MACKS

It's hard to believe until you see it with your own eyes, how a peice of hardend steel the size of trunion can snap like a twig. Ive even saw a few brake from 58 rears!

Glad to hear that, did you notice if you engine brake works any better? it should have a little more stoping power.

All mack engines with the dynatard cam have to have the valves adjusted at tdc, the marks on the damper look like a saw cut on the outside edge of the damper, if you cant find them you can make your own, first find the timing degree marks and at top dead center line just go over it with a piece of chalk and write 1and 6 then going clockwise 120 degrees make another line and mark 3 and 4 then another 120 degrees mark 5 and 2, when you done with your art work the three lines should be evenly spaced. to get number 1 on tdc of the compression stroke open the injector line for number 1 at the pump then bar the engine and watch for the line with number 1 and 6 when it comes up the timing pointer if you get a squirt of fuel your all set if not go around again, when you get number 1 up adjust the valves for that cylinder then turn the damper till number 5 comes up to the pointer and adjust the valves for the number 5 cylinder and keep going till your done. It's a pain in the butt to do but it's worth doing it right. Have fun!!

Push down on the back side of the rocker to make sure its tight against the push rod, is this a 2 valve or a 4 valve and do you have an engine brake. clean your vibration damper of and look close it should have three sets of marks spaced at 120 deg one mark for cyl 1 and 6 one for cyl 3 and 4 and one for cyl 2 and 5 start with number 1 on tdc on the compression stroke then rotate in normal direction to get number 5 at tdc then do the same for 3-4-6-2. the valves must be adjusted at tdc on the compresson stroke. If the cam was broke I don't think it would run at all..

You have to adjust the valves in firing order with each piston at TDC, look for the marks on you vibration damper the firing order is 153624 make sure you push down on the back of each rocker when you adjust it. Good Luck

I would fix it now it's only gonna get worse, it's not a big job and the seals don't cost that much, if the dealer gives you a crazy price just do it your self, if you don't have a seal installation tool try to borrow one or buy one, if you do any work on you truck such as brakes you will be glad you bought it.

I just picked one up on e-bay for 50 bucks for one of my rd's I see them on there once in a while, if your not in a rush check it out.

I don't have the number of hand but look up ram welding or alloy metal works there right next to each other off rt 110 and do very good work. By the whay I sometimes work for south fork asphalt out your way maybe whele meet up one day.

LITrucker, where are you from, when I see LI I think of Long Island NY if so I know of some one who makes fuel tanks.

It's really very simple, the maxi can has to seprate chambers one is for parking and one is for service, the parking brake chamber has a very strong spring behind the diaframe, when you aplpy the parking brake it exhausts the air from that chamber and the spring then applies the brake, the service brake side only works when you step on the brake peddle.

Thank you very much Rob for all that info, once I get into it and see how bad it is I'll more than likley do it the way you did, Thanks Again

Rob, how hard is it to replace the roof on the R model I have to do something with mine its rusting all along the back. Thanks for any info you can give me.

80-90 is your best bet for year round use ,it's what mack recomends.

It sounds like the problem with your tranny is comeing from the back end of the box, you can remove the back end with out pulling the whole tranny, just disconect the linkege to the back and unbolt it pull it straight back, one thing to watch for is short peice of copper tube in the end of the main shaft dont loose it and when you put the tranny back togather dont use any siicone, thats what happened to mine a small peice found its way into the main shaft and pluged the oil hole under one of the gears. Also most of the whine you hear in the quad box comes from the berings on the back end of the out put shaft they must be ajusted right, if you have the back end rebult the tranny shop will set them up for you. Good Luck

I can't wait to see the price tag on that truck.

If you put more fuel to it, it"s gona need more air put the big blower on it, the some one thats on a 300, but why are ya messin with a good thing, the 237 was a great motor set a factory spec.

Do you have the drum type parking brake on the back of the tranny if so make sure it's not loose, I always had a problem with mine the bolt that holds the flange to the output shaft would loosen up and make it vibrate. You gotta push real hard up and down on the drum to see if it moves.

OK Thanks for info, I must have the electric model I got to check it out I don't like the way it shifts from third to fourth it seems to hold to long but all other gears shift fine. Thanks

Bump!!!

I know a lot of guys running the four valves from the mid eighties with no problem.

Question for AutomaticMack, In one of your posts you said to keep your modulater cable in adjustment, on a 90 mack would I have one if so where is it and how do you adjust it, and what does it do. Thanks for any info. the tranny is a ht750.

Used is the way to go in the dump trucking business in fack I think its the only way unless you have some kind of great account, I work in new york, mostly asphalt I'm very lucky if can get 140 days a year. at 640 a day you do the math!!

I own a 1990 mack rd ten wheel dump with a ht750 als. automatic and I like it a lot, It only has a 275hp four valve but it runs out great and is even better off road ya cant stop this truck in the mud and soft sand.The only problem is when I drive it once in a while my left foot keeps going for clutch pedal.

To answer you question, I've only seen one out working here on long Island it was green cab and green dump body the truck was bran new first day working on an asphalt job. It held up the job all the drivers were checking it out!

If your talking about a straight five speed I don't think your gonna like it, you wont have a real low gear for off road. Whats wrong with the ten speed or go with a six speed low hole. The eaton fuller web site has a calculator for figuring the mph.