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I have a 91 Toyota 4x4 running 4:88 with 33 mud terrain tires with tru -tracs front and rear. my question was weather or not the ring and pinion is any weaker or not going up hills in reverse rather that crawling up forward. I seem to be able to go up more stuff in reverse i think because the heavy front end is pushing like a front wheel drive car instead of pulling going forward at starts hopping
 

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weakyota91 said:
I have a 91 Toyota 4x4 running 4:88 with 33 mud terrain tires with tru -tracs front and rear. my question was weather or not the ring and pinion is any weaker or not going up hills in reverse rather that crawling up forward. I seem to be able to go up more stuff in reverse i think because the heavy front end is pushing like a front wheel drive car instead of pulling going forward at starts hopping
Yes the gear sets are weaker in reverse, as is your reverse gear which is straight cut. You are running on the coast side of the gears.

I think they are 30% weaker? I'm taking this from the Hi-Pinion Reverse rotation gears are ~30% stronger than Lo-Pinion gears when put in the front diff. but are weaker in reverse and when put in the rear diff, they run on the coast side. My thinking on this may be flawed though.

So (driving forward)
LP Gears in the rear diff run on the drive side of the gear set
HP gears in the front diff run on the drive side of the gear set

HP gears in the rear diff run on the coast side, and they are weaker than LP
LP gears in the front diff run on the coast side, and they are weaker than HP
 

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Yeah, in reverse you're running on the "coast" side which is weaker.
But that's the rear 3rd only (unless you have a High Pinion 3rd in the front, which uses reverse cut gears).
 

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Wgasa's post is correct for Taco's, but not for Pretacos...

You have a "normal" cut low pinion diff in the front, which is actually STRONGER in reverse. The rear is stronger going forward.

Tacos have a "reverse" cut high pinion front diff, which makes both the front and rear stronger going forward.
 

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Where am I wrong for either pretaco or tacoma?
Wgasa's post is correct for Taco's
Taco: LP rear HP front (strong going forward)

but not for pretacos
PreTaco: LP rear and LP front (front is stronger in reverse)



or did I miss something?
 

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Wgasa84 said:
Yes the gear sets are weaker in reverse, as is your reverse gear which is straight cut. You are running on the coast side of the gears.
Maybe not wrong - but misleading/confusing. On a low pinion front (as in the Pretacos), going forward you are on the coast side and in reverse you are on the drive side.

I thought square cut gears are stronger. Helical gears are used even though they're weaker because they are so much quieter, but it's been a while since I took Machine Design.

Wgasa84 said:
Taco: LP rear HP front (strong going forward)
PreTaco: LP rear and LP front (front is stronger in reverse)
Exactly

The question is, though, should you be 'wheeling, towing, or recovering in reverse? With a Taco or 3rd+ Gen 4Runner, absolutely not. But with a preTaco, I think it could be argued that the front 7.5" diff is SIGNIFICANTLY weaker than the rear and that going in reverse might be a good idea as it "adds" strength to the front diff which is already the weaker of the two - probably balancing them out actually, strength-wise. Thougts?
 

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RedRunnertc said:
Maybe not wrong - but misleading/confusing. On a low pinion front (as in the Pretacos), going forward you are on the coast side and in reverse you are on the drive side.

I thought square cut gears are stronger. Helical gears are used even though they're weaker because they are so much quieter, but it's been a while since I took Machine Design.


Exactly

The question is, though, should you be 'wheeling, towing, or recovering in reverse? With a Taco or 3rd+ Gen 4Runner, absolutely not. But with a preTaco, I think it could be argued that the front 7.5" diff is SIGNIFICANTLY weaker than the rear and that going in reverse might be a good idea as it "adds" strength to the front diff which is already the weaker of the two - probably balancing them out actually, strength-wise. Thougts?
There are mixed opinions about this topic from a lot of people. I have had ASE certified Instructors tell me the strength was the same in either direction and then others say the reverse is weaker. As far as contact area goes, it does not matter wether you are going in forward or reverse, It's the same, The only difference is going forward, the ring and pinion gears pull together because they are helical gears. In reverse, they tend to push apart wich causes excelerated wear and sometimes failure. Obviously this depends on HP or LP.

As far as straight cut vs. helical cut, some say straight is stronger, some say there is no difference. Straight cut gears are definitely noisy which is why mfg's use helical cut gears instead. Straight cut gears have more complete contact per tooth but in a helical cut gear, the tooth contact area can be wider due to the curvature of the tooth, but it is not contacting the entire tooth at one time. You have more than one tooth in contact usually but you will never have the entire tooth contacing another in a helical gear set. But to answer your question, I have heard many people say it is better to climb,pull, etc in a forward direction. I have personnally never blown a r&p by doing things in reverse but I try not to do thing that will break the vehicle. If nothing else, It makes sense that the drive side of the gear would be stronger and take more abuse due to the fact that they are worn togther better than the faces on the "coast" side. They are both always touching but the drive side is under load much more than the coast side making the r&p have better and more contact area.
 

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RedRunnertc said:
Maybe not wrong - but misleading/confusing. On a low pinion front (as in the Pretacos), going forward you are on the coast side and in reverse you are on the drive side.

I thought square cut gears are stronger. Helical gears are used even though they're weaker because they are so much quieter, but it's been a while since I took Machine Design.
I probably used the wrong term. I have only heard that the reverse gear in the tranny is significantly weaker than the forward gears. I have not yet had to take apart my tranny so, personal experiance isn't there. I believe Showstop has toasted his reverse gear in his tranny, he may have more indepth information

Exactly

The question is, though, should you be 'wheeling, towing, or recovering in reverse? With a Taco or 3rd+ Gen 4Runner, absolutely not. But with a preTaco, I think it could be argued that the front 7.5" diff is SIGNIFICANTLY weaker than the rear and that going in reverse might be a good idea as it "adds" strength to the front diff which is already the weaker of the two - probably balancing them out actually, strength-wise. Thougts?
For the front LP diffs being stronger is only as strong as the gear set, and other componets. I'd ventrue to say the ~30% in strength gained by being on the drive side of the gear set is offset by the smaller ring/pinion gears in the 7.5" diff, even though the Rear 8" would now be on the coast side.

I have yet to break a rear R&P, but I busted a front HP in reverse (most of the weight of the vehicle was on the front and I was having to drop the cluch to get up the 2' ledge I slid into)... so my thinking may be a bit off. That being said, the PO had 4:56's in the rear diff, and stock 4:10's in the front (which are known to be brittle as 4:10 gears go). Something had to give, I'm glad it was the front gears and not something in the rest of my drivetrain.
 
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