Brandt

Usually a syncho - especially if it does it when the trans is cold.

I think the OP used the word underpowered and was referring to HP rating. I didn't read the whole thread but it is my belief the Mack rates the HP where the rubber meets the road. Other HP is rated at the crankshaft. Detroit, Cat and Cummins don't know what type of driveline you are putting behind their engine, so they can't rate it at the rear wheel. Generally you loose 60-75 HP going thru the trans and diffs, so a 427 Mack is actually around 500 at the crankshaft.

A 427 Mack will show you 427 HP on a dyno. A 425 Cat or 430 Detroit will show you approx 360-375 on a dyno. If you are using an RTLO trans my 500 Detroit shows 460 on the dyno. The "L" in the trans model means it is a LOW inertia trans and doesn't rob as much HP.

I have a 1070B 12 spd. The info the dealer told me was it has an .78 OD

FYI: The taller the OD the less fuel efficient you are. Ideally a direct with 2.90's or 3.08 gears ... would be best.

Turns out Mack wired this truck - BASIC. The T/S and brake share the same wire. I can't split them for the pup, so the pup has to be wired the same way. Not that I need a separate light for the T/S, and a separate light for the brake, but it would be nice to have that option.

The drop deck that I pull w/ the Western Star uses the outside (of 3) lights for the T/S and the inside 2 for the brake. If I ever pull the drop deck with the Mack all 3 will be T/S and all 3 will be brake.

I think the ABS just needs a constant 12V to the pup/trailer. I remember when I had a spread axle I could drop the air in the rear axle and strap it up (if I was light). When I did this the ABS light would come on because one axle was spinning and the other axle was not. I didn't do this too often as it goofed with the ABS.

Thanx gearhead.

The axles that I am using to build the pup, have ABS, my Mack doesn't. I'll hook them up, if they become a problem, I'll disconnect them.

I've got the hole burnt in the pintle plate and am working on the wiring. Everything is color coded but I don't know what the colors are for. So far I have some figured out but there are some that I have questions about. Can somebody tell me if these are correct?

Red = brake lights

White = ground

Blue = ABS (my pup is equiped but the Mack is not - does this matter?)

Brown = tail or clearance (which one?)

Black = marker or clearance or tail ???

Green = Right T/S

Yellow = Left T/S

I'm not sure on the tail, marker and clearance lights.

Do I have the T/S correct??

What about the gears?? Am I OK there?? I was thinking about something in the 3.90 range. I don't know if changing the gears is cheaper or getting a set of cutoff's from a camel back.

If I can fix the 12 speed, I will keep it. I hope it is just the air filter or regulator. - I like easy!!

Sounds a bit out of my price range

First there is no synchro in the 12 speeds, check the air regulator to make sure you have the correct working pressure. Try to change the air filter on it also. Other then that it could be to much wear in the air piston that shift it.Putting an 18 mack in it is a major waste of money in my opinion. Get an hi flow oil pump, that should solve your jake problem and for more power, pitsburg muffler is another waste of $$. Call Harold at north west truck center for more power 800-665-9248

Air Regulator? Where is it - what does it look like?

Air Filter - didn't know it had one. This could be the problem!!

Thank you for being gentle with my ignorance about Mack's.

Just got off the phone w/ NW Truck Center (Harold was out for the day). They recomended an injector upgrade and said the turbo should be OK.

Both Pyro and Boost gauge are on the short list. I already put holes in the dash for them.

I have had this truck for 8 years and have put very little into it. Next summer I may be working it daily and need to make it more reliable.

'91 RD690S

Maxidyne EM7 300 4 VH

12 speed TRTXL 1070B

Mack diffs w/ 4.42 gears (CRDPC92, CRD93)

Camel Back

Double frame

The syncro in the trans is GONE. Going up or down - everytime I move the button on the stick it grinds. It is particularly bad when I move the button to go down and the stick to go up a gear. My options are to replace it with a Mack 18 spd, replace it with an Eaton 18 spd (and have a new drive shaft made) or rebuild this trans. I like the Eaton idea as it will get me better fuel mileage, but the Mack 18 spd is built a bit stronger. Your thoughts??

I need more HP. I got spoiled with a 60 series 500 HP and now feel the Mack is under powered. I will be adding a Pittsburg Power muffler and maybe a turbo this winter. Any other hod rod ideas?? I want to pull a pup with this and will be grossing 92,000 lb. While a 300 may get me by in Ohio, it will be a real struggle at 5000' in the "hills" of WY and MT.

My jake brake is weak. The truck didn't come w/ this, I added it shortly after I bought the truck. I got the parts from a salvage yard in IL. I was told that there is a kit to increadse the oil pressure and get a stronger jake brake. I have no other info. If anybody knows how to get more braking power out of my jake, I am very interested!!

I also need several small parts. I recently blew a steer tire and it wiped out my passenger side headlight assy. The hood is mildly cracked but I can work with it. Other than the dealer is there a place that has Mack parts like this?? Aftermarket is OK as long as they are not chineese parts.

Sorry for the lengthy post, but I always had the $$ to pay a mechanic when I was running over the road. Now that I am semi-local I want to do more myself as well as I don't have the money to pay somebody else.

No "R" model should die in vain. Thru this death others may live!!

I'm looking at the parts I can use to keep mine alive. Does the owner want to part out the truck??

Nice dump! Post a side shot of the WS too when you can.

I don't have too many pix right now, but here are 2

OK so that didn't work. I'll have to find out how to post pix on here.

Wasn't sure if a '91 was considered a "classic" or modern. Glad it falls into the classic area.

I also have a 91 RD 690 S. I found this site while looking for parts. I'm not attempting to hi-jack this thread but I need the headlight assy/bezel/mounting brackets. Blew a steer tire yesterday and when a big floater lets go it does some damage. I never did any fiberglass work but it looks like I'm gonna learn!! If there are some good parts suppliers out there - I'm all ears.

New here and found this site out of desparation. Blew a steer tire yesrteday and am looking for parts for a 91 RD 690.

The truck is set up as a 12yd dump truck and is ALL MACK. EM-7 eng - 300 HP. Mack 12 speed w/ 6 reverse gears. Mack 4.42 diffs , I think 48,000 lbs - maybe 46K?

I have a bunch of questions but will troll around a bit rather than show my ignorance right away .