This is a REV servo from an 80E I built back in april . The customer just now installed, when he did he found he had no reverse but went and drove it arround and when he came back he had reverse even at WOT it held no issues. Drove and shifted perfectly in all forward gears, Parks truck , Lets cool down check fluid all good goes to drive it again NO REVERSE so he repeats what he did before but this time no reverse still.
Brought to me I opened and found this,
Any ideas I have not run onto this before,
Odd pressure spike?
Weak or not visually damaged servo that just busted?
I ordered an adaptacase billet one to replace it. But still odd, This is not a HI perf unit just a 3500 series truck with a standard rebuild . AFL. TCC VALVE.


Something else I should look at or for ?

 

Does the customer have a teenage son ?

 

Yes but this happened right after start up its very weird , something I have not actually seen , BUT apparently it happens as the after market does make a billet replacement for it.
I have built these to run max line all the time full manual in 1200 hp trucks and never seen this, I am assuming just weaker from age, maybe an internal crack I could not see when i built it.
Just odd to me .

 

Frank those 1996 and UP Low-Reverse Servo Pistons are prone to cracking after spikes in Reverse-Boost Pressures (Often over 300 PSI.) and become a ticking time-bomb.

Sonnax sells a Reinforcement Kit, and a few Companies have Billet Servo Pistons to replace them.




-Marcello III

 

I ordered a billet one from adapacase

 

We have used the Sonnax Billet Servo Piston in Units that must retain the Reverse-Boost Circuit.
Sonnax Billet Servo Piston shown below:




However, We more commonly eliminate the Reverse-Boost Circuit when raising Line-Pressure...
And always eliminate this Circuit with Fixed Line-Pressure.

Machine a Flat on the Reverse Valve-Land of the Boost Valve, and install a Set-Screw in the Reverse-Boost Passage of the Pump Assembly.

 

This is just a stock 3500 truck used for hauling towing and plowing , So I think the billet one will be fine, My only concern is he started out with no rev then drove truck around and had perfect rev then after sitting had none again ever even after driving, KINDA weird.