Caravelle 1965

[Greenpeace]

Ta; that is, I assume, the test I mentioned in post #6 (so: R8, not R10 -memory!) - he wouldn't have his hands out of the window if the rears locked! (Not that they would, even with limiter valve removed.)

The test is a little open to interpretation though.
They state "to achieve 4-wheel lockup proved to be difficult", but they didn't say impossible?
They say "there are only two black lines because the front and rear wheels track in the same path", which alludes to; if they hadn't have, there would be four black lines?
Then they refer to 65 mph stops with "the wheels locked". I could be wrong, but I reckon if it was only the front wheels locked, that's probably what they would have written?

 

[harrisonati]

Yes, you have to wonder if age or contamination is a factor. I found this period R8 road test, and it sounds like a new R8 braked very well with the valve in situ.

View attachment 229227View attachment 229228

I have the unfashionable opinion that Renault got it pretty much right with their pressure limiting valves. In most cases, I think that if braking improves with the PL valves removed, then the valve was defective and not working properly! My R1090 Dauphine doesn't have a PL valve and I can lock both fronts and rears at various times, but rarely all four wheels at the same time. If I had later model with a troublesome PL valve, I would try to fix it, not remove it!
In any case, Renaults always had good braking systems! My experience with braking problems with cars of the Dauphine, R8, R10 era includes dealing with horrifically inadequate braking performance of the small Fords that I campaigned in Series Production racing in the mid 1960s. The most difficult was a 1500cc Cortina with front discs and rear drums - the rear axle would 'wind up' causing violent tramping. The rules didn't allow many changes to anything, but brake linings were 'free'. My fix was to use the hardest rear lining that I could find, then araldite lead from 6B pencils to the shoes ahead of the linings and in the rivet holes. I also would rub the rear friction surfaces with a 6B pencil before every race. That effectively 'knobbled' the rear brakes but made the car controllable under heavy braking. As suggested above, with a background in Holdens, Zephyrs, Falcons, small Fords etc, Renault braking systems were a revelation!

 

[Greenpeace]

I have the unfashionable opinion that Renault got it pretty much right with their pressure limiting valves. In most cases, I think that if braking improves with the PL valves removed, then the valve was defective and not working properly! My R1090 Dauphine doesn't have a PL valve and I can lock both fronts and rears at various times, but rarely all four wheels at the same time. If I had later model with a troublesome PL valve, I would try to fix it, not remove it!
In any case, Renaults always had good braking systems! My experience with braking problems with cars of the Dauphine, R8, R10 era includes dealing with horrifically inadequate braking performance of the small Fords that I campaigned in Series Production racing in the mid 1960s. The most difficult was a 1500cc Cortina with front discs and rear drums - the rear axle would 'wind up' causing violent tramping. The rules didn't allow many changes to anything, but brake linings were 'free'. My fix was to use the hardest rear lining that I could find, then araldite lead from 6B pencils to the shoes ahead of the linings and in the rivet holes. I also would rub the rear friction surfaces with a 6B pencil before every race. That effectively 'knobbled' the rear brakes but made the car controllable under heavy braking. As suggested above, with a background in Holdens, Zephyrs, Falcons, small Fords etc, Renault braking systems were a revelation!

Yes, I guess the only certain way of knowing would have been to remove the valve from a couple of brand new cars and performed back to back brake testing.
There's no shortage of repro limiting valves for sale, which might suggest a high failure rate?
My father was a mechanic, and one of his favourite sayings was "if a part didn't need to be there, the manufacturer wouldn't have put it there".
Having said that, I've just taken the rear factory anti-roll bar off my Austin A30.
Internet consensus seems to be they corner better without them, unless an accessory front bar has been fitted.
I'll soon find out, I'm off for a drive now.

