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Thread ID: 70604	2006-07-09 05:47:00	Automatic transmission	Lizard (2409)	PC World Chat

Post ID	Timestamp	Content	User
469633	2006-07-09 22:35:00	I've had both. I'd have to say autos are probably the sensible option in Auckland. All that stop start, killed the clutch on my Triumph.	pctek (84)
469634	2006-07-09 22:57:00	How dose the park mode in an auto work. Dose it put some sort of pin into something and locks everything up ?? Trevor :) Yes, quite well described. It basically drops a "peg in a hole", more correctly a pawl into a notch. en.wikipedia.org	godfather (25)
469635	2006-07-09 22:59:00	Was I baited? :confused: Could you detect a slight aroma of sardines, Joe?	godfather (25)
469636	2006-07-10 02:17:00	How dose the park mode in an auto work . Dose it put some sort of pin into something and locks everything up ?? Trevor :) Modern transmissions do not use pins and I cannot say that I have ever seen any using them either . . . . . . they use a cogged wheel and a matching pawl that drops into a slot to hold the output shaft . . . . allowing the drive wheels to be held from turning . The parts are very tough (case hardened to Rockwell 45-55 "C" scale) and they don't usually ever require replacement at overhaul time . Files and hacksaws just bounce on them and won't cut . Here's a typical parking pawl arrangement, this is a C4 Ford auto transmission: . imagef1 . net . nz/files/ParkingPawlAssembly . jpg" target="_blank">www . imagef1 . net . nz The inner splined hole matches splines where the output shaft runs through it to the driveshaft . This is typically the last internal part in the tailcase of the transmission, except for the rear bushing, seal and output yoke to the u-joint . Transfer cases for 4-wheel drive would be bolted on here at this point if it was so equipped . Here's another shot of one you might recognize in NZ shops . . it's a fairly universal transmission we call a ZF . . . You can see in the pix the blue from the heat treating to harden the hub and pawl; not very robust, but cheap to build for Jaguars, LandRovers and some UK econoboxes: . imagef1 . net . nz/files/ZF_pawl_assy . jpg" target="_blank">www . imagef1 . net . nz Notice with both of those parking pawls and hubs that the chance of getting INTO park while in motion is impossible . You will make a lot of noise trying it . . . and quite frankly, I have never heard of one getting damaged by doing that . It just cannot get into the slots on the hub if they are moving too fast . One saving grace is that the pawl itself is spring-loaded and will not be forced into the hub even though the shifter and linkage tries to put it in . It will just bounce until the speed gets 'way below a walking speed . In the days of building old MOPAR (Chrysler) Torqueflites, the old 727A and 904, when the governor got stuck right after a rebuild (and they always did for some reason) we'd just take the misbehaving vehicle out for a short test drive without the customer along, and get to about 35 mph, and then shove the gearshift into park to rattle the governor weights loose . . . it always worked . Whilst we are talking auto transmissions, here's a shot of a band from inside the trans case: . imagef1 . net . nz/files/200Band . jpg" target="_blank">www . imagef1 . net . nz Modern transmissions do not have band adjustment provisions . Here's an input drum from a THM7004R/GM's 4-speed with overdrive auto, and lock up torque convertor . All the horsepower of the engine goes thru here right after the torque convertor . This is a stamped steel assy with a few spin-welded parts . These don't fail, but they look frail . . . looks are deceiving! This is one of the more complicated input drum/shaft assemblies with multiple clutches and pistons to activate it . . . . but they work well: . imagef1 . net . nz/files/THM7004R_Input_drum . jpg" target="_blank">www . imagef1 . net . nz And here's a blow-up of how a very simple direct drum and clutches looks from a late model PowerGlide, a 2-speed aluminum transmission capable of 800 to 1,000 horsepower when built right . . . the friction plates are alternated with the steel flat plates, and there is never any slippage allowed . . . . they die very fast that way: [the blue stuff is assembly lube . . . blue to make it easier to differentiate from the red of the fluid so a small leak can be spotted after building] . imagef1 . net . nz/files/PG_Drum_&_Pack . jpg" target="_blank">www . imagef1 . net . nz Here's a THM 350-C that I recently built: . imagef1 . net . nz/files/th350-1 . jpg" target="_blank">www . imagef1 . net . nz Hope this helps clear things up .	SurferJoe46 (51)
469637	2006-07-10 03:51:00	Modern transmissions do not use pins and I cannot say that I have ever seen any using them either . . . . . . they use a cogged wheel and a matching pawl that drops into a slot to hold the output shaft . . . . allowing the drive wheels to be held from turning . The parts are very tough (case hardened to Rockwell 45-55 "C" scale) and they don't usually ever require replacement at overhaul time . Files and hacksaws just bounce on them and won't cut . Here's a typical parking pawl arrangement, this is a C4 Ford auto transmission: . imagef1 . net . nz/files/ParkingPawlAssembly . jpg" target="_blank">www . imagef1 . net . nz The inner splined hole matches splines where the output shaft runs through it to the driveshaft . This is typically the last internal part in the tailcase of the transmission, except for the rear bushing, seal and output yoke to the u-joint . Transfer cases for 4-wheel drive would be bolted on here at this point if it was so equipped . Here's another shot of one you might recognize in NZ shops . . it's a fairly universal transmission we call a ZF . . . You can see in the pix the blue from the heat treating to harden the hub and pawl; not very robust, but cheap to build for Jaguars, LandRovers and some UK econoboxes: . imagef1 . net . nz/files/ZF_pawl_assy . jpg" target="_blank">www . imagef1 . net . nz Notice with both of those parking pawls and hubs that the chance of getting INTO park while in motion is impossible . You will make a lot of noise trying it . . . and quite frankly, I have never heard of one getting damaged by doing that . It just cannot get into the slots on the hub if they are moving too fast . One saving grace