Centrifugal Regulator - Strip Down and Overhaul

I'm itching to get my engine back in the car and so it was inevitable that I got round to finishing rebuilding the centrifugal regulator - a job I had started previously but not finished.

How It Works - More Or less......
The main job of the centrifugal regulator (aka centrifugal governor) is to ensure a smooth transition between standstill and first gear. That's it.

The front of the centrifugal regulator unit is a bell chamber. Within this is the governor. The pulley spins the governor in this chamber and the degree to which it is compressed by this spinning action, determines the position of a slide valve (pushed by a spring) within the main body that performs a ‘gating’ action. 

Centrifugal regulator slide valve

With first gear selected, hydraulic pressure is fed to the clutch cylinder and the clutch is disengaged. As the engine revs build, the (increasingly faster) spinning of the centrifugal regulator arms compress the length of the governor under a scissor action, creating room to allow a slide valve inside to move forward.

The governor. The spinning arms fold out, compressing the
main spring and shortening the length of the component

As engine rotations build and cross a threshold, this slide valve movement and ‘gating’ action allows hydraulic pressure to be released from the clutch cylinder – which begins to engage……For my 1968 car, clutch drag should begin at between 700rpm and 750rpm. There is an adjuster screw in the end of the pulley shaft. If unscrewed, the clutch comes in sooner (lower engine revs). If screwed in, clutch drag occurs at higher revs.

With accelerated idling speed being set at about 900rpm and the clutch biting at about 725rpm, with the car in gear and your feet off the pedals, the car reaches accelerating idling revs, the clutch engages and car creeps forward......

The governor of the centrifugal regulator plays no part in clutch operation between other, higher rev, gear changes on a bvh car. Instead, this is all controlled by Magik.

However the centrifugal regulator does have a second clever trick of its own and associated with deceleration: upon sudden braking in any gear (so an emergency stop), hydraulic fluid is pushed from the brake circuit to a second, different chamber in the centrifugal regulator. It pushes against a powerful spring-loaded piston that does not move under ordinary driving. In an emergency stop, the pressure on this piston and big spring are sufficiently great to move them. This in turn moves an attached pushrod. The pushrod is essentially the base on which the spring behind the slide vale sits: if the ‘spring base’ moves back, the spring exerts less force on the slide valve………which slides back and opens the gate to feed fluid to disengage the clutch. In short, when you brake sharply, the DS shouldn’t stall! This extra brake-related function is also why, on a bvh car, you bleed one of the front brakes by connecting a bleed hose to the centrifugal regulator).

How it all works.....

A fuller, (more accurate!) explanation is covered in Citroens ‘Hydraulic Course Notes’. There are a couple of versions of these. Manual 844 is available to view online via the "Citroen-DS-ID.com" website. You can find a link to it at the bottom of the list here:

Manual 844 - Hydraulic Course Notes

Charles Vyse also covers operation of the centrifugal regulator in his ‘Goddess’ book - available through "Lulu.com" publishing on the internet.

Replacement of the pulley bearing is covered in Operation Dh.314-3 in section 2 of volume 2 of Manual 814, but there are no rebuild instructions. However, instructions for stripping and rebuilding are demonstrated in two Youtube videos by ‘DSSMPassion’. Here's a link to the first part:

Video of centrifugal regulator strip down

The Manuals do, though, have a useful sectional diagram that show all the bits inside. 

I had started to give the centrifugal regulator a cosmetic makeover back in July 2015. I had removed the bell chamber to inspect the bearing, replacing the perished silent blocks and cleaned the outer surface with a glass bead blaster before priming ready for painting.Then I put it in a box for 3 years…..

How I left it back in 2015....

This summer, I decided to do a more thorough job on the internals. Compressing that three year gap, here’s a description of what I did.

Silent blocks

These are a layer of a rubber compound sandwiched between two steel rings and they absorb vibration.

A silent Block (or 'bloc')

They are pressed into the ‘eyes’ on the pump base. When the silent blocks perish, the centrifugal regulator goes out of alignment – putting a strain on the pulley. This causes premature wearing of the shaft bearing.(Not sure why the centrifugal regulator has them, whereas the high pressure pump pump does not…..). As the DSSMPassion video shows, silent blocks can either be pressed out using the new replacement block you intend to fit or, as I did, using a suitably sized socket......... 

