D2Denny

Low PSI when warmed up. My Mack manual says 29.5 lb at 3 7/8 inches. Had pan down all looked good. No sign of brg material in pan sump or in filter. Regulator spring is next easiest avenue to pursue.

Anyone know of a parts supplier that might still have on oil PSI regulator spring? Called Watts and no luck. Was able to get a part # 572GC110. Have the Mack specs on this spring, so if I can't find a new one I'll check it and shim to the correct height and poundage.

Here is a tip on your wood floor. When I built my hot rod, I opted to put a 3/4" marine plywood floor back in. If wood was good enough for 4 million Model A's it would be good enough for me, plus it gives the car and floor a more solid feel. For the bottom side of the plywood I obtained a sheet of 22 gauge pre-painted steel siding metal from our local barn siding manufacturer. (They have rolls of this stuff in various colors that they roll into corrugated barn siding). Using 3M contact adhesive in a spray can, I sprayed both pieces, let it tack up and bonded them together. Once the floor is installed and bolted down it looks like a steel floor from below, sheds water, and is easy to clean oil and grease from. Top side got the dynamat, padding, and carpet treatment. Sure helps to keep the heat and noise at bay.

OK. As previously mentioned, I have a 36" driveline. That is the distance between the Transmission output yoke and Diff input yoke. Obviously, the auxiliary boys know something I don't. Can you direct me to an auxiliary box to use that is so super short in length, that I can fit it in the allotted space (36") along with its input and output shafts, the required 4 u-joints, and a slip yoke, and still maintain adequate articulation to allow for rear axle suspension movement? From my recollection a Spicer 7041 is close to 24" long from its front companion flange to the center of the rear yoke. That would only leave me 12 inches to install the two connecting drive shafts and required slip yoke.

G model Macks were produced 4 years 1959 - 1962. A total of 2181 were built with 318 being G-75's 67Rmodel: If you could provide a name or contact # for the Va. place I'll give him a call. If its in the Wytheville Va. region I could turn it in a long day. Thx Dennis

67Rmodel Thanks for the response. I have reached out to both firms with a request for a feasibility assessment and ballpark cost. We'll see what response I get. In any case I wouldn't take this route until next winter as I doubt that this could be accomplished before show season. As to replacing the entire rear assembly as some have suggested, (I hate to be a wise guy) but please refer to the last sentence in my original post. I didn't want to list the litany of reasons for not doing a complete axle swap at the time. I have already gone through the wheel ends in regards to brakes and seals. I want to retain the 24.5 Dayton hubs and rims It has to be a top loader for driveline requirements with an acceptable ratio Chances of finding a "drop in" complete axle assembly to fit my requirements are about as slim as finding just a carrier assembly. I understand upgrading the entire rear unit is certainly possible and within my skill set, but the time, effort, and cost is not justified for a truck that might be driven 500 miles a year. If i need to go a distance with this truck it will go on the trailer and I'll go down the highway at 75MPH in air conditioned comfort dragging it behind my Autocar. I have to believe there is a CRD91 carrier out there somewhere with an acceptable ratio.

67RModel: I have called Adelman's some time ago. The parts man had never heard of a CRD91, let alone having one on the yard. As for having a new helical ring gear and pinion designed, machined from scratch, and properly heat treated, I really can't see this being cost effective. However if you could provide me with the name of one or two firms that you know of that provide this service, I'll give them a call on the feasibility and cost of this endeavor. Dennis

Matt: Thx for the reply but I shot that angle a while ago. The 91 series has a totally different mount bolt pattern and size than the 92 and 93 series. Also, the axle shaft spline diameter is larger on the 91 series.

I have a several hundred page Mack Salesman's book from the early 60's. In searching out other models that have a RADL 515 rear, I came across these pages on pricing for the then newly announced F Model. Enjoy!

The CRD91 carrier is a top loader. With the short wheelbase and length of the triplex trans, the driveline is only 36" long. A front loader carrier would drop the diff input shaft about 1 foot. This would make for an untenable driveline angle. Thats the reason Mack used this rear axle assembly on the original build.

My G-75 came from the factory with a RADL 515 drive axle and CRD91 carrier assembly. The ratio is 6.45. Even with the TRTL720 trans and tall rubber, it maxes out at 60 MPH against the governor. The other ratios available were 4.39, 5.07, and 5.46. I checked with all the truck junk yards within 50 miles of North Central Ohio and no luck on a possible replacement with a better ratio. I checked with several of truck gear unit rebuilders to possible re-ratio it, but no parts are available for this carrier anymore. Anyone know of any possible sources of a replacement CRD91carrier in Ohio or half way into the surrounding states? Replacing the entire drive axle assembly with a later model top loader to get a better ratio is not an option at this time.

