Running SU's with no oil in the dampers?

[karls59tr]

A friend of mine never checks the oil in his TR3 SU dampers. He says it's not necessary! Makes me crazy.I say you get better throttle response and the engine performs better. What's the down side to leaving them dry..... and what's the general consensus on this?

 

[Banjo]

If they are totally dry, what will generally happen is they will open too fast, and the engine will have a stumble on acceleration. the harder the acceleration, the more noticeable the stumble. It'd be like a standard carb with a bad accelerator pump.
If he had his carbs set way to rich, the stumble bay be far less noticeable.

 

[Roger]

Depends on the state of tune, strength of spring, and a bunch of other variables. Early SUs had no dampers at all, nor did they have springs, but the piston was heavy and didn't tend to oscillate much. When springs were introduced, the dampers' job was literally to damp their oscillations, not to act as a spring themselves. So you can run a dry SU with a strong spring and mitigate the acceleration stumble that Banjo refers to.

However, I do suspect that some owners check far too often and overfill their SUs and Strombergs, too. In the SU case in particular, there's nowhere for the oil to go and it won't evaporate quickly. So folks fill 'em up, then when they check again, there's less oil so they fill 'em up again. In fact, part of the problem is due to vehicle manuals being wrong. They indicate far too high a level! Once you fill an SU, then replace the damper, then run the engine to WOT, the oil level will end up somewhat below the top of the hollow damper tube in the piston, and that's where it should be.

 

[foxtrapper]

Coming from a motorcycle background, where there is almost never any oil in the dashpots, I thought the SU oil stories were silly and had to be fabrications.

Tried running without oil, several times over the years. Remarkably bad results in every case, on the street. Slam down on the gas pedal, and the engine would fall flat on its face. On really rough dirt roads, I could even hear the pistons clacking as they bounced up and down.

I run the lightest oil I can on any given SU setup. Generally, I find Dexron ATF to work just fine for me. It dampens things just enough to prevent bog, without causing thick oil throttle lag.

 

[vivdownunder]

Easiest way to check dashpot oil is to unscrew the dampers and check that they have resistance. If a dashpot needs topping up, I like to lift the piston fully to see the top of the tube and fill to about 1/2" down. So the damper brass valve is fully into the dashpot before it feels the oil.

Then there's no surplus dashpot oil to cause trouble.

I've found SAE20 oil to be ideal for our home climate, which is similar to CA.

Viv.

 

[TR3driver]

In fact, part of the problem is due to vehicle manuals being wrong. They indicate far too high a level!

FWIW I believe that was deliberate. They also specify a mileage interval for filling them that high, and I believe that the intent was for the excess oil to work it's way down between the center rod & the bearing in the dome, to lubricate the bearing. The excess oil then drips out through the bottom of the piston and gets sucked into the engine, where it does no harm.

But the concept was overly complicated, and the later manuals indicate the lower oil level.

And I agree about the 20 weight. It's gotten hard to find in auto stores around here, so I bought a quart from MMC. 20W50 works almost as well, though, at least for me.

 

[rlich8]

Just as a shock absorber for suspension - or "damper" in British english, all it really does is slow down the jounces and rebounds. Really it's a simple but very effective system.

Just grab a quart of ATF and viola, you're set for about 10 years.