Three Speed Overdrive

[plumber452]

Does anyone know if the tail shaft section of a four bolt three speed manual over drive will work on a seven bolt non overdrive three speed manual transmission? Thanks

[capev86]

no.....they are two different generations of transmission. you need the tail shaft from a 65 and newer trans.........it is a full syncho (except reverse) whereas the the earlier saginaw was like of the 4 speeds....no synchro on first gear.

[plumber452]

Do you think it's worth giving up the synchro for the benefits of the overdrive?

[capev86]

i would not want to give up my newer transmission for a 50's unit. plus, it is very nice to be able to shift into first gear without the vehicle being dead still, among other things. the whole unit is better. you need to find a 65 and newer OD tail shaft for your trans. i am going this route on my 72 burb 3/4 ton.....changing from a 4.57 to a 4.10 final drive and eventually adding the OD unit. it will be almost as good numerically as a 3.73 with a 700r4, and 3/4 tons have slightly taller tires so i know i'll be able to cruise comfortably on the highway. the old style unit would be great for someone doing a stock style restoration on a 57 chevy! i heard that ford used a similar overdrive in the 50's and the guts are heavier duty than what the chevys got. you might be able to apply that kind of thinking with the later style trans too.

[plumber452]

Thanks for the input. I just bought this 1/2 ton with a 292 with a 3:73 rear. It sounds like it's turning 4000 rpm at 55 MPH. I thought about 3:08 gears but I'm afraid it wouldn't have much taking off from a stop.

[capev86]

funny....my dad has used his 84 and 87 burb (both with 3.373) in third gear (1:! ratio) while towing on the highway and it isn't bad at all (overdrive is nicer, though). even my 72 burb with 4.57 rear is only turning about 3100rpm at 60mph. it just sounds really load because its a v8 with big everything....not a cushy little car with good aerodynamics and sound deadening. get the overdrive on there and you will enjoy highway driving. a 3.08 rear sucks. my dad put the axle from his 84 in his 87 because this was very apparent using the truck for anything around new england. it went from a slug to peppy and it didn't really lose any gas mileage (still around 18 on the highway) because it takes a certain amount of power to move a 5,000 pound truck down the road.

[plumber452]

I think I'll try to identify this four bolt side cover overdrive I bought sell it and keep my eye open for a seven bolt overdrive.

[capev86]

there is a good core on ebay for $350 with most all the parts you need. i just missed on a good rebuilder that sold on ebay for like 50 bucks a week ago....i just couldn't spare the cash. most people that have them want money for them 'cause they are rare these days. many of these overdrives got junked decades ago when the (rebuild able) solenoid quit.

[rsavage]

You might consider a 4+3 standard out of an older (80's) vette. They were, I believe Doug Nash units that incorporated a super T 10 4 speed and an automatic OD. They were hardy units and can be wired to go into OD manually. Saw one on craigs list a month or so ago fairly reasonable.

[Conroe trucker]

I have one and you could easily live with the older unit until you found a newer one.

You do remember how to double clutch for first them don't you?
(How old are you?)

Some of the parts change out, and a 55-57 guy will give bucks for an older unit.
They reproduce the solenoid now, but not the GOVENOR.
It is the most fragile thing and must be treated with care, do not throw it around, you break the govenor and the unit will not operate as intended, it will still operate, but not as neatly.

I have two, let me know if you have questions.

Mike