Street SB w/2.74 and 430 rear about 450HP. Bigger trans tunnel for the 518 plus reliability? Never knew anybody that used a gearvendor. Any thoughts?

The gear venders seem really reliable and they have excellent customer service from what I have seen with Drag Week people. The 518 has a better overdrive ratio but I imagine that it costs more HP to run over a 727 and GV combo but I don't know for certain.

I keep kicking around overdrive with an A500 behind my small block but have never pulled the trigger. My motor loves causing at 3500 its super smooth and quiet, but when I do drag week I wouldn't mine being able to run 10mph faster lol. 65mph on some of the major interstates can be sketchy sometimes.

Will the GV fit in the tunnel without modification?

My dad talked to a Gear Vendor rep at their booth on drag week. He said it only required a small dent in the trans tunnel to clear. We were asking about a 904 in an A body though, a 727 might be different.

The actual GV ratio is rounded off to .78:1 but is actually =1/(1+(22/77)) or .77778:1.
GV also allows creating 2 intermediate gears by engaging it in 1st or 2nd.
For a 727 this makes:
1st 2.45:1
1st + GV 1.91:1
2nd 1.45:1
2nd + GV 1.13:1
3rd 1.00:1
OD .778:1

GV when not in use is like a clean neutral and robs no HP, only weight. On the other hand, if the 518 is like an A500, you are spinning the entire OD section even when its not in use....I was told I was losing as much as .5 in ET from this on my old pro street truck.

I have a GV in my GMC Dually with 4.10s; installed 1996 and it's been bulletproof.
Probably the best upgrade I've done to it in terms of highway RPM & MPG.
At the same time, its T400 got a rebuild.
Looking at the cost of an OD trans, and the cost of any rebuilds, it was the less-expensive long-term plan.
It's arguably a wash at this point, though, because the trans has been fine.
But it was also a less complicated way to get OD in the truck.
Not sure how that compares to the OP's needs & goals, but my experience has been very good.

The 500/518 has a noticeably better OD than the Gearvenders. That was the deciding factor for me. As to the power loss, that is an interesting question. Does anyone know for sure the difference?

What body is it going in? Only a little massaging was required to put the 518 in my Cuda. As to reliability, a properly built 518 can handle what you throw at it. It handles my 540 Hemi as easily as it handles the diesels.

In fact, how about a well built 500? It takes less power to drive. Would require even less ,if any, tunnel mods. And is lighter than even the Gearvenders.

When going behind a big block, the bell housing situation makes the conversion more complicated/expensive. But for small blocks, the 500/518 seems a shoe-in.

https://smrtrans.tripod.com/smrtransmissionsintro/id6.html

It’s the same with the 727 also ,have one in a 73 Cuda
Jim F

the gearvendors maintenance schedule is a little steep
"Recommended service interval – change fluid every 5,000 miles depending on severity of duty."
https://www.gearvendors.com/install.html


Joe

Had a GV in my 69 Super Bee. All I had to do was dimple the tunnel for clearance for the two studs on the top rear of the housing. Had it behind a 512 stroker and never had any issues. I liked the GV because you can select overdrive in any gear. Use to wind it out in second then select overdrive, wind it out again then shift to third. I had a reverse manual valve body in it.

IMO, you can build a sweet A500 or A518 for the steep price of a gearvendors. I think the splitting gears is a neat idea but not practical given feedback from people that have them. I'd be curious if the previously stated 1/2 second loss in ET is accurate, that's pretty substantial.

I want to say if you have full manual control of a A500 or A518 you can engage overdrive in 2nd and 3rd? Not positive though.

I would also like to know about power loss with an A500 or 518

On the 518 the o/d only comes in after 3rd gear, I have one I ran behind a 392 first gen in a 58 Ply wgn, no lightweight combo and plenty of torque and it never missed a beat, I wouldn't be suprised if it is a parasitic pig though.

Comparing 518 OD to GV @ 3,000 RPM cruising, GV is 382 RPM higher (12.7% faster).

Will GV accept drive & direction from both ends?
Can the mounts be reversed front/rear?
Driveshaft length is the same, U joints are?
See where I'm going?

Can it be used as both 7778:1 overdrive (3.55:1 axle becomes 2.76:1 to kill RPM, reduce gas use, NVH cruising) and by swapping input ends as 1.286:1 underdrive (3.55:1 axle becomes 4.56:1)!!

Easier than changing a ham since you lose no fluid or gaskets, need not pull the axles, etc. The GV is partially subsidized by not buying another 9" center section.

There must be a good reason not to do this that I can't see...

You would be applying power in the opposite rotational direction. I wouldn’t think the gears are cut in such a way as to hold up to that. Don’t know for sure though.

Aahhh...
Helical vs. straight cut?
IIRC worms almost lock up if turned backward (some LSD based on it).
It it worked GV would advertise it.

Yes they can under or overdrive

Don Garlits blew part of his right foot off using a overdrive in his last front engine dragster along with cutting the car in half when his homemade O.D. tranny exploded on the starting line the old Lions Drag Strip in 1970
Under drive tranny have work well for many, many years It takes power to overdrive anything anytime