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1951 Pontiac Chieftain


PhilA
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Recieved a pair of new old stock tail light lenses in the mail. They're in great shape. Half an hour in the ultrasonic bath got them nice and clean.

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Bright, compared to the old ones.

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They look nice in the sun and the reflectiors work well, too.

Hopefully that'll reduce the number of people looking to drive into the back end of the car when I'm slowing down.

 

Phil

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5 hours ago, hairnet said:

70s rayodot in the back window ftw

I would but Raydyot never sold stuff here.

I could get an old Grote light for the window. I need to run wire for a single brake light to the back from the switch.

 

Phil

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2 hours ago, PhilA said:

I would but Raydyot never sold stuff here.

Phil

:D

it was meant as a joke - you know the ones i mean they looked square but werent quite and the ribbed lens i think?

used to see bangers using them (fek im old) - in no way can your car be called a banger :)

 

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9 minutes ago, hairnet said:

:D

it was meant as a joke - you know the ones i mean they looked square but werent quite and the ribbed lens i think?

used to see bangers using them (fek im old) - in no way can your car be called a banger :)

 

I do, they were sold as fog lights.

Keeping an eye open for suitable ones- typically ones from the era are quite expensive.

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  • 4 weeks later...

Went out last night to get a chocolate malt. 

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On the way home, I pushed on the brake pedal to turn into this street and the pedal hit the carpet. I drove the rest of the way using the handbrake, and upon parking up there was the unmistakeable smell of DOT3 under the car and a small pool. It was too dark then so this morning I jacked the car up to investigate.

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Found the culprit, on full suspension compression the fuel line was interfering with the brake line. It went pop (fuel line is ok, it was rubbing over a long edge versus short edge of the brake line there).

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Discovered the new exhaust managed to hit the only place there's a brake pipe too. 

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So two for two, rerouted a new pipe to avoid both places.

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Bled up and tested. Múy bien.

 

Phil

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  • 2 weeks later...
  • 4 weeks later...

Alrighty, where were we? Oh yes, just driving about and enjoying the car.

However, the gearbox is acting up again so I need to pull the valve block off (again) after having done done research. There's a ridge that wears in on the narrow part of the valve stem which causes the 1-2 valve to hang up.

I'm going to have a go at removing that and getting the valves to shuttle better again.

Phil

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I took the valve block off.

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Cleaned it and made sure the valves operate correctly.

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Went for a drive. Cold it's much better. Hot, still the same old nonsense.

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12 hours ago, PhilA said:

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I took the valve block off.

 

Cleaned it and made sure the valves operate correctly.

 

Went for a drive. Cold it's much better. Hot, still the same old nonsense.

I’m sure it’s a PITA for you, but I’m certain you’ll fix it.
It does make very interesting reading for us though. 

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4 hours ago, Jenson Velcro said:

I’m sure it’s a PITA for you, but I’m certain you’ll fix it.
It does make very interesting reading for us though. 

It feels like one valve isn't going back to where it should rest. Trouble is, all 9 of the valve shuttles were moving fine so I'm not sure what the deal is.

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A surprise box arrived.

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A gift of reversing lights! Proper guide ones, for the car.

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A bit fusty with the old, burned out 6V bulbs in still.

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Cleaned them up.

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A comparison between the correct ones and the ones that were fitted.

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Those look better.

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Nice and bright, too. They need new foam rubber bases made up because the Chevrolet ones they came with make them sit at a goofy angle.

Phil

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After having done about 50 miles in it today, doing the valves makes the most noticeable difference to the running. At 45 (pretty much bang on 2000 rpm) it's near silent and progression is made deftly.

In other news I'm now pretty sure I've got something sticking in the throttle modulator circuit on the gearbox to cause the gears to act weird.
Mind you, twice today it changed gears perfectly, through all 4 from a standing start. The throttle modulator is meant to do 2 things: First it modulates the line pressure going to the servos and clutches, making a full throttle gear change much more violent and positive than one at light throttle. That is a simple bleed valve that's opened.
Second it changes the road speed at which the gears change, by putting part of the bleed pressure behind 3 pistons that boost the gear change springs.

So, a catch up on that- the governor spins with road speed, and increases pressure behind the 3 main gear change pistons. Each has a spring (or springs) which are each harder to compress than the last, meaning as road speed increases, pressure against the springs rises, the weak spring is overcome and the valve shuttles, causing the gears to change to 2nd. Then again to 3rd as the second valve shuttles, and then finally 4th. The valves are prevented from shuttling also by the pistons which have force in proportion to gas pedal position behind them meaning a higher road speed pressure is required to shuttle them if the gas pedal is pressed down.

