| Author | Message | ||
     Martyn Paul Yet to post message Username: martynpaul Post Number: 1 Registered: 7-2013 |
Hello all, This is my first post so please excuse any breach of etiquette. My '97 Turbo R recently had a major service after being laid up for 18 months. Included was new transmission fluid and filter. When in D, the transmission seems to up-change properly although the change from third to fourth is a little woolly under power. The TCC seems to engage in fourth as small changes in throttle during cruise do not result in a marked change in rpm. The problem comes when lifting off the accelerator at speeds under 50 mph. The engine rpm drops immediately to idle and the car coasts. Over 50 mph the rpm stays put and slowly bleeds away as the car slows down. In 3rd or 2nd, lifting off the throttle results in the same phenomenon, although when the transmission is cold there is an attempt at engine braking at first and then the rpm drops to idle. I assumed the problem was something to do with the exchange of fluid, so the first thing was to check the level. I did this after a long run, with the car level, the engine running and in park. I found that the level was somewhat below the minimum line on the dipstick so I topped up to the hatched area with about half a litre of Dextron II fluid. It made no difference. I have researched the issue in the IETIS and online and there seems to be no one fault that could cause these symptoms. I have not yet taken the car back to the Bentley "expert" who had carried out the servicing, but when I do I will ask him if he can carry out a pressure test to determine what's going on. It seems strange that there is no "Check Gearbox" warning. It could be however that there are some stored fault codes that can be retrieved by connecting the Mastercheck gizmo. My own theory is that the filter has been incorrectly fitted and an o-ring is displaced which could cause poor pump suction at low engine speeds resulting in low pressure. Any ideas would be appreciated. Cheers, Martyn | ||
| Ernest Carty Experienced User Username: edcarty Post Number: 13 Registered: 12-2012 |
Hi Martyn It would appear that the problem does arise from the change in fluid/filter This so called Bentley EXPERT should have never sent out the car in this condition .The level in these boxes must always be kept to the MAX level you say you topped up to the min level using half a litre of Dexron 2 obviously this should not have been needed had the Expert done the job properly.With regard to the braking effect this should be achieved through change down from top to 3rd ,remember these boxes use a lock up device operated through the Torque converter which cuts in at about 50 MPH and you should notice a drop in RPM at this point,it would appear that because the service was not carried out correctly some internal damage may have been done to the transmission ie clutches and brake bands etc.I WOULD strongly recommend you contact this EXPERT and get him to rectify the problem at NO COST TO YOURSELF.In future use a different source for your servicing .Hope this helps somewhat as without actually driving the car it is a bit vague as to what exactly is happening as you do not say whether or not the up/down changes are taken place at the correct speeds and throttle positions. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 536 Registered: 6-2009 |
If you end up with the original service facility trying to absolve themselves of all responsibility, which is a distinct possibility, then the next step from a service perspective is to get the car to a reputable transmission shop. A big saving grace is that these cars have a transmission shared by millions of other GM vehicles and virtually any competent transmission shop is willing to take a look (even if they hesitate at first) once you make them aware of this fact. I will disagree, but just slightly, with Mr. Carty with regard to the fluid level. As long as you are somewhere in the area at or above MIN and at or below "MAX" you will be just fine. You can actually do more damage from the fluid foaming if above the MAX level than if it's ever so slightly below the MIN level. But that cross-hatched area is entirely within the zone of correct function. Still, I would try to have the fluid showing MAX when the car is hot and idling in "Park" on a level surface. Given that you have a 1997 model year car I have to believe you used Dexron-III (or a Dex/Merc variant formulated to a Dexron-III spec). Dexron-II, in all its variants (II, IID, IIE) were all out of production well before 1997 and your car would have had Dexron-III as its original fluid. I haven't seen any ATF formulated to any of the Dexron-II specs available for purchase for many years now. It is perfectly safe to use Dexron-VI, the current formulation, as well. GM, the "spec maker" and licensing agent, maintains that each progressive iteration of Dexron is fully backward compatible with prior iterations. Fluids made to the Dexron-III spec are still widely available, but GM no longer officially licenses to that specification. [The number jumped directly from III to VI, there were no IV nor V fluids.] Brian | ||
| Martin Taylor New User Username: martin_taylor Post Number: 5 Registered: 7-2013 |
These transmissions will fail in this way if the teeth to the governor shear off, mine did this after standing for some time and the lubrication in that area of the transmission must have dried out, the transmission behaved like it was in kickdown mode and free wheeled when I lifted off the accelerator. It is a 10$ part on the early transmissions at least. | ||
| Arthur F. Unregistered guest Posted From: 203.217.31.208 |
Could be the torque converter lock up clutch. These converters usually lock up in fourth around 70 to 80 kmh . (Message approved by david_gore) | ||
