76 D700 Heavy Hauler Project

[70chall440]

I have threads going on a number of forums trying to find someone/somewhere that I can find some information and assistance with this project. I picked this truck up in a trade and first impressions were that it was pretty solid. It has a 360 2V, AT and 12' flat bed. After getting it home I threw a quick tune up and carb kit and it runs pretty well. It had some rust issues on the firewall which required pulling the dash out and a few rust issues on the floor which I repaired.

The intent of the truck was to make a car hauler. After looking it over carefully, it is possible but will require quite a lot of work and since I have 2 trailers I am not sure if I want to continue with this path or not. However I have recently run into a problem with the brakes. when I was working on the rust on the cowl I discovered that the MC was leaking. I found another one as it seems they were used on IH school buses as well. Got the new MC in and then all a sudden the front brakes would drag or lock up almost immediately upon trying to move the vehicle. talked to a guy in MA who specializes in truck parts who told me that the MC was defective and despite looking like the right part contains some incorrect "valving", and that he was the only source for a replacement ($400). I decided to disassemble the old and new MC to see what was/is different; turns out they are identical in every respect. I then thought it might be one of the boosters (has 2); however I disconnected them to see if the brakes continued to drag so I don't believe it is the booster. I bled what I could (it has 10 bleeder valves); however 3 of the 4 valves on the front wheels were frozen up.

I know "think" that the brakes are physically dragging as it seems they grab and then slowly release over time. The problem is that it has 10 1 1/2" lug nuts per wheel and the hub is massive. I had to purchase a torque multiplier (a device to remove the lug nuts). My plan now is to jack the vehicle up, get the brakes to drag and then crack a line at the booster to see if they release, if they do then the check valve in the booster is suspect. If they don't, then I need to pull the hubs.

if anyone on here has experience with these trucks I would love to hear from you.

[MOPAR FANATIC]

  Don't know what type of brakes are on it but if equiped with wheel cylinders or calipers is it possible the piston are sticking/stuck then slowly releasing do to rust issue's just went through this problem on two different dailey drivers,ended up puting new brake calipers on them and corrected my problem. 

[70chall440]

Definitely drums all the way around. Each wheel has 2 cylinders and there is a booster for each end. For the front, I "think" that the front uses a unique single sided wheel cylinder (one facing forward and one facing rearward). The issue facing me right now is getting the huge wheels and drums off to look at the brakes.

[roadman5312]

Definitely drums all the way around. Each wheel has 2 cylinders and there is a booster for each end. For the front, I "think" that the front uses a unique single sided wheel cylinder (one facing forward and one facing rearward). The issue facing me right now is getting the huge wheels and drums off to look at the brakes.

                    Could you use a cherry picker ?  Hook the chain to a stud.  ?     Just thinkin.       

[70chall440]

only if I welded something to the lug nut/s and with 10 per side that would be a lengthy endeavor.

[70chall440]

There is a tool for it called a torque multiplier; multiplies your input by 78 times. Big trucks are a different world.

[roadman5312]

There is a tool for it called a torque multiplier; multiplies your input by 78 times. Big trucks are a different world.

                  I worked heavy equip in the field many years. I was addressing getting the wheels and drums off. You could jack each wheel off the ground, leaving enough tire touching to break the lug nuts loose, use the torque multiplier to get the lug nuts off, then remove the wheel. Then you could hook a cherry picker to a stud, pull the bearings and pull the drum off.  Just thinkin. 

 

[70chall440]

got it, I took that completely wrong. that is a good idea. My bigger issue is getting those brakes working, but I wont know until I get under it and get the wheels/drums off. The other issue is finding/getting the parts which seem to be made out of pixy dust and unicorn horn. I know these parts were used on other vehicles but it is difficult to track down. I talked to one guy who specializes in big trucks and such and basically it came down to "buy parts from me or you are screwed". The problem is that there isn't enough people (that I have been able to find) that are knowledgeable in these trucks or the style to assist in issue resolution, so I have to slowly figure it out; thank god for a service manual...

[70chall440]

So, I did some automotive archeology tonight on the truck. I pulled the massive front tire off, then got the hub and drum off. I couldn't find anything outwardly wrong although it was pretty dirty and the axle bearings are due for re-lub. I could not spin the hub by hand, this could be a result of the massive amount of surface contact area, could be also be in part to the bearings being a little dry. I did try pushing on the brakes and nothing happened; I didn't lean on them hard because I didn't want the wheel cylinders to pop out but I just wanted to see if anything would happen, it didn't. The brakes were tight on the hubs but not excessively so. Doesn't look like the cylinders were/are leaking but to be honest, I am not sure if they are working all; however when I have tried to move the truck it seems that they are.

[70chall440]

An interesting side note is that the manual I have which goes to 75 shows these same brakes except pointing front/back whereas these are up and down (top and bottom if you prefer). Looking at them closely, I would say the back plate has been off at least on the drivers side (haven't checked the pass side yet). So either they made a change in 76, omitted this setup in the manual, or someone put them together wrong. I am going with option #1 at this stage as both sides are the same, so if someone did change it up, they did both sides. My manual does should a top/bottom set up for a rear axle, but not a front.

[70chall440]

Today's update: I picked up the new wheel cylinders and commenced to disassembling the left side brakes. Not overly difficult just a little different than what I have seen in the past. Once I got the brakes off, I took off the brake lines and then the wheel cylinders. I discovered that both wheel cylinders on the drivers side were completely jammed with gunk which appears to be a combination of rust, water, dirt and brake fluid. I tried to disassemble them but they are stuck together. What I think is that that the brake line pressure did force them out but then they were stuck there which is why I was having the problems. I cannot say this is "the" problem but is certainly is a "a" problem. Have to wait until next week to get the new wheel seals so I can repack and reassemble the drums and hubs. Tomorrow I will do the right side as I have to build one of the brake lines; it wouldn't come off so I had to cut it.

[crash340]

mmmmmm yummy! I think it will go along way to resolving your issues for sure

[Chryco Psycho]

the bolt pattern for the backing plate doesn't look like it would line up if you rotate them 90*

[70chall440]

I agree, changing these wheel cylinders should help significantly.

I looked at the bolt patter as well; it was definitely made to fit the way it is. The brakes are pretty simple but the return springs are very stiff... I had to pull out some tricks to get them off and back on.

[jimynick]

Remember, brake fluid is hygroscopic and absorbs water, which is why those cylinders look like they're out of the Titanic. If they're that ugly, you can pretty well bet the rest of the system won't be pretty either and I'd suggest changing or at least, flushing them all out until they run clean. The lines will be corroded internally and the last thing you want/need is to blow a brake line with a load on it- or by itself either, really. Seems like a decent truck and should be worth the extra work to be and feel safe in it on the road. But that's just my