So, the incorrect behavior is thus:
First gear will hold until 3rd gear engages, often missing 2nd or engaging it very briefly. 4th then will not engage until high road speed is achieved. Sometimes releasing the gas pedal makes it shift, other times not and it'll hang in 3rd.
As road speed decreases, it'll sometimes go 4-3-1 and then suddenly to 2 with quite a jerk.
Reverse often engages the parking pawl with the engine running.

Things to bear in mind, the throttle modulator piston is not sprung. It is only returned by hydraulic pressure against the lever arm that actuates it.
There's a secondary shuttle for the line pressure modulator.


Either one of the pistons that push against the gear change valves is sticking open and preventing correct movement or the throttle modulator valve is acting janky.

The throttle modulator valve has been recipient of minimal attention because it's in the top half of the valve block.

I think I'll start there, so perhaps this weekend if the weather allows I'll drop the oil and pull the valve block off again and check the modulator valve assembly in great detail.

It's proven it can change smoothly and correctly. It just needs to do it more often!

Phil

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I find this thread and your persistence with getting the gearbox to work inspiring - I’d have launched the whole lot across the garage in frustration by now. Also fascinating to see how an automatic gearbox works, I’d just assumed it was voodoo and black magic, but your explanations actually make it sounds reasonably simple*….

Hope that when you split the modulator valve there is something obviously fixable! 

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Nicely explained.  Think a lot of folks get scared off by things like this because they look complicated - and they are.  However they're not anywhere near as scary if you take the time to do your research and learn what you're looking at.  The big picture diagnosis involving understanding how the system actually works is great to see too.

 

I really need to try to write up a similarly understandable explanation of how the fuel mixture is controlled (particularly during warmup) in the K-Jetronic system as so many people seem to think that works purely based on witchcraft...and a lot of the write ups I've seen almost look to have been deliberately written to make it sound as complicated as possible...when it really is a pretty simple system.

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5 hours ago, Zelandeth said:

Nicely explained.  

Like you say with the K-Jetronic system, the overall concept is fairly straightforward (inject fuel at a rate to achieve a clean burn per engine speed) plus all the other things the carburetor had to do (acceleration enrichment, cold start enrichment, and so on).

The way it achieves that, via valves and pressure regulation, bimetallic heaters and mechanical timing devices is what people are scared of, because those bits aren't immediately visible, don't really come apart nor do they come with a good explanation (saying that, there's a few good explanations on the Internet that I found for the system).

The same applies to this- the concept of epicyclic gears is fairly straightforward once you realize what happens when the various parts of them are forced stopped, and just how the gearbox achieves that, and how, in this case the (not the Simpson 3-speed common-ring design) three gearsets interact. 

Ultimately, with some valves and stuff you could computer-control this gearbox electronically without much difficulty. The most complex part would be to get the 2-3 shift smooth. Like the K-Jetronic system, limited feedback of post-process is what determines how well the system can work. The inclusion of position sensors in the gearbox and closed-loop knock and oxygen sensing in the K-Jetronic would bring them well into line with any modern system (within mechanical capability). 

 

All good fun learning about it, though. 

 

Phil

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13 minutes ago, PhilA said:

The same applies to this- the concept of epicyclic gears is fairly straightforward once you realize what happens when the various parts of them are forced stopped, and just how the gearbox achieves that, and how, in this case the (not the Simpson 3-speed common-ring design) three gearsets interact. 

 

giphy.gif

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9am, 30C. Time to work on the car.

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Drained the catch pan of the oil from last time. Bit grubby.

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Drained this lot down and pulled the valve body. I focused more on the top half and the throttle modulator circuit. Ultrasonic bath, thoroughly cleaned and all the shuttles polished and checked for movement.

Put it all together and went for a road test.

It no longer engages the parking pawl when put into reverse with the engine running.

It doesn't drop to 1st gear now from 3rd when slowing down to turn and gently accelerating (would go 4-3-1-2-1 before).

Occasionally sticks in first but can now be persuaded to change gently to 2nd by tapping the throttle most of the time.

 

Verdict: imperfect but better

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Ugh. It got even more warm. Sun was baking my legs putting the valves back in, taking it out was good because that side of the car was in the shade.

 

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Put some oil thickener in and went did a test drive. A little better in the heat- though before coming to a halt, a brief full throttle application in 4th appears to clear it up and causes it to cycle down through the gears correctly, and then pull away after having been stopped correctly also.

Stopped for an old fashioned cherry coke, which was much appreciated in this heat.

 

Phil

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