 

[harrisonati]

Yes, I guess the only certain way of knowing would have been to remove the valve from a couple of brand new cars and performed back to back brake testing.
There's no shortage of repro limiting valves for sale, which might suggest a high failure rate?
My father was a mechanic, and one of his favourite sayings was "if a part didn't need to be there, the manufacturer wouldn't have put it there".
Having said that, I've just taken the rear factory anti-roll bar off my Austin A30.
Internet consensus seems to be they corner better without them, unless an accessory front bar has been fitted.
I'll soon find out, I'm off for a drive now.

Conventional wisdom in the era before limited slip diffs were practically available was that you should concentrate roll stiffness at the non-driving end. Thus a RWD

 

[harrisonati]

Conventional wisdom in the era before limited slip diffs were practically available was that you should concentrate roll stiffness at the non-driving end. Thus a RWD

The full text is: Conventional wisdom in the era before limited slip diffs were commonly available was that you should concentrate roll stiffness at the non-driving end. Thus a front engined RWD car would have the front suspension very stiff in roll. The resultant understeer was mitigated by using negative camber on the front (and often extra castor, which helped in slow corners when steering angles were higher.) Period photos of racing Lotus Cortinas etc often showed the inside front wheel lifted off the road. Thus, the entire weight on the inside side of the car was available for traction of the rear driving wheel out of corners. In that era, 'conventional wisdom' of the motor sports inclined people was scathing of Austins and Standards with their rear roll bars. I think that you've done the right thing removing the rear roll bar!

 

[Fearless Leader]

I like the R8/10 brakes but, like others, recommend deletion of the rear pressure limiting valve. That action almost eliminates front brake locking in the wet - the main vice of standard brakes &, owing to more difficult modulation, one that would be exacerbated with a booster.

I wish I knew that 50 years ago. I hated my R8 locking up the fronts in the wet.

 

[Greenpeace]

The full text is: Conventional wisdom in the era before limited slip diffs were commonly available was that you should concentrate roll stiffness at the non-driving end. Thus a front engined RWD car would have the front suspension very stiff in roll. The resultant understeer was mitigated by using negative camber on the front (and often extra castor, which helped in slow corners when steering angles were higher.) Period photos of racing Lotus Cortinas etc often showed the inside front wheel lifted off the road. Thus, the entire weight on the inside side of the car was available for traction of the rear driving wheel out of corners. In that era, 'conventional wisdom' of the motor sports inclined people was scathing of Austins and Standards with their rear roll bars. I think that you've done the right thing removing the rear roll bar!

Well I'm pleased to report the Austin has gone from a strong oversteerer to a mild understeerer with the removal of the rear anti-roll bar. The understeer transitions to mild oversteer at relatively high speeds, but I'm pretty sure the rear tyres are the cause there, as they are too wide for the rims.
I might have a play with the tyres pressures and see if I can get it a little more neutral, but all in all its handling is now firmly in the competant bracket.
I seem to recall reading somewhere that the Phase 3 GTHO Falcons had slightly better lap times with their rear anti-roll bar removed?

 

[Greenpeace]

I came across this video in my travels this morning. I'm guessing most of you would have seen it before, but I'll post it in case you haven't.
The "drive it like you stole it" starts at the 3:58 mark.

 

[harrisonati]

I wish I knew that 50 years ago. I hated my R8 locking up the fronts in the wet.

Assuming proper settings and adjustment, the R8 pressure limiting valve would come into play only if the pressure necessary to cause front lock up in the wet was higher than the pressure which caused rear lock up in the dry. It may be that the pressure limiting valves caused problems because they were faulty or maladjusted. I can certainly lock the front wheels of my Dauphine in the wet, and it doesn't have a pressure limiting valve. However, only the load sensitive pressure limiting valves fitted to R12s and R16S could really deal with a variety of conditions and loads.

