Brake Servo snags?
Discussion
Thought I'd better keep this enquiry car specific (Griff/Chim).
Have any of you knowledgeable folk ever suffered brake servo snags? I think this is what I'm experiencing at the moment. I've left an enquiry with J and L spares but'd be grateful for your thoughts whilst awaiting a reply and prep'ing the spanners.
Here's some symptons:
Prior to a two month lay-up for the fitting of new poly bushes, upsized discs, braided hoses, coil-overs and a wishbone refurb', the Griff seemed to occasionaly suffer from what felt like brake unasistance. This was at low engine speeds (1k rpm) only. The vacuum hose was serviceable and with the wheels off and access to the underbelly, there were no obvious signs of malfunction.
During what was a major undertaking (para 3, 1st sentence), all removed components that were to be reused, were checked over and assessed. Everything is now back together and the brake system bled and checked for leaks (fluid out/air in); all appears good. However, whilst giving the system a cautious on road functioning, the braking feels unassisted: period! The pedal is stiff under boot; though the car hauls itself down with no other untoward symptoms. I guess this narrows things down to the Master cylinder or servo; the latter being my reckoning. Does the Griff servo contain a piston or a diaphragm? If a piston, I could explain the symptoms with a seizure.
Your thoughts please guys; though my wallet has enjoyed two months unburdened by Griffy Gas Guzzlin', it needs a good old shake down.
Bruce
Have any of you knowledgeable folk ever suffered brake servo snags? I think this is what I'm experiencing at the moment. I've left an enquiry with J and L spares but'd be grateful for your thoughts whilst awaiting a reply and prep'ing the spanners.
Here's some symptons:
Prior to a two month lay-up for the fitting of new poly bushes, upsized discs, braided hoses, coil-overs and a wishbone refurb', the Griff seemed to occasionaly suffer from what felt like brake unasistance. This was at low engine speeds (1k rpm) only. The vacuum hose was serviceable and with the wheels off and access to the underbelly, there were no obvious signs of malfunction.
During what was a major undertaking (para 3, 1st sentence), all removed components that were to be reused, were checked over and assessed. Everything is now back together and the brake system bled and checked for leaks (fluid out/air in); all appears good. However, whilst giving the system a cautious on road functioning, the braking feels unassisted: period! The pedal is stiff under boot; though the car hauls itself down with no other untoward symptoms. I guess this narrows things down to the Master cylinder or servo; the latter being my reckoning. Does the Griff servo contain a piston or a diaphragm? If a piston, I could explain the symptoms with a seizure.
Your thoughts please guys; though my wallet has enjoyed two months unburdened by Griffy Gas Guzzlin', it needs a good old shake down.
Bruce
Hi Grouch
Good to hear you're still out there.
Yup, the wallet's recently taken a bit more of a hammering in my pursuit of Griffy optimisation. It may well have to withstand some more, subject to remedying that within my post. With only two days per week in which to keep two cars mobile, a business to run and a house to renovate time is precious. That's why I'm trying to get a consensus as to my current mechanical woe.
YHM
Bruce
Good to hear you're still out there.
Yup, the wallet's recently taken a bit more of a hammering in my pursuit of Griffy optimisation. It may well have to withstand some more, subject to remedying that within my post. With only two days per week in which to keep two cars mobile, a business to run and a house to renovate time is precious. That's why I'm trying to get a consensus as to my current mechanical woe.
YHM
Bruce
Hi Bruce, Brake servo quite a simple device really, 2 individual chambers seperated by a diaphram, constant vacuum chamber perminantly under influence of inlet manifold depression, variable vacuum chamber. There is an operating rod that passes through the centre of the diaphram and pushes the master cylinder primary piston, the pressure assistance that is given to this rod during brake application is dependant on the vacuum level of the variable vacuum chamber. This is controlled by the valve fitted in the variable vacuum chamber.When the brake pedal is pushed, the valve allows atmospheric pressure to enter the variable chamber,this pressure is now greater than the constant pressure chamber and so servo assistance is now given.
Common faults are ;
Vacuum hose leaks
Faulty non return valve
Perrished diaphram
Blocked or restricted air filter (servo)
Have you tried the simple servo operation test?
Push brake pedal several times to empty it of vacuum (engine off)
Push brake pedal firmly, start engine, brake pedal should now drop slightly if assistance given.
Regards Dave
Common faults are ;
Vacuum hose leaks
Faulty non return valve
Perrished diaphram
Blocked or restricted air filter (servo)
Have you tried the simple servo operation test?
