To fix or not to fix, that is the question.

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

JP8Charter

Junior Member
Joined
Jan 28, 2025
Posts
1
Reaction score
0
Location
Phoenix
First Name
Jim
Truck Year
1977
Truck Model
C15 Sierra Classic
Engine Size
v6
1077 GMC C15 Sierra Classic Long Bed.
We are selling our truck, and have taken it to a reputable mechanic who works on Classic vehicles.
We have a list of “fixes” and have done some of them, but the transmission is slipping. Should we pay the money to fix it and sell it for more money, or should we leave it as is.
We do not have the tools, space, or knowledge on transmissions to fix it ourselves.
We “think” it is slipping. It’s an automatic. It won’t come out of first gear unless you manually shift it to L1 then L2 and then back into drive.
We added more transmission fluid because it was leaking due to sitting so long. And we added a fluid for gear slippage (that might not be a word)
Need help.
To fix or not to fix.
Or possibly pay to have it diagnosed.
It needs over $7000 work of work. And has already had about $10,000 of work done to it.
Thank you for any advice.
 

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
10,167
Reaction score
19,654
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
It is probably a vacuum modulator. $25.00 part 30 minute fix. No special tools not even a jack if you are skinny like me.
 
Last edited:

mtbadbob

Supporting Member
Supporting Member
Joined
May 9, 2021
Posts
849
Reaction score
1,440
Location
Montana
First Name
Bob
Truck Year
1987
Truck Model
V20
Engine Size
350
Try to just snug up tranny pan bolts. 90% of the time, they are just finger tight and that's why it's leaking...
 

Smtty58

Member
Joined
Mar 19, 2026
Posts
45
Reaction score
45
Location
Mass.
First Name
Lyle
Truck Year
1990
Truck Model
R3500 Crewcab
Engine Size
350
Take it to a good tranny shop and get a quote. C15 probably has a Turbo 350, those are plentiful in junkyards, if you want to go that route.
 

Latest posts

Forum statistics

Threads
48,666
Posts
1,074,154
Members
43,333
Latest member
duncan_schawalder
Top