I will have to outsource that job which probably means mucho dinero - will have to wait a bit. Thanks again! Scott | ||
| Gary McFarland (Gearheadgary) (209.128.99.4)
Rating: N/A |
Is it only the rears that have the springs? I remember all kinds of cautions about opening them up, but I always replaced them as a unit. Gary | ||
| BrianMCI96A3 (65.41.212.128) Rating: N/A |
Gary, its been a long long time since I actually had to change out a front brake diaphram, but spring brakes are only used on the rear axles... the ones that go BANG, if you open them up improperly. If I recall correctly there is a smallish spring in the front chambers too, but about a tenth the diameter in thickness. Brian | ||
| Scott Whitney (66.82.9.31) Rating: N/A |
The rears have a long bolt that is stored right along side the chambers which can be used to cage the spring for work, or if you have to move the coach off the side of the road with no air pressure etc. I would not be surprised if there was some small spring in the fronts to retract the rod when airpressure is released. But I'll find out soon enough if this cold damp weather lifts and I can get under there to remove them. Someone on the board will probably know the answer before that! Scott | ||
| mel 4104 (208.181.100.80) Rating: N/A |
Scott,do your self a favour and DO NOT try repairing the back spring brake pot just get some shop rebuilt at a truck parts supply outlet. the 2 things that haveinjured or killed more people while repairing equipment are spring brakes and split rims on tires they had a safty sem. up our way years ago showing the danger of spring brakes. they put one in a safty device and put the caging bolt in and then removed the bolt holding the two pieces together ,then banged the pot ,the push rod and one section ended up 100 ft down the parking lot.here if it is not going back for rebuild to the supplier we take the cutting tourch and cut through the side and cut the spring in half before it goes in the scrape bin, so that no one wanting the grade 8 bolt will get hurt or killed taking it apart. they are not that expensive to get exchange ones . mel 4104 | ||
| Gary McFarland (Gearheadgary) (209.128.99.4)
Rating: N/A |
that was the shop policy where I used to work at. We didn't even mess with the fronts. Gary | ||
| bruceknee (12.76.21.221)
Rating: N/A |
hi, there should be no air leaking anywhere with pressure applied to the pedal. the diaphrams are easy to change, there is a small spring in the fronts, but you will be able to hold the chamber together with 1 hand as you take off the clamp, take out the old pancake and put in the new one. pick up an extra one, they are cheap. | ||
| Scott Whitney (66.82.9.11) Rating: N/A |
Mel, thanks for the info. I have no intention of messing with the rears. They are not leaking. I was just adding additional FYI info for other readers in my last post. Gary, why did your shop not mess with fronts? I know they are cheap to replace the whole thing, but even cheaper to replace the diaphrams. Since I am doing my own work, might be more economical to change the diaphrams than the whole unit. I'll decide when I get them on the bench and get exact pricing. Bruce, thanks for the hands-on info. I am about to head under the bus and take a look now that the sun is out and it is a bit warmer. Scott | ||
| jim mci-9 (209.240.205.60) Rating: N/A |
any spring brake chamber ive seen for sale at a truck parts store has the rear part of the chamber permanently attached...at least since the mid '90's... you can't take it off.. its crimped on... for safety....you can take the service side apart for diaphram replacement....daiphrams are cheap... but if the center section is worn out... allowing air to leak from the park side to the service side, it needs a replacement..... whole 30/30 brake chambers cost less than $30... its not worth trying to rebuild one....single 30's and 24's are like $25....the roto-chamber type... like on the rear of my mci9 are around $400.... cheapest ive found....thats why i'm converting to a single service brake only... and putting the park brake on the rear of the allison.. onn the driveshaft.... | ||
| Gary McFarland (Gearheadgary) (209.128.99.4)
Rating: N/A |
Gary, why did your shop not mess with fronts? Just the way it was, I didn't ask. Could be insurance company stuff. for instance in the boatyard I have my boat in, they'll give you 120v, bot not 240v. They say insurance company rules. I guess, since everyone knows 120V will kill you, near as I can figure is the Insurance company is afraid of you being "more dead". They may have had claims from aircan disassembly events, maybe they banned all aircan work. Gary | ||
| Scott Whitney (66.82.9.35) Rating: N/A |
