| Author | Message | ||||
     Patrick Francis Frequent User Username: jackpot Post Number: 328 Registered: 11-2016 |
Hi All again Wishing you are all safe and well. My 1974 Silver Shadow, SRH 17968 has the 3 speed gearbox which has always used Dexron oil. Over time this has gone from Dexron to Dexron2 and now to Dexron3 without any issues. I have done a bit of research and have discovered the diffrence between normal and Dexron oil etc. The question I have is that my gearbox goes into gear very well and very smoothly, both into D and into R, when the car has just been started even with the revs up high due to the automatic choke. still being on. But when she has warmed up, she becomes very slightly cluncky going from N into D, but more so into R. This makes me think that the gearbox works more smoothly if the oil is slighlty thicker, but there is no option of choosing a thicker or thinner Dexron oil, as we can with engine oil viscosity. Has anyone experienced the same thing? Does anyone have any opinions or suggestions on it? Thanks | ||||
| Larry Kavanagh Frequent User Username: shadow_11 Post Number: 613 Registered: 05-2016 |
Hi Patrick, I have three ideas regarding the cause of your clunky gear selection when the engine is warm compared to the smoother gear selection when the engine is still relatively cold and all these theories could well be wrong: 1) The ATF level is too high causing too much pressure when the fluid expands as it heats up and/or 2) Your radiator fins may be clogged and/or your viscous fan might be worn out which would reduce the radiators cooling effect on the ATF causing the transmission oil to overheat. The ATF circulates through the bottom portion of the coolant radiator. This would be more apparent if the car is idling in situ rather than being driven on the road when air would be pushed through the radiator. If this is the case you should notice your engine temperature rising higher than usual when the engine is running while the car is stopped and 3) Your engine revs may be set a little too high which would cause the gear selection to be more clunky especially when the ATF is hot. | ||||
| Larry Kavanagh Frequent User Username: shadow_11 Post Number: 614 Registered: 05-2016 |
then of course there's the obvious possibility that the ATF and filter may be due a change. | ||||
| Patrick Francis Frequent User Username: jackpot Post Number: 330 Registered: 11-2016 |
Hi Larry Thanks for that, but all points are good. I change oil and filter on the gearbox every 5 years or so, last change 6 months ago, and used a good Castrol Dexron3. ATF level is good. Viscous coupling new 18 months ago and works very well. Also checked and cleaned and serviced all rads when I did this, including the little pipe that cools the steering fluid. Engine idles at 700ish when warm - but a lot higher when cold and gear changes are smooth as silk with thicker colder oil...... | ||||
| Martin Taylor Experienced User Username: martin_taylor Post Number: 180 Registered: 07-2013 |
When the oil is cold it takes longer to go through the selector valve and engage the clutch in the gearbox so there will always be a difference. Your idle should be 600, a little higher when A/C is on if a compensator is fitted. Soft engine mounts or diff mounts can cause such issues as the torque throws everything in the other direction when reverse is selected. Get someone to move the gear lever for you and check to see how much movement you have in all the mounts etc | ||||
| Patrick Ryan Grand Master Username: patrick_r Post Number: 2215 Registered: 04-2016 |
Hi Patrick, My 72 Shadow SRH12255 had exactly the same issue. At high RPM with the choke on, it just slipped beautifully into gear, D or R. A problem with the vacuum supply to the modulator, was an issue, and a newer type of modulator was fitted. Problem solved. I can’t remember exactly what modulator was fitted, plus all paper work went with the car when I sold it. Mine was sorted by the local auto trans specialist. But any auto trans specialist who knows the very typical GM Turbo Hydro 400 fitted to these cars will sort it immediately. . | ||||
| David Gore Moderator Username: david_gore Post Number: 3655 Registered: 04-2003 |
