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Hi all. Has anyone used Silicone Based Brake Fluid (SBF) on an XJS facelift with the Teves ABS system? The manuals all say DOT 4 fluid, but I can see no reason not to use SBF and Automec (SBF maker) say it is OK, but it would be nice to hear if anyone has switched without problems.
The fluids do not mix and I am not about to take all the calipers off and completely clean out the brake cylinders. In other cars I have switched I just bleed it until there are almost no bubbles of yellow fluid coming through, but I've never changed a car with ABS before. Has anybody actually used SBF in an ABS car and done the changeover this way successfully?
As you're UK based, the way we refer to the "year" of our cars, is often different to that of US owners. So, when you refer to a 1995 XJS, it's important to clarify if it's got the Teves II or Teves IV system. If your VIN is earlier than 198335, then you've got a Teves II setup; if it's later than 198335, then you've got a Teves IV setup.
I wouldn't change to Silicone in either system. However, I think it's even more important to really think about the choice if you've got a Teves II system. The Teves II is a really complex system using a separate Pump & Accumulator, and a complex Actuation Unit with an adjoined ABS Valve block. I feel it could be really difficult to fully flush through the synthetic fluid, which should not be mixed with Silicone fluid. To me, it's not worth the risk.
The Teves IV is a somewhat more typical ABS system, but this needs to be flushed using the Jaguar software which can force the opening of the ABS valves.
So, it's a personal choice, but not one I would choose.
However, if you do decide to go down this route and you've got a Teves II system, please ensure that you understand the Teves procedure for bleeding the brakes, the rear in particular; it is not the same as a traditional bleeding procedure.
Thanks for that good info. Mine is the Teves II sysyem. I wasn't aware there was a later version!
I am aware of the bleed procedure and have been given the details of how it is done.
I have swapped other classic cars by just doing a "long" bleed until hardly any old fluid comes through, but I can't say that it completely gets rid of every last drop of DOT 4 fluid. It has never been an issue in my other cars, but they are not ABS. I have read a few comments about the possibility of SBF aerating in the Teves II system, but Automec (the producer of the SBF I would use) say that is not the case and that it should be fine.
Personally I can't see why it should be a problem even if a bit of the old fluid remains in the system. I was just hoping someone here had done it successfully before.
If you do decide to go ahead, you might have to do a number of flushes. There are a number of areas that will be difficult to fully clear of the old fluid, particularly the passages in the ABS valve block that are normally closed until the ABS kicks in on a lock-up. I'm very wary of suggesting it, but the only way you can push the old fluid through those passages (other than completely dismantling it) would be to actuate locking on all wheels a number of times to allow the valves to open / close and push the fluid fully through. I'm not sure I'd try that. So maybe a full flush, let the fluid mix itself slowly over a few days, another full flush etc? Could be expensive on silicone fluid.
I'd also start by syphoning out as much of the fluid from the reservoir first and fill with silicone before you start. It's really difficult to get to the back part of the reservoir, which takes a separate feed to the pump on the other side of the car. You could carefully remove the reservoir, empty it, replace and fill with silicone, then wait to let any air bubbles from the ports surface to the top, before you then start bleeding. But there will be a chance that you introduce air to the Actuation Unit, which can then be a pain to bleed out.
I haven't done this. However, if the '95 calipers are the same design as '91, you will likely retain the old fluid in the front calipers. I just repaired a friend's XJ-S front brakes. The fluid entry to the caliper is halfway up. The bleed screw is at the top. The lower two cylinders and bridge drilling ports will retain the old fluid, because the path of least resistance while bleeding will bypass the lower parts of the caliper.
Regular fluid flush with DOT 4 will expose that old "trapped fluid" to drier fluid and maybe it wicks out the moisture if there is any? If the new fluid is SBF it can't pull any moisture out. Maybe the same principle applies to the ABS system cavities? Maybe I'm over-thinking it, I usually do! If I couldn't be 100% sure of 100% replacement - I wouldn't do it.
The caliper fluid would concern me the most, since that's at the hot end of the system, where boiling is most likely to occur.
Solid crud in lower ports
Cleaned out OK
Rebuilt with new pistons and seals
If the caliper isn't solid like these, its easy to clean the calipers without separating the halves: Remove the pistons and flush through the ports with an air hose. Replace the rubber hoses as well. Flush the system out with the brake calipers off the car. That still leaves the original question of getting the fluid out of the ABS cavities...
I think I added more questions, but hope this is helpful and maybe others could comment on the concern of trapped old fluid in the caliper?
Why would you want to use SBF? SBF is often used on the braking system of cars used for racing where high speed braking is required. Reason being that SBF has a higher boiling point.
Using SBF is irreversible. If you ever wanted to go back to DOT 3 or DOT 4 every component of the braking will have to be replaced because you can never flush out the SBF. It creates a silicone coating on all of the brake components. Just saying!
Paul - I was planning on emptying the reservoir first, but thanks for the advice about the rear cavity. I'm certainly not going to be dismantling the ABS to get oil out of the inner recesses! I had a reconditioned unit fitted last year as it was causing one front brake to stick on and now it's working fine.
Dave - my calipers are almost new as I replaced them thinking that was causing the binding brakes, but it turned out to be the ABS (hence getting that reconditioned, see above). If I do go ahead with the SBF I'll probably open the bleed nipples and push the pistons back in fully to empty the cylinders as best I can.
Sanchez - My reason for using SBF is mainly because if it leaks (which may not get noticed while it is in winter storage) then at least it won't strip the paint. This is what has happened now as the Delay or Restrictor valve has started seeped this spring. I now have an inner wing to repaint! Also, it doesn't absorb moisture so doesn't ever need changing. For these reasons I can't see why I would ever go back to DOT 4.
Getting the old DOT 4 fluid out of the ABS valves might be a bit of a pain as Paul has pointed out, so not sure I'll go ahead just yet. I should have got them to do it while the ABS unit was being changed. It might be a step too far now!
Silicone Brake Fluid in Teves ABS (1995 XJS)
