75CF611

No the diaphram has a hole in it and every time you press on the accelrator it leaks air.

I have a 75 CF611 with the Thermodyne 6 and allison ht-740 auto tranny. The williams air valve that is connected to the tranny and the throttle is leaking air and needs to be rebuilt. Where can I get one the dealer says it is a discontunied part.

Could be, I know that the pump is cooled by the coolant. I think one of them go to the in cab heater as well.

There are not any wires going into the engine cover so I guess we don't have an engine brake but thats alright weren not pulling that much weight anyway. Yes the raidator has shutters on it but it has been a long while since they last worked. Where would the valve that works them located at. Thanks fo all the help.

Ok I got some pics the first one is of the switch and the second one is where we think it goes into the engine. If anyone knows what that is on the motor let me know.

I don't know for sure what is the front brake limiting valve. In the console where the pump engage switch, e-brake, and battery switch is another switch. It has a plat that says dry road and slippery road on it and it is an air switch. We have a 05 FFA pumper tanker at the dept that has a jake brake and the onn/off switch is labeled the same way so I thought that is what it was. I need to trace the air line and see where it goes. I do have an air line that goes in to a maifold that comes out the head and has the coolent filter and the upper raidator hose connected to it. Does anybody know what that is for. I will try to get some pics of the setup in the next day or 2.

My 75 CF-600 has the factory engine brake I have always called them jake brakes but I know that mack calles them something else. How is it supposed to work mine dosent feel like it does anything. I know that the switch has to be in the dry road position but that is all I know. Can anyone tell me how this system is suppose to work.

I have the 10r20 tires but the difference between the 2 isn't that much. We really don't want to turn the fuel up on this truck was hoping to leave it stock. The 5th wheel camper weighs right around 13k and we figure the truck after it is completed to be around 20 giving us a GVWR of around 33k. I have found a set of 4:25 gears that will fit localy and are considering them. After talking to my dad he would be happy with a road speed of around 60-65. We arent looking to break and speed records but crusing the interstate at 45mph is not an option. I have looked at the aux transmissions and if i could fine one that could be shifted on the fly and has a final drive raito of 0.70:1 that would be perfect. Since the CF-600 is a fire truck with the transfer case that engages the pump we figure we can use that setup to shift a overdrive unit. Do they make a planitary gear style overdrive for a medium duty truck? We have also looked at the option of a 2 speed rear axle. I also have brought up the option of swapping the allison out with a Eaton 5 ot 6 speed tranny and we are not completly opposed to that but we bought this truck partly because it had the auto in it. We have three fire trucks at my dept with allison autos 2 are 5 speeds and one i think is a 4 speed. I am going to go look at them and see which tranny they have and what the rearend raito is in them. I know that both of the 5 speeds are governed at 74 mph but the other one I don'T know yet. I am going to drive it and see what the redline is and how fast it will go. It is a 89 Ford C-8000 with a 3208 cat and the aformentioned allison with the same shift pattern as the mack. We were looking at the fords but I really like the mack a whole lot more and hope we can fix this problem so we can keep the truck. We are going salvage yard hopping friday to see if there is any way around this problem. Any way thanks for the info and anything else you could provide would be very helpful.

I talked to the place that you mentioned earlier and they need the VIN but it is at home so I will do it later. I started another thread in the driveline section and there I posted my dif numbers that were stamped on the carrier. I have thought about a overdrive unit but do not know where to get one.

There are a couple in my area and we were planning on doing that on friday. Can I swap the entire axle with a different one (ie spicer/eaton unit) if i can't find a mack.

I have a 75 CF-600 with the thermodyne motor and a Allison ht740d tranny. The rear axle is a 6.36 ratio and only allows the truck to go a max of 43 MPH. I was going to use this truck to pull my 36' Fithwheel camper that weighs around 14k lbs on the interstate. As you can see a top speed of 45 is not going to work. I have done the math and figured out to run 65 mph I will need 4.10 gears and to run 70 it would take 3.81s. Are either one of these raitos available and how hard is it to change. I have changed them out on Pickups before but nothing this big. If I could find just a carrier that would be the best way. The numbers on the side of my axle are, 6.36 11KHA4159CP5 117 9Z7851 84KH572B The bottom number is the casting number and it is a Mack unit. Any help I can get would be greatly appreciated.

Me and my dad Just bought a 1975 CF600 pumper to conver to a tractor to pull his 5th wheel camper. The only problem is that it has the 6.36 gears and will only go 45mph. What raito do we need to go at least 65, 70 would be better, and where would we get them from.