As it turns out, after taking my brake cans off (yuck, horrible dirty job sitting in the dirt with my whole body scrunched inside the wheel wells), they are held together by a half inch nut on one side and a star pattern bolt head on the other. Which I don't have a tool for. So I ain't gonna fuss with taking them apart either. Will just replace them as whole. I think I will need to pull the air fittings and maybe the clevis pin part - don't know if new ones come with that piece. Decided to replace the rubber airlines to the brake cans too. They are bit checked and cracking so I might as well do it now instead of roadside sometime later. Scott | ||
| mark (66.43.13.31) Rating: N/A |
Hi, Scott! Some time ago I got this link here on BNO and recorded it. I've read it and found it to be very informative... give it a look-see! It's at www.atca-inc.net/its13.htm hope this helps! mark 75 gillig 636D | ||
| Tim Jones (Torquester) (12.86.10.188)
Rating: N/A |
Hi Scott, "star pattern bolt head" sounds like external Torx, these are getting more popular...another tool to buy for your box. "Will just replace them as whole." A good idea in my opinion. It is not too expensive to replace the whole can. Be sure to get the instructions for cutting the rod to the correct length. They usually need to be cut to length, as per the application before installation. "Decided to replace the rubber airlines to the brake cans too. They are bit checked and cracking so I might as well do it now instead of roadside sometime later." Good idea, cheap insurance....remember...replace everything with parts that are EXACTLY the same...same length and diameter hoses, same size can, same air line fittngs , any changes can cause timing differences in the system creating an inbalance. hth, Torquester | ||
| Scott Whitney (66.82.9.48) Rating: N/A |
Pricing follow-up. I called my transit parts supplier (Muncie) and they wanted $200 a piece for the chambers! So I ordered a couple diaphrams at $2ea. instead. Then I went down to my local Freightliner dealer and we determined they were Type 20 (whatever that means, but they are not the common 30-30 that I hear about). Anyway, for 80 odd bucks I was out the door with two new chambers, two new hoses and bushings to make the airlines mate. The chambers were about $30 something each - which seemed in line with what I had been told to expect. So when the diaprams come by UPS, I'll just put them with my old brake chambers as spare parts. As soon as it stops raining, I'll install the new chambers. Scott | ||
| Jim Shepherd (Beltguy) (67.235.113.14)
Rating: N/A |
I am glad Scott decided to change the whole units. When I worked at Gates, we made brake diaphrams and I ran the lab that tested them. We ran two cans against each other to get the fatigue cycle we needed. We had several instances of break can fatigue failures. Some just developed small cracks and would probably not create an immediate catastrophic problem, while others had a total separation and that would leave you with no brakes on that axle. We had one fail as the technician was about to do some work on an adjacent unit and it almost hit him – would have hurt him pretty bad. We sure changed our procedures after that. Having said that, our units went many thousands of cycles before we had any problems, but I did not even blink when I made the decision to change the whole unit. Jim Shepherd Evergreen CO '85 Eagle 10 | ||
| Ian Giffin (Admin) (64.228.43.167)
Rating: N/A |
Hi Scott, Here are a couple of pictures of the front service brake and the rear spring brake components, clearly showing the location and relative sizes of the springs which others in this thread have mentioned. I hope they are helpful to you and other viewers. Regards, Ian www.busnut.com   | ||
| DonTX/KS (205.187.92.194)
Rating: N/A |
Excellent point Jim, I had never even considered that factor when slapping in another diaphram in a 50 year old or so bus. Sit under the wheel well sometime and have someone put about 100lbs of application pressure on the treadle, and you get the full understanding that on a 30 SQ inch pot, that lets you see 3000 lbs of pressure at work, each time you hit the brakes. Excellent pictures Ian, helps people see that there is not a lot of rocket science in a simple brake pot. Do you have a DD3 picture as clear and informative that you can post also? | ||
| Scott Whitney (66.82.9.33) Rating: N/A |
Just a quick follow-up. I installed the new brake cans today. Pretty straightforward and easy. I chopped the rods down to the length of the original cans, bolted them in, installed the new air lines, and re-adjusted the brakes. Now when I stomp full bore on the brakes, no more hissing and the pressure holds steady until my knee gives up. I again wedged a bar under the steering wheel and went underneath with the brakes fully applied. All looked (and sounded) fine. Will road test some time later. Thanks for all the advice and the informative blow-up pics. Scott | ||
| Ian Giffin (Admin) (64.228.43.24)
Rating: N/A |
Hi Don, Just saw your message now! The only picture I have of a DD3 is the outside; I don't have a picture of the roller cam inside that "locks" the spring. Regards, Ian www.busnut.com  | ||
| Chuck Lott (68.19.80.102) Rating: N/A |
Here's a link to the Bendix page with the desired info http://www.bendix.com/downloads/service_data_sheet/dd3-sd3.pdf |