Overdrive Question

[JKB1957]

I have a "D" type O/D trans in my Spitfire that will not hold in overdrive, and engages slowly. If I try to accelerate while the O/D is engaged it slips back into direct drive. I have replaced the solenoid and changed to 30 wt non-detergent oil. Any suggestions on what to try next.

 

[TR4nut]

I've only worked on A type o/ds but it would be good if you could put a pressure gauge on it and see how much pressure you are able to build. It sounds like you have a problem with low pressure there.

 

[Geo Hahn]

In case it is helpful, here's a link to Jay H's gauge for the OD:

https://webspace.webring.com/people/tj/jholekamp/

 

[TR3driver]

I'll third the pressure test. Without it, you are just shooting in the dark.

I take it you cleaned the filter screen and didn't find anything out of the ordinary?

 

[JKB1957]

The O/D and trans were rebuilt and have less then 200 miles on them, so I haven't pulled the filter off to look at it. I have already pulled the relief valve on top of the O/D and cleaned that out. Worked a little better after this, so I may do this again and pull the filter off. I guess if I find any "black fuzzy" particles on the filter it will be time to call up the person who rebuilt it and have a talk. If I don't find any "B.F." particles then I may go for the pressure test.

 

[Andrew Mace]

FWIW (probably not much), I have never seen anything other than 80 or 90 weight gear oil recommended by Triumph for the small car gearboxes, dating all the way back to their origin in the Standard 8 of 1953.

 

[TR3driver]

it will be time to call up the person who rebuilt it and have a talk.

IMO, you should have done that already. You shouldn't have to be troubleshooting a fresh rebuild.

 

[JKB1957]

Success! I went and pulled the filter. No issues. Then I pulled the control/relief valve again and there I found a small, maybe 1/16" piece of metal. I know it was metal because it stuck to my magnet. That was it. I buttoned it all up, took it for a ride, and I have an overdrive that worked!
To respond to two statements. I had not called the O/D rebuilder because I like to fix things myself if I can. Luckily this time things worked out for the best. If the O/D was still not working he would have been my first call tomorrow. As for the 30 wt oil I went to that from Redline after resding an article on the Quantumechanics website that recommended that wt. In retrospect it wasn't the oil, so the Redline should work fine.

 

[hondo402000]

30 wt motor oil and 80-90 gear oil are partically the same, they have different designations and thats where the confusion comes in. but have about the same viscosity, So I have been told by a very reliable source

Hondo

 

[TR3driver]

Roughly the same viscosity (90 weight is closer to 40 weight), but different additives. Gear oils have "extreme pressure" additives that address the high pressure, wiping contact found in gears (particularly hypoid gears). 30ND has basically no additives.