rob vanharten

What is stronger a Bravo XR, or a TRS left hand turn?

rob vanharten

Really no one has any thoughts on this?

rufusgrouse

There is no question that the trs is stronger. If preload is increased by 10% with sufficiently tight bearing bores, and Mercruiser high performance gear lube is used, the tr/trs wins every time.

picklenjim

After reading the thread "XR Damage" over in the General Q&A section and being a 22 year owner of a TRS I would have to think the TRS. I have run 500+ hp through them for years and high hours with no problems.

LAKE EFFECT

The LH rotation TRS runs its prop shaft drive gear behind the pinion, putting that gear in the weaker part of the lower case/bullitt. This is the weakest link of the TRS, you can hard shim the LH drive instead of using the load ring. Hard shimming adds a lot of stability to the bullitt and gear set.

Having run both TRS and Bravo in higher HP situations, your question is a loaded one. The TRS is bigger in almost every aspect compared to a Bravo(transom assm, shafts, upper gears, etc). But it is an old drive being produced from 1974 to 1994, and parts are getting harder to find. The Bravo has a ton of upgrades available to beef them up, but if your thinking a conversion, first try the hard shimming thing, its a lot cheaper.

The Bravo and TRS share the same bullitt diameter load ring, and bearing carrier retainer nut. You can use Bravo hard shims on the TRS.

LE

JIMG

good advice but the right hand drive being the weaker of the trs. the left hand rotation has the gear in the front of the housing and is the stronger one.

picklenjim

This is what I always thought. The RH has the drive gear and bearing riding in the carrier which could possibly have some slight movement. The LH has the bearing and gear riding solidly in the case. Even with hard shimming the carrier is not going to be as solid as the case.

rufusgrouse

A physics debate about driven gears, either left or right misses the reality of what happens most frequently in both tr/trs drives; and that is "pinion failure". The smaller diameter of the pinion compromises wear. The surface hardening of any gear only goes so deep. The load against the pinion causes premature wear of the support bearing above the pinion, and this fact complicates the issue. Any repair procedure to the lower gearcase should include replacement of said bearing.

LAKE EFFECT

Sorry my f-up... The right lower on the TRS is the weaker because of what I stated. The Bravo's LH rotation upper is weaker because the upper drive gear is pushing on the top cap, and the RH gear pushes on the case.

As far as the pinion bearing debate. The TRS is harder to setup because the lower case upper roller pinion bearings get there preload from shims in the upper case, if not setup with correct preload, bearing failure will occur.

The Bravo lower is easier to setup because the shims are in the lower, and a $25 dollar tool replaces the upper housing during setup, so you only have to check rolling preload of the lower. In the TRS setup you have to get the upper preload, put the cases together and check the overall drive preload to calculate the actual lowers preload.

LE

cigrocket

iTrader: (3)

Seems to be alot of TRS setup lately in the the classifieds and swap forums. Seems like you can pick up a spare close to the cost of a xr gear set. I had TRS's on my CIG MISTRESS for 90 hours with almost 700hp naturally aspirated. Until I had the The right lower on the TRS go because of the pinion gear. Still I have to say, I liked the shifting capabilities of the boat with the TRS. Of course you do have added weight of the drive and tranny, and a hell of a lot more gear lube. Good luck. Also depends on driver