I have an old Wonderbread truck converted to RV. It's been retro-fitted with a cumins 5.9 12-valve mated to an old clark 5spd OD and an Eaton 2-spd rear axle... after an hour or so on the road, the gearbox warms up and as it warms it starts to howl, growl and whine... it gets so loud I put in my earplugs to avoid fatigue. I know the gearbox is old but it's still shifting smooth and there never shows much particulate after oil changes. But it IS loud- I am told it's the OD (5th) gear that is so small and takes so much load it just wears out the bearings... I have also been told by a Heavy-truck mechanic that the noise is resonating into the van body because the mounts are bolted to the transmission- he said there should be two mounts forward on the engine and two mounts back on the bell-housing and none on the transmission casting/box itself. Can anyone comment on this problem? I'm about to go deaf! Whaaat? Deaf, I say! Thanks, all.
It takes an hour, huh? What could cause that besides warming up? I'd be thinking about a transmission cooler, maybe an old power steering pump run off a jackshaft off the crank pulley to slow it way down? or an electric pump? Do you know what temperature it reaches when it starts doing this, and is it related at all to the outside temperature?
That sounds more like a drive axle issue, It takes alot longer to warm up the drive axle than the trans. In most cases.-- If you do decide to change out the transmission I would go with something like a Eaton 5306 or 6306 model. As far as the rear mounts go if the rubber mounts them selves are ok there shouldn't be a problem. Rear axle howl and noise can travel right up the drive line. Truck Shop
You might be able to tell if you take oil samples from the transmission and rear axle. Also, confirm the transmission has the right oil in it?
Yeah, some of those gearboxes (I am not sure about the Clark) took non-detergent 30W and a tube of Moly Di I think? Later on it was ATF....