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Transmission Swap


Jason N
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Hello everyone, this is my first post. I have been reading up and learning quite a bit through your forum. I'm a long time Mack fan so this site is more than great. I have a 87 R688ST single axle Mack dump that is in great shape. I have been thinking of making a transmission change. It has a 672ci e-6 300 Mack motor with a straight 5 speed(1078). For off road work, backing with a load and just for the heck of it, I would like to put a twin stick six speed in it. The 5 speed is in great shape and I am having a little trouble justifying a swap.. However It's getting to be a long winter and it seams like it might be a good challenge with added rewards. Would anyone give me some advice on weather or not this is a good/bad idea, or if I should just leave it alone. Is it a very straight forward process for someone with good basic skills to be able to handle? Also what should I expect to spend on a used "good condition" six speed, and what would my 5 speed be worth? Thanks -Jason

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Hello everyone, this is my first post. I have been reading up and learning quite a bit through your forum. I'm a long time Mack fan so this site is more than great. I have a 87 R688ST single axle Mack dump that is in great shape. I have been thinking of making a transmission change. It has a 672ci e-6 300 Mack motor with a straight 5 speed(1078). For off road work, backing with a load and just for the heck of it, I would like to put a twin stick six speed in it. The 5 speed is in great shape and I am having a little trouble justifying a swap.. However It's getting to be a long winter and it seams like it might be a good challenge with added rewards. Would anyone give me some advice on weather or not this is a good/bad idea, or if I should just leave it alone. Is it a very straight forward process for someone with good basic skills to be able to handle? Also what should I expect to spend on a used "good condition" six speed, and what would my 5 speed be worth? Thanks -Jason

It's a very good idea. It will save your clutch by giving a deep enough reduction to get moving off road, and will make the truck more versatile with its 5 reverse gears.

Top speed on the road will remain the same, as the TRL1078 5 speed and the TRXL107 and TRXL1071 6 speed transmissions are all direct (1:1 ratio) in high gear.

.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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Yep. the 6 speed will give you one lower forward gear and 5 reverse gears. top end stays the same as your 5 speed. the 6 speed comes in 2 stick or air shift. There are a few versions of 6 speeds,you will need the one HK just mentioned. If you want to increase road speed you will have to look for transmissions that work well with the Maxidynes, A 12 speed is a option but they are getting hard to find.

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Hi Jason - Don't forget that you have to put the 6 or 10 or 12 speed into a gear and the hi-lo-rev lever into neutral to use your PTO to lift your dump. It's no bother if you are always dumping in a single tip but if you are trying to spread the load, it can be a nuisance as you have to keep dropping into neutral to lift the hoist. For spreading, the system on the 5 speed or the old 6 speed O.D box is simpler where you don't have to put the main box into a gear, only when you want to move forward. Best Regards - Michael.

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Hi Jason - Don't forget that you have to put the 6 or 10 or 12 speed into a gear and the hi-lo-rev lever into neutral to use your PTO to lift your dump. It's no bother if you are always dumping in a single tip but if you are trying to spread the load, it can be a nuisance as you have to keep dropping into neutral to lift the hoist. For spreading, the system on the 5 speed or the old 6 speed O.D box is simpler where you don't have to put the main box into a gear, only when you want to move forward. Best Regards - Michael.

This problem can be solved with a Mack rear mounted PTO. You do not need to have the Main in gear to run the PTO.

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you can spread a load with the 6 speed put the pto in when the bed starts to raise put the main in 1st put the compound in low pull out like you normaly would. trip the gate start shifting the main. just be sure you put a cable on the bed to stop the hoist pump when the bed tops out or it will bind the pump and possibly bust it..joe

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This problem can be solved with a Mack rear mounted PTO. You do not need to have the Main in gear to run the PTO.

