Volvo 760 Long Life Design Faults

[Laird Scooby]

It's a Yazaki on my 760 Bob, fairly sure it was also Yazaki on the 740 i designed and built the LED bragraph gauge for.
That said, mine only needs three connections, +ve, -ve and sender, all of which can be picked up from the OE PCB and is much simpler in design than the multiboard OE unit. Each segment of the bargraph represented about 1.3 gallons (60L tank ~13.2 gallons) so the 3 red segments on the bottom of the scale gave a "reserve" of about 4 gallons.

[aardvarkash10]

Nice bit of design too Dave - you clearly had too much time.

[Laird Scooby]

Originally Posted by aardvarkash10

Nice bit of design too Dave - you clearly had too much time.

Thanks Ash - i think!

The longest part of the deign was finding out the resistance of the sender at empty and full, after that it was fairly easy.
Then i took the old gauge out and worked out how to fit a display, i had some of those bargraph displays which saved me drilling 10 3mm holes for 10 LEDs along the scale on the gauge.

I also have a 30 LED vacuum gauge that i designed to use one of the sensors on my Rover, a 70-0-70 ammeter designed to read voltage drop across the main cable from fusebox to battery (again on the 827 - alternator + goes direct to the fusebox where everything else is fed from so one cable to the battery, starter cable separate) and display it as a centre zero LED in a bank of 20 LEDs and a couple of others but have to confess they are still in the prototype stage simply because i haven't bothered sorting a nice case and fitting them!

[Laney760]

Originally Posted by Rversteeg

About the ZF-gearbox: I have heard people before claiming that the oil pump is located on the outgoing shaft and therefore not running when stationary, but is this really the case? If oil is not pumped around, how can the converter transfer any power and how will the hydraulically actuated clutches engage first gear when you want to set off?
There seems to be design flaw in the gearbox. When coming from D, and P or N is selected, the oil pressure to the first clutch pack is not bled off easily enough. As long as there is residual oil pressure, this clutch pack will remain partially engaged, resulting in heating / burning of the friction material while idling in P or N. When revving in P or N the gearbox will heat up even quicker. I guess when the gearbox was new, this bleeding would have been quick enough, but that it will get slower over time due to contamination.
This is also the reason behind a service bulletin to wait for at least 90 seconds before doing an emission test with the engine running at 3000 rpm.
Could this be the background of the dubious ZF reputation and the "oil pump is not engaged when idle" story?

The engine must never be emission tested at 3000rpm on cars fitted with the ZF gearbox. This is how the Volvo Bulletin instructs garages to emission test cars fitted with a ZF and when I used to get my 760 MOT'd I always used to take this bulletin to the garage / tester:


Volvo TSB 2525, 9/91:

Before beginning the "High Idle Emission Test Sequence" make sure the car is at operating temperature. Place transmission into "park" and switch the ignition off for 30 seconds. Restart, but DO NOT move the selector through the forward or reverse gears before or during the test and DO NOT EXCEED 2000 RPM. The first stage of the test is at 1850 rpm for 30 seconds, the second stage is at normal idle for 30 seconds. If you fail the test and have to do it again, then DO NOT proceed with the programmed catalyst preconditioning test sequence. Abort the test, place the transmission into "park", precondition the catalyst at 1850 rpm for 4 minutes, then allow the engine to revert to normal idle and check the tailpipe emissions. Under no circumstances must you exceed 2000 rpm during any part of the test.

[volvo B230ET]

Originally Posted by 360beast

I will have an AW71 with hydraulic lockup and propshaft available when I do my manual conversion if you wanted to do away with the ZF gearbox.

Thank you for the reply,I have been doing some research into this and the AW seems to be the better and longer lasting option,If you wouldn't mind could you contact me when/if you decide to dispose of it, and i don't suppose you know if the gear ratios are larger do you ?

[Laird Scooby]

Originally Posted by volvo B230ET

Thank you for the reply,I have been doing some research into this and the AW seems to be the better and longer lasting option,If you wouldn't mind could you contact me when/if you decide to dispose of it, and i don't suppose you know if the gear ratios are larger do you ?

Have a look at Pg55 (by document reader page counter, not the documents page numbers), the AW has a 4th/overdrive ratio of 0.69 compared to 0.73 on the ZF.

http://www.myvolvolibrary.info/Tech_...DataPocket.pdf

In real world figures, if 3000rpm gave you 75mph before, it'll now give 79mph as the AW has a higher overdrive ratio.

[nu11eaf]

Other design faults are the door card tops wrinkle up on every 740/760 and brittle plastic in sunroof slide mechamism that falls apart over time.