Small socket to press out the silent block

  ......and larger socket to act as a catching cup.

Large socket used as a catching cup

If following this route, the smaller socket needs to be big enough to engage with the metal edge of the outer ring, but needs to be able to pass through the hole comfortably.

Small socket passing through the regulators 'eye'

The socket pushes out the silent block

Fitting new blocks is pretty much the same technique. The outer rings of the original silent blocks appear to have a bevelled edge – possibly to help with fitting. The repros I used did not have this edge but were still easily pressed back in place.

Pulley Removal

The bell chamber is held to the main body with three bolts. It’s dry inside – so I didn’t need to worry about hydraulic fluid pouring out. In addition to the bolt holes, it also has a ‘breather’ hole – so if you plan to bead blast the regulator to clean it, you need to blank this off to keep the blasting medium away from the moving parts of the governor inside.

With the bell housing removed I detached the governor. 

Citroen recommend using a special puller to remove the pulley – but that isn’t practical. As in the DSSMPassion video, I had carefully gripped the main body block of the governor in a vice (do NOT grip the moving arms and bend them)........

.....and then had used a rubber strap wrench to then remove the pulley. It has a standard direction thread.

With the pulley removed, the governor part was withdrawn from the bell chamber part.

If you are planning to change the bearing (these are often a cause of failure in centrifugal regulators), then this can be done by drilling out the four rivets hidden behind the pulley and removing the covering plate from the inside. 

The riveted cover hides the bearing

With the plate removed, the bearing can be pressed out (actually it's pressed 'in' from the outside into the cup of the bell chamber) - much like the silent blocks. You can refit the cover plate using pop rivets - they end up hidden behind the pulley.

Main Body Dismantling

The slide valve was removed.

Removing the slide valve

I undid the two nuts from the end plate. When first taken apart, there had been the remains of a paper gasket on the end plate.

There was a large spring inside the end chamber and, with the nuts removed, the body helpfully pulled itself apart.........

.....leaving the main body, the end bracket and another segment sandwiched inbetween.

Middle segment

The middle segment has what I will describe as a ‘front chamber’ and an ‘end chamber’.

End Chamber of Middle Segment

This is the 'anti-stall' device if you will. A push rod (whose end emerges into the front chamber)........ 

........passes through a hole between the two and is connected to a cupped piston in the end chamber. The piston cradles a strong spring – the one held in place by the back plate.

At first, with the thing in pieces, I wasn’t convinced that it was a piston in the end chamber as, even though the spring was removed, the push rod showed no signs of movement. Surely it was only the big spring in the end chamber which was meant to hold the piston back? With the spring now removed, why was this so stiff?

I had to carefully use a drift on the cap that fits over the push rod end to confirm that the piston, did in fact move, and was able to get it out.

The push rod was held on the end of the piston by a flat disc which was, in turn, held in place by a circlip. That was easily undone.

End chamber piston and push rod

Pushrod

I gave the piston a clean and gentle polish. It, and the bore, looked okay - no scratches, no rust, no pitting. I re-inserted the piston with some LHM and moved it up and down in the bore. Better. There is an ‘O’ ring inside the inner circumference of that chamber to stop leaks past a piston. When that was replaced the piston would be even stiffer.

'O' ring in the groove in the end chamber

Front Chamber of Middle Segment

Sitting loose on the end of the emergent end of the pushrod was a cap, a spring, and on the other end of the spring – another cap. This second cap pushed on the end of the slide valve in the main body.

Slide valve and spring assembly in front chamber

With the stripping and priming work already having been done three years earlier, all the internals were given several generous slooshes with ‘Mek’ and the passageways blown out with compressed air.

All the bits - and more!

The Rebuild

Masking off the hydraulic pipe holes and bleed valve holes, I loosely assembled the unit using some suitable bolts and finished the painting job I had started three years before. Once dry the unit was broken down to it’s constituent pieces again.

Repainted and ready for the rebuild

The rebuild kit you can buy includes two large ‘O’ rings, a paper gasket, three small ‘o’ rings’ for the pipe seal, two silent blocks, and a bearing. I’d already replaced the silent blocks and didn’t need the bearing – so only needed the large ‘O’ rings and the gasket.

I knew the sizes of the ‘O’ rings I needed from the parts manuals but couldn’t easily find what I needed in the right size. Instead, however, I managed to find a NOS ‘Part 719’ This is the complete seal set for the centrifugal regulator! 

