Can both Teves 3 and 4 both be reverted to OldVac?


I’m part way through a 5 speed conversion on an '89 XJS with ABS Teves 3.
I removed all the ABS parts, and put in an older vacuum booster, as part of the manual pedal box.
A friend has a '95 XJS 4 litre with Teves 4, and is having trouble with it.
Can you swap in an older pedal box and master for his car the same way?

I think that is crazytalk. Nothing wrong with Teves 4, wish my 94 had it.

He should just fix whatever is wrong and enjoy that fine car.

Yeah, I tend to agree with exMBman: The Teves III is dangerous, but the Teves IV is an excellent system. We haven’t heard of any problems at all. Perhaps he could post his issues here and we could all learn something!

That said, I’m pretty sure reverting the Teves IV to a non-ABS vacuum boosted brake system would be cake. Heck, I’m not even sure you have to replace anything; you might be able to simply pull a fuse or something. The vacuum booster is already there, no need to mess with the pedal box, booster or master cylinder.

Kirbert is absolutely right - pulling the fuse to the T4 ABS ECU simply puts you in a basic vacuum boosted hydraulic 4 wheel brake system . No restrictions or kinky things like the T3. In fact when the T4 is active / armed any detected fault will turn it off, and you will be exactly as above - a normal Vacuum boosted hydraulic 4 wheel brake system with no restrictions - of course no ABS. I fail to understand why anybody would want to turn off or disable a working T4 ABS system - I also know some are delusional about their driving skills.

That person is a good friend of mine.

Thank you all very much.
I’m a little sheepish; I should have figured that the T4 already has a Vac booster, and is far less prone to the evils of the T3.
Sorry, I should have thought this through, and looked at his car first.
I’ll get the codes/issues and report,