1999 4wd suburban front wheels bind turning


#1

I’m used to my 2000 4wd Silverado, with 4wd engaged and not much snow, experiencing front wheel binding when turning particularly going up an incline.

My wife complained yesterday of something similar with her '99 4wd Suburban. Although she said there was snow on the ground. I’m fairly sure she said she also had the problem when the 4wd was off when the road cleared.She described her situation less as binding than as the wheel locking then breaking loose. The problem seemed to go away after her car warmed up several miles later.

  1. Is front wheel binding normal with 4wd engaged and not much snow on the ground?

  2. Is it likely that these older trucks are losing some rear differential accuracy (for want of a better term) and still sort of engaged having been disengaged?

  3. I have not checked her power steering fluid.

Suggestions/answers?

Mark


#2

Skip 4wd, otherwise plan for a min$1200 repair. Probably transfer case or front differential failing.


#3

A true 4WD vehicle has a center transfer case.

A true AWD vehicle has a center differential.

A 4WD transfer case doesn’t allow the output drive shafts, front/rear differentials to rotate at different rates.

AN AWD center differential allows the output drive shafts, front/rear differentials to rotate at different rates.

A 4WD drive vehicle cannot be driven on drive pavement while turning because the transfer case output shafts and front differential can’t allow the front tires to rotate at different rates. And this causes the differential to bind.

An AWD drive vehicle’s center differential allows the output shafts and the front differential to rotate at different rates while turning. And it doesn’t bind.

So, with 4WD, the traction conditions must be such that it allows all four tires to spin. Especially while turning. Otherwise the drive train will bind.

Tester


#4

The front driveline may not have disengaged. The actuator motor may be getting cranky or the connection may be corroded.


#5

I think @NYBo has it. Everything @Tester posted is correct but the GM part-time push button AWD systems do tend to get a bit sticky when they un-lock. The transfer case, when set to AWD mode, locks the front hubs with an actuator so the front driveshafts are connected. In AWD mode, when the rear slips the front is engaged but the driveshafts always rotate. This system can feel like its binding in tighter turns.

When you hit 4WD, the transfer case locks the front and rear together and binding will occur unless the pavement is slippery. When you go back to 2WD, the front hubs are supposed to unlock but they get sticky if not used very much and tend to stay locked for a bit. You will feel some binding when that occurs. Don’t worry about it unless it never unlocks.


#6

Thanks again–


#7

This morning, I printed out selected portions of your (Mustangman) message for my wife’s understanding. After she read it she said, "you know, now that I think of it it wasn’t a grinding of the wheels but a moaning coming from the engine when I tried to turn’. (virtual ‘hand to my head’) I then went to the garage, started the engine and didn’t have to turn the wheel to hear a really sick sound. I shut off the engine, checked the steering fluid and couldn’t see a level. Drove to the store in my truck for fluid. Her Burb took all 12 oz. The question now is where is the leak. I’ll make an appointment with my mechanic tomorrow.

Mark


#8

A very small leak over a loooong time can go completely unnoticed.

A question for you, does this SUV have a vacuum brake booster (big round can behind the master cylinder) or hydro-boost (a smaller gizmo with power steering lines going to it)?

If it has hydro-boost, check the brake operation as well as refilling the fluid. The hydro-boost may have sprung a leak or the accumulator (the cylindrical can attached to the booster) may have gone flat. The accumulator is there so you have power assist for at least 1 brake apply if the engine stalls.


#9

Excellent idea @Mustangman. A failing hydro-boost can quickly trash the entire brake system.


#10

I just took a few pictures of the engine to let you all decide what brake type she has.


#11

Why in the world did you not do that when she said there was something wrong?


#12

Because she specifically said the front wheels were hard to turn no mention of groaning or any other sound. It was only this morning that she virtually changed the description after I showed her the post from here.


#13

You have a standard vacuum booster. The hydro-boost system is found in trucks with diesel motors as diesels don’t produce adequate manifold vacuum to power the brakes.


#14

I agree that OP has a standard vacuum brake booster

However, hydroboost systems are also found in plenty of non-diesel applications

One of the reasons for choosing this is space. For instance, Astro vans have hydroboost, and they certainly don’t have large diesel engines. There’s simply not enough room for a vacuum brake booster

I believe the original BMW 6 series also used a hydraulic brake booster, for example


#15

Learned something new today. Thanks!


#16

What did I miss, went from steering noise, low power steering fluid to brakes? My similar car had leaking where the lines connected to the rack.


#17

[quote=“Barkydog, post:16, topic:100445, full:true”]
What did I miss, went from steering noise, low power steering fluid to brakes? My similar car had leaking where the lines connected to the rack.
[/quote]The noise turned out to be low power steering fluid. @db4690 recommended that the OP check to see if the truck has a hydro-boost power brake system because the hydro-boost uses the power steering system for power. However, the OP’s truck has a regular vacuum brake booster, so it is not a possible source of a power steering fluid leak. In the Suburban, only diesels use the hydro-boost system, although hydro-boost is used in some gas-engined vehicles because there is no room for a vacuum booster.

I think that sums up the progression!:blush:


#18

Don’t put words in my mouth

I did NOT recommend to check if the truck has hydro-boost. You’re either jumping the gun, or letting your imagination get away from you

I’m not blind, you know

I saw OP’s pictures, which clearly show that it has a vacuum brake booster. And you can see I made my comments AFTER OP posted the pictures. Considering I wrench for a living, I’d like to think I know how to differentiate a hydraulic brake booster from a vacuum brake booster. Are you suggesting I can’t . . . ?

My earlier comments were meant for YOU specifically. I was merely pointing out that lots of non-diesel vehicles use that system

Stop trying to


#19

Oops, it was @Mustangman who suggested he check for a hydro-boost system. Mea culpa.


#20

My truck - a Chevy Avalanche - has used both systems depending on the options (no diesels). I am pretty sure hydro-boost can give a higher boost ratio than a vacuum booster.

I happen to like it a quite a bit. The brake engineers I’ve worked with hate the system’s pedal feel. I find it much more positive than vacuum on a big truck.