Adjusting Vacuum brake?

[Malcolm Towrie]

I posted a while back about a Canadian MkII carrier with low compression on 4 cylinders and poor running. The distributor rebuild fixed the poor running, but I didn't set up the vacuum brake adjustment. I left the adjuster backed off, intending to adjust it when the carrier was driven, based on listening for ping as per the Ford service manual.

Well I took it for a drive and I noticed two things. I couldn't hear any ping in first or second gear with the gas pedal to the floor. I'm not sure if that was because of engine noise. And the carrier struggled to pull second gear when turning in soft dry dirt. By struggling, I mean the engine pulled cleanly and smoothly, but rpm dropped with gas pedal on the floor, like I was in too high a gear. I should say I have never driven a carrier before and I have no idea what to expect.

I assume the engine labouring while turning in second gear is not normal? I suppose this is due to the low compression, but I'm wondering if some of it is due to over-advanced ignition timing since the vacuum brake isn't doing any retarding under load. How do you adjust the vacuum brake in a carrier?

Malcolm

[Lynn Eades]

Hi Malcolm, I could get shot to pieces here but here goes.
You a not likely to hear the ping in a carrier. Too much track noise, fan noise etc.
Yes the carrier will labour while turning in second gear (depends on conditions. Soft is worse)
As a rule, all turns involving the brakes are executed in 1st or 2nd gear.
When you brake one side, immediately the other side has to turn twice as fast.

The vacuum brake should have just a small amount of drag because it stabilizes the cam (dampens out the "rattle about" of the points cam) which makes it fire evenly.(and when it's supposed to)
The dizzy was designed around 68 octane fuel, you are probably running fuel in the range of 91 octane. It probably won't ping anyhow, because of the modern fuel.
Lets see what others have to say.

[Malcolm Towrie]

Thanks, Lynn.

When you say carriers labour a bit turning on soft ground in second gear, do you mean even doing just a "track-twist" turn, or only when doing a "braked" turn? Seemed to me ours laboured in second even doing the track-twist turn.

Would it be correct to adjust the vacuum brake so it just contacts the disk at idle, which I can see by watching the timing light just start to retard? Because the vacuum at idle is up around 20", so at high loads, when the vacuum drops to near zero, the full spring tension will be braking the disk.

Malcolm

[Tony Smith]

Originally Posted by Malcolm Towrie

Would it be correct to adjust the vacuum brake so it just contacts the disk at idle, which I can see by watching the timing light just start to retard? Because the vacuum at idle is up around 20", so at high loads, when the vacuum drops to near zero, the full spring tension will be braking the disk.

Malcolm

That's about the right spot. An important thing to check is the condition of the leather brake pad. If the leather has gone dry and hard, or worn, or has ANY kind of lube contamination it won't have the same hold on the breaker plate, likewise if the edge of the plate has any rust or roughness, it will bind on the brake pad and give you bad timing.

[Lynn Eades]

Tony, were my comments about right?

[Tony Smith]

Originally Posted by Lynn Eades

The vacuum brake should have just a small amount of drag....

Originally Posted by Malcolm Towrie

Would it be correct to adjust the vacuum brake so it just contacts the disk at idle....

Originally Posted by Tony Smith

That's about the right spot.

Lynn, I think we're all in agreement!

[Malcolm Towrie]

Thanks, guys. I can see why this particular way of adjusting timing for engine load didn't catch on.

Just to confirm, does a carrier engine in good condition struggle doing a "track-twist" turn on soft, dry soil in second gear, or only when doing a "braked" turn?

Malcolm

[rob love]

Originally Posted by Malcolm Towrie

Thanks, guys. I can see why this particular way of adjusting timing for engine load didn't catch on.

Just to confirm, does a carrier engine in good condition struggle doing a "track-twist" turn on soft, dry soil in second gear, or only when doing a "braked" turn?

Malcolm

Track warp turns should be almost un-noticeable. By track warping, you are talking about only the first 90° turn of the wheel. Any turn beyond that will be very noticable in second.