Volvo overdrive slips

Do you know the remedy for this problem?

The car is a 940 estate, '92 vintage, with manual 4-speed gearbox and with solenoid-operated overdrive.

The symptom is that the overdrive doesn't fully engage when the car has been driven for a few miles (i.e. when it's fully warmed up).

When the overdrive button is depressed, the '5' indicator lights up, and the revs drop, just as if the ratio has changed, but under load the ratio appears to slip and the car behaves as if in 4th gear.

When the car is stone cold the overdrive behaves impeccably, engaging/disengaging both promptly and positively.

Tia.

I would look to the solenoid, windings probably breaking down. Sorry,don't have any info on this car to help you further.

Thanks johnnyfishing.

Is your advice based on knowledge of solenoids, or more specialised knowledge of the Laycock overdrive?

Only from the solenoid point of view I'm afraid. Having had little experience of working with Volvo's I can't even tell you how or where to access it. If it is easily accessible I would think it's the cheaper option to change it or have it tested.

Thanks again.

Softus, you should try looking at MGB websites and forums, a good start is Chris Betson at Octarine services http://octarine.mywowbb.com, he should be able to help or if not put you in touch with someone who reconditions Laycock overdrives.
regards johnwr

Hi Softus,

I'm assuming you have a Laycock OD unit to play with then. Some info based on the D & J types..

I have a '72 GT6mk3 with a Laycock OD. It has a cone clutch, which is engaged by oil pressure within the OD unit itself. The oil pressure is allowed to build by energising the OD solenoid so that it operates the hydraulics.

Some things that tend to cause the OD internal clutch to slip.
1. thin oil - caused by overheating or worn out from age.
2. oil additives such as slick50 or other teflon based products.
3. blocked OD oil filter (steel mesh filter inside OD housing with magnetic washer to collect particles)
4. breakdown of the OD clutch lining - sometimes to the point where only the rivets are left to provide the friction.

These will show up as the OD cutting in/out when warm but fine when cold.

A solenoid problem usually gets easier when warm as it generally tends to get gummed up with cr*p, which is harder to shift when cold.
Occassionally the wiring to the solenoid gets chaffed and intermittently shorts out causing the solenoid to disengage. this happens throughout the temperature range though.

Try an oil change first as well as cleaning the filter.