I took the plate under the roller brush off my tempo and can't get it back on. Are there instructions that I can use to try and get it back together or do I have to take it to the shop?

The bearings on the ends of the brushes can get clogged with things e.g. hair and this can cause the roller to seize.

Perhaps the belt is stretched. Replace it with Hoover belt # 38528-033. Remove the rug plate on the bottom ( 4 screws ), and remove the brushroll. Place the belt around the motor shaft first, then position it around the brush, and push the brush back into the housing. Expect resistance from the belt, as it must be stretched several inches. After the brush is in place, turn it with your fingers to be sure the belt is centered, and not pinched between the brush and the housing. After replacing the bottom plate the vacuum should be ready to use.

1. Turn vacuum over so base of powerhead is facing up.
2. Remove the two screws near the roller.
3. Release the two hooks over the brush by pushing outward.
4. Gently lift and remove the plate.
5. Lift and remove brush roller.
6. Remove belt.
7. Place belt over roller in the area with no bristles.
8. Insert brush back into holder and loop belt over motor shaft.
9. Rotate the roller a few times to make sure the belt is properly positioned.
10. Replace the plate over roller, making sure the front tabs line up with the slots on the base.
11. Flip down to secure hooks.
12. Press down on plate to secure it.
13. Replace screws.
14. Turn roller a few times.

And you're done.
The manual with illustrations and instructions can be found using the below link.

http://www.dirtdevil.com/search.aspx?q=UD40135&type=3

therre are usually aprings that hold the brush in position or a spacer thaqt turns when you adjust the height. turn the vacuum over and remove the plate covering verything. make sure your unplugged first. it usually takes about 5-6 phillips head screws. look for loose ,broken or missing parts. make the the roller is taken out and is carefully cleaned of all hair etc esp that just at the edge of the roller where it meets the monting devices. the hair and debris often gets stuck there and once removed works much better. also make sure the belt is not stretched and is slipping on the brush. if it is replace it. good luck.carefully reassemle the parts you removed being very aware of what postiotn everything was in when you took it apart. make sure everything has proper clearance and then test your vacuum. if you find broken or missing parts replace them first ofcoarse.

Eureka says size U BELT... NO!! I have tried this numerous times. I finally took off a belt from an old vac. and it works !!! dirt devil size 5 belt is the way to go!!

there is a blockage behind the roller brush remove the roller plate and the roller and check the inlet hose for a blockage also remove the bag and chek the inlet to the bag for some type of obstruction. Don the Vacuum Doctor Alb, N.M.

remove 4 screws fromthe bottom of the vac. this will allow you to remobe the baseplate and expose the belt & roller. put the new belt on the roller first and then pull it to the motor shaft. Note: remove the roller and the housing under it to clean out any debris buildup. re-install baseplate and screws.

I’m happy to assist further over the phone at https://www.6ya.com/expert/robert_b96ba3f038cf317c

I have had problems with the belts on my Mach 5 overheating (smell of burning rubber) and also with the motor overheating and shutting down.
I learned the hard way that one of the issues might be that the roller/brush on the bottom of the unit has a metal bearing inside the roller/brush that can become clogged with hair (both human and pet hair) which effects performance of the unit.
It’s fairly easy to fix.
Lay the vacuum on the floor so that you can see the roller/brush. Then remove the phillip head screws that hold the protective plastic plate over the roller/brush. (There are about 6 screws that hold this plastic protective plate in place) Also, you will be removing the (1) screw that also holds the plastic plate over the belts. There are (2) belts that you can remove and when in doubt replace these (2) belts for around $9.00.
Once you have the protective plastic plate off that covers the roller/brush disconnect the belt is around the roller. Take the roller and cut off any hair that is wrapped around the roller. Next, grab the roller by each end and twist the ends caps and (1) of the ends will unscrew. Once you have unscrewed one of the ends remove any hair or dust that is trapped under this cap. (Be careful not to lose the small metal washer that sit on top of the bearing)You will notice under this cap is a metal bearing that can become clogged and jammed with hair. The hair should come out fairly easy and allow the brush to spin fairly easy once you have screwed the end caps back in place test that it spins freely. If it doesn’t spin freely replace the roller/brush with a new one for about $23.00.
When you put the belts back on the thick rubber one (Belt # 40201-271) has probably become stretched and should be replaced for about $3.00. The small diameter belt that goes over the roller/brush probably does not usually need to be replaced and does not usually fit very tight. I have heard that people will take the small roller/brush belt and turn it upside down to get a better fit.
I just did this on my Mach 5 and it runs like a new machine. I did end up replacing the roller/brush head.
Hopefully you will find this useful.

Turn your vacuum over and remove 6 screws holding down the cover plate which has the roller brush under it. Remove cover plate and pull up on brush. Belt will come off with the brush. Put back together in reverse order with new belt.

Turn the machine upside down. Take the screws out of the bottom plate and remove it. take out the brush roller and old belt. Wrap the new belt around the metal shaft of the motor first and put the roller inside the belt loop and use the roller as leverage to stretch the belt up to the brush housing and slide the roller in place. Give the roller a spin by hand the make sure everything moves freely before you use it. It should spin with out much effort, if it doesn't you probably have the belt pinched, and you need to free it up before putting the bottom plate back one. It will take a little elbow grease, but it will go on.

Hoovers usually list what kind of belt they take on the serial tag.

Good Luck