Hi . I have a 1978 pace car with 7300miles recently bought it and done about 500 miles , what I experienced was when coasting down a slight incline running at 3000rpm the tach dropped to 1000 which felt like it disengaged like my 535 BMW was meant to do but when I went back on the gas the revs were up at 3500 and holding and not going into 3rd, I manually shifted to 2nd then immediately back to 3rd and it changed . This down shift started when on very light throttle and also into neutral and into 3rd also made it change.
I have the throttle down to the floor and set the kick down cable and locked at that , which I believe is the correct way, the gearbox to manifold vacuum pipe I tested it by connecting a pipe and sucking vacuum and putting my tong to see if the vacuum was held which proves there is no pipes have gone bad.
the modulator looks fine but do you think its a possible cause and replacement is whats next. The other strange noise I have had is when setting off and selecting 2nd so I can get it onto the secondaries is like a dry buzz noise like a distant horn , that only how to explain it , this dosent happen all the time but on the odd occasion , the gearbox strangely seems todo this when its hot , the level has been checked in park and ticking over and its up to the hot line.
The change some times from second to third seems to waft slowly from about 3500 and not a hard shift infact like its not sure kind a change , any help would be appreciated. Geoff Yorkshire , UK

 

I would start with a basic trans service, fluid, filter,and band adjustment.

 

Was the transmission fluid pink when you checked it? When you do the transmission service, I would recommend getting a complete flush in order to get all of the old fluid out.

 

Is pink and was changed about 4 years ago but its only done 7,300 miles
going to change the filter and fluid and the vacuum module and pull out the governor to check the nylon gear . it only does this when fully hot . cheers

 

The fluid Is pink and was changed about 4 years ago but its only done 7,300 miles
going to change the filter and fluid and the vacuum module and pull out the governor to check the nylon gear . it only does this when fully hot . cheers