miro

Starter may have a thermal protection switch that is defective, try changing starter

Sounds like you have a bad primer (hand) pump

I doubt a coolant filter will help your problem. There is no filter media in them. They contain DCA and slowly add that to the coolant. You can get the same affect by testing the DCA, with test strips, each service with test strips and topping it up. Don't think that just dumping it in will fix the problem. too much is as bad as not enough.

If you're torquing them with a 1ïnch gun and then a six ft bar, you're stretching the studs. You only need 280 ft lbs of torque on a 3/4 stud

Check your motor mounts and crossmembers. If these break the frame can flex and cause that kind of problem

I think you'll find most people in North America, buy exchange transmissions and diffs, warrenty and availability are main considerations

Check Toe and Wheel alignment

I agree with 39 Baby Mack check the over center spring on the throttle lever

Actually I remember Mack had a kit to install shocks on the front drive axle. The lower bracket bolted to the back to pocket rubber bolts and the top one was one of the trunnion bolts

You said it needed a clutch. If this has the push style clutch you might not have to change it. Mack used to put L shaped spacers between the pressure plate and flywheel, held down by the bolts. If you have this all you have to do is one by one remove those spacers and re-tighten the pressure plate.Hang on to those spacers you'll need them if ever you do need to put in a new clutch. Also a word of warning those old clutches and brake blocks are made of asbestos, do not breathe the dust!

Maybe a dumb question, but how do you work on the engine? Doesn't look like the cab can tilt.

Check for a bad ground from engine

I am looking for an inexpensive computer reader, that would read mileage and or hours, and would work on any modern system. It does not need to do any diagnostics or tests.

I have Googled it and saw some Chinese units for about $170 dollars, anybody have any experiance with them

Put some ultraviolet die in the cooling system, run it for a day and check the engine with a blacklight. Be sure to check the bottom of the air dryer and the intake of the compressor (if it is fed from the engine intake) and the engine oil itself( Not very likely if its not milky)

How old is the truck? Does it have Positive ground?

Also check the clevis pin for being seized, this will also stop them from adjusting

It still sounds like the check valve from the dryer to the tank. If it does not close off, air keeps leaking back from the tank out the unloader, until pressure drops then the unloader kicks back in. Does not sound like you have tried that one yet.

I am just curious, you say the trucks had Remack engines, do you know if the were replaced because they were wore out or as a maintenance item?

The low flo rad has a baffle plate in it and the cooling flow goes from the top to the bottom and back up to the top so that it actually goes through the rad twice. This was a very troublesome feature on these engines. Cummins actually had a kit to change the cooling to single pass but very expensive. If you're going to buy a BC3 to change things over its easier to put the 3 in. Or put an early N14 in

If the big cam 4 has low flow cooling that could be a problem fitting a rad.

Like you all said it is speed related and I still say you are getting harmonics in the frame because of the missing cross members. Remember you said it got worse tightening the frame bolts!!!

I never used valve stem seals, always replaced the guides and miked the valve stems.

Years ago, when they where common, you were able to buy kits for the shafts and to make up your adapter, and make the cables also, could try some antique truck wreckers to see if any one has a kit

Hi Skip, About the main caps, don't forget the 865,6 had buttress bolts on them to hold them tight, (four bolt mains) I don't think I would try to build up the bores better to go oversize also they have to be properly installed and torqued (in sequence) and also they used tapered con rod bushings that had to be burnished before they were machined to fit the pin

Just to try and ease your mind, you have tried just about everything in the front and it has not helped, and you say you feel it in your bum, listen to your bum. Have a Merry Christmas everyone.