1974 GMC 4905 potential towing problem

Ryker · August 07, 2018, 07:19:54 PM

This bus has been a bit of a saga. I pulled into an rv park that had a very steep and narrow driveway. Drove over a concrete slab and came off the end of it and smashed the radiator. Turned it off right away so no overheating, and had it towed to Ted in Williams, CA to replace the radiator and fan. All good but the tow guy was a bit of a know-it-all. He put a small slice in the side of my brand new Michelin tire but maybe worse, he removed the axle from the rear driver side but not from the passenger side. He claimed that only one axle had to be removed. When I got it to Ted's, which is 50 miles (our speed was about 55 mph), Ted was not too pleased. He said there could be some damage since we did not remove both axles but no way to tell except to drive it. So who is right, Ted or the tow guy? I am taking it on a 500 mile trip in a couple weeks and would rather not have it break down on me along the way.

chessie4905 · August 07, 2018, 07:37:06 PM

That's not good. When only one axle is pulled, the remaining axle is turning the differential side gear, the two smaller gears (spider gears) and the opposite differential side gear. Due to the design of differentials the other gears are going to spin at twice the speed of the gear that is still connected to the axle shaft that was not removed. These gears aren't designed for these speeds and receive less lube since the differential carrier isn't rotating, and supplying splash lube to those gears, especially at those rpms. The only way to properly check for damage is to pull differential and inspect gears. Hard to check for noise with engine running. Another option would be to drive a couple miles after back on road and pull an oil sample. Those rears are pretty robust, so maybe you got lucky. 50-50

Ryker · August 07, 2018, 09:25:26 PM

Similar to what Ted said, 50/50. I wonder if I have some recourse with the towing company? Any recommendations of shops to bring it to near Sacramento? Ted does not want to do this job.

chessie4905 · August 08, 2018, 04:53:53 AM

Do you know what differential ratio you have? 4:11 or 4:27? The reason I ask is the 4:11 rears are scarce and I'd really want to have rear checked close before any damage ruins the ring and pinion.

luvrbus · August 08, 2018, 05:20:32 AM

I prefer they pull both axles,they just don't always do it the problem with pulling both axles on long distance tows you lose the lubrication on the hubs.Interstate Towing towed a 4905 here to the shop about 8 years ago from Flagstaff 200 miles with just 1 axle removed it had no damage it is still going but there is always a 50/50 chance

Ryker · August 08, 2018, 07:23:22 AM

Great news Luvrbus! I hope for the same result. They were going to put it on a trailer but I was just a bit too tall with the satellite dome.

How do I figure out my differential ratio? I do have the 3 speed Allison auto.

Iceni John · August 08, 2018, 07:33:17 AM

When my bus was towed last year after its new fan motor burst, the tow truck driver removed only the passenger-side axle shaft because the tow was only 6 miles and slow (25 MPH) on city streets. If the tow had been further or faster he told me that he would have removed either the driveshaft or both axle shafts.

John

chessie4905 · August 08, 2018, 12:19:48 PM

4:27 ratio.74 mph@2400 with 315?80-r22.5. Probably 69@ 2150

Dave5Cs · August 08, 2018, 02:43:08 PM

Ryker, These guys do Buses of all kinds. in West Sacramento, CA
http://www.valleypowersystems.com/portfolio-view/west-sacramento/

Geoff · August 08, 2018, 03:13:41 PM

So, Ryker, does your GM have a crash box or V730? I wonder because the older manual shift transmissions get lubed even when being towed. I know that is the case with older 4 speed (not 5 speed) trucks/cars. And if the V730 had a rear pump it would self lube if being towed. I don't know the answer, but I know I can tow my older service truck (1976) without pulling the driveline.
Geoff

tuccitown · August 09, 2018, 02:37:58 PM

The wet clutch four speeds used a engine driven pump to lubricate the bearings, I don't think they would self lubricate to well under tow.

Thanks,

Jack

TomC · August 10, 2018, 09:11:37 AM

If you can get under the bus, always easier to pull the drive shaft, then pulling the axle half shafts. Then you don't have to worry about loosing lube. Good Luck, TomC

Ryker · August 11, 2018, 09:52:12 AM

Geoff, mine has an auto, the Allison VS2-8.

Chessie, it is geared pretty high. I don't think I have seen the tack go much over 2000 and 75 mph is a breeze. It also crawls up hills but in the notes that came with the bus, the PO said it weighs 38,000 pounds! Too much hardwood in that thing but I do love it.

Dave, thanks for the West Sac tip. I have it at a shop in West Sac now getting the entire suspension replaced (shocks, sway bar bushings, all air bags, stab bushings, etc.)

I have learned a lesson but for now, I guess life goes on and if something happens, that is when I get it fixed. Kevin in Arizona said, "nothing money can't handle."

luvrbus · August 11, 2018, 10:32:01 AM

Quote from: Ryker on August 11, 2018, 09:52:12 AM

I have learned a lesson but for now, I guess life goes on and if something happens, that is when I get it fixed. Kevin in Arizona said, "nothing money can't handle."

Kevin L does have a way with words huh Ryker and he is a smart guy

Geoff · August 11, 2018, 03:07:01 PM

Quote from: TomC on August 10, 2018, 09:11:37 AM
If you can get under the bus, always easier to pull the drive shaft, then pulling the axle half shafts. Then you don't have to worry about loosing lube. Good Luck, TomC

Pulling the driveline is the way to go, the problem with that is that buses are so low to the ground the tow truck driver doesn't want to hassle with it. Even the one that only pulled one axle was lazy-- he should have pulled both. And they won't tow from the back which would also free the gear train.