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Bob uk
Unregistered guest
Posted From: 94.197.122.84
Posted on Sunday, 17 August, 2014 - 02:22:   Edit PostDelete PostView Post/Check IP

The valve chest in an auto box spool valves which direct the oil to the correct path. Obvious that bit.

What is not so obvious is that often a spool valve will have equal pressure either side and by lowering the pressure on one side causes a pressure difference which moves the spool.

Often the spool has different diameters either end which further complicates because to balance the spool the pressures will be different.

Of course no body but gear box super expert in a white coat would alter anything.

Now apply all the above into any examination of any hydraulic system. It quickly becomes obvious that the makers info becomes extremely important.

(Message approved by david_gore)
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Jan Forrest
Grand Master
Username: got_one

Post Number: 622
Registered: 1-2008
Posted on Sunday, 17 August, 2014 - 21:45:   Edit PostDelete PostView Post/Check IP

I can't see that as much of a problem with our older cars. All the gearboxes were bought in as standard units and simply nailed into the cars 'as is'. The technical info should be widely available in the manufacturer's 'historical/obsolete files'.
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Bob uk
Unregistered guest
Posted From: 94.197.122.79
Posted on Sunday, 17 August, 2014 - 23:20:   Edit PostDelete PostView Post/Check IP

Tough old boots GM 400 autobox.
Cheap to rebuild cheap bits. Well almost cheap.
The comment was not really only about gboxes but how stuff looks obvious and then it isn't. I have tried many times to figure out stuff to find the deeper I go, more complicated stuff pops up. I thought I knew how a guitar amp worked until my mate started explaining reversing bias on the valve grids.

(Message approved by david_gore)
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Jan Forrest
Grand Master
Username: got_one

Post Number: 624
Registered: 1-2008
Posted on Monday, 18 August, 2014 - 20:41:   Edit PostDelete PostView Post/Check IP

And that's before you get into the combination of positive and negative feedback! I still find it hard to figure out why a valve final stage will blow if left open output, but can feed into a short circuit all day long without harm.
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Bob Reynolds
Prolific User
Username: bobreynolds

Post Number: 145
Registered: 8-2012
Posted on Monday, 18 August, 2014 - 21:29:   Edit PostDelete PostView Post/Check IP

"All the gearboxes were bought in as standard units and simply nailed into the cars 'as is'."

Exept that RR decided to 'improve' it by adding an electrical actuator on the side, thereby reducing the reliability and making it more complicated.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 986
Registered: 6-2009
Posted on Tuesday, 19 August, 2014 - 01:24:   Edit PostDelete PostView Post/Check IP

Bob R,

And we shan't even get into some of the safety issues that ensue without a safety interlock on the whole setup and how easy it is to bump the gear changer from one to another.

This is one of those features that I don't really understand why it continues to survive (or at least I think it does - it went through the SZs at a minimum). I have yet to hear any driver complain about the effort required to shift any other luxury make that doesn't include electric actuation, and those systems are so much more reliable and robust.

I've driven a Silver Seraph, but I honestly don't recall whether it had electric gear actuation. All cars later than that are in the "I've seen 'em, not driven 'em" category.

Brian
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Bob uk
Unregistered guest
Posted From: 94.197.122.80
Posted on Tuesday, 19 August, 2014 - 06:40:   Edit PostDelete PostView Post/Check IP

In the early days of autoboxes in the UK Borg Warner 35 in the main were fitted with no adjustments for particular engines, one size fits all. Small engines need very careful matching else they lose to much power and end up sluggish and bad mpg.
Especially the torque converter stall speed.

The electric shift is dangerous because on a mot test a young mechanic reached in the car with engine running and in neutral to check right hand indicator and put the car in drive-----------

The Ford fiesta cost 500 to repair and I got a new rad shell New bumper new number plate and.a.respray to RR standards which cost 6500. I had to pay 150 excess and then my legal expenses policy recovered the 150 and 400 for loss of use. Which was 2 months. The RR agent gave me a Xj8 to drive for 3 weeks of it and a W124 merc for the rest.

I felt so sorry for the mechanic.

(Message approved by david_gore)
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 3052
Registered: 4-2003
Posted on Tuesday, 19 August, 2014 - 08:03:   Edit PostDelete PostView Post/Check IP


quote:

"All the gearboxes were bought in as standard units and simply nailed into the cars 'as is'."




Not really. The first Hydramatics in 1952 were built at Crewe from GM kits but with the RR servo and ride control bits added. From 1954 Crewe did most of the finishing as well as the assembly. That continued until 1977 even with the TH400/3L80. The first transmission fitted to a Crewe car from a GM box as a complete unit was for the Silver Shadow II. The electric actuator is a trivial external mechanism. Yes, the TH400 is very cheap to overhaul in Australia, having been fitted to many mass-produced locally-built GM cars in the 1970s and 1980s albeit with the Chev bellhousing. A full overhaul including fitting will cost less than $4,000 even at an expensive shop.

RT.
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Bob uk
Unregistered guest
Posted From: 94.197.122.80
Posted on Tuesday, 19 August, 2014 - 10:33:   Edit PostDelete PostView Post/Check IP

Further to what Richard has said,
RR had a licence from GM for gboxes and other stuff.
The torque converter is matched to the engine and maybe not sure different settings.

UK price is about 600 plus converter. However I have had a few jag ones done and often it's just a.few bits and it's good to go and most were under 400 ( now prices not then).
I had one that.cost 750 because the car was put in park at 70 mph!!!.
The only thing that can give trouble ate the.vacuum module which is a.five min job and they are cheap. And the.electric change. And the.wiring in the plug to.the gear box. The plug is filled with silicon. Dig out and resolder the wires back and.refill with silicon. It took me a whole day of prodding to find why the park would work nasty awkward job.

(Message approved by david_gore)