| Author | Message | ||
     Mark Aldridge Prolific User Username: mark_aldridge Post Number: 176 Registered: 10-2008 |
The temperature dropped to freezing a few nights ago, and the gearbox on my 1983 Mulsanne was reluctant to change up for about 200 metres after turning out of the drive and reluctant to change as normal for about a mile. Weather is now milder and it is OK. Gearbox oil and filter changed within last 1000 miles Dexron 3 oil. Suggestions ? or is the gearbox getting close to overhaul ? Mark | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 1112 Registered: 6-2009 |
Mark, The first thing I'd check is the vacuum modulator and the connections to it. Small leaks can develop in old hosing, particularly when its cold, only to "seal themselves up again" once things warm up a bit. It's a simple check in any case. Brian | ||
| Bob uk Unregistered guest Posted From: 94.197.122.78 |
Assuming that when the oil was changed that the sump wasn't full of bits of friction linings and the box was working fine before the oil change then because the gearbox is as tough as old boots then the gearbox is fine. Brian is correct about the module valve. It relys on vacuum to modulate gear changes along with the governor. When accelerating the vacuum is lower this delays the change up. The faster the governor turns on the box output shaft the higher the pressure sent to the valves. At a certain pressure the valve opens and directs fluid to a band cylinder or a clutch cylinder to engage another gear. The vacuum module when on low vacuum bleeds off this pressure which delays a gear change. If the rubber connecting tubes are dicky then low vacuum will occur at the module when it should be higher. To test the function of the module accelerate then lift off and the box should change up. To compensate for high altitudes the module has a bellows inside which adjusts the module should you wish to drive up mountains. Sometimes these modules will leak and allow the engine to suck out the gear oil. if it is suspected that the module diaphragm is leaking check inside the rubber vacuum pipe for oil it should be dry. Ford C3 box used to do this. The modIle pushes into the box and is clamped by one bolt. There is a short rod inside which falls out. It is a ten minute job to fit done quite few over the years. The module is available from autobox shops New and used. The module is round and fitted to the front right hand side just behind the converter bell housing. The small rubber pipe going up and forward is the vacuum hose. (Message approved by david_gore) | ||
| Jean-Pierre 'JP' Hilbert Experienced User Username: jphilbert Post Number: 14 Registered: 9-2013 |
I got myself an adjustable vacuum regulator, that solved 80% of my hard 1-2 shift. www. rostra.com part number 51-0020-00-00 http://www.rostratransmission.com/pdf/rostra-modulator-application-guide.pdf Give it a try! | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 3125 Registered: 4-2003 |
The ubiquitous el-cheapo red stripe and double red stripe modulators are reasonable compromises if you want to go aftermarket instead of genuine, but quite some tinkering is needed to achieve reasonable changes and characteristics to your individual satisfaction. Unless you live in an alpine region or in the tropics where the weather changes are acute, the lack of altitude compensation (i.e. ambient air pressure compensation) on those cheap modulators will not cause too many problems. They do have a reputation for being cheap and nasty, but in reality they are not too bad. At $15 you get what you pay for. RT. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.93 |
Even when going up mountains maybe a delayed change up is better on steep apline passes. At sea level vacuum with throttle closed is about 21 inches hg. At 5000ft its about 19 inches. The missing barometer bit is not a problem. At £8 each even if it only lasts 20,000 miles is good value. It's so easy to change you could carry a spare. For vacuum pipe I use diesel injector leak off pipe. The stuff I get from the diesel shop has cotton braided covering and looks very smart, and of course completely impervious to oil and under bonnet temperatures. (Message approved by david_gore) | ||
| Mark Aldridge Prolific User Username: mark_aldridge Post Number: 177 Registered: 10-2008 |
Thanks all, we will check the vac unit tomorrow, weather permitting and also the autotrans overhaul shop has suggested removing the governor assembly and washing it out in petrol or brake cleaner . I wish the vac units were £8 in the UK; nearer £80 here ! Mark | ||
| Jean-Pierre 'JP' Hilbert Experienced User Username: jphilbert Post Number: 16 Registered: 9-2013 |
Bob, would you be able to post a pic of this tool you constructed? | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 3126 Registered: 4-2003 |
Fantastic modification for those skinny ones who lie under the car and gaze at the 3L80 transmission daily. Ha ha. Governor. You can buy a kit to tweak these if you have the patience. My Turbo R was upshifting at 3900 rpm, that is just 95km/h 1-2, so I kitted it to change at 4400. It took ages to select the correct weights with many iterations, but the end result is excellent. With the 2.28:1 final drive, the upshifts are 110km/h 1-2 and 180km/h 2-3 unless you hold it manually to go faster. Nice. You know when you hit the 110km/h speed limit in Australia because the Turbo R shifts up from first to second gear. R. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.72 |
