I have a 68 427 with a TH400 tranny that shifts into second then third before I reach 25 MPH. Is there some way I can adjust this?

Rog

 

First, has there been any work done on the car?
Like engine, intake, tune-up, Etc.?

If not, try adjusting the vacuum modulator. The modulator is on the pass. side of the trans, toward the front. It is round, about 2-2 1/2" diameter, and will have a metal vac. line from the engine, with a short piece of rubber hose connecting the metal line to the mod. Pull the hose off. Inside the "nipple" on the mod. will be a small screw. Use a small "pocket" screwdriver, and turn the screw in to shift later, out to shift earlier.

If your car has the large, "canister" style modulator, there should be a set-screw with a nut, on the very end of the mod.(not where the vac. hose goes). Use a screwdriver to hold the screw, and a wrench to loosen the nut, and then turn the screw in, for later shifts, out for earlier shifts. Be sure to tighten the nut after adjusting.

If ,when you take the vac. hose off, trans fluid runs out, then the mod. is ruptured, and needs to be replaced. Normally, a ruptured mod. will make the trans shift very late, but other symptoms are possible.

Normal shifts speeds should be:
1-2 shift @ 18mph
2-3 shift @ 28mph.
Personal preferences can be adjusted up or down with the mod. adjustment.

Try this, and let us know how it works!

Yes there hase been work done, the engine has been rebuilt and the tranny shop had rebuilt the transmission. It has a new vacuum modulator so I dont think that could be the issue. I will try the adjustment screw.

 

Thanks very much Adam

??!!! Ever had a NEW light bulb burn out soon as you turned it on!

I agree that it is probably not a bad mod., but I have learned in this business, "Never say never!!"

Has it been shifting like this since the o/h on the trans, or is this something that just started? If it's been like that from day one, then the adj. will(should) do the trick.