brake master cylinder pushrod

[chicagojeff]

Dear all,
a while back i posted some questions about the relatively different amount of brake effort needed to stop my car (S3 coupe with no-servo dual master cylinder) versus my experience with two friends' cars using single circuit. Theirs just seem to need a lot less effort. Most commentators seemed to feel that dual versus single circuit shouldn't matter in terms of pedal effort. So the next obvious question was whether I had the wrong MC--that is, the larger diameter Girling-- that without the boosters needs a lot o' leg. Nope. I have the correct one.

So another theory, which is supported by my relatively low pedal height, is that with better pedal height, maybe achieved with a longer pushrod, the feel will improve and the effort needed to push will seem more like the single circuit cars' brakes.

Anyone know what the proper pushrod length is? And any reason to expect this to be the problem? Much thanks, Jeff in Really Frigid Chicago

[MickG]

Hi Jeff,
The standard length of both clutch and brake pushrods is 3.125 inches or 80mm. This is measured from the centre of the clevis pin to the under side of the domed head.

Regards Mick G

[UAB807F]

I'm not sure it will reduce the effort in practice, although there might be a psychological "feels better" to it because your foot won't be as close to the bulkhead !

My car has higher pedals due to longer pushrods, I fitted adjustable ones to both the clutch & brake cylinders so I can get it exactly what suits me best. I think if you're considering changing the brake rod, rather than just guess at the new length buy 2 adjustables and do both.

Brian

[Jeff@Jae]

My late S3 had a dual circuit master cylinder from new and it was actually a different bore size (.75" IIRC) than the later, more common S4 with a .7" bore. This was a S3 S/E with rocker switches but NOT a Super Safety car. I recall it was a pretty firm pedal compared to the S4 .7" m/cylinder with a short pedal travel and since these late Fedral S3s were the first Elans to use that type of brake master cylinder I have since suspected they were simply sized wrong by Lotus or Girling. If I still had that car I would've dumped that tandem master cylinder and gone to a single circuit type like the earlier S3 and S2 cars. I mean, who has seen a caliper fail unless woefully neglected in maintenance ? A longer pushrod maybe an acceptable alternative.

[tim22]

I just fitted a replacement brake master cylinder over the week-end - it came from a Lotus dealer so I was confident it was simply a matter of replacing old with new. The replacement push rod measures 80mm from centre of clevis pin to the crown of the domed head ... rather than the underside as posted below. This was obviously too long for my +2S because the brakes wouldn't release after being used a few times, presumably because travel of the plunger was restricted and the valve seal was blocking return flow through the inlet port. The old push rod is 12mm shorter and refitting the shorter rod allowed the brakes to release as before. However, the pedal now feels a bit low in comparison - I think the optimum length must be somewhere in between these two and I'm considering changing to an adjustable rod.

Has anybody else had the same problem?

Tim
+2S 1971