On Facebook, there has been mention of a quick release valve for the SCG gearbox. Apparently when you move the selector to neutral the gearbox picks neutral instantly, due to the fitting of a "quick release" valve, rather than hanging on to the gear for an "excessive period of time"!

Never heard mention of this before, it's apparently a recognised mod, not having had a gearbox stick in gear, (more the opposite), anyone shed any light on why this was thought necessary?

My bus number (if any): RTL 960, RM 1585, RMC 1485 and several RTs

Brian
They are better described as quick exhaust valves and in the main to my knowledge I have come across them on Leopards and Atlanteans that have direct air gearchange ie no electric selector or EP unit.
The idea is that rather than all the air exhaust back through the gear selector unit which is by the driver in the cab they release the deselected gear air by the gearbox thus speeding up disengagement and potential damage to gearbox

Norgren S513 is the unit used and is serviceable as its just a cup washer seal that seals on the cup bit and exhausts against the lip

HTH

Mark

My bus number (if any): RM1414 sort of

I remember these, Brian, from back in the Seventies. National Express used to have a lot of their semi- auto Leopards fitted with them. If you synchronize your gears in a Leopard the changes are nice and smooth but the temptation is slam the lever through, with the risk of the bands grabbing. Poor driving technique gave an uncomfortable ride and risked damaging the gearbox. The quick release boxes had a very distinct sharp ‘whistle’ as the gear changed so as a coach pulled away you immediately knew it was so fitted.

Thanks Mark and Danny, not heard of them before on RMs, their installation was quoted as if it was across the board.
Are they really necessary on a Routemaster with an EPV valve or are they more common with Routemasters that have had auto disengaged?

My bus number (if any): RTL 960, RM 1585, RMC 1485 and several RTs

From what I've been told by Lionel Moss, one of the leading experts on these things, they were fitted to the "modernised" buses to match the gear changes to the more powerful (?) engines fitted to try to reduce brake band wear and additional forces on the rest of the transmission.

If your RM has an AEC engine, throw them away, not required! For any other engine, in my view with the use these buses get nowadays, throw them away, not required.

I've done away with them on 2532 fitted with a Cummins series engine and the gear changes seem a bit smoother. I've also done away with the air throttle dip valve. More bits fitted=more bits to go wrong.

Are we not mixing up quick exhaust valves which were never fitted to RM afaik given the near proximity of the EP valve with the restictor valves which are different between the gears
The restrictor valves do what they say and even though the GB is fed at reduced air pressure it slows the flow of air so the band is slowly applied rather than the sudden bang of getting 60-80 PSI
These restrictor valves are housed in the first little double male? connector coming out of each piston cover underneath
A friends Leopard has one of the quick exhaust valves fail and just pass air and someone being helpful removed it for him along with the restrictor, several months later bits of brake band came out with a gearbox oil change which was precipitated by a bit of slip and jerk in said gear, result is that the lining had elongated the rivet holes because of the banging on at full reduced force of that gear, box out and away for repair

Mark

My bus number (if any): RM1414 sort of

These were fitted at mechanical refurbishment as part of the CAV 551A gearbox operation modification. The purpose being to negate the perceived excessive wear to the brake bands likely to result from the increased torque developed by the more powerful engines being fitted. This would eliminate as far as possible the wear caused while two bands were partially engaged during changes. The QEVs in conjunction with the throttle dip were intended to prevent full throttle gearchanges taking place.

Presumably if the vehicle is driven in semi auto mode and the revs allowed to drop between leisurely gear changes these quick release gearbox valves and a throttle dip become superfluous ?

My bus number (if any): RML 2747

I've seen all sorts of combinations of QEVs and restrictor valves fitted at both ends, so there's no apparent standard for them, though logic would suggest the QEV at the gearbox end and restrictor at the ep end.

My bus number (if any): RML2532,GS67,MLL721,MLL738 and an RT.

Talking under my RML today with roy, (not myself, the other one)he reminded me that the gearbox on 2534 is plumbed according to the set-up instructions given in the CAV booklet issued when the RMs were fitted with the later control panels, qev's on 1st and 2nd on the gearbox, restrictors on the ep block..

My bus number (if any): RML2532,GS67,MLL721,MLL738 and an RT.