In the late 70's CF transitioned from the 855 engine to the VT903 in our Line Haul tractors. Early on, there were cam follower and cam failures. This was due to fuel dilution caused by leaking injector o-rings. The root cause of this was that the Injectors were secured by only a single bolt crab style hold down. This and the harmonics and vibrations of the V8 caused the o-rings to flatten out and pass fuel into the engine. The problem was solved by incorporating an injector o-ring change into the PM schedule. I believe it was somewhere in the 150,000 mile range. As a side note, as we were working through this problem, we were talking to the Cummins engineers and they were telling us of the 1200 HP 903's that were used in army combat vehicles. This was full military power. When they were questioned on the longevity of such an over fueled engine their answer was the Army told them the average time a tank survived in a tank battle was 20 minutes so they needed the engine to last a little longer than that. As for me I always preferred an inline 6 cyl engine but the 903 was far superior to the 6v-92 that CF was transitioning to from the 8v-71at about the same time.

4 10X22 rims and tires removed from my G-75. Rims in really nice condition. Tires are 40 years old, They are hard round and black with 30% tread. $100. for all. located in the Mansfield Ohio area Dennis 419-545-2706

This truck only has a bypass oil filter with a 750 type element in it. So at this point nobody is sure how the screen was installed in the oil sump??

Went to change the oil in my G-75. Decided to pull the bottom cover in the pan to clean the screen. Removed cover and found no screen. Looking into the removed cover I see the remains of 4 spot welds. Was the screen detachable or was it welded to the cover? Going to have to pull the pan as the tin cover or shroud at the bottom of the oil pump and pickup tube is cracked. Don't want it to completely fall free and potentially block off the flow to the pump.

Here is a tip on pressurizing a fuel system: Cut an 8 or 9 inch circle around the valve stem in an old innertube. Secure it to the fuel tank filler neck with a large hose clamp. Pressure the tank up to 5 to 8 PSI through the valve stem and bleed the system. I have done this numerous times both on trucks and old Cat equipment. I keep one and an assortment of clamps in my traveling tool box.

6368 thanks for taking the time to look this up. However, the SKF seal listed fits a 4.375 shaft and my axle has a 4.875 shaft. The seal I got is a SKF 48769

Wow, lots of tribal knowledge here. Just the info I needed. Thanks Terry and Joey. I'll ditch the inner seal and I think I have zeroed in on a CR seal that will work.

Started replacing the Drive axle wheel seals in my G with a RADL 515 axle. When I pulled down the right side, I was surprised to find 2 seals in the hub. One in the normal position and one in the center of the hub separating the inner and outer bearing chambers. It appears that the inner wheel bearing is sealed off from any oil supply other than what is placed in the hub when installing the entire assembly. Is this correct? The seals are Trostel #'s T55173 and T55068. My old school NAPA dealer searched through all his old catalogs and couldn't cross these over to a current part number. Anybody happen to have current seal part numbers for these? If not, I'll be off to my local bearing supplier. Also, the days are long gone when I could hump on and off a hub and drum assembly by myself. Thought about it the night before and came up with the idea of using my homemade mechanic's seat. I Screwed a couple of plywood slats the seat, ginned up 2 "clips" to bolt the hub to the slats, and used a bottle jack under the axle housing to match the height exactly. The hub and drum assembly slid off easily and safely. Will be able to reinstall easily without damaging the seals.

Mike: Glad you are out of the hospital and hopefully on the mend for good. Got both your items and they were good. As for the entry, the fabricated stirrup steps worked well, and I have the right side almost done. Might switch out the single hand grabs for 32" handrails on each side if I can find some that fit and look like they belong. Dennis

Just found the cigar lighter in the G and it still works. Now to get one of the plug-in USB adapters for the cell and Bluetooth speaker so I have tunes. You forgot the most important item in any truck today. THE CUP HOLDER! Have to gin one of these up. Don't know how anyone back in the day drove without one.

here is the third photo with the inner fender installed

All G's have that stub on the hub cap. Left foot goes there first, right foot on the step at the left rear of the cab then the left foot all the way up into the cab. The stirrup step cuts that distance down by 8 inches and is much safer for us old guys.

Absent any usable info from this forum, I proceeded to mock-up a step from 1/8" welding wire. When I got the shape and dimensions to an acceptable design, I made it up in steel. Increasing the complexity of the install is that the G has a sheet metal inner-fender on the left side. I had to create a substructure to attach to a structural portion of the cab, install the inner fender, and attach the step through the inner fender to it. The step has improved the entry effort 50% and the exit experience 100% as you now have a step visible to land your foot on. I still have to fab up a similar step on the right side, but it will be much easier as there is no inner fender. I can fasten the step directly to the floorboard.

Larry One thing I do know for sure is that the O-ring is the same between the Luberfiner 750 bypass filter canister and the Mack dual element filter canister. Had my old school NAPA store confirm this with their catalogs. The O-ring NAPA part # is FIL 5114. Cost $10.00. They got it in one day from the warehouse.