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| | | | Joined: Jul 2016 Posts: 53 'Bolter | | 'Bolter Joined: Jul 2016 Posts: 53 | I have a 1968 Chevy C30 cab and chassie with a twelve foot flat bed dump. It has a 400 turbo auto transmission. The transmission isn't equipped with the park
feature.
It's my understanding GM omitted it to prevent transmission damage from heavy loads being parked without the use of the emergency brake or chocking the wheels.
I would like to add the park feature to the trans for convenience. Is their a simple modification that can be done by dropping the pan ?
Thanks ,Rich
Rich
68 C30 CST dually flatbed dump
58 Viking 6500
| | | | | Joined: Sep 2011 Posts: 1,453 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,453 | The only simple modification I know of is to install a later TH400.
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Mar 2010 Posts: 10,279 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,279 | I would be shocked to find out that your TH400 could not simply have a park pawl and return spring installed to give you that feature.
It may well require removal and some disassembling to do it.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Jul 2019 Posts: 24 New Guy | | New Guy Joined: Jul 2019 Posts: 24 | I agree with 52Carl. Been a bit since I've been in the bottom of a 400 but iirc there will be a linkage running from the selector back to a tapered pin that forces the parking pawl up to engage one of the drums. this is held in place by a bracket and the pawl itself has a spring to retract when the pin is moved. I think the pivot pin for the pawl gets driven in from the external rear of the case and the hole is plugged with a small cup plug.
Not seeing many good pics in a google search. The only problem I could see running into trying to install the setup would be some of the holes not being drilled out.
Chris
Too many to work on
4 bolts, 2 square bodies, 4 GMT400s...and those are the keepers
| | | | | Joined: Mar 2019 Posts: 1,003 'Bolter | | 'Bolter Joined: Mar 2019 Posts: 1,003 | Get a set of wheel chocks. Will last 4ever unless you forget to pic em up like I have. | | | | | Joined: Jul 2000 Posts: 2,192 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,192 |
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
| | | | | Joined: Mar 2005 Posts: 1,636 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 1,636 | I'm not sure why a later 400 would be needed. 65 and up had park except for the heavier trucks. But, you might drop the transmission pan and with a flash light look towards the back of the transmission to see if the slotted disc for the park pawl to engage is there. You should be able to see the slotted edge just barely. They may have simply left the actuator rod off so it could not be placed in park. You might get lucky and simply install the linkage inside to complete the parking pawl engaging the slots in the disc.
Or find another 1968 TH400 and install it. Check overall lengths and whether or not the driveshaft yoke slides in or is held on with a nut.
You might have to remove the tail cone to install a spring and part of the actuator, but that's not hard to do,.
One other option is to take the transmission down and take it to a rebuilder and they can get the parking mechanism set up.
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