Characteristics of DG box?

[djm16]

I have had a search and not come up with a consistent answer.
Mine is a 1963 3 litre Mk IIb .
The box is DG AR5? not so sure about the last bit.

According to the WSM, only early MkIs had "first gear start". Mine will start in second gear unless I floor it through the kick down.

But I also read that the intermediate gear hold should force a first gear start. Now I am confused.

Furthermore, the intermediate gear hold seems to make very little difference to the gear changing 2 to 3. I have the solenoid rotated fully anti-clockwise from below, it definitely clicks on when operated.

[enigmas]

The DG (Detroit Gears) automatic is one heavy and complex unit. The big down side with the box is not it's strength but the amount of power it saps from the engine before any driving energy reaches the back wheels. They worked well on big cubic inch American V8s but produce lack lustre performance on Rover 3 litres and even 3.4 Jaguars. Unless you love the gearbox, a manual 4 speed (with overdrive) transforms the car. No disrespect...I've driven examples of both with autos and when changed to a manual box. The change in the character of the car is remarkable.

[Phil Nottingham]

Its quite simple yours like my Mk2c will normally start in 2nd - flooring will start it in first and it will then change up/down  as in kickdown mode OR moving the column switch DOWN will start it in 1st and up changes to 2nd and direct top will be delayed OR move big column lever to "L" and it will stay in 1st

Simples

I think its a far nicer box than cheapo crude BW 35 and has lockup in top so acts just like modern boxes such as the ZF HP4 that everyone thought so advanced 35 years ago

Is heavy though

Is fluid correct is MUST be at correct level and if not and run any length of of time especially if it was low then the box will be ruined - the band scan be adjusted which may help

[djm16]

Thanks Phil.
I will recheck the fluid level.

It seems to work well except that with the column lever down (and the solenoid working and adjusted to maxiimum effect) it still starts in 2nd gear.

Any ideas?

Regards
David

[cstorey]

I agree with Phil that the DG is a really lovely box , and infinitely superior to the 35 . On Jaguars it worked extremely well, BUT despite the fact that they had much more torque than the Rover , they did not use the start in intermediate arrangement, but always started in low, hence ( contrary to what someone else said )  the acceleration was always good from rest even with the Mark IX and early mark 10 . It is a long time since I have dealt with one, but I suggest you look at your kickdown cable adjustment . It sounds possible that you need to shorten it fractionally, but don't overdo it as the changes will become very bumpy i.e. shorten it just a mere fraction at a time and see what difference it makes

[djm16]

Thanks,
I looked at the kickdown operating connections. I have it so that the kickdown pull rod is as far forward as it will go with the accelerator clamped to the floor.

Yet there is no kickdown above 40 mph. Still the intermediate gear hold (essentially a manual kickdown) is ineffective. This suggests to me a fault in the governor? Weak spring perhaps? I have no previous experience of these boxes so I do not know what faults might be common.

[cstorey]

David : I have now looked at my workshop manual , and discover that the Rover box was of two types , the earlier of which used all 3 gears from rest, and the later of which had the intermediate start as its normal mode. However, the controls in each case are astonishingly complex and can result in either box starting in intermediate . The earlier box has a number in the range R5B1000 onwards, and the intermediate start boxes have a K suffix after the number. It is the intermediate speed hold knob which complicates things, and I quote from the manual 

    1st speed start models - these cars normally start in low, but if the car is brought to  a halt with the intermediate speed hold in operation the car will then start from rest in intermediate

     2nd speed start models - normally start in intermediate except at heavy throttle openings .....If the car is brought to rest with the intermediate hold in operation  the car will then start in low

    Thus, contrary to what we might expect, the first speed start cars will in fact start in  intermediate if the speed hold is left in operation , and vice versa for the 2nd speed start boxes

    I wonder if yours is the earlier box, and either the inter speed hold is selected, or is sticking on, or is misrigged ?

[djm16]

Thanks for the replies above. I think I have the problem under control. Just about everything was wrong!

First I will describe the function of the governor.

It is a centrifugal device that at increasing RPM operates a valve to cause an upward gear change. Two weights on a scissor action with a spring opposing. As the engine goes faster output shaft does faster[see followup post below], the weights pull the scissors closed against the spring.

The governor control lever supplies an additional input, progressively pulling the scissors open and opposing the drive to operate the up-change valve. The governor control lever is linker directly to the accelerator pedal, so that the more the accelerator is depressed, the less able the governor is to triggered an up-change. At extremes of accelerator pedal depression the inhibition of the governor valve should cause a down-shift. This is not a discrete event in the way that turning an overdrive switch is, but is variable depending on rpm and accelerator depression.

The intermediate hold operation - whether cable or electrical - this is a complete misnomer. Whichever means is used, the result is the same, that the governor control arm is moved independently of the accelerator to a position close to maximum throttle. It could therefore be better labelled "manual kickdown lever".

Lastly the bolt and locknut on the back of the extension case that on mine was broken off, this is called the "governor cam stop". Elsewhere in the manual is a cryptic reference to using it to adjust gear change speeds. Again, massively misleading. It has no immediate effect on gear change speeds. Instead, it sets the maximum movement of the governor control lever. Screwing it in reduces the maximum range of movement, screwing it out allows a wider range of movement. It is a fail safe device to stop your IQ challenged repair man (or owner) from over-revving the motor by driving at 70mph in 2nd gear (or 50mph in first).

Note that none of the above affect the zero load change up speed 2nd to 3rd, which is at exactly 14 pmh.

OK, so what was wrong?

1) The adjustable governor control rods from the accelerator to the governor control arm - one was too short, the other too long. Easy enough to fix.

2) The rod linkage on the control arms was secured to the outer hole on the control arm. I remembered reading here that it should be the inner hole.

3) The intermediate gear hold (IGH) solenoid was mounted the wrong side of the "reaction bracket". I have to confess that would have been me! Obvious now with the manual to hand, but in my defence I was convinced that I was replacing it how I found it.

Everything now works as it should with the IGH causing the required delay in upshifting - vital to me as I live at the bottom of a long hill, kickdown now working, and up changes are now more appropriately dependent on throttle opening so that the engine no longer lugs at low speeds.

[harvey]

Nov 4, 2015 23:27:42 GMT djm16 said:

It is a centrifugal device that at increasing RPM operates a valve to cause an upward gear change. Two weights on a scissor action with a spring opposing. As the engine goes faster, the weights pull the scissors closed against the spring.

It's not as the engine goes faster, it's as the roadspeed increases.

Nov 4, 2015 23:27:42 GMT djm16 said:

2) The rod linkage on the control arms was secured to the outer hole on the control arm. I remembered reading here that it should be the inner hole.

I'm pleased you remembered that. I certainly remember writing it.

[djm16]

I'm pleased you remembered that. I certainly remember writing it.

Read more: roverp5.proboards.com/post/new/9301#ixzz3qgtfSxKB

Thanks for that.

[cstorey]

Glad you're sorted, David