Selenium ajax dynamic pagination base spider

I am trying to run a basic dynamic pagination spider, but I am not getting any success with the crawl. I used selenium ajax dynamic breakdown. url I'm using: http://www.demo.com . Here is my code:

# -*- coding: utf-8 -*-
import scrapy

import re

from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor

from scrapy.selector import Selector

from scrapy.spider import BaseSpider

from demo.items import demoItem

from selenium import webdriver

def removeUnicodes(strData):

        if(strData):

            #strData = strData.decode('unicode_escape').encode('ascii','ignore')

            strData = strData.encode('utf-8').strip() 

            strData = re.sub(r'[\n\r\t]',r' ',strData.strip())

            #print 'Output:',strData

        return strData


class demoSpider(scrapy.Spider):
    name = "demourls"

    allowed_domains = ["demo.com"]

    start_urls = ['http://www.demo.com']

     def __init__(self):
        self.driver = webdriver.Firefox()

    def parse(self, response):
        print "*****************************************************"
        self.driver.get(response.url)
        print response.url
        print "______________________________"



        hxs = Selector(response)
        item = sumItem()
        finalurls = []
        while True:
            next = self.driver.find_element_by_xpath('//div[@class="showMoreCars hide"]/a')

            try:
                next.click()
                # get the data and write it to scrapy items
                item['pageurl'] = response.url
                item['title'] =  removeUnicodes(hxs.xpath('.//h1[@class="page-heading"]/text()').extract()[0])
                urls = hxs.xpath('.//a[@id="linkToDetails"]/@href').extract()
                print '**********************************************2***url*****************************************',urls


                for url in urls:
                    print '---------url-------',url
                finalurls.append(url)          

                item['urls'] = finalurls

            except:
                break

        self.driver.close()

        return item

      

        
        
        
      

    

my items.py

from scrapy.item import Item, Field


class demoItem(Item):



    page = Field()
    urls = Field()

    pageurl = Field()
    title = Field()

      

        
        
        
      

    

when i try to scan it and convert it to json i get my json file as:

[{"pageurl": "http://www.demo.com", "urls": [], "title": "demo"}]

      

        
        
        
      

    

I cannot crawl all urls as they are dynamically loaded.