Push brake pedal several times to empty it of vacuum (engine off)
Push brake pedal firmly, start engine, brake pedal should now drop slightly if assistance given.
Regards Dave
Thanks for the replies and sorry for not getting back sooner; the current work situation seldom provides the opportunity for Internet access.
J and L spares contacted me first thing Monday morning
and went through the probabilities. Number one being some restriction in the vacuum hose; possibly by being collapsed somewhere out of sight or by some other blockage. The servo diaphragm could also have become perforated through being perished by fuel or some other means. I'm sure I'd hear a hiss as air was sucked in through the vent and possibly a change in engine note/speed if this were the case. Looks like another weekend in overies leaning over the front wing or in a foot-well. I'll bear your suggestions in mind and get back to this post after the weekend.
Thanks again for the input
Hamish
The new shocks are the ally bodied version of GAZ that Derek (Absolutely Shocks) has been pushing. I doubt there's much to be had in weight saving over the steel items and despite what is said, I feel sceptical about any benefit in heat dissipation. I simply paid the extra for the fact that they come fitted with spherical eye-end bearings straight outa the box (they can be fitted to the steel units). I'd been warned that they could induce a clattery and jarring ride but, combined with the new bush set, this hasn't proven to be the case. In fact it's altogether a very smooth and quiet experience. Once I've got the main Servo issue sorted, I'll be able to form something more of an opinion.
Bruce
J and L spares contacted me first thing Monday morning
and went through the probabilities. Number one being some restriction in the vacuum hose; possibly by being collapsed somewhere out of sight or by some other blockage. The servo diaphragm could also have become perforated through being perished by fuel or some other means. I'm sure I'd hear a hiss as air was sucked in through the vent and possibly a change in engine note/speed if this were the case. Looks like another weekend in overies leaning over the front wing or in a foot-well. I'll bear your suggestions in mind and get back to this post after the weekend. Thanks again for the input
Hamish
The new shocks are the ally bodied version of GAZ that Derek (Absolutely Shocks) has been pushing. I doubt there's much to be had in weight saving over the steel items and despite what is said, I feel sceptical about any benefit in heat dissipation. I simply paid the extra for the fact that they come fitted with spherical eye-end bearings straight outa the box (they can be fitted to the steel units). I'd been warned that they could induce a clattery and jarring ride but, combined with the new bush set, this hasn't proven to be the case. In fact it's altogether a very smooth and quiet experience. Once I've got the main Servo issue sorted, I'll be able to form something more of an opinion.
Bruce
O.K, spent Saturday re-checking the brake system and giving it another bleed just incase some air had been hiding around some cheeky bend: it wasn't.
The servo, from what can be seen, appears to be serviceable and performing as advertised and the vac' hose is intact along its length. In conjunction with this and advice from contributors, I reckon the thing is o.k.
I also removed the Non-Return-Valve from the plenum for an assessment and this is also doing its thing. However, I reckon that when the engine revs drop to a figure of 800 or below, the vacuum within the plenum is insufficient to unseat the NRV. Dunno 'bout yours but my revs often dip to this sort of figure when giving way at junctions or manouvering (maybe I should cut this out!); they recover after a couple of seconds or so. It seems odd that though the engine isn't behaving in any way other than I've ever known it, the symptom has manifest itself fairly recently and I'd rather it wasn't there. It may well be worthwhile replacing what can only be an inexpensive component; perhaps a NRV is available with a lower rated spring?! Within a short while the new discs and pads will be bedded sufficiently for a serious foot stomp and verdict.
It's jolly good to have the thing rolling again though; it's just a shame that after a two month lay up there's no f****n'sunlight left!
The servo, from what can be seen, appears to be serviceable and performing as advertised and the vac' hose is intact along its length. In conjunction with this and advice from contributors, I reckon the thing is o.k.
I also removed the Non-Return-Valve from the plenum for an assessment and this is also doing its thing. However, I reckon that when the engine revs drop to a figure of 800 or below, the vacuum within the plenum is insufficient to unseat the NRV. Dunno 'bout yours but my revs often dip to this sort of figure when giving way at junctions or manouvering (maybe I should cut this out!); they recover after a couple of seconds or so. It seems odd that though the engine isn't behaving in any way other than I've ever known it, the symptom has manifest itself fairly recently and I'd rather it wasn't there. It may well be worthwhile replacing what can only be an inexpensive component; perhaps a NRV is available with a lower rated spring?! Within a short while the new discs and pads will be bedded sufficiently for a serious foot stomp and verdict.
It's jolly good to have the thing rolling again though; it's just a shame that after a two month lay up there's no f****n'sunlight left!
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