The Stovebolt Site Forums The Parking Lot Big Bolts 1966 GMC Clutch and Water Leaks

Hello Again.

I have posted other questions about my 1966 GMC HM5500 truck, and I am slowly working my way toward fixing what I know about. I have a clue about most of what needs to be done, it is just getting to it - although the more I do the more problems I seem to find. But there are two things that I want to know more about before digging deeper - either on my own or into my wallet.

First is the clutch. The truck has a 351C v6 engine, a new process 5-speed transmission, and an Eaton vacuum operated 2-speed differential. These all seem to work. But I am concerned about the clutch. I have repaired the previously leaking hydraulic linkage and replaced both the master and slave cylinders with what appear to be correct parts. This has fixed the brake fluid leaks, but the clutch still does not work right. It releases at the top of the pedal rise, and does not engage until the pedal is nearly all the way up. I have tried moving the fork position nut on the slave cylinder shaft, but there is almost no adjustment left to move the fork away from the cylinder, while moving the fork closer to the cylinder makes the problem worse (clutch will not engage). So it appears that I need more adjustment than I have available. I don't know enough about clutches to understand what this means. Any suggestions about cause and repair would be greatly appreciated.

My other, more immediate problem is that water is getting into the cab (which creates rust and electrical connection problems on the inside to go with those on the outside). In one case, water is collecting at the passenger corner of the dash board and then dripping onto the floor. On the driver's side, it is dripping off the framework holding the steering column. The truck is parked by a corral many miles from my house, so I am not there when it rains and would rather not go through the mud to look for leaks in the rain. My best guess is that the windshield seal is leaking. But again, any experience with this or advice on what to do would be greatly appreciated. I would hate to pull and re-seal the windshield to find out that the leaks are coming from somewhere else.

Hy JRMunn, Merry Christmas, as a clutch wears the freeplay in the clutch pedal disappears so adjustment is required to get the freeplay back(clearance between the throwout bearing and pressure plate actuation levers), your clutch disc may be worn out. If you can adjust the linkage to establish some freeplay and then see where the clutch engages, if it engages at the end of the pedal travel I would say the clutch is worn out. As to the water leaks, the best you can do is try injecting some sealer between the rubber and the cab metal and between the glass and the rubber, any good automotive glass shop should be able to supply the needed equipment and materials or do the job for you. Quite often the pinchweld in the windshield opening of the cab has rusted away, the only way to tell is to remove the windshield and inspect. But try the sealer first, hope that helps.

The water leak is most likely holes rusted into the channel where the windshield rubber attaches. A repair method we used frequently when I owned a body shop involved removing the glass, sandblasting the flange to get to bare metal, and filling the rust holes with a product made by 3M called "Aluma-Lead". I don't think it's in production anymore, but a suitable substitute would be Devcon Epoxy Aluminum. The alternative would be cutting the rusted metal out and welding in patches, which is a long, tedious and expensive process unless you're doing all the work yourself.
Jerry

Thank you 3B and Hotrod Lincoln, and Merry Christmas!

As I feared, it sounds like time to pull the transmission to inspect the clutch and pull the windshield to get it re-sealed. Having laid under the truck looking at the large (and heavy) transmission and related mechanisms for a dump bed, I am not inclined to take this on in the field. So I will probably drive the truck to an experienced mechanic's shop and have a new clutch installed to be done with it. I am not prepared to remove the windshield on my own either (and would hate to break it without knowing if a replacement is available). But I can try to seal the edges and now realize that I can check to see if the seal is leaking by covering it with PVC tape and then hoping for more rain to test it.

Thanks again for the advice. It is greatly appreciated. I still think this project will end up as a good ranch truck with the advantages of lower licensing and insurance costs and being exempt from most state inspections.

I have changed several clutches and/or removed transmissions for servicing by putting a 4X4 wooden timber through both door window openings and using a come-along to lower the trans to the ground. It's a simple, safe way to handle heavy stuff. I've managed to remove, repair, and reinstall lots of heavy transmissions out on the side of the road that way while I was running a 24-hour road service for trucks.
Jerry

On your water leak, one other source of a leak may be the cab marker lights. I know my 77 C30 had that problem.

I'd check the cab lights,as well.on my windshield channel,i had a few areas where the rubber was dried-out,and getting bad. I gently pried these areas up,(between the channel and metal,IF metal's not rusted),and carefully laid in a thin bead of neoprene. (Caulk gun type). The reason i chose neoprene,is because it stays pliable,in almost any kind of weather,and lasts about 30 years.I had a couple of marker lights,that didn't seal between the gasket,and the roof. water was getting in through the wire grommet. I pulled the housing up far enough to run a bead,making sure to seal the grommet,as well. for clean-up,just soak a corner of a lint-free rag in gasoline,and it'll clean-up,without damaging the paint,or trim,(if equipped). Hope this helps.

Thanks again for the suggestions. I am intrigued by trying to fix the clutch myself, but wonder if this is the place to start because I want to get the truck working for use during the coming summer while having other projects that also need attention. I am going to put PVC tape over the windshield seal to make sure it is the leak source - and, if it is, to help keep the interior dry until we get to warmer weather. The truck doesn't have lights on the top of the cab, but I do need to check cab seams that are showing some rust and cracking.

Again, thanks! This truck is different than vehicles I have worked on before, and I need all the help I can get.