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Currently my 7 uses DOT5 Silicon brake fluid, its had it in the brake lines since I bought the car.

The pedal feel has never been brilliant, its just a bit soft and uninspiring. I've bled lots and lots of fluid through but get no air bubbles so I'm confident that there is no air in it, the pedal doesn't pump up and maintains constant pressure.

Everything else is in tip top condition, I've got HI-Spec 4 pot calipers up front and it has a rear disc conversion.
So the question is, should I change the brake seals before I refill with a normal DOT4/5.1 type fluid?

Doing some internet trawling its difficult to get a definitive answer (thats probably not surprising!)
Silicon should not be mixed with standard fluid but what effect, if any, will it have had on the rubber seals?
I could just drain out the fluid, then blow out the lines with an air line and then flush out the system with some methylated spirits, blow it all out again and then refill with normal fluid.
Changing the rubber seals is going to be a pain but probably a sensible thing to do (?)

Your thoughts please

Chris

I used silicon fluid in 't Kreng, when that car was put back on the road in 1997.
Silicon fluid was removed 6 years and 65.000 km later.

When I changed from silicon back to DOT4 I flushed the system with methylated spirit.
After that I used a little more DOT4 then necessary while re-filling and bleeding the system, as an extra flush.

I didn't change the seals and they have been fine ever since.
But I usually change the brake/clutch once every 1-2 years to get rid of moisture and debris.

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1981 TR7 FHC (Sprint engined a.k.a. 't Kreng
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DOT 5 is said to have a little compression interatomically which is borne out from a friend that has it in his Spitfire. He said he didn't know if it was that or if there was a little air trapped in the rebored and sleeved master cylinder that he had done by Apple Hydraulics. I was going to use it, I had rebuilt all cylinders as a matter of course and flushed line with propanol and blew out the lines. I chickened out when reading (mostly here) of all the trouble people had getting a firm pedal due to air in system. I never had a problem even switching out old fluid every two years. Sometimes wonder if I should have used DOT 5 any ways. I know of a lot of various collector car guys that use it with no problems. The urban legend of rubber incompatibility when switching comes from when DOT 5 was first used and it attacked the existing rubber. The formulation has since been tweaked (or rubber changed, whatever). The reputation dies hard (let me tell you about the TR7 reliability legend.... oh, you all ready know). Now with the poor quality of rubber we get these days all bets are probably off. It wouldn't hurt to change the rubber as a matter of course any ways but don't get the generic kits, go with a brand name like TRW where you pay a few bucks more but stand a better chance of getting better rubber.

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