 

[harrisonati]

Well I'm pleased to report the Austin has gone from a strong oversteerer to a mild understeerer with the removal of the rear anti-roll bar. The understeer transitions to mild oversteer at relatively high speeds, but I'm pretty sure the rear tyres are the cause there, as they are too wide for the rims.
I might have a play with the tyres pressures and see if I can get it a little more neutral, but all in all its handling is now firmly in the competant bracket.
I seem to recall reading somewhere that the Phase 3 GTHO Falcons had slightly better lap times with their rear anti-roll bar removed?

That's pretty much what I would have expected!

 

[jaahn]

Assuming proper settings and adjustment, the R8 pressure limiting valve would come into play only if the pressure necessary to cause front lock up in the wet was higher than the pressure which caused rear lock up in the dry. It may be that the pressure limiting valves caused problems because they were faulty or maladjusted. I can certainly lock the front wheels of my Dauphine in the wet, and it doesn't have a pressure limiting valve. However, only the load sensitive pressure limiting valves fitted to R12s and R16S could really deal with a variety of conditions and loads.

My personal opinion on the reason the designers used that pesky pressure limiting valve is thus this may be coloured by reading in past times !)
Back in the day when these cars came out most ordinary people did not go around locking their wheels up in the dry normally. But in the home country the value of good even braking under adverse conditions like snow, ice, rain, mud was considered important. So distributing the braking force between the four wheels under lighter applications was important and that was achieved by good weight distrubition and by the normal matching of the piston size to the expected wheel loads. It worked well for the average family punters who were the target market.
Then to prevent the rears locking up under high weight transfer in fast stops in the dry the valve cut the rear pressure increase at some point to keep the car from spinning out ! This valve was never looked at back in the day and the brakes worked well. But as the years went by they were usually found to be non operational due to lack of fluid changes/rust etc and possibly prevented much pressure getting to the back at all.
Jaahn

 

[4cvgordini]

My personal opinion on the reason the designers used that pesky pressure limiting valve is thus this may be coloured by reading in past times !)
Back in the day when these cars came out most ordinary people did not go around locking their wheels up in the dry normally. But in the home country the value of good even braking under adverse conditions like snow, ice, rain, mud was considered important. So distributing the braking force between the four wheels under lighter applications was important and that was achieved by good weight distrubition and by the normal matching of the piston size to the expected wheel loads. It worked well for the average family punters who were the target market.
Then to prevent the rears locking up under high weight transfer in fast stops in the dry the valve cut the rear pressure increase at some point to keep the car from spinning out ! This valve was never looked at back in the day and the brakes worked well. But as the years went by they were usually found to be non operational due to lack of fluid changes/rust etc and possibly prevented much pressure getting to the back at all.
Jaahn

Mmm! - when I "emergency" brake-tested the demonstrator R10 back in the late sixties (see post #6), it was a new vehicle & had, therefore, a new valve. It locked fronts (only) in the dry. So did the (new)R8 1100 my mother bought at my request in 1965 (obviously I didn't persist to the point of flat-spotted tyres) & the (new)66 one that replaced it (which I still have & which was bought because I put the 65 one on its side after a wild night's drive).
I submit that "lovely when new but troublesome if not maintained properly" is a false hypothesis.

 

[harrisonati]

Mmm! - when I "emergency" brake-tested the demonstrator R10 back in the late sixties (see post #6), it was a new vehicle & had, therefore, a new valve. It locked fronts (only) in the dry. So did the (new)R8 1100 my mother bought at my request in 1965 (obviously I didn't persist to the point of flat-spotted tyres) & the (new)66 one that replaced it (which I still have & which was bought because I put the 65 one on its side after a wild night's drive).
I submit that "lovely when new but troublesome if not maintained properly" is a false hypothesis.

Could it have been a case of too high an initial rate of application of brakes car causing the locking the front wheels? A more gradual application allows weight transfer to take place before applying the final pressure.

 

[Greenpeace]

That's pretty much what I would have expected!