Hi David - Where do you attach the PTO to the rear of the 6/10/12 speed boxes? I have never seen one here in Australia only the side mounted ones. Joe is right about spreading. This is the way I have done it for the last 30 years but it is not as convenient as the 5 speed where you can throw it in and out of gear easier when spreading.Best regards - Michael

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Thanks for all the advice. Does anyone know if I should expect to run into any hang ups with the conversion? or is everything interchangeable? What should I expect to spend on a used twin stick. Any advice on how to tell by looking at one if it's in good shape, or will I not know until I run it? Thanks again -Jason

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cant really tell by looking at it what condition it is in. If it has lots of oil leaking it may need seals. Check the mounts as sometimes I have seen the bolts round out in the alum case. The twin stick will need a 2nd hole in the floor but its easy to make as its directly next to the other stick. Many people will remove the seats and floor boards to get better access to the top of the trans. Drive shaft lenght may need to be adjusted..I cant recall how much longer the 6 speed is? I have seen those old 6 Speed boxes sell as low as $250!The avg I see is between $500-$1000. the 12 speeds sell for alot more. the 6 speed box is pretty simple and can be rebuilt fairly cheep. those gears are stronger than superman and rarely need to be replaced. The Forks and shift rails wear or get damaged faster. If your looking to do a cheep repair I suggest you rebuild the shift cover as that will tighten up the feel of the box. Also do the rear main and Shaft seals while its out. Its one of those jobs that you have to ask yourself.."When the trans is out what els should I replace?"

Trent

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Thanks for all the advice. Does anyone know if I should expect to run into any hang ups with the conversion? or is everything interchangeable? What should I expect to spend on a used twin stick. Any advice on how to tell by looking at one if it's in good shape, or will I not know until I run it? Thanks again -Jason

Jason -

It looks like you have received some excellent responses to your questions. A couple of items that have not yet been covered might interest you. When purchasing a used 6-speed don't forget you will need the entire shifting

arrangement original to that transmission. Avoid trying to convert transmissions from cab-overs to fit your conventional. Keep in mind your application when selecting the version you wish to purchase. The TRXL107 will have a

low hole ratio of 14.10 and a first gear ration of 8.59 just like your 5-speed and the remaining forward gears will be the same as well. Four of the five reverse gears will be lower than the one reverse gear of the TRL1078 5-speed. This is a huge plus for off-road work. The TRXL1071 had (if memory serves me) a much lower "low hole" for mixer applications. These variations are identified by the stampings on the drivers side flat spot, along with the build number (11KBA....). The markings are X107 and X1071 for these six-speed versions and D107/D1070, T107/T1070 for ten and twelve speed direct / overdrive transmissions. Try to find a unit that has the same output yoke size as your existing setup so that all you need to do is shorten the drive-line, if not check to see if your old yoke will fit.

I agree that it is difficult to hurt a triple counter-shaft Mack transmission. My 12-speed lost a counter-shaft

bearing and almost ran out of oil, the only damage was a broken shift rail. I also had difficulty with spreading

material and the rear mounted Mack PTO is the answer. My RS712LST had a Mack PTO but it was not in use. Even with the spreading issues, I never took the time to hook it up. The truck is now gone but I still have that PTO waiting for a new home.

Holdigr

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Jason,

I've got an 87 r600 that i'm looking to put an overdrive tranny in. It's got an extended range TRXL107 with the rear mounted pto. Email me back the tranny is good could use some seals though, maybe busings in the aux stick . Gene redstarcontracting@hotmail.com

Hey guys I've got an air shift 6 speed and a t2050 overdrive tranny the air shift was out of a burned MR so no shift knob however then can be had from PAI.. I dont know why you would avoid a tranny from a cabover from what I can tell all a guy needs to do is change the mounting brackets over and change the stick....... the 2050 is a 40% over if that what your looking for...?

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Hey guys I've got an air shift 6 speed and a t2050 overdrive tranny the air shift was out of a burned MR so no shift knob however then can be had from PAI.. I dont know why you would avoid a tranny from a cabover from what I can tell all a guy needs to do is change the mounting brackets over and change the stick....... the 2050 is a 40% over if that what your looking for...?

If he's got 4.17 or 3.87 rears as most of the TRL107, 1076, 1078 equipped trucks did, then the T2050 will not be geared low enough in 1st or reverse to get moving without slipping the shit out of the clutch.

If memory serves correctly, the TRL1078 would be 8.59 in 1st gear and the T2050 is 5.24 or something like that.

The .60 overdrive of the T2050 would put the truck over 100 mph @ 2100 in high gear, also not necessary or desirable.

