1980 Chrysler 75, model 758H0B, Trim pump springs

[Generic]

New to the forum, new to boating, and new to fixing boats. After spending a couple of days researching and coming up short, I decided it was time to put the question out to the experts.

I'm having an issue with fluid leak down (the motor won't stay up) and was able to diagnose the problem as a failure of the "medium spring" in the tilt/trim pump (the spring has 5 coils that have broken due to corrosion).

I'm trying to source a replacement spring and don't have some of the details I need to find a replacement. Here's what I DO have based upon what I have measured on the existing spring:

Wire Diameter: .040"
Outside Diameter: .226"
Compressed Length: .645" (this is just a guess)
Free Length: 1" (this is also a guess based upon how much unbroken spring I have and adding back 5 coils)
Coil Count: around 15 (another guess)

What's got me stumped is the Spring Rate (lbs/in). What am I shooting for? I've found springs with similiar attributes that have a spring rate of 14 lbs/in, or 40 lbs/in, or 60 lbs/in. My layman's guess is it's a pretty heavy spring, but I'm not sure what problem will result from a spring that is too heavy. I would guess that going too light would not fix the issue and too heavy would prevent the pump from raising the motor. (It's another of my guesses, so if I'm wrong please let me know; this literally is my first visit to the land of hydraulics)

Also what material type is best? I'm guessing high carbon steel, or high carbon steel music wire... but I really don't know.

Does anyone have the specs for the springs in a 1980 Chrysler 75 trim pump? The medium one is the broken one, but I may as well replace both. Here's a diagram:



I also may need to source a poppet valve (is that what it's called? The little valve that the spring is pushing against). The current one is a little chewed up from the broken spring. I think I can make it work, but finding a new one would be better.

Any pointers to tracking these parts down would be much appreciated.

 

[RRitt]

Re: 1980 Chrysler 75, model 758H0B, Trim pump springs

go to grainger and buy 3-4 different values of 1" die springs around your target size. try the different springs until one of them gives you 1800-2300PSI into the downward facing port. That's the spring to use. They vary from year to year. The spring tension is related to the size of the hole in your regulator seat. If you are trying to calculate it mathematically then its a surface area at 2000PSI equals spring tension at 3/16" compression. It's easier to just stick in a spring and read the PSI.

 

[Generic]

Re: 1980 Chrysler 75, model 758H0B, Trim pump springs

go to grainger and buy 3-4 different values of 1" die springs around your target size. try the different springs until one of them gives you 1800-2300PSI into the downward facing port. That's the spring to use. They vary from year to year. The spring tension is related to the size of the hole in your regulator seat. If you are trying to calculate it mathematically then its a surface area at 2000PSI equals spring tension at 3/16" compression. It's easier to just stick in a spring and read the PSI.

Sounds simple enough. Looks like I'll be heading to Graingers tomorrow. Thank you for the insight.

If I find one that's giving a reading shy of 1800 (and I'm out of spring options), can I just add a few shims to increase the pressure? I believe there were 4 shims under the broken spring. On the same note, is there any reason to put the shims back in if I find a spring that meets the pressure requirement without them?

 

[RRitt]

Re: 1980 Chrysler 75, model 758H0B, Trim pump springs

75HP 1980 Chrysler? You should work just fine with anything over 1000psi. You are a prime candidate for the $90 chinese valve body. Your year probably has the solid brass check valve seat and will cost $120 to rebuild because the check valve has to be replaced. But your horsepower isn't more than the chinese product can handle and the age of your engine suggests that you don't do a lot of skiing or towing. If the springs don't work out, then just search ebay for the $90 special.

 

[Generic]

Re: 1980 Chrysler 75, model 758H0B, Trim pump springs

No luck finding suitable springs that were small enough diameter yet stiff enough. The corrosion on the check valve was more extensive than I originally thought so I ended up ordering the chinese valve body for $89. I also decided it was time to replace the motor as the existing one is quite rusted and will most likely fail soon. As it was, it was leaking water into the reservoir which probably accellerated the failure of the pump. The replacement motor ran $139.

Hate spending the money, but I suppose it's better than shelling out the $500-$600 that some sites charge for replacements. I only need it to last a few years so it should be a good solution.

Thanks again for the help.