I sometimes use 2 position around town on the hilly bits and the car goes with great aplomb no sweat. I been in a turbo where the driver had it locked in 2 and very impressive. Most drivers of autos have had no training in autobox cars and came from manual cars. The UK system is that if you pass on an auto then you can only drive auto cars. If you take manual then it covers both. I have shown a few mates how to get the best from an autobox and they were surprised at how much faster the car is and how to use the gas pedal to get upward changes. I use the gas pedal to hold second to 30mph then lift off and the box shifts to top for waft mode. Allowing higher revs makes the converter to go high ratio. This means that fuel consumption is about the same. About 40 mph my engine is spinning over at 1500 rpm in top with lots of torque available. The engine is dead silent. At the air con course they also used the same stuff for the various vacuum actuators because the oem stuff most use is not very good and goes stiff, and overtime one is remove to check whatever they split. Which completly messes up the flaps etc. My jeep has a vacuum system for the charcoal canister map sensor fuel pressure thingy. Which was leaky. So I replumbed in the leak off pipe stuff no more problems 6 years. Also the vents for the SU pumps. It is actual fuel rated hose so also carb overflow pipes. What special tool. (Message approved by david_gore) | ||
| Bob uk Unregistered guest Posted From: 94.197.122.90 |
Mark if the vacuum pipe is dry then the module is fine. It's a simple diaphragm with a spring that cannot really fail to work. The Ford ones still worked even with a dodgy diaphragm. I once saw a module that had a rust hole in it. Which was immediately obvious. Used modules are ok to use. £80 sounds wrong because this module is very common try jaguar. I would try the car again because it is possible for a valve spool to be jammed with a microscopic bit of dirt which has now cleared it self. If not then the governor can be removed without taking the gearbox out. The governor is the best place to start should the problem persist and the module vacuum is good and working. To do a proper job the pressure gauges are needed to check the governor pressure. The gearbox shop will have the pressures and equipment to measure. (Message approved by david_gore) | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 3127 Registered: 4-2003 |
Bob, you have a high-revver with a top speed of barely 200 thanks to that 3.08 rear axle. My Conti R has the 4L80 transmission and lumbers along at 1600 rpm for a road speed of 100 in overdrive (same 3.08:1 axle as yours as my Conti has the sporty gearing) with the converter locked. Top speed in first is the same in the Conti as on a Silver Shadow - a crappy 85, but at least the four-speed 4L80E (it’s a 3L80 with an overdrive strapped to its rear) allows a reasonable top speed at last. 2.28:1 final drive and 110+ in first gear on the Turbo R is far more fun. RT. | ||
| Mark Aldridge Prolific User Username: mark_aldridge Post Number: 178 Registered: 10-2008 |
Removed the pipe from the Vac unit, and there is a restrictor slotted in between the steel pipe and the vac unit. The rubber pipe covering the joint between the units is I suspect original. The problem was the restrictor was blocked with oily deposit which presumably has condensed in the vac steel pipe over the years. Clearing this seems to have resolved the gearchange issue. Mark | ||
| Bob uk Unregistered guest Posted From: 94.197.122.82 |
26mph per 1000rpm. That used to be a higher than normal ratio. cars usually had 20 mph per 1000 30 mph being 1500 rpm which is just right. New stuff in top gear can be as high as 40 mph per 1000. 6 speed gearbox. In manual cars around Town I usually use up to 3rd. This gives easy running at 30 mph. And one is less likely to exceed the speed limit. My jeep is 4 speed with lock up converter. Top gear starts at 38 mph and lock up 46 mph. In Town it stays in third. Top is like an over drive. I will say the gearbox is quite smooth. It's a straight 4 litre six so it pulls quite well. I don't Labour engines because it wastes fuel and makes the car feel unresponsive. (Message approved by david_gore) | ||
| Bob uk Unregistered guest Posted From: 94.197.122.82 |
Panic over. Cost no money at all. I didn't know it had a restrictor. I thought the size of the pipe did that. Interesting maybe one can alter change ups by playing about with a restrictor. My Jeep has a sport button. This delays the change ups a bit. Maybe if a solenoid valve was fitted to the vacuum line one could have a sport button. There again just put it in 2. (Message approved by david_gore) | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 3128 Registered: 4-2003 |
Turbo R, 2.28:1 final drive, 60km/h (38mph) less maybe 2.5% converter slip in top (3rd) gear per 1,000 RPM. Conti R 3.08 final drive, 60km/h (38mph) in 4th (overdrive) gear with the converter locked. It locks above 80 on light throttle and always above 200km/h. Silver Shadow and early non-Turbo SZs (3.08:1) in 3rd: : 45km/h/(28MPH) less 2.5% converter slip per 1,000RPM – same as a performance-spec (3.08:1) Conti R held in 3rd.. | ||
| Bob uk Unregistered guest Posted From: 94.197.122.87 |
A higher final drive ratio also increases the gap between the intermediate gear ratios. Because of the torque converter ratio of between 2.1 to 11 and 1 to 1 I think of each ratio being variable. Like cvt. Some industrial vehicles have a converter and one gear for forward and reverse. It works well with large diesels that have low top speeds like quarry trucks. Some of these vehicles would be dangerous over 20 mph so extra gears is pointless. More and more cars are autos and I have driven things like jag xj6 with manual boxes and the auto version always drives nicer. The off line acceleration maybe slower on an auto but in the real world grand prix starts from traffic lights is a sure way to have an accident. Its from 20mph to say 80 mph where the action is. Some cars don't have good 0 to 60 times but the midrange is good. My jeep is like that, lock it in 3rd and 2500rpm and it goes fast. 190bhp and 1700kgs. Over 100 bhp per ton. I will give Chrysler one thing they make nice straight sixes and auto 4x4 boxes. it has high and low in 4 and 2 wheel drive. On road either 2 or 4 can be used. Off road low locks the centre diff and I can lock the centre diff in high but not on tarmac. Plus lsd rear diff. All it needs is better on road brakes. They will stop the plot but lack the delicacy of my Shadow. In the slippery stuff the jeep does as well as a Range Rover. Plus I can run in 2 wheel drive thus using less go go juice. I don't bother with manuals. The maintenance costs are the same. And nowadays kits are available with DVDs for autoboxes thus diy is easier. (Message approved by david_gore) |
