JoeH

https://www.truckpaper.com/listing/for-sale/31897769/1987-mack-rd688sx-flatbed-trucks

Nearest I could find, has budd front wheels, can't tell about the rear axles though....

https://truckpartsinventory.com/part-details/82219704/used-stud-pilot-budd-rear-wheel-end-spoke-hub-for-sale

Pulled this off the googleweb. Haven't been able to find a P/N. Gonna hop on Truck Paper and look up RD/DM SX models and see if anyone has budds. Then you can pull a VIN off the truck,go to Mack and get drive hub part numbers.

How many miles and which auto trans is in it?

Dumb question, is the seal the problem? I have an etech ai350 that the old seal had popped out, we replaced it, still leaked! Pulled it apart, looked closer, and it turned out the aluminum flywheel housing was cracked from starter motor (10 o'clock) to the passenger side around 3 o'clock! 

There is room for the GMC here in there other truck brand section.  All our trucks are Mack's, except for a 1995 Ford L8000 single axle cab chassis we picked up for $2500 from a local oil delivery company I drove for briefly.  We slapped a dump on it and a salt spreader a year or two later.  The right truck is the right truck to come along at the right time.

If humidity is an issue in your shop air you can run it the air through 20 to 30 ft of metal pipe before the air hits the hose, this should allow any humidity in the compressed air to condensate before it gets to the hose. You'll want a purge valve (just a regular ball valve) on a vertical drop of pipe near the air hose coupling to be able to blow any excess moisture out as it collects.  Blowing moisture with you paint is horrible, I have to use the air hose on the far side of the garage from the compressor to paint.  The air goes 40ft across the ceiling through a metal pipe then drops 12 ft down from the ceiling to the air hose connections. By the time the air gets to the hose there's negligible humidity in it.

Not sure what dents this cab has, I can't see any.  If you know a good body guy that could moonlight a couple hours for you filling them in/sanding them down after work then you'd be well on your way to paint.

*Dewaxing should happen right before primer and paint! Then don't touch it, the oils from your hands will transfer and cause fisheyes. 

You can UTECH epoxy primer that thing and stick it outside in the rain for 10 years and you want have a spot of rust on it so long as you dewaxed everything so you dont have any fisheyes in the primer, and you managed to get every bit of metal covered.

The UTECH primer can be followed up shortly with paint, but if you wait more than I think a week it gets too hard for the paint to bond, so you'd have to scuff the primer down to give the paint something to stick to.

On 3/13/2024 at 3:04 AM, allfritz123 said:

We have finally got to the bottom or top of the problem with the donor engine.   It seems it has a bent lifter on #6 intake and that is why the rocker was dancing back and forward on the rocker tube.   We are wondering why this could have occurred?  Any thoughts?  The engine ran real nice and starts immediately even with a bent push rod!  We measured the gaps before adding the jake brake and that particularly one came in correct at .016. 

Weak valve spring or over-revving the engine. Either will cause the valve to float, which could result in a bent rod.

Glad you got it working. I think you mentioned your system has fine mesh screens in the fittings. I could see this being the blockage point with cold hydraulic oil.  

We got our truck with 415k miles, so no idea how it was from factory, but this is how it was routed when we bought it. "Push" function first T's into the passenger cab mount latch, then splits to go to tilt ram and the driver cab mount latch. "Pull" function just goes to retract the tilt ram.  When the cab comes over center and starts coming down on its own weight it creates enough pressure on the "push" circuit to force the latches back open. Once the cab is seated, the springs on the latches hook the cab to keep it locked down. I assume your truck is the same way, but yours is 24 years older than mine.

Not sure how the "push" circuit creates the resistance during "pull" function to open the latches, there may be a small orifice the oil has to pass through in order to return to the pump. Not sure why you're having the problem you're having! Something must be acting as a check valve somewhere, or the cylinder is binding!

I think I have at least 3 different style sending units on my fleet.

Just reading back through, title says you already know they're stud pilot; I assumed they were aluminum rims bc they look polished, but I guess that's just a wheel cover?

Note the above is for Budd rims, I'm not referring to spoke rims at all in the above comment.

There's Hub Pilot hubs and Stud Pilot hubs.  In the picture of your truck it looks like you have Stud Pilots. The rim's stud holes need to be tapered, and the lug nuts have to be cone shaped.  Our 1979 R686ST is this way.  The lug nut cones center the rim on the hub. On Hub Pilots the rim will not have the cone taper, and the rim will center on the hub by sitting into a casting on the center of the hub. This style requires longer wheel studs.

Also, aluminum rims are fatter than steel around the bolt pattern, so you need longer studs for aluminum than for steel wheels I believe. That could be your issue.  Truck probably had steel rims originally.

Quick Google search pops up CX613/CXN613. Highway Tractor version of the same cab Granites use, with a different hood.

I think the Vision is the CH? Or the Volvo powered CHU maybe?

42 minutes ago, other dog said:

https://www.facebook.com/share/r/ZeREmSDptneRvC65/?mibextid=xCPwDs

Wow, thank God that was at a low traffic time. 

Better angle of the 1979.

My 1979 r686st. Hard to see what's going on but black from the truck harness grounds to screw, orange from pigtail mates to same screw. Other wire on pigtail butt connected to other wire from truck harness.

My 1995 RD688S, has a type with 2 screw terminals.

One wire gets mounted to a screw on the sending unit, the other gets mounted to the terminal on the . middle of the sending unit.