1948 Roadmaster Power Top/Windows - Adding Fluid

I am helping a friend with a recently acquired 1948 Buick Roadmaster convertible. Neither the top or windows will operate. The windows will go down but not up. When you try to raises the windows or operate the top you can hear the pump motor quietly whirring. We are thinking it may be low on or out of fluid. There is some fluid wetness on the bottom of the pump that may have come from leaking. Can someone please gives us a step by step for adding fluid? Do you add it to the bowl under the pump that is held on by a wire retainer by removing the bowl and adding? We also understand these systems originally used brake fluid but some people have converted to ATF. We assume the compatible brake fluid would be DOT 3 (?)

Bob,

I owned a 1948 Super Convertible for over 30 years so I am very familiar with the Hydro-lectric system. Here are a few things you need to know. First the window and seat cylinders are the single-acting type, that is they use hydraulic pressure to extend the piston and external spring tension to retract the piston. When you operate a window in the down direction, the switch sends power to a solenoid valve at the bottom end of the cylinder. The valve opens and the external spring pulls the piston down, the fluid returns back to the pump reservoir. When you operate the window in the up direction, the solenoid valve opens AND the pump operates. Fluid under pressure pushes the piston up in the cylinder and closes the window.

If the pump is operating when you try to close a window or operate the top and nothing is happening you could very well be low on fluid OR there could be a mechanical issue with the pump. You are correct in that fluid is added to the reservoir under the pump. Adding fluid can be a very tricky one man job. You have to lay under the car and using one hand release the bail wire from the reservoir can while keeping the can in place so it doesn't fall off and get fluid all over you, the car and the floor. Don't ask me how I know this. If the system already has brake fluid in it refill with DOT3 or 4. DO NOT use silicone fluid. You can convert to ATF or light hydraulic oil but EVERYTHING needs to be thoroughly flushed out first.

Once you get the reservoir off, make sure you clean out all the sediment which is likely to be in it. If you find that there was already a good amount of fluid in the reservoir, the pump is probably the problem. Brake fluid is nasty stuff when it sits around a long time and depending on long is has been since the the system was services, things could be pretty gummed up inside. Parts are available to repair/rebuild these pumps and they are not complicated to work on. You should also check the condition the flexible hoses which connect the pump to the firewall and the doors to the jamb. If the hoses look questionable, be sure to replace them before going any further. The system operates at around 200psi and if there is a leak, brake fluid is great paint remover! There is a very detailed section on the Hydro-lectric system in the 1948 Buick shop manual and this would be VERY useful to you if you need to work on the system.

I hope this helps.

If you go to ATF you will need to upgrade all your seals. I changed over all lift cylinders but not the pump or junction valve under the back seat. Also made new door hoses. All was working well but there is a leak somewhere. I'm loosing fluid and have not found the lake yet. The reservoir has to be very full. If it's a quart low system will not work.

Mike,

Thank you very much! This is EXACTLY the information we were looking for. We didn't know where to start. Your post tells us and gives us confidence to get underway. It is a very nice car but I fear we have a leak somewhere. Getting some fluid in there and operating the windows and top should tell us where.

Phil,

We plan to use DOT 3 brake fluid unless we find the system has ATF in it. I will post progress as we tackle this over the next week or so. Again, thank you both.

You know that "Been there, done that, and got the T shirt" saying? Fill that reservoir, snap the bale wire on, and you'll know where it came from.

Bernie

Bob,

I'm glad you found that information useful. A lot of guys are afraid of these old hydraulic systems but they are pretty straight forward once you understand a little about how they work. Something else I forgot to mention, if you have access to an early to mid 50's MOTORS Manual, you will find excellent information regarding system operation and procedures to disassemble and repair the pumps. Have fun!

I have the same t-shirt that Bernie has. As has been said, most likely your problem is the reservoir is low on fluid. When you fill it back up, running the system a lot will usually bleed the air out of it. You can speed up the bleeding process by loosening one of the fittings that is easily accessible (not many are) and tightening it back up when fluid starts to come out, but give it a try without that first. It is designed to be self-bleeding if everything works properly.

Pete Phillips, BCA #7338

1950 Roadmaster 76-R with that system...

The reservoir was easy to get to and get off. It has red fluid in it - I assume ATF. Another quart of ATF brought it to about an inch from full. After this the windows went up very slow and jerking one time, then wouldn't go up again. The top went down and up very slowly one time and then had to have help to move the second time. Checked the reservoir and it was still about an inch from the top. When operating the window switch the motor still whirrs but the windows don't move.

What does this sound like to you guys? Next step is a pump rebuild?

Bob,

Before you do anything else, check to make certain that your battery is fully charged. If it isn't, charge it up and then try to operate the system again. The fact that you were able to raise the windows and operate the top one time seems to indicate that the pump is capable of producing the required pressure but I suspect your battery is now weak.

I agree with the battery charging. My solenoids wouldn't work unless I rev'ed the engine. I run a 6V alternator now which fixed that problem. When I switched over to ATF the system worked for a while then quit. I have not put Viton seals in the pump yet and it still works so far.....

Thanks for the input guys. The battery appeared strong before trying to operate the windows and top and I did the attempts with the engine running and revved up. But, who knows? I will try it again with a fully juiced battery.

Happy Thanksgiving. We finally found the issue with the windows and top barely moving! Those suggesting making sure the battery was fully charged were close. A mechanic friend was over to see the car and he suggested making sure all the terminal connections were clean and tight, especially the pump motor ground strap. I sanded all the terminal connections, put on a little diaelectric grease, and tightened them good. Like magic the windows now go up and down as they should. Haven't tested the top yet but expect the same.

Thanks again for the help and support.

Thanks for posting the final solution to your problem. Possibly this will help someone else in the future. Glad to hear you did not have a serious ($$$) issue.

bb