The T2050 was usually used with 5.05 or 5.55 rears.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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Hey guys I've got an air shift 6 speed and a t2050 overdrive tranny the air shift was out of a burned MR so no shift knob however then can be had from PAI.. I dont know why you would avoid a tranny from a cabover from what I can tell all a guy needs to do is change the mounting brackets over and change the stick....... the 2050 is a 40% over if that what your looking for...?

Thanks but I am looking for a plain jane, old school twin stick. I like the nastalgic idea of a twin stick (in my 23 year old truck) and it sure will be nice to have those lower gears. Is their a possibility of everything hooking up without any hangups? Will i deffinatly need to change driveshaft length? I found one an hour and a half from home that the guys says was completely rebuilt 10 years ago. He bought off a friend as a spare but never installed it, he wants $950 for it. Any advice??? Thanks everybody for your help

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If he's got 4.17 or 3.87 rears as most of the TRL107, 1076, 1078 equipped trucks did, then the T2050 will not be geared low enough in 1st or reverse to get moving without slipping the shit out of the clutch.

If memory serves correctly, the TRL1078 would be 8.59 in 1st gear and the T2050 is 5.24 or something like that.

The .60 overdrive of the T2050 would put the truck over 100 mph @ 2100 in high gear, also not necessary or desirable.

The T2050 was usually used with 5.05 or 5.55 rears.

yeah thanks i was letting both guys know what i had I am fully aware that the 2050 is a 40 overdrive I have had 4 in my fleet in addition to 3 2060's and 2 2070's which also have 40 over high gears. just try'n to offer a good deal to the guys here, i gotta lot of mack stuff.. in my few years as a mack owner.... most of my 2050, 2060, and 2070's were in front of 6.34's although i've got a few 5.55 and 1 5.05.

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The trucks I've had with T2050 and T2060's have had 5.73 rears. These trans have a .6 overdrive which is not 40%. .6 input yields 1.00 output. 1.00 input yields 1.67 output, or a 67% gain. These are very fast transmissions.

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The trucks I've had with T2050 and T2060's have had 5.73 rears. These trans have a .6 overdrive which is not 40%. .6 input yields 1.00 output. 1.00 input yields 1.67 output, or a 67% gain. These are very fast transmissions.

I've owned 2 DM's that had 2070's with 5.73 rears and 1 DM that had a 2070 with 4.64 rears all on 11R22.5 rubber.

The 5.73's were a little on the slow side on the highway, but great for off road hauling.

The 4.64 ratio was way too high for a 2070, on a level road when loaded you had to start off in 2nd lo, then split to 1st direct in order to avoid slipping the clutch. 1st direct was too high to start off with the 4.64's.

Regarding the overdrive, a .60:1 overdrive is also known as a 40% overdrive, as Maxville stated. With .60:1 the input shaft makes .60 of a revolution to 1 revolution of the output shaft, therefore the output shaft is turning 40% of a revolution more for each revolution of the input shaft, hence the "40% overdrive" designation.

I've always referred to it as .60, or whatever the ratio that is being used, but some refer to it inversely as the percentage of overdrive.

.

"If You Can't Shift It Smoothly, You Shouldn't Be Driving It"

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The output is turning 167% faster than the input (.6 x 1.67 = 1.002). If it was 40% faster it would be a .71 overdrive (.71 x 1.4 = .994). If it was a .5 overdrive it wouldn't be 50%. The output is turning 1 rev for .5 on the input. That's 100% faster or a 200% overdrive (the output is turning twice as fast as the input).

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Hello everyone, this is my first post. I have been reading up and learning quite a bit through your forum. I'm a long time Mack fan so this site is more than great. I have a 87 R688ST single axle Mack dump that is in great shape. I have been thinking of making a transmission change. It has a 672ci e-6 300 Mack motor with a straight 5 speed(1078). For off road work, backing with a load and just for the heck of it, I would like to put a twin stick six speed in it. The 5 speed is in great shape and I am having a little trouble justifying a swap.. However It's getting to be a long winter and it seams like it might be a good challenge with added rewards. Would anyone give me some advice on weather or not this is a good/bad idea, or if I should just leave it alone. Is it a very straight forward process for someone with good basic skills to be able to handle? Also what should I expect to spend on a used "good condition" six speed, and what would my 5 speed be worth? Thanks -Jason

Jason I have a mack X1071 6speed with low-hole 2 stick it came out of a 1984 mack are you interested --Rocky

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