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Gear Vendors Overdrive Disadvantages?

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The_Stig

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Discussion starter · #1 ·
Hi guys, haven't bothered you for a while now with stupid, irate questions but here's on I'm hoping will go on for a little bit. I've got a 454 that I'm planning on getting around 500-550 hp with behind a M20 (which I've got questions about too). Now this build is a street performer with a trip to the strip maybe once a month. I was set to tread lightly on the Muncie until I had enough money to buy a TKO-600 and sell it but I just recently found out about the GV o/d unit. I've read alot about them, but I've got one question.

What are the disadvantages? Aside from the cost and a few installation problems (especially when dealing with a manual), everyone says there isn't one. The loss in hp is something like 1 for every 400?!?! I can't see that being 100% truthful. Weight isn't an issue because you can always shed weight in other places and this isn't a drag car so that's not a disadvantage.

Thanks,
Mitch
 
#3 ·
physically large and heavy, may need floor mods, expensive. but, strong and reliable. virtually the only way to get OD in many applications.
 
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#5 ·
LOL GRANDSON ON COMPUTOR! what I was going to add is that imho nothing shifts as nice as a Muncie and with a gearvenders you have overdrive plus a gear-splitter. I have seen a few people with 5-speeds have issueswith shifting,noises,etc. Poor guys like me just throw in 3:08's but if I Ever get some cash I will go with the gear venders set-up myself.just my 2cents.
 
#6 ·
I want to use one on a future build too. My only concerns were how much driveline power loss there was going to be and the effect on the driveline angle with a significantly shortened driveshaft.
 
#7 ·
I used one in my '69 Chevelle and without major floorpan mods, the driveline angles are not going to be correct. I had a decel vibration around 70-60 mph.

I liked the way the GV upshifts but the downshift was not refined at all. It would be OK with a manual trans car where you might use the clutch to downshift it.

It has an internal pump that will consume a bit of HP besides frictional losses. I wouldn't expect it to be any more than 5-10 HP typically, and IMO most of the HP losses many enthusiasts are worried about are insignificant in the combos they are running.
A typical street strip car isn't fast enough or serious enough to worry about 5, 10, or even 20 HP drivetrain loss.
My guess is the GV would be very similar to running a true OD trans as far as HP losses. Some parasitic loss due to rotating, frictional, and pumping losses.
 
#8 ·
I have one in my 68 behind a TH400. I agree with Jake, the drive line angles are way off. I used adjustable upper control arms from UMI. I now have equal & opposite 3 degree drive shaft angles, not perfect but the car cruises at all speeds with no vibration.
It shifts up really nice into OD but again like Jake mentioned the down shift can be a little clunky. If you decide to go with a gear vendor try to get the back of the unit as high as possible when you do your floor pan & cross member "mods" to reduce your angles, this worked best for me.
 
#9 ·
I took my driveshaft to be modified and the driveshaft guy said he didn't want to cut the original '65 shaft - he used one that did not have the 'taper' at the one end. Cost about $60 and I still have the original driveshaft should I want to go back to original.

Be advised, however, that if you want to go from a PG to a t350/400, you cannot just buy the parts that would allow it to work on the different tranny. You will have to ship everything back to them and they will sell you a new setup. Weird and annoying...
 
#10 · (Edited)
Here is an Advantage!

I have built some GearVender units behind the M23W series transmission. The ratios of the M23W that I used were: 2.568:1 - 1.908:1 - 1.366:1 - 1.00:1 for an even RPM drop through all 4 gears.

The OD ratio of the GearVenders unit is .78:1 and you can engagement the OD of the unit in any gear of the manual transmission at full throttle. Consider this a free shift if you will without using the clutch!

Follow along as I show you the effective ratio of each gear of the M23W as you engage the OD.

M23W X the GV OD for each gear.....

2.568 x .78 = 2.003:1
1.908 x .78 = 1.488:1
1.366 x .78 = 1.065:1

As you can see, you are almost shifting into the next gear of the M23W except for the 2-3 shift, did I mention without using the clutch?!

With a manual transmission, you disconnect the transmission and the clunking is not as much of an issue like an automatic.
 
