KP2

Thanks but I already have a reman on the way. I am glad to know there are some out there. I was beginning to wonder. Do you have a salvage yard or just deal with certain parts?

Not sure what you mean about stripping the shaft inside and out. When I removed the shaft we had to remove the bottom retaining “plate” and then the seals were under that with a washer that had a groove around the edge at the top of the seal area. The seals outside were removed too. I believe there was one seal and a dust seal outside. I ordered a reman gear through Watts Truck. I tried to find one in salvage and other reman shops but never did. Being the age of these boxes I don’t know what shape it would have been in anyway coming from a salvage yard. I was going to do machine work on the shaft, build it up and turn it back down. After reading the comments on here, if I understand correctly, it seems the correct was is to turn the shaft down to the bottom of the groove and reseal. The groove was fairly deep so I don’t know about machining on it. In the end I have to feel safe driving the truck and not worry about that shaft. I am disappointed that I could not simply buy a replacement shaft. If they reman the boxes why can’t they just reman the shaft? Money? Liability? Maybe combination of the two?

When we put the sleeve on the shaft we ordered a sleeve to fit the sleeve and not the shaft so I wouldn’t think we stretched it too much. However I am not sure if the seal that was installed was meant for the higher pressure in the gear box. The groove in the shaft was large and I after I thought about it awhile I just decided to find a reman and not machine it. Mistake maybe. Costly yes. Thanks for the explanation.

I did remove all the seals down to a bare shaft. I don’t remember snap rings. I just bought this truck and it was leaking some around the shaft when I got it. I thought it was change the seals and be done. But I wasn’t aware that there maybe a groove worn in the shaft and that changed things. I had a man helping me that has done this type of work all his life and thought we had it back right but apparently not.

Thanks. It is a Shepard gear. I really don’t know if the machine shop in my area could do it just right. I know they cut down shafts for tractors but I felt more at ease getting the reman. I have had other parts made but for some reason my gut said go reman.

Thank you. I was hesitant to weld then cut down the shaft because I thought it may weaken it. I thought by putting the wear sleeve over the worn area and a new seal would do the same as cutting shaft down and putting a sleeve but I have no experience doing machine work.

I think with shipping both ways, they want the core back(1200 core deposit), it will be about 2700. It is supposed to be a Sheppard. The salesman said it was a genuine Mack reman.

I have a library nearby, how good it is I am not sure. It is worth a shot. Thanks for the suggestion.

The steering gear was leaking by the input shaft. I was told I could take the top off and replace the seals. After removing the top I discovered the shaft had a groove in it. On these forums the only option after finding the groove I saw was to buy another gear. I tried putting JB Weld in the groove and turning it back down on a lathe, installed new seals. It held for a few minutes then started leaking again. Removed shaft again, installed wear sleeve and new seals. I ran it about two hours and it started leaking again. I searched for days and could only find one gear through Watts Truck. Weller would reman one for me but they had to have mine first so that would be a drawn out deal. So I have ordered the one through Watts. It was $2500. I called a few salvage yards and could not find one. Several places I called wouldn’t even bother to answer the phone or call back after I left a message. I had considered taking the shaft to a machine shop, have the groove welded up and then turned down but was not sure about the integrity of the shaft after doing that. Anyone ever done that before? Is there anyone on these forums with a RD688 that has had this same experience? If so what did you do?

Supahonky, did the book you ordered help out? I just bought a 1992 RD688s and am pulling what’s left of my hair out trying to figure the wiring out.

Thanks Joey Mack. Sounds like you have an impressive library. I hope you find your notebook. Surely there was an owner’s manual with these trucks. That would be some help. If I see manuals for 600 series would that include my truck?

Thank you. The transmission is an Eaton 9 speed. I found a E-7 overhaul manual on Ebay so that is a possibility. I think maybe an owners manual that would layout what instruments were in the dash and just general information would be a help. The wiring behind the dash Is terrible. I really need a wiring diagram to try to work that out but in the end I may have to rewire to get the basic things working and be happy. I see books for 1997 RD and later but not the 1992 to 1997.

I have been searching for manuals and wiring diagrams for my truck and the only ones I see(manuals) that may work are on eBay. The manuals are for a R600 truck. I am thinking that this is the 600 series and would include the RD688. Don’t want to buy the wrong manuals so any advice would be appreciated. Thanks.

Thanks for the followup. I just bought a 1992 Mack RD688s and I am working on the interior lights.