Lucky find: set 719 

Some of the seals in this set are standard seals that are easily obtained, but crucially, the set included the two big ‘O’ rings that I needed.

That was a lucky find: it just goes to show that it really is worth familiarising yourself with the parts manuals and diagrams.

Set 719 as listed in parts manual 562

As I say, the after-market rebuild sets contain two big 'O' rings so presumably the usual suppliers had better luck than me at sourcing them - so don't worry if you can't find set 719.

I still needed a gasket.……. After posting him a paper template, Toni – my go-to guy for gaskets – came up trumps with a replacement. And several spares - compensating for the poor artwork of my 'brass rubbing' template.

Toni came up trumps with a selection of gaskets

With everything set to go, I winkled out the old seal from the end of the main body.

 Ready to fit the new seal.

But first I made sure the metal surface was flat and free of obstructions – such as paint runs. The long threaded rods were refitted to the main, front body – ready to receive the middle segment and end plate.

NOTE: The parts diagram seems to suggest there is a paper gasket between the end chamber and the main chamber - part 25 in the photo below. I could see no evidence that a paper gasket had been fitted here, and the ‘O’ ring that is fitted here (part 51 in the diagram) should make a paper gasket unnecessary anyway? 

Part 25 is shown in the wrong location?

The new sealing ‘O’ ring on the open end was coated with LHM and replaced.

I fitted the second seal in the inner groove of the middle segment.

To fit this ‘O’ ring, I adapted a trick learned when rebuilding the clutch cylinder: I use a long M7 bolt with a suitably sized washer on it, to act as a ‘false’ floor in the bore - to stop the seal pushing in too far (and missing its groove).

Bolt and washer used to locate the 'O' ring

With the seal located, the bolt and washer were then easily extracted, leaving the new seal in place.

The end chamber piston and push rod were re-assembled. The slotted collar was slipped over the groove in the push rod and was then mated to the piston end.

The circlip kept the push rod assembly in place.

The circlip holds the pushrod to the piston

All assembled

The push rod was lubricated with LHM and re-inserted through the hole dividing the chambers.

I always knew that the piston would need to be ‘encouraged’ past any new seal, but it took a hefty tap with a rubber hammer to achieve this. Once fitted, I gave the push rod a tap from the other end - just to make sure that the piston was able to move. It was still very stiff – but surely due in no small part to the new rubber seal. This piston is part of the emergency braking function and only moves when considerable hydraulic pressure is applied. If, after rebuild, I keep stalling – I’ll know where to look!

In the front chamber of the middle segment, I capped the end of the push rod, seated the small spring over the cap, and then fitted the cap to the other end of the spring.

This middle section was then slid over the two long rods and up against the front section.

At the back end, of the assembly I refitted the large spring in the cup end of the (already stiff) end piston. I fitted the gasket that Toni had kindly made me over the two long rods. 

Fitting Toni's gasket

Before I bolted everything up, I checked that the middle section and end plate were the right way round relative to the front, main, body.

The end spring is powerful, so I applied some pressure on the end to help with tightening the nuts up. The studs for the hydraulic pipe assembly were refitted and the two bleed nipples were refitted.

Bell Housing - Reassembly

With a liberal coat of LHM, the slide valve was inserted into the open end of the main assembly. The small end of the slide valve goes into the body – such that the big end will be the one contacting the governor in the bell housing.

Re-fitting the slide valve

If doing this job, but not replaced the bearing, then at least check that it remains greased. Splatters around the inside of the bell chamber are a good indicator of whether the bearing is drying out.

Grease Splatters - replace or lubricate the bearing

My bearing had lost grease, but was still okay – so I simply added a little more grease. Standing the bell housing on end like a cup, I re-greased my bearing by heating some heavy grease to melting point, then pouring it onto the bearing – which I had already pre-warmed. The grease filled the bearing and a little of the bell chamber. I left the grease to cool and harden before wiping off the excess.

The governor part was slotted through the bell chamber and carefully gripped in a vice once more. With some thread lock on the shaft end, the pulley was refitted using a rubber strap wrench. With the slide valve already in place, the bell chamber was bolted back on to the main body and the long adjusting bolt was put back  in the ‘nose’ – I will set this up later.