Downshifting question!
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Logistics Pro
Joined: Jan 2021
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From: Fairhope Alabama
Downshifting question!
So I tow a lot although not super heavy but I tow a lot for my business, and as such I'm downshifting all the time when slowing down instead of using just my brakes. My question is when downshifting, obviously you can downshift too early and over rev the motor but would downshifting to a gear that would rev it up to say 2,500 or so RPM be downshifting too early? I'm downshifting a gear that makes it jump up like that it's usually a little harder to get it in gear meaning it takes a little more Force but when you're going down a hill with a load I'd like to be slowing down. We don't have a whole lot of hills down here but, I had to slow down rather quickly earlier and downshifted and everything seemed fine downshifting to 2500 rpm but I just want to make sure it's okay for the synchros putting that much extra pressure on the shifter to get it to go into a lower gear. Thanks.
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From: Lake Hartwell, GA
Tristan, when down shifting, try to rev match the engine speed before and as you let up on the clutch pedal. Once the clutch pedal is up, then you can start to use the transmission to slow the vehicle. This is how I do it when towing our 5th wheel and it works quite well even in mountainous areas like MT, UT and ID.
I usually try to be in the desired gear when descending a grade and allow the transmission to maintain speed with quick stabs from the brakes if needed. Sometimes I need to drop into 2nd or 1st when descending a grade and I will rev match, even then.
I usually try to be in the desired gear when descending a grade and allow the transmission to maintain speed with quick stabs from the brakes if needed. Sometimes I need to drop into 2nd or 1st when descending a grade and I will rev match, even then.
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Logistics Pro
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From: Fairhope Alabama
If I try to put it down into a gear that will rev up to around 2500, it seems like I hear the synchros whining a little bit and it doesn't quite want to go in gear but if I push just a smidge harder it'll go right in. I just don't like the whining sound from the synchros.
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Logistics Pro
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From: Fairhope Alabama
Tristan, when down shifting, try to rev match the engine speed before and as you let up on the clutch pedal. Once the clutch pedal is up, then you can start to use the transmission to slow the vehicle. This is how I do it when towing our 5th wheel and it works quite well even in mountainous areas like MT, UT and ID.
I usually try to be in the desired gear when descending a grade and allow the transmission to maintain speed with quick stabs from the brakes if needed. Sometimes I need to drop into 2nd or 1st when descending a grade and I will rev match, even then.
I usually try to be in the desired gear when descending a grade and allow the transmission to maintain speed with quick stabs from the brakes if needed. Sometimes I need to drop into 2nd or 1st when descending a grade and I will rev match, even then.
Lead Driver
Joined: Oct 2005
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From: Ponca City, OK
I'm not familiar with the ZF's all that much, but I assume they have a hydraulic clutch. If so have you checked the fluid and possibly tried bleeding the system. I used to have an old Toyota Pickup that had a minor leak in the clutch hydraulics and it would act kind of like that when it got low.
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Logistics Pro
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From: Fairhope Alabama
I'm not familiar with the ZF's all that much, but I assume they have a hydraulic clutch. If so have you checked the fluid and possibly tried bleeding the system. I used to have an old Toyota Pickup that had a minor leak in the clutch hydraulics and it would act kind of like that when it got low.
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From: Reed Point, MT
There's nothing wrong with it.
Every time you downshift, the gear you are trying to engage needs to speed up (as well as the countershaft and clutch disc). As the transmission wears - mostly the synchronizer cups which are typically brass and have grooves cut in them to shear the fluid between them and the cones (the steel part connected to the gear itself) - this speeding-up takes longer and causes the whine you're hearing.
When the grooves are worn to the point they are nearly smooth, the cups will basically hydroplane on the cones and no amount of force on the shifter will be able to match the speed required to allow the gear change. Then you'll get the grinding into gear on downshifts. Then $$$.
Every time you downshift, the gear you are trying to engage needs to speed up (as well as the countershaft and clutch disc). As the transmission wears - mostly the synchronizer cups which are typically brass and have grooves cut in them to shear the fluid between them and the cones (the steel part connected to the gear itself) - this speeding-up takes longer and causes the whine you're hearing.