#11 ·
I have a GV behind a 454 with a TH454. I love it.
I don't have anything bad to say about it except that I want a 2nd one to have double overdrive.
 
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#12 ·
I have had mine for about 5 or 6 years - LOVE IT! It is behind my 496/TH400 with 4.10 (F&rd) rear (about 3.20s in OD!) Functions like a 4 speed OD TH400 in AUTO mode! Down shift does clunk, but I don't really see this as an issue. At the strip, I shut it off to take advantage of the 4.10s, then when 3rd winds out, kick it on for a 4th gear. I have adjustable upper control arms so setting the pinion angle isn't a big deal, and had a new driveshaft made with the 1350 u-joints. Had to massage the floor a little and modify the TH400 crossmember, but nothing drastic. Added bonus is, if you sell the car, remove it and use it in your next ride.
John
 
#13 ·
I don't know how to edit my post, but I meant TH400. NOT TH454....duh...
 
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#14 ·
Be careful using a GV as a "splitter" If it bangs into gear hard, it's going to hurt things. Ive seen an M22 destroyed by one, which is one of the things that led to the M23 program. We tread lightly with the gear vendors unit, because of its clutch design, it can engage very aggressively if its not installed properly. Jody is a great builder, I wouldn't worry about his installation. However, if someone had never built something like this; I would encourage them to get a closer ratio gearset and just use the GV as an overdrive only.
 
#15 ·
Auto Gear said:
Be careful using a GV as a "splitter" If it bangs into gear hard, it's going to hurt things. Ive seen an M22 destroyed by one, which is one of the things that led to the M23 program. We tread lightly with the gear vendors unit, because of its clutch design, it can engage very aggressively if its not installed properly. Jody is a great builder, I wouldn't worry about his installation. However, if someone had never built something like this; I would encourage them to get a closer ratio gearset and just use the GV as an overdrive only.
Click to expand...
The problem with the GV unit is that the extension housing has no way of piloting the output shaft. You have no rear bushing and are piloting the Muncie output on the sloppy spline fit of the GV input. Also when you shift from the driven side you are going to snap / shock the gear train because your lash is working in the opposite load direction. Most people.. these issues don't matter,if you can deal with the added weight and oddball drivetrain angles. I don't like them.
 
#16 ·
Well, I can't speak for a standard transmission setup. I only have it on a TH400.
 
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#17 ·
Auto Gear said:
Be careful using a GV as a "splitter" ... just use the GV as an overdrive only.
Click to expand...
I always thought the 'gear splitter' aspect was way oversold. I don't see how you can do that practically. Going from 1 to 1-OD is fine, but try going from 1-OD to 2nd. You have to disengage the OD as you are shifting and hope the timing is right. Might could do it in a truck granny shifting to keep in the RPM range for towing, but racing or practical street use for a hot rod? I don't see it happening...but that is just MHO. Neat idea, but...
John
 
#18 ·
Ok, I do agree with that. Gearsplitting a hot rod is cumbersome.
I like it with my toyhauler behind me. The gearsplitting is nice. I am not trying to redline and power shift here....

Even if I could not gear split, I would still use the overdrive. No doubt.
 
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#19 ·
I have one on a SB350 w/th350 w 3.73... I was slightly dissapointed that the gearing wasn't higher/lower. I was turning 3500 rpm at 65mph...after installing it only dropped it to 3000 at 65mph. Was hopeing for around 2200...and they don't offer other gears...
 
#20 ·
I have a GV that came in a truck that I bought. WaterWalker is right, the gears only drop the RPM a fairly small amount and that can't be changed. However, you can change the rear gears or tire size so that you get a workable system.

Not so effective in a hot rod car, but if you drop the gears to be taller then you might find a sweet spot using 2nd +OD to replace what would have been the 3rd + No OD. Not saying that's fun, but at least an option.

One down side of the GV is that the adapters are BIG $$$. Big $$ for no reason other than they gotcha.

Mine sits in a truck that's not used any more. I'd like to have it in my 4x4 truck. They want some $700.00 for the stupid adapter. $700.00 !!!! BS!

Otherwise, great unit, just wish they had more reasonable prices, esp for those of us that already have one and just need parts.
 
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