I recently changed the transmission oil, removed and verified OD solenoid function according to Haynes manual procedures, after having verified electrical continuity from the shift lever OD switch to the solenoid and cleaning the contact points on the OD relay (of Hungarian manufacture), replaced in 2001 by the previous owner.

I have since found that the OD engages infrequently. When I engage the OD, I mostly perceive no indication of OD engagement. When I switch off the OD, a perceptible lunch in the drive train occurs, even though the shift into OD never occurred. There are 225,400 miles on the vehicle. Could the OD clutch surfaces be worn? Are parts available? Could a mechanically skilled owner make the repair? What might repair cost?

If anyone can explain what is causing the drive train lurch and the probable cause of the OD malfunction, I would be most appreciative! I would very much like to restore OD function!

Thank you very much!

Jim

 

is this a manual or automatic overdrive? they are completely different.

the manual OD's are lycoming J units, same as many vintage british sports cars used. if you can find a shop that specializes in TR, MG, etc sports cars, they can probably overhaul it.

the automatic OD is integral in the transmission, and if its actually failing, will require a transmission overhaul.

 

The OD is a Laycock type J...

 

arrg, hahahah, 'lycoming'

rusty neurons. I plead the fifth! make mine scotch.

yah, LAYcock J overdrives on the manuals.

 

Thank you very much for the tip! The following website:J Type Overdrive Part I, tells just about everything there is to tell about Laycock J ODs, but, apparently, (I have not read the post in detail) fails to suggest how, if they are as sturdy and reliable as claimed, they might fail. Usually mechanical devices, and there were/are, reportedly, millions of these OD units made, tend to manifest a mode or modes of failure that is/are unique to the device. Might there be a reader of this post, with much experience with these OD units, who can suggest the type of failure that likely results in intermittent OD function? Anybody care to hazard a guess what a rebuild would cost?


And Pierce, might the problem be that the neurons are not so much rusty as that they are overly lubricated with scotch!?


Many thanks to all for your thoughtful and helpful suggestions!


Best wishes,


Jim

 

MYSTERIES OF THE LAYCOCK DE NORMANVILLE OVERDRIVE

 

part IV of that article on troubleshooting lists a number of failure modes.

 

I spent hours this AM composing a response to the most recent posts, which, as usual, I have found to be very helpful, only to discover that my reply effort failed, apparently, because I had somehow become logged out, perhaps because I took so long.

While Lev is a man of few words, they have been very helpful. While glancing over "Mysteries of the Laycock OD", I noted that a system pressure test would be a good initial diagnostic effort.

I have a Fluke PV 500 Digital Pressure/Vacuum Module with a maximum range of 600 psi. I wonder if I could use that for the test? Since I have never conducted a pressure test at such high and potentially dangerous pressures, helpful advice would be welcome! I'll sign off now to do my homework! Again, many thanks for the very helpful suggestions!