When the grooves are worn to the point they are nearly smooth, the cups will basically hydroplane on the cones and no amount of force on the shifter will be able to match the speed required to allow the gear change. Then you'll get the grinding into gear on downshifts. Then $$$.
Fleet Owner
Joined: Jun 2004
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From: Rio Rico, AZ.
Are you sure your clutch is disengaging 100%? If it's difficult to row the gears up or down, and with your syncros complaining as well, try this: 0 mph, engine off, parking brake engaged. Push clutch down and select any gear you want. Now start the engine and try the same thing. But push clutch down and hold for three or so seconds to give the gears enough time to quit spinning, then select any gear you want. If there's a stiffness going into any gear, that means the input shaft is still spinning even with the clutch pedal pushed to the floor. Which means your clutch is not fully disengaging and needs some attention.
It's a real easy test on a vehicle that doesn't have syncros on reverse because it will grind the gears until you turn the engine off.
It's a real easy test on a vehicle that doesn't have syncros on reverse because it will grind the gears until you turn the engine off.
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Logistics Pro
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From: Fairhope Alabama
Being as this is my first stick shift, I've never driven a transmission without synchros. Although I will say as stated previously, I always Rev match. Was mostly just wondering if it was a bad thing that the synchros were whining when trying to put it in a lower gear and have the motor rev high to slow me down. This transmission only has around 40 to 50 k miles on it. I don't know who rebuilt it because the new transmission was put in before I bought it. I wouldn't think I would be having any issues but I just wanted to be sure. 👍 Thanks!
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Logistics Pro
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From: Fairhope Alabama
Are you sure your clutch is disengaging 100%? If it's difficult to row the gears up or down, and with your syncros complaining as well, try this: 0 mph, engine off, parking brake engaged. Push clutch down and select any gear you want. Now start the engine and try the same thing. But push clutch down and hold for three or so seconds to give the gears enough time to quit spinning, then select any gear you want. If there's a stiffness going into any gear, that means the input shaft is still spinning even with the clutch pedal pushed to the floor. Which means your clutch is not fully disengaging and needs some attention.
It's a real easy test on a vehicle that doesn't have syncros on reverse because it will grind the gears until you turn the engine off.
It's a real easy test on a vehicle that doesn't have syncros on reverse because it will grind the gears until you turn the engine off.
But I did your test, it goes in gear with the truck running just as easy as it does with the truck off. Which considering I just did a full clutch r&r a little over a year ago that was to be expected. I can quite literally put it in any gear with my pinky with the truck running. I'd say clutch is disengaging nicely!
It's not like it's super hard to get it to go in gear when downshifting it's just that it whines a little bit before it goes in gear. To be fair I don't give it any time when downshifting for the gears to "slow down" Or speed up. I take it out of gear and stick it straight into the next gear rather quickly in a quick fluid motion. Maybe I'm trying to downshift like a track car and that's the problem.....
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Logistics Pro
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From: Fairhope Alabama
This product may interest you.
https://youtu.be/ZmWPuWjSmwA
Edit: His technique through the corners sucks.
https://youtu.be/ZmWPuWjSmwA
Edit: His technique through the corners sucks.
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Logistics Pro
Joined: Jan 2021
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From: Fairhope Alabama
There's nothing wrong with it.
Every time you downshift, the gear you are trying to engage needs to speed up (as well as the countershaft and clutch disc). As the transmission wears - mostly the synchronizer cups which are typically brass and have grooves cut in them to shear the fluid between them and the cones (the steel part connected to the gear itself) - this speeding-up takes longer and causes the whine you're hearing.
When the grooves are worn to the point they are nearly smooth, the cups will basically hydroplane on the cones and no amount of force on the shifter will be able to match the speed required to allow the gear change. Then you'll get the grinding into gear on downshifts. Then $$$.
Every time you downshift, the gear you are trying to engage needs to speed up (as well as the countershaft and clutch disc). As the transmission wears - mostly the synchronizer cups which are typically brass and have grooves cut in them to shear the fluid between them and the cones (the steel part connected to the gear itself) - this speeding-up takes longer and causes the whine you're hearing.
When the grooves are worn to the point they are nearly smooth, the cups will basically hydroplane on the cones and no amount of force on the shifter will be able to match the speed required to allow the gear change. Then you'll get the grinding into gear on downshifts. Then $$$.
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