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patrick acarnley
Yet to post message
Username: eta

Post Number: 1
Registered: 11-2021
Posted on Thursday, 04 November, 2021 - 16:24:   Edit PostDelete PostView Post/Check IP

Hi All, new to RR and this forum.

My car is Nov '85, VIN 14624, twin SU, 3 speed GM400 gearbox. 97K miles indicated, not verified, but believable.

The problem/s is/are; a) no reverse. This manifested itself after about 100 miles of driving. On taking it for a 24 mile 'hard' drive on B roads and motorway, it also appears that; b) the car is not going in to top. I arrive at this conclusion as at 50 - 60 mph, on a very light throttle, moving the column selector from D to I makes no difference. I would also say that the engine is starting to sound 'busy'. I had hoped the hard drive might have loosened things up but no.

The car has been well maintained with a recent Dextron 2 and filter change. Having said that, when I got the car and driven about 35 miles and parked up, the car would not go into reverse. On checking the ATF level it was well below MIN. The previous owner (a mechanic) came out, topped up the ATF and reverse worked, albeit with some coaxing. The previous owner said that reverse had always been 'lazy' on this car. The car was laid up for about a year in a weatherproof shipping container.

I have cleaned up the column change selector 'bridge' contacts and selector arm. The actuator on the side of the box appears (visually) to be cycling.

Your advise please. Am I looking at a complete g/box rebuild?

Many thanks.
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Mark Aldridge
Frequent User
Username: mark_aldridge

Post Number: 762
Registered: 10-2008
Posted on Thursday, 04 November, 2021 - 20:13:   Edit PostDelete PostView Post/Check IP

The old gearbox in my Shadow had a reluctance to reverse uphill or up a slope, it just slipped. The final death was the failure of the front oil seal. If it is reluctant to go into top, check the kickdown switch in the car is not sticking.Has the filter "O" ring sealed correctly?
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Neville Davies
Experienced User
Username: nev_davies

Post Number: 81
Registered: 09-2006
Posted on Monday, 08 November, 2021 - 18:49:   Edit PostDelete PostView Post/Check IP

Patrick.Make sure the fluid is checked with the engine running,the fact that the fluid was low and the symptons you have would indicate that the Top and Reverse clutch is probably burnt out. The other friction materials will also be damaged and the only practical answer is a full rebuild or another autobox.
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David Gore
Username: david_gore

Post Number: 4032
Registered: 04-2003
Posted on Tuesday, 09 November, 2021 - 07:49:   Edit PostDelete PostView Post/Check IP

Mark and Patrick - both of you have a T400 transmission requiring a full overhaul including clutch plate replacement.

I did a full overhaul on the T400 transmission on DRH14434 after the fluid line from the transmission to the radiator fluid cooler leaked all the fluid from the transmission driving up to my garage. I managed to get the car into my garage but destroyed the internal clutch plates by friction arising from the loss of transmission fluid.

I removed the transmission from under the car after lifting it onto heavy duty body supports and making a holding frame for my floor jack which would allow the transmission to be supported and pulled back from the bell housing for overhaul and then lifted back and moved into place after completing the overhaul.

I used a B&M T400 transmission overhaul kit I purchased from a US supplier which had a very comprehensive guide enclosed which made the overhaul easy provided you followed the instructions.

The only item not included was a special front "wave" plate for the 1st gear clutch installed at RRMC's direction to give a smooth imperceptible "take up" to match the GM Cadillac T400 which included a similar plate. I was able to source this plate from a local auto transmission parts specialist who carried these in stock.

The actual overhaul was straight forward and within the capabilities of a competent DIY owner following the B&M guide and the relevant sections in TSD2476 [available free from the Australian Technical Library]:

A copy of the B&M T400 transmission kit overhaul manual is attached below:

B&M T400 Overhaul Instructions.pdf (13620.8 k)

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