Re the GM Turbo 400 - don't overlook the fact RRMC had these transmissions modified from the normal GM specification by the fitting of a "wave" clutch plate to allow some "slip" when the clutch activated to give a "smooth" gear engagement commensurate with Rolls-Royce standards. The downside was the clutch plates had a life of around 95,000 miles before they had to be replaced due to noticeable slippage and "slurred" gear changes. | ||||
| Patrick Francis Frequent User Username: jackpot Post Number: 331 Registered: 11-2016 |
Thank you all - very interesting information. I’ll be having a look over the next days and keep you updated. Modulator vacuum pipe probably first stop. | ||||
| felipe heuser Experienced User Username: felipe Post Number: 98 Registered: 07-2017 |
I always thought engaging a gear when revs are high would damage the transmission; hence always wait until warm with normal idling... | ||||
| Patrick Ryan Grand Master Username: patrick_r Post Number: 2219 Registered: 04-2016 |
Felipe, My car slid into gear so silky smooth at high idle forward or reverse. It was amazing. Just disappointing when it was hot it would bang horribly into gear. | ||||
| David Gore Moderator Username: david_gore Post Number: 3658 Registered: 04-2003 |
Patrick, This is not normal - I would suspect a sticking valve spool in the valve body for some reason when the transmission is hot. Another possibility could be a failed O-ring on the top of the fluid pick-up tube from the fluid pan. I will have to dig out my T400 overhaul book to see if you can remove the valve body after removing the oil pan without having to drop the entire. transmission. Replacing the O-ring is a simple but messy job after removing the full pan unless you have fitted an after-market drain plug [highly recommended].  | ||||
| Patrick Francis Frequent User Username: jackpot Post Number: 332 Registered: 11-2016 |
Thanks Daviid - I’d appreciate that. | ||||
| David Gore Moderator Username: david_gore Post Number: 3659 Registered: 04-2003 |
Patrick, Have attached a copy of the B&M Guide to rebuilding the Turbo 400 Automatic Transmission - this involves removal of the transmission from the vehicle however it also covers strip down and rebuilding the individual components after they have been removed from the transmission. There is a good guide to possible causes of transmission problems on pages 24 and 25 plus a list of tools and parts needed on page 26. I have also enclosed Section T from Workshop Manual TSD2476 and refer you to pages 143 to 308 which covers the Turbo 400 3 speed torque convertor transmission. Unfortunately almost 25 years have elapsed since I overhauled the T400 transmission and my memory is hazy on the details and I cannot rely on it to advise you in more detail.
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| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2286 Registered: 09-2004 |
Nothing that a good workout will cure. That's the rolling done with the roller. LPG running well.  | ||||
| Patrick Francis Frequent User Username: jackpot Post Number: 333 Registered: 11-2016 |
Hi David Thanks for those. Things are not bad enough to delve into frightening territory yet, but I have downloaded and saved the documents just in case..........! Patrick - I hope you remembered to engage 4wd! | ||||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2287 Registered: 09-2004 |
Patrick, the ground is dry as a bone, looks like another drought this summer. BTW the LSD is still working well if the ground gets soft, ground clearance would be a problem though. | ||||
| ross kowalski Prolific User Username: cdfpw Post Number: 1349 Registered: 11-2015 |
Patrick L, That has to be in my top five "Rolls Royce used as a farm implement" pictures, heck, maybe top three. Also, you have LSD?, I didn't even know that was an option | ||||
| Stephen Bardwell New User Username: cobard71 Post Number: 9 Registered: 03-2020 |
Mssr rolls and royce are spinning in their graves about now I fear. | ||||
| ross kowalski Prolific User Username: cdfpw Post Number: 1350 Registered: 11-2015 |
As I recall in the original film, Max was driving a semi tanker?....Hmmm.  | ||||
| Patrick Ryan Grand Master Username: patrick_r Post Number: 2220 Registered: 04-2016 |
Terrific photoshopping mate. That was the second movie Ross. | ||||
| Patrick Francis Frequent User Username: jackpot Post Number: 334 Registered: 11-2016 |
LSD? May not be found on the car, but a lot of it being smoked at the moment by the looks of things.  |
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