Transmission Pressures Velvet Drive on Detroit 4-53

Hi Guys:

The port transmission has been plagued with problems with the prior owner and now I have inherited them. It is currently in rebuild shop for the third time in 7 months.

They register pressure of only 115 hot after partial rebuild. I am told that it should be 120 - 135 with this "old" style body and as high as 135 - 150 with a newer style.

So the question is: Do I accept 115, or rebuild it further in hopes that it will deliver up to 135 or scrap it and opt for a newer style unit? Do the two transmissions need to have balanced pressure or is it ok for one to yield more than the other? Will that measurably affect operative performance? The vessel is a Hatteras 48 LRC. Thanks. Jim

Jim Felds
M/V Kokomo
Hatteas 48 LRC
MTOA 5401

Is it slipping? What are you measuring the pressure with? Oil pressure senders and gauges are not super accurate. If you're getting 115 and the low end of the range is 120, that could easily be within the accuracy of the gauge. Maybe the better question is how low can the oil pressure be before the transmission starts slipping.

Transmission oil pressures don't need to match. Either the transmissions slip or they don't.

Ted

What has been going wrong with the tranny? Usually a pretty solid box unless built wrong.

What does pressure do with raised and lowered rpm? What does pressure do cool vs hot? If it remains basically constant, the pressure regulator is doing its job and controlling pressure. If it drops way down with both heat and low rpm, then there is an issue.

Also, check case temperature during a long-ish run. Some clutch slipping or dragging will cause case temp to go way high.

Don,t really know the gear but I wonder about "partial rebuild".
To me a rebuild should be a rebuild.
I have read that the pressure regulator spring should be replaced with new, not reused.
Also the guy who wrote about his re,re said the rebuilds replaced with a higher pressure spring, not a lot but higher.
No idea now although I may have bookmarked it at home. Send me a pm and remind me and I will check when at home in a few days.
Worn parts may cause excess leakage internally.
Pressure guages should be mechanical, good quality.