is that the pawl itself is spring-loaded and will not be forced into the hub even though the shifter and linkage tries to put it in . It will just bounce until the speed gets 'way below a walking speed . In the days of building old MOPAR (Chrysler) Torqueflites, the old 727A and 904, when the governor got stuck right after a rebuild (and they always did for some reason) we'd just take the misbehaving vehicle out for a short test drive without the customer along, and get to about 35 mph, and then shove the gearshift into park to rattle the governor weights loose . . . it always worked . Whilst we are talking auto transmissions, here's a shot of a band from inside the trans case: . imagef1 . net . nz/files/200Band . jpg" target="_blank">www . imagef1 . net . nz Modern transmissions do not have band adjustment provisions . Here's an input drum from a THM7004R/GM's 4-speed with overdrive auto, and lock up torque convertor . All the horsepower of the engine goes thru here right after the torque convertor . This is a stamped steel assy with a few spin-welded parts . These don't fail, but they look frail . . . looks are deceiving! This is one of the more complicated input drum/shaft assemblies with multiple clutches and pistons to activate it . . . . but they work well: . imagef1 . net . nz/files/THM7004R_Input_drum . jpg" target="_blank">www . imagef1 . net . nz And here's a blow-up of how a very simple direct drum and clutches looks from a late model PowerGlide, a 2-speed aluminum transmission capable of 800 to 1,000 horsepower when built right . . . the friction plates are alternated with the steel flat plates, and there is never any slippage allowed . . . . they die very fast that way: [the blue stuff is assembly lube . . . blue to make it easier to differentiate from the red of the fluid so a small leak can be spotted after building] . imagef1 . net . nz/files/PG_Drum_&_Pack . jpg" target="_blank">www . imagef1 . net . nz Here's a THM 350-C that I recently built: . imagef1 . net . nz/files/th350-1 . jpg" target="_blank">www . imagef1 . net . nz Hope this helps clear things up . As always, very interesting - thanks for the info, Joe . The pics make it pretty clear how the pawl and notch work - but here's an idle question: for all it's hardening, what would be the maximum degree of incline you would leave an Auto in "Park" without the handbrake on? Cheers Lizard	Lizard (2409)
469638	2006-07-10 03:56:00	Echo the same thanks Joe, that's highly educational . My wife did try selecting Park when cruising to a stop in our very first Auto, and it made a hell of a noise before finally "engaging" when it did stop very abruptly! I would doubt that there is a hard-and-fast answer to the incline question Lizard, as the car weight would be a major factor in the matter . But I would not leave it in park on any incline without the handbrake on .	godfather (25)
469639	2006-07-10 04:10:00	I have been intrigued by this correspondence. In 1967 we lived in Seattle - a city that makes Dunedin look pretty flat. Many stop signs were on very hilly roads and I was advised to get an automatic that stopped the car from going backwards when stationary - without using PARK. I had a Dodge charger and it did just that. I wonder now if this is a design just not available anymore. Anyway living in Christchurch I don't need it. Tom	Thomas01 (317)
469640	2006-07-10 05:06:00	As always, very interesting - thanks for the info, Joe . The pics make it pretty clear how the pawl and notch work - but here's an idle question: for all it's hardening, what would be the maximum degree of incline you would leave an Auto in "Park" without the handbrake on? Cheers Lizard If you look closely at either of the two parking pawls, you'll see a "cam" in the form or a "bulge" in the activating rod that gets between the pawl/arm and the plate that it (the rod/cam) rides upon . Here's what happens: The gear selector, operated by the vehicle operator is forced into the narrow area that will push the pawl into the hub notch . If there is a non-notched area that the pawl falls on to, and the vehicle makes no motion because the parking brake has been set, then the pawl is just happy to sit there until there is a notch available to it should the driveshaft turn a little . The cam/bulge-part is spring loaded and has the ability to jump into a notch position at the next opportunity . If the vehicle rolls ever so slightly, one may hear the "click" as the pawl falls into a notch . This is why it is adviseable to always set the parking brake first . In actuality . . . the parking brake is for parking . . . the "Park" position of the transmission is just a safety device should the brake fail or not hold . If you only use the "Park" on the transmission and don't at least back it up with the parking brake, you run the risk of internal transmission damage in the event another vehicle makes hard enough contact while yours is parked . I have seen cases cracked from this sort of impact, and there are a number of other things that can be bent into the wrong position making "Park" questionable at the least from that point on . Now as to the power of "park" on the transmission: Most vehicles are capable of dragging the drive wheels on dry pavement while in park via the transmission . I don't think there is any need to fear the holding authority of it, at least not on inclines which a human can get into and out of the vehicle and remain standing .	SurferJoe46 (51)
469641	2006-07-10 05:11:00	Yeah thanks for the info Surferjoe46 and Godfather. Great reading. Trevor :)	Trev (427)
469642	2006-07-10 05:17:00	Being a belt&braces type when it comes to actual parking, rather than intersection stops, I always use the handbrake as well as Park . . . even on the flat . I guess old manual habits die hard . . . But while I'm in a "car thread," maybe one of you knowledgeables can answer a question about my Japanese import Subaru Legacy 2 . 00 wagon? . There are several Legacy models & the handbook (I got the English translation) covers them all, which can be confusing . But the question isn't technical - just curiosity . Mine is a TS-R . Does anyone know what those letters stand for? Edit: I see Joe has confirmed (while I was thinking ) that my belt-&-braces parking isn't overkill after all . Thanks, Joe .	Laura (43)
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