| Graham Burn Experienced User Username: graham Post Number: 12 Registered: 6-2013 |
Hi Martyn, just wondering if you got to the bottom of your problem as I get the same happening occasionally on my 1987 Turbo R, I put it down to the idle being so low there's not enough hydraulic pressure from the pump allowing the car to 'freewheel'? but if you found a fault I'd like to know. My car had a recon gearbox some time ago, can't remember when I've got the bill but before I got it so I assumed the box to be OK. Thanks Graham | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2872 Registered: 4-2003 |
Martyn, That is no problem. It is a feature. There is no way that engine braking can occur in fourth gear with a 4L80E. The overdrive unit has a roller (sometimes mistakenly called a sprag) one-way clutch for overdrive (fourth gear) and a conventional clutch for direct drive (3rd gear and below). When in fourth gear, ie overdrive, the one-way clutch only engages when driving. On overrun it freewheels. That's what a one-way clutch is supposed to do. There is no band to allow overrun engine braking in fourth gear. In third, the overdrive direct clutch (ie the one with clutch plates to lock the drum for the 1:1 ratio) engages. The other forward clutches are all engaged in third too, so you have engine braking. In second when held by the gear selector, a band locks the drum so you have engine braking then too. The Torque Converter Clutch TCC only engages with a steady throttle in fourth above 80km/h. It disengages whenever you touch the brake. However, if the transmission overheats, the TCC engages all the time in second, third and fourth. A thermistor in the transmission controls that via the ECU. The TCC does noy affect engine braking in fourth as the overdrive unit is freewheeling on overrun in that mode. RT. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2873 Registered: 4-2003 |
Graham, Your car has the 3L80 (THM400) transmission with no overdrive. Yours being a 1987 like mine was delivered overseas. No injected Turbo Rs were sold in Australia for the 1987 model year as the cat systems were still under development and not available until the KE3-Motronic injection of 1988-89. Yours probably has that incredible 2.28:1 final drive ratio like my 1987 Turbo R. Engine braking in third is only very slight. There is a hill on the motorway near Mittagong, New South Wales, where the police car waits at the bottom. The Turbo R will hold 115 in top (third) gear going down the hill but only just. That super-tall gearing allows only minimal braking as the torque converter allows the engine speed to drop somewhat. Annoyingly, my Continental R (4-speed 4L80E) would run away to 140 or so down the hill so I have to select third. That is because the transmission freewheels. Incidentally, the 4L80E in the Conti is a recent overhaul, and I found that the TCC had disintegrated. With the Conti’s special sprint-off-the-line 3.08:1 final drive, the gearing in fourth is almost identical to that of my Turbo R. That maintains a sky-high top speed whilst giving it the traffic light advantage over the Turbo R. Australian-spec 3-speed and 4-speed Turbo Rs, along with the Conti Rs, have the 2.69:1 final drive. In a 3-speeder that limits the top speed to just 240km/h. With time and a little downhill help, in Germany I regularly hit the 4,500RPM redline in my Turbo R, meaning a theoretical 270km/h, thanks to the 2.28:1 gearing. A few engine tweaks did no harm I may add. Not much use now that the car is in Australia though. RT. | ||
| Ernest Carty Experienced User Username: edcarty Post Number: 14 Registered: 12-2012 |
Richard ,If you read Martyns thread he says that his car is 97 Turbo r therefore it will be fitted with the 4L80E series Transmission this was standard throughout this series as the TMH400 was long gone. The only difference being that some cars were fitted with different Final Drive ratios dependant on Spec or Country .The TCC on this later transmission does indeed freewheel when in overun in 4Th gear as you have stated previously as you also stated that Engine braking only occours in 2ND and 3RD.With regard to Martin Taylors comment that the Governor could have failed it would be noticed in the up/down shift points being very much out of range so this is very doubtful in the 4L80E as this box does communicate via the ECU.I hope this clears up some misunderstand re Transmission fitments. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2874 Registered: 4-2003 |
Pretty much what I wrote. Martyn has a 4L80E like my Continental R which freewheels. Graham has a 3L80/TH400 as does my Turbo R which is a three-speeder which does not freewheel. Final drives are 3.08, 2.69 or 2.28. | ||
| Graham Burn Experienced User Username: graham Post Number: 13 Registered: 6-2013 |
Well I understood you Richard! Thanks for the info Graham PS I'm in the UK so have the tall back end  | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2876 Registered: 4-2003 |
Thanks, Graham. By the way, Martin T, there is no mechanical governor as such on the 4L80E (E for electric-electronic control). That was dropped when the electric-electronic control came with the four-speeders. Although most mechanicals are the same as on a 3L80, the governor function is done by the ECU with speed sensors at the front and rear of the transmission and a TPS. Likewise, the vacuum modulator is deleted in favour of the Throttle Position Sensor TPS (a linear potentiometer not to be confused with the on-off Throttle Position Switch TPS which does, among other things, kickdown on 1987-1992 3L80s) and a bunch of air pressure sensors. Throw in a microprocessor ECU, some thermistors, electric shift solenoid valves, and geeks loved the 4L80 E. Great stuff, but I fear that the older TH400/3L80 is far more reliable long-term in those areas. As an Electrical Engineer, dare I say that ? RT. |