I checked the rear pressures which I'd set a couple of weeks ago to 25 psi and the LH one had dropped to 22 psi. Mmm....anyhoo I set them both at 28 psi, checked the fronts (which I'd set a few days ago to 24 psi) and they were still OK.
Went for another drive and the bit of initial understeer was gone, (I'm thinking the low rear tyre was causing that), and the mild oversteer at higher cornering speed was gone too. The car just goes where you point it, until the outside front tyre starts to break free.
Hard to believe that just putting narrower tyres on the front, removing the rear sway bar and fiddling with tyre pressures a little, have turned the handling from genuinely frightening, to safe and predictable, but there you go.

I was pretty sure there was a better car hiding in there somewhere after I read this.

 

[Greenpeace]

Going back to the original subject, this is what Autocar said in 1965 when comparing the boosted Gordini brakes to the standard R8 brakes.

 

[JohnW]

The full text is: Conventional wisdom in the era before limited slip diffs were commonly available was that you should concentrate roll stiffness at the non-driving end. Thus a front engined RWD car would have the front suspension very stiff in roll. The resultant understeer was mitigated by using negative camber on the front (and often extra castor, which helped in slow corners when steering angles were higher.) Period photos of racing Lotus Cortinas etc often showed the inside front wheel lifted off the road. Thus, the entire weight on the inside side of the car was available for traction of the rear driving wheel out of corners. In that era, 'conventional wisdom' of the motor sports inclined people was scathing of Austins and Standards with their rear roll bars. I think that you've done the right thing removing the rear roll bar!

I guess for the opposite with FWD, that's why track racing Fiat 128s always cocked up the inside rear wheel?

 

[JohnW]

Going back to the original subject, this is what Autocar said in 1965 when comparing the boosted Gordini brakes to the standard R8 brakes.

View attachment 229317

Funny, because the R8 brakes at low speed do not feel dead at all. When I first drove ours in 1973, I remember complaining that they felt terrible, with no sensitivity and heavy pedal pressures. Maybe seized callipers? I don't know. The main change I've made just happens to be throwing away the pressure limiting valve...

 

[Greenpeace]

Funny, because the R8 brakes at low speed do not feel dead at all. When I first drove ours in 1973, I remember complaining that they felt terrible, with no sensitivity and heavy pedal pressures. Maybe seized callipers? I don't know. The main change I've made just happens to be throwing away the pressure limiting valve...

I've no idea. I found the Autocar test on the standard R8 and they actually had two test cars supplied as well.

 

[Aln]

I am also a believer in removing the pressure limiting valves from rear engined Renaults. In all cases so far, the fronts still lock first if provoked in all conditions, even in my Alpine GTA Turbo.

 

[Andrew Watkins]

I have the unfashionable opinion that Renault got it pretty much right with their pressure limiting valves. In most cases, I think that if braking improves with the PL valves removed, then the valve was defective and not working properly! My R1090 Dauphine doesn't have a PL valve and I can lock both fronts and rears at various times, but rarely all four wheels at the same time. If I had later model with a troublesome PL valve, I would try to fix it, not remove it!
In any case, Renaults always had good braking systems! My experience with braking problems with cars of the Dauphine, R8, R10 era includes dealing with horrifically inadequate braking performance of the small Fords that I campaigned in Series Production racing in the mid 1960s. The most difficult was a 1500cc Cortina with front discs and rear drums - the rear axle would 'wind up' causing violent tramping. The rules didn't allow many changes to anything, but brake linings were 'free'. My fix was to use the hardest rear lining that I could find, then araldite lead from 6B pencils to the shoes ahead of the linings and in the rivet holes. I also would rub the rear friction surfaces with a 6B pencil before every race. That effectively 'knobbled' the rear brakes but made the car controllable under heavy braking. As suggested above, with a background in Holdens, Zephyrs, Falcons, small Fords etc, Renault braking systems were a revelation!

Easy to be unfashionable these days when you know what your talking about and rely on evidence.